text:
Intervention | |
An EEG recording at Dalhousie University |
MeSH | D004569 |
OPS-301 code: | 1-207 |
Electroencephalography (EEG) is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain.[1] In clinical contexts, EEG refers to the recording of the brain's spontaneous electrical activity over a short period of time, usually 20–40 minutes, as recorded from multiple electrodes placed on the scalp. Diagnostic applications generally focus on the spectral content of EEG, that is, the type of neural oscillations that can be observed in EEG signals. In neurology, the main diagnostic application of EEG is in the case of epilepsy, as epileptic activity can create clear abnormalities on a standard EEG study.[2] A secondary clinical use of EEG is in the diagnosis of coma, encephalopathies, and brain death. A third clinical use of EEG is for studies of sleep and sleep disorders where recordings are typically done for one full night, sometimes more. EEG used to be a first-line method for the diagnosis of tumors, stroke and other focal brain disorders,[3] but this use has decreased with the advent of anatomical imaging techniques with high (<1 mm) spatial resolution such as MRI and CT. Despite limited spatial resolution, EEG continues to be a valuable tool for research and diagnosis, especially when millisecond-range temporal resolution (not possible with CT or MRI) is required.
Derivatives of the EEG technique include evoked potentials (EP), which involves averaging the EEG activity time-locked to the presentation of a stimulus of some sort (visual, somatosensory, or auditory). Event-related potentials (ERPs) refer to averaged EEG responses that are time-locked to more complex processing of stimuli; this technique is used in cognitive science, cognitive psychology, and psychophysiological research.
Contents |
A timeline of the history of EEG is given by Swartz.[4] Richard Caton (1842–1926), a physician practicing in Liverpool, presented his findings about electrical phenomena of the exposed cerebral hemispheres of rabbits and monkeys in the British Medical Journal in 1875. In 1890, Polish physiologist Adolf Beck published an investigation of spontaneous electrical activity of the brain of rabbits and dogs that included rhythmic oscillations altered by light.
In 1912, Russian physiologist, Vladimir Vladimirovich Pravdich-Neminsky published the first animal EEG and the evoked potential of the mammalian (dog).[5] In 1914, Napoleon Cybulski and Jelenska-Macieszyna photographed EEG-recordings of experimentally induced seizures.
German physiologist and psychiatrist Hans Berger (1873–1941) recorded the first human EEG in 1924.[6] Expanding on work previously conducted on animals by Richard Caton and others, Berger also invented the electroencephalogram (giving the device its name), an invention described "as one of the most surprising, remarkable, and momentous developments in the history of clinical neurology".[7] His discoveries were first confirmed by British scientists Edgar Douglas Adrian and B. H. C. Matthews in 1934 and developed by them.
In 1934, Fisher and Lowenback first demonstrated epileptiform spikes. In 1935 Gibbs, Davis and Lennox described interictal spike waves and the 3 cycles/s pattern of clinical absence seizures, which began the field of clinical electroencephalography. Subsequently, in 1936 Gibbs and Jasper reported the interictal spike as the focal signature of epilepsy. The same year, the first EEG laboratory opened at Massachusetts General Hospital.
Franklin Offner (1911–1999), professor of biophysics at Northwestern University developed a prototype of the EEG that incorporated a piezoelectric inkwriter called a Crystograph (the whole device was typically known as the Offner Dynograph).
In 1947, The American EEG Society was founded and the first International EEG congress was held. In 1953 Aserinsky and Kleitman describe REM sleep.
In the 1950s, William Grey Walter developed an adjunct to EEG called EEG topography, which allowed for the mapping of electrical activity across the surface of the brain. This enjoyed a brief period of popularity in the 1980s and seemed especially promising for psychiatry. It was never accepted by neurologists and remains primarily a research tool.
Source of EEG activity[edit]
The brain's electrical charge is maintained by billions of neurons. Neurons are electrically charged (or "polarized") by membrane transport proteins that pump ions across their membranes. Neurons are constantly exchanging ions with the extracellular milieu, for example to maintain resting potential and to propagate action potentials. Ions of similar charge repel each other, and when many ions are pushed out of many neurons at the same time, they can push their neighbours, who push their neighbours, and so on, in a wave. This process is known as volume conduction. When the wave of ions reaches the electrodes on the scalp, they can push or pull electrons on the metal on the electrodes. Since metal conducts the push and pull of electrons easily, the difference in push or pull voltages between any two electrodes can be measured by a voltmeter. Recording these voltages over time gives us the EEG.[8]
The electric potential generated by single neuron is far too small to be picked up by EEG or MEG.[9] EEG activity therefore always reflects the summation of the synchronous activity of thousands or millions of neurons that have similar spatial orientation. If the cells do not have similar spatial orientation, their ions do not line up and create waves to be detected. Pyramidal neurons of the cortex are thought to produce the most EEG signal because they are well-aligned and fire together. Because voltage fields fall off with the square of distance, activity from deep sources is more difficult to detect than currents near the skull.[10]
Scalp EEG activity shows oscillations at a variety of frequencies. Several of these oscillations have characteristic frequency ranges, spatial distributions and are associated with different states of brain functioning (e.g., waking and the various sleep stages). These oscillations represent synchronized activity over a network of neurons. The neuronal networks underlying some of these oscillations are understood (e.g., the thalamocortical resonance underlying sleep spindles), while many others are not (e.g., the system that generates the posterior basic rhythm). Research that measures both EEG and neuron spiking finds the relationship between the two is complex with the power of surface EEG in only two bands (gamma and delta) relating to neuron spike activity.[11]
Clinical use[edit]
A routine clinical EEG recording typically lasts 20–30 minutes (plus preparation time) and usually involves recording from scalp electrodes. Routine EEG is typically used in the following clinical circumstances:
- to distinguish epileptic seizures from other types of spells, such as psychogenic non-epileptic seizures, syncope (fainting), sub-cortical movement disorders and migraine variants.
- to differentiate "organic" encephalopathy or delirium from primary psychiatric syndromes such as catatonia
- to serve as an adjunct test of brain death
- to prognosticate, in certain instances, in patients with coma
- to determine whether to wean anti-epileptic medications
At times, a routine EEG is not sufficient, particularly when it is necessary to record a patient while he/she is having a seizure. In this case, the patient may be admitted to the hospital for days or even weeks, while EEG is constantly being recorded (along with time-synchronized video and audio recording). A recording of an actual seizure (i.e., an ictal recording, rather than an inter-ictal recording of a possibly epileptic patient at some period between seizures) can give significantly better information about whether or not a spell is an epileptic seizure and the focus in the brain from which the seizure activity emanates.
Epilepsy monitoring is typically done:
- to distinguish epileptic seizures from other types of spells, such as psychogenic non-epileptic seizures, syncope (fainting), sub-cortical movement disorders and migraine variants.
- to characterize seizures for the purposes of treatment
- to localize the region of brain from which a seizure originates for work-up of possible seizure surgery
Additionally, EEG may be used to monitor certain procedures:
- to monitor the depth of anesthesia
- as an indirect indicator of cerebral perfusion in carotid endarterectomy
- to monitor amobarbital effect during the Wada test
EEG can also be used in intensive care units for brain function monitoring:
- to monitor for non-convulsive seizures/non-convulsive status epilepticus
- to monitor the effect of sedative/anesthesia in patients in medically induced coma (for treatment of refractory seizures or increased intracranial pressure)
- to monitor for secondary brain damage in conditions such as subarachnoid hemorrhage (currently a research method)
If a patient with epilepsy is being considered for resective surgery, it is often necessary to localize the focus (source) of the epileptic brain activity with a resolution greater than what is provided by scalp EEG. This is because the cerebrospinal fluid, skull and scalp smear the electrical potentials recorded by scalp EEG. In these cases, neurosurgeons typically implant strips and grids of electrodes (or penetrating depth electrodes) under the dura mater, through either a craniotomy or a burr hole. The recording of these signals is referred to as electrocorticography (ECoG), subdural EEG (sdEEG) or intracranial EEG (icEEG)--all terms for the same thing. The signal recorded from ECoG is on a different scale of activity than the brain activity recorded from scalp EEG. Low voltage, high frequency components that cannot be seen easily (or at all) in scalp EEG can be seen clearly in ECoG. Further, smaller electrodes (which cover a smaller parcel of brain surface) allow even lower voltage, faster components of brain activity to be seen. Some clinical sites record from penetrating microelectrodes.[1]
Research use[edit]
EEG, and the related study of ERPs are used extensively in neuroscience, cognitive science, cognitive psychology, neurolinguistics and psychophysiological research. Many EEG techniques used in research are not standardized sufficiently for clinical use.
Relative advantages[edit]
Several other methods to study brain function exist, including functional magnetic resonance imaging (fMRI), positron emission tomography, magnetoencephalography, Nuclear magnetic resonance spectroscopy, Electrocorticography, Single-photon emission computed tomography, Near-infrared spectroscopy (NIRS), and Event-related optical signal (EROS). Despite the relatively poor spatial sensitivity of EEG, it possesses multiple advantages over some of these techniques:
- Hardware costs are significantly lower than those of most other techniques [12]
- EEG sensors can be used in more places than fMRI, SPECT, PET, MRS, or MEG, as these techniques require bulky and immobile equipment. For example, MEG requires equipment consisting of liquid helium-cooled detectors that can be used only in magnetically shielded rooms, altogether costing upwards of several million dollars;[13] and fMRI requires the use of a 1-ton magnet in, again, a shielded room.
- EEG has very high temporal resolution, on the order of milliseconds rather than seconds. EEG is commonly recorded at sampling rates between 250 and 2000 Hz in clinical and research settings, but modern EEG data collection systems are capable of recording at sampling rates above 20,000 Hz if desired. MEG and EROS are the only other noninvasive cognitive neuroscience techniques that acquire data at this level of temporal resolution.[13]
- EEG is relatively tolerant of subject movement, unlike most other neuroimaging techniques. There even exist methods for minimizing, and even eliminating movement artefacts in EEG data [14]
- EEG is silent, which allows for better study of the responses to auditory stimuli
- EEG does not aggravate claustrophobia, unlike fMRI, PET, MRS, SPECT, and sometimes MEG [15]
- EEG does not involve exposure to high-intensity (>1 Tesla) magnetic fields, as in some of the other techniques, especially MRI and MRS. These can cause a variety of undesirable issues with the data, and also prohibit use of these techniques with participants that have metal implants in their body, such as metal-containing pacemakers [16]
- EEG does not involve exposure to radioligands, unlike positron emission tomography.[17]
- ERP studies can be conducted with relatively simple paradigms, compared with IE block-design fMRI studies
- Extremely uninvasive, unlike Electrocorticography, which actually requires electrodes to be placed on the surface of the brain.
EEG also has some characteristics that compare favorably with behavioral testing:
- EEG can detect covert processing (i.e., processing that does not require a response) [18]
- EEG can be used in subjects who are incapable of making a motor response [19]
- Some ERP components can be detected even when the subject is not attending to the stimuli
- Unlike other means of studying reaction time, ERPs can elucidate stages of processing (rather than just the final end result) [20]
- EEG is a powerful tool for tracking brain changes during different phases of life. EEG sleep analysis can indicate significant aspects of the timing of brain development, including evaluating adolescent brain maturation.[21]
Relative disadvantages[edit]
- Low spatial resolution on the scalp. fMRI, for example, can directly display areas of the brain that are active, while EEG requires intense interpretation just to hypothesize what areas are activated by a particular response.[22]
- EEG determines neural activity that occurs below the upper layers of the brain (the cortex) poorly.
- Unlike PET and MRS, cannot identify specific locations in the brain at which various neurotransmitters, drugs, etc. can be found.[17]
- Often takes a long time to connect a subject to EEG, as it requires precise placement of dozens of electrodes around the head and the use of various gels, saline solutions, and/or pastes to keep them in place. While the length of time differs dependent on the specific EEG device used, as a general rule it takes considerably less time to prepare a subject for MEG, fMRI, MRS, and SPECT.
- Signal-to-noise ratio is poor, so sophisticated data analysis and relatively large numbers of subjects are needed to extract useful information from EEG [23]
Combining EEG with other neuroimaging techniques[edit]
Simultaneous EEG recordings and fMRI scans have been obtained successfully,[24][25] though successful simultaneous recording requires that several technical difficulties be overcome, such as the presence of ballistocardiographic artifact, MRI pulse artifact and the induction of electrical currents in EEG wires that move within the strong magnetic fields of the MRI. While challenging, these have been successfully overcome in a number of studies.[26]
Similarly, simultaneous recordings with MEG and EEG have also been conducted, which has several advantages over using either technique alone:
- EEG requires accurate information about certain aspects of the skull that can only be estimated, such as skull radius, and conductivities of various skull locations. MEG does not have this issue, and a simultaneous analysis allows this to be corrected for.
- MEG and EEG both detect activity below the surface of the cortex very poorly, and like EEG, the level of error increases with the depth below the surface of the cortex one attempts to examine. However, the errors are very different between the techniques, and combining them thus allows for correction of some of this noise.
- MEG has access to virtually no sources of brain activity below a few centimetres under the cortex. EEG, on the other hand, can receive signals from greater depth, albeit with a high degree of noise. Combining the two makes it easier to determine what in the EEG signal comes from the surface (since MEG is very accurate in examining signals from the surface of the brain), and what comes from deeper in the brain, thus allowing for analysis of deeper brain signals than either EEG or MEG on its own.[27]
EEG has also been combined with positron emission tomography. This provides the advantage of allowing researchers to see what EEG signals are associated with different drug actions in the brain.[28]
In conventional scalp EEG, the recording is obtained by placing electrodes on the scalp with a conductive gel or paste, usually after preparing the scalp area by light abrasion to reduce impedance due to dead skin cells. Many systems typically use electrodes, each of which is attached to an individual wire. Some systems use caps or nets into which electrodes are embedded; this is particularly common when high-density arrays of electrodes are needed.
Electrode locations and names are specified by the International 10–20 system[29] for most clinical and research applications (except when high-density arrays are used). This system ensures that the naming of electrodes is consistent across laboratories. In most clinical applications, 19 recording electrodes (plus ground and system reference) are used.[30] A smaller number of electrodes are typically used when recording EEG from neonates. Additional electrodes can be added to the standard set-up when a clinical or research application demands increased spatial resolution for a particular area of the brain. High-density arrays (typically via cap or net) can contain up to 256 electrodes more-or-less evenly spaced around the scalp.
Each electrode is connected to one input of a differential amplifier (one amplifier per pair of electrodes); a common system reference electrode is connected to the other input of each differential amplifier. These amplifiers amplify the voltage between the active electrode and the reference (typically 1,000–100,000 times, or 60–100 dB of voltage gain). In analog EEG, the signal is then filtered (next paragraph), and the EEG signal is output as the deflection of pens as paper passes underneath. Most EEG systems these days, however, are digital, and the amplified signal is digitized via an analog-to-digital converter, after being passed through an anti-aliasing filter. Analog-to-digital sampling typically occurs at 256–512 Hz in clinical scalp EEG; sampling rates of up to 20 kHz are used in some research applications.
During the recording, a series of activation procedures may be used. These procedures may induce normal or abnormal EEG activity that might not otherwise be seen. These procedures include hyperventilation, photic stimulation (with a strobe light), eye closure, mental activity, sleep and sleep deprivation. During (inpatient) epilepsy monitoring, a patient's typical seizure medications may be withdrawn.
The digital EEG signal is stored electronically and can be filtered for display. Typical settings for the high-pass filter and a low-pass filter are 0.5-1 Hz and 35–70 Hz, respectively. The high-pass filter typically filters out slow artifact, such as electrogalvanic signals and movement artifact, whereas the low-pass filter filters out high-frequency artifacts, such as electromyographic signals. An additional notch filter is typically used to remove artifact caused by electrical power lines (60 Hz in the United States and 50 Hz in many other countries).[1] As part of an evaluation for epilepsy surgery, it may be necessary to insert electrodes near the surface of the brain, under the surface of the dura mater. This is accomplished via burr hole or craniotomy. This is referred to variously as "electrocorticography (ECoG)", "intracranial EEG (I-EEG)" or "subdural EEG (SD-EEG)". Depth electrodes may also be placed into brain structures, such as the amygdala or hippocampus, structures, which are common epileptic foci and may not be "seen" clearly by scalp EEG. The electrocorticographic signal is processed in the same manner as digital scalp EEG (above), with a couple of caveats. ECoG is typically recorded at higher sampling rates than scalp EEG because of the requirements of Nyquist theorem—the subdural signal is composed of a higher predominance of higher frequency components. Also, many of the artifacts that affect scalp EEG do not impact ECoG, and therefore display filtering is often not needed.
A typical adult human EEG signal is about 10 µV to 100 µV in amplitude when measured from the scalp[31] and is about 10–20 mV when measured from subdural electrodes.
The EEG recording can be analysed using various programs; e.g., using free open-source toolboxes for Matlab, such as, EEGLAB, Fieldtrip, NBT, SPM, or commercial software packages such as Brainvision Analyzer.
Since an EEG voltage signal represents a difference between the voltages at two electrodes, the display of the EEG for the reading encephalographer may be set up in one of several ways. The representation of the EEG channels is referred to as a montage.
- Bipolar montage
- Each channel (i.e., waveform) represents the difference between two adjacent electrodes. The entire montage consists of a series of these channels. For example, the channel "Fp1-F3" represents the difference in voltage between the Fp1 electrode and the F3 electrode. The next channel in the montage, "F3-C3," represents the voltage difference between F3 and C3, and so on through the entire array of electrodes.
- Referential montage
- Each channel represents the difference between a certain electrode and a designated reference electrode. There is no standard position for this reference; it is, however, at a different position than the "recording" electrodes. Midline positions are often used because they do not amplify the signal in one hemisphere vs. the other. Another popular reference is "linked ears," which is a physical or mathematical average of electrodes attached to both earlobes or mastoids.
- Average reference montage
- The outputs of all of the amplifiers are summed and averaged, and this averaged signal is used as the common reference for each channel.
- Laplacian montage
- Each channel represents the difference between an electrode and a weighted average of the surrounding electrodes.[32]
When analog (paper) EEGs are used, the technologist switches between montages during the recording in order to highlight or better characterize certain features of the EEG. With digital EEG, all signals are typically digitized and stored in a particular (usually referential) montage; since any montage can be constructed mathematically from any other, the EEG can be viewed by the electroencephalographer in any display montage that is desired.
The EEG is read by a clinical neurophysiologist or neurologist (depending on local custom and law regarding medical specialities), optimally one who has specific training in the interpretation of EEGs for clinical purposes. This is done by visual inspection of the waveforms, called graphoelements. The use of computer signal processing of the EEG—so-called quantitative EEG—is somewhat controversial when used for clinical purposes (although there are many research uses).
EEG has several limitations. Most important is its poor spatial resolution. EEG is most sensitive to a particular set of post-synaptic potentials: those generated in superficial layers of the cortex, on the crests of gyri directly abutting the skull and radial to the skull. Dendrites, which are deeper in the cortex, inside sulci, in midline or deep structures (such as the cingulate gyrus or hippocampus), or producing currents that are tangential to the skull, have far less contribution to the EEG signal.
The meninges, cerebrospinal fluid and skull "smear" the EEG signal, obscuring its intracranial source.
It is mathematically impossible to reconstruct a unique intracranial current source for a given EEG signal,[1] as some currents produce potentials that cancel each other out. This is referred to as the inverse problem. However, much work has been done to produce remarkably good estimates of, at least, a localized electric dipole that represents the recorded currents.[citation needed]
EEG vs fMRI, fNIRS and PET[edit]
EEG has several strong points as a tool for exploring brain activity. EEGs can detect changes over milliseconds, which is excellent considering an action potential takes approximately 0.5-130 milliseconds to propagate across a single neuron, depending on the type of neuron.[33] Other methods of looking at brain activity, such as PET and fMRI have time resolution between seconds and minutes. EEG measures the brain's electrical activity directly, while other methods record changes in blood flow (e.g., SPECT, fMRI) or metabolic activity (e.g., PET, NIRS), which are indirect markers of brain electrical activity. EEG can be used simultaneously with fMRI so that high-temporal-resolution data can be recorded at the same time as high-spatial-resolution data, however, since the data derived from each occurs over a different time course, the data sets do not necessarily represent exactly the same brain activity. There are technical difficulties associated with combining these two modalities, including the need to remove the MRI gradient artifact present during MRI acquisition and the ballistocardiographic artifact (resulting from the pulsatile motion of blood and tissue) from the EEG. Furthermore, currents can be induced in moving EEG electrode wires due to the magnetic field of the MRI. EEG can be used simultaneously with NIRS without major technical difficulties. There is no influence of these modalities on each other and a combined measurement can give useful information about electrical activity as well as local hemodynamics.
EEG vs MEG[edit]
EEG reflects correlated synaptic activity caused by post-synaptic potentials of cortical neurons. The ionic currents involved in the generation of fast action potentials may not contribute greatly to the averaged field potentials representing the EEG .[9][34] More specifically, the scalp electrical potentials that produce EEG are generally thought to be caused by the extracellular ionic currents caused by dendritic electrical activity, whereas the fields producing magnetoencephalographic signals[35] are associated with intracellular ionic currents .[36]
EEG can be recorded at the same time as MEG so that data from these complementary high-time-resolution techniques can be combined.
Normal activity[edit]
The EEG is typically described in terms of (1) rhythmic activity and (2) transients. The rhythmic activity is divided into bands by frequency. To some degree, these frequency bands are a matter of nomenclature (i.e., any rhythmic activity between 6–12 Hz can be described as "alpha"), but these designations arose because rhythmic activity within a certain frequency range was noted to have a certain distribution over the scalp or a certain biological significance. Frequency bands are usually extracted using spectral methods (for instance Welch) as implemented for instance in freely available EEG software such as EEGLAB or the the neurophysiological biomarker toolbox.
Most of the cerebral signal observed in the scalp EEG falls in the range of 1–20 Hz (activity below or above this range is likely to be artifactual, under standard clinical recording techniques).
Comparison table of EEG rhythmic activity frequency bands[edit]
This article may be too technical for most readers to understand. (January 2013) |
Band | Frequency (Hz) | Location | Normally | Pathologically |
Delta | up to 4 | frontally in adults, posteriorly in children; high-amplitude waves |
Theta | 4 – 8 | Found in locations not related to task at hand |
Alpha | 8 – 13 | posterior regions of head, both sides, higher in amplitude on non-dominant side. Central sites (c3-c4) at rest |
Beta | >13 – 30 | both sides, symmetrical distribution, most evident frontally; low-amplitude waves |
Gamma | 30 – 100+ | Somatosensory cortex |
Mu | 8 – 13 | Sensorimotor cortex |
While these are the universally recognized frequency ranges that researchers tend to follow, many scholars use their own specific range boundaries depending on the frequencies they choose to focus on. Additionally, some researchers define the bands using decimal values rather than rounding to whole numbers (for example, one researcher may define the lower Beta band cut-off as 12.1, while another may use the value 13), while still others sometimes divide the bands into subbands for the purposes of data analysis.
Wave patterns[edit]
- Delta is the frequency range up to 4 Hz. It tends to be the highest in amplitude and the slowest waves. It is seen normally in adults in slow wave sleep. It is also seen normally in babies. It may occur focally with subcortical lesions and in general distribution with diffuse lesions, metabolic encephalopathy hydrocephalus or deep midline lesions. It is usually most prominent frontally in adults (e.g. FIRDA - Frontal Intermittent Rhythmic Delta) and posteriorly in children (e.g. OIRDA - Occipital Intermittent Rhythmic Delta).
- Theta is the frequency range from 4 Hz to 7 Hz. Theta is seen normally in young children. It may be seen in drowsiness or arousal in older children and adults; it can also be seen in meditation.[42] Excess theta for age represents abnormal activity. It can be seen as a focal disturbance in focal subcortical lesions; it can be seen in generalized distribution in diffuse disorder or metabolic encephalopathy or deep midline disorders or some instances of hydrocephalus. On the contrary this range has been associated with reports of relaxed, meditative, and creative states.
- Alpha is the frequency range from 8 Hz to 12 Hz. Hans Berger named the first rhythmic EEG activity he saw as the "alpha wave". This was the "posterior basic rhythm" (also called the "posterior dominant rhythm" or the "posterior alpha rhythm"), seen in the posterior regions of the head on both sides, higher in amplitude on the dominant side. It emerges with closing of the eyes and with relaxation, and attenuates with eye opening or mental exertion. The posterior basic rhythm is actually slower than 8 Hz in young children (therefore technically in the theta range). In addition to the posterior basic rhythm, there are other normal alpha rhythms such as the mu rhythm (alpha activity in the contralateral sensory and motor cortical areas that emerges when the hands and arms are idle; and the "third rhythm" (alpha activity in the temporal or frontal lobes).[43][44] Alpha can be abnormal; for example, an EEG that has diffuse alpha occurring in coma and is not responsive to external stimuli is referred to as "alpha coma".
- Beta is the frequency range from 12 Hz to about 30 Hz. It is seen usually on both sides in symmetrical distribution and is most evident frontally. Beta activity is closely linked to motor behavior and is generally attenuated during active movements.[45] Low amplitude beta with multiple and varying frequencies is often associated with active, busy or anxious thinking and active concentration. Rhythmic beta with a dominant set of frequencies is associated with various pathologies and drug effects, especially benzodiazepines. It may be absent or reduced in areas of cortical damage. It is the dominant rhythm in patients who are alert or anxious or who have their eyes open.
- Gamma is the frequency range approximately 30–100 Hz. Gamma rhythms are thought to represent binding of different populations of neurons together into a network for the purpose of carrying out a certain cognitive or motor function.[1]
- Mu ranges 8–13 Hz., and partly overlaps with other frequencies. It reflects the synchronous firing of motor neurons in rest state. Mu suppression is thought to reflect motor mirror neuron systems, because when an action is observed, the pattern extinguishes, possibly because of the normal neuronal system and the mirror neuron system "go out of sync", and interfere with each other.[41]
"Ultra-slow" or "near-DC" (Direct current) activity is recorded using DC amplifiers in some research contexts. It is not typically recorded in a clinical context because the signal at these frequencies is susceptible to a number of artifacts.
Some features of the EEG are transient rather than rhythmic. Spikes and sharp waves may represent seizure activity or interictal activity in individuals with epilepsy or a predisposition toward epilepsy. Other transient features are normal: vertex waves and sleep spindles are seen in normal sleep.
Note that there are types of activity that are statistically uncommon, but not associated with dysfunction or disease. These are often referred to as "normal variants." The mu rhythm is an example of a normal variant.
The normal Electroencephalography (EEG) varies by age. The neonatal EEG is quite different from the adult EEG. The EEG in childhood generally has slower frequency oscillations than the adult EEG.
The normal EEG also varies depending on state. The EEG is used along with other measurements (EOG, EMG) to define sleep stages in polysomnography. Stage I sleep (equivalent to drowsiness in some systems) appears on the EEG as drop-out of the posterior basic rhythm. There can be an increase in theta frequencies. Santamaria and Chiappa cataloged a number of the variety of patterns associated with drowsiness. Stage II sleep is characterized by sleep spindles—transient runs of rhythmic activity in the 12–14 Hz range (sometimes referred to as the "sigma" band) that have a frontal-central maximum. Most of the activity in Stage II is in the 3–6 Hz range. Stage III and IV sleep are defined by the presence of delta frequencies and are often referred to collectively as "slow-wave sleep." Stages I-IV comprise non-REM (or "NREM") sleep. The EEG in REM (rapid eye movement) sleep appears somewhat similar to the awake EEG.
EEG under general anesthesia depends on the type of anesthetic employed. With halogenated anesthetics, such as halothane or intravenous agents, such as propofol, a rapid (alpha or low beta), nonreactive EEG pattern is seen over most of the scalp, especially anteriorly; in some older terminology this was known as a WAR (widespread anterior rapid) pattern, contrasted with a WAIS (widespread slow) pattern associated with high doses of opiates. Anesthetic effects on EEG signals are beginning to be understood at the level of drug actions on different kinds of synapses and the circuits that allow synchronized neuronal activity (see: http://www.stanford.edu/group/maciverlab/).
Biological artifacts[edit]
Electrical signals detected along the scalp by an EEG, but that originate from non-cerebral origin are called artifacts. EEG data is almost always contaminated by such artifacts. The amplitude of artifacts can be quite large relative to the size of amplitude of the cortical signals of interest. This is one of the reasons why it takes considerable experience to correctly interpret EEGs clinically. Some of the most common types of biological artifacts include:
- Eye-induced artifacts (includes eye blinks, eye movements and extra-ocular muscle activity)
- ECG (cardiac) artifacts
- EMG (muscle activation)-induced artifacts
- Glossokinetic artifacts
The most prominent eye-induced artifacts are caused by the potential difference between the cornea and retina, which is quite large compared to cerebral potentials. When the eyes and eyelids are completely still, this corneo-retinal dipole does not affect EEG. However, blinks occur several times per minute, the eyes movements occur several times per second. Eyelid movements, occurring mostly during blinking or vertical eye movements, elicit a large potential seen mostly in the difference between the Electrooculography (EOG) channels above and below the eyes. An established explanation of this potential regards the eyelids as sliding electrodes that short-circuit the positively charged cornea to the extra-ocular skin.[46][47] Rotation of the eyeballs, and consequently of the corneo-retinal dipole, increases the potential in electrodes towards which the eyes are rotated, and decrease the potentials in the opposing electrodes.[48] Eye movements called saccades also generate transient electromyographic potentials, known as saccadic spike potentials (SPs).[49] The spectrum of these SPs overlaps the gamma-band (see Gamma wave), and seriously confounds analysis of induced gamma-band responses,[50] requiring tailored artifact correction approaches.[49] Purposeful or reflexive eye blinking also generates electromyographic potentials, but more importantly there is reflexive movement of the eyeball during blinking that gives a characteristic artifactual appearance of the EEG (see Bell's phenomenon).
Eyelid fluttering artifacts of a characteristic type were previously called Kappa rhythm (or Kappa waves). It is usually seen in the prefrontal leads, that is, just over the eyes. Sometimes they are seen with mental activity. They are usually in the Theta (4–7 Hz) or Alpha (8–13 Hz) range. They were named because they were believed to originate from the brain. Later study revealed they were generated by rapid fluttering of the eyelids, sometimes so minute that it was difficult to see. They are in fact noise in the EEG reading, and should not technically be called a rhythm or wave. Therefore, current usage in electroencephalography refers to the phenomenon as an eyelid fluttering artifact, rather than a Kappa rhythm (or wave).[51]
Some of these artifacts can be useful in various applications. The EOG signals, for instance, can be used to detect[49] and track eye-movements, which are very important in polysomnography, and is also in conventional EEG for assessing possible changes in alertness, drowsiness or sleep.
EKG artifacts are quite common and can be mistaken for spike activity. Because of this, modern EEG acquisition commonly includes a one-channel EKG from the extremities. This also allows the EEG to identify cardiac arrhythmias that are an important differential diagnosis to syncope or other episodic/attack disorders.
Glossokinetic artifacts are caused by the potential difference between the base and the tip of the tongue. Minor tongue movements can contaminate the EEG, especially in parkinsonian and tremor disorders.
Environmental artifacts[edit]
In addition to artifacts generated by the body, many artifacts originate from outside the body. Movement by the patient, or even just settling of the electrodes, may cause electrode pops, spikes originating from a momentary change in the impedance of a given electrode. Poor grounding of the EEG electrodes can cause significant 50 or 60 Hz artifact, depending on the local power system's frequency. A third source of possible interference can be the presence of an IV drip; such devices can cause rhythmic, fast, low-voltage bursts, which may be confused for spikes.
Artifact correction[edit]
Recently, independent component analysis techniques have been used to correct or remove EEG contaminates.[49][52][53][54][55] These techniques attempt to "unmix" the EEG signals into some number of underlying components. There are many source separation algorithms, often assuming various behaviors or natures of EEG. Regardless, the principle behind any particular method usually allow "remixing" only those components that would result in "clean" EEG by nullifying (zeroing) the weight of unwanted components. Fully automated artifact rejection methods, which use ICA, have also been developed.[56]
Abnormal activity[edit]
Abnormal activity can broadly be separated into epileptiform and non-epileptiform activity. It can also be separated into focal or diffuse.
Focal epileptiform discharges represent fast, synchronous potentials in a large number of neurons in a somewhat discrete area of the brain. These can occur as interictal activity, between seizures, and represent an area of cortical irritability that may be predisposed to producing epileptic seizures. Interictal discharges are not wholly reliable for determining whether a patient has epilepsy nor where his/her seizure might originate. (See focal epilepsy.)
Generalized epileptiform discharges often have an anterior maximum, but these are seen synchronously throughout the entire brain. They are strongly suggestive of a generalized epilepsy.
Focal non-epileptiform abnormal activity may occur over areas of the brain where there is focal damage of the cortex or white matter. It often consists of an increase in slow frequency rhythms and/or a loss of normal higher frequency rhythms. It may also appear as focal or unilateral decrease in amplitude of the EEG signal.
Diffuse non-epileptiform abnormal activity may manifest as diffuse abnormally slow rhythms or bilateral slowing of normal rhythms, such as the PBR.
Intracortical Encephalogram electrodes and sub-dural electrodes can be used in tandem to discriminate and discretize artifact from epileptiform and other severe neurological events.
More advanced measures of abnormal EEG signals have also recently received attention as possible biomarkers for different disorders such as Alzheimer's disease.[57]
Various uses[edit]
This section relies on references to primary sources. (May 2012) |
The EEG has been used for many purposes besides the conventional uses of clinical diagnosis and conventional cognitive neuroscience. An early use was during World War II by the U.S. Army Air Corps to screen out pilots in danger of having seizures;[58] long-term EEG recordings in epilepsy patients are still used today for seizure prediction. Neurofeedback remains an important extension, and in its most advanced form is also attempted as the basis of brain computer interfaces. The EEG is also used quite extensively in the field of neuromarketing.
Honda is attempting to develop a system to enable an operator to control its Asimo robot using EEG, a technology it eventually hopes to incorporate into its automobiles.[59]
EEGs have been used as evidence in trials in the Indian state of Maharastra.[60][61]
EEG and Remote Communication[edit]
The United States Army Research Office budgeted $4 million in 2009 to researchers at the University of California, Irvine to develop EEG processing techniques to identify correlates of imagined speech and intended direction to enable soldiers on the battlefield to communicate via computer-mediated reconstruction of team members' EEG signals, in the form of understandable signals such as words.[62]
Low-cost EEG Devices[edit]
Inexpensive EEG devices exist for the low-cost research and consumer markets. Recently, a few companies have miniaturized medical grade EEG technology to create versions accessible to the wider public. Some of these companies have even built commercial EEG devices retailing for less than $100 USD.
- In 2004 OpenEEG released its ModularEEG as open source hardware. Compatible open source software includes a game for balancing a ball.
- In 2007 NeuroSky released the first affordable consumer based EEG along with the game NeuroBoy. This was also the first large scale EEG device to use dry sensor technology.[63]
- In 2008 OCZ Technology developed device for use in video games relying primarily on electromyography.
- In 2008 the Final Fantasy developer Square Enix announced that it was partnering with NeuroSky to create a game, Judecca.[64][65]
- In 2009 Mattel partnered with NeuroSky to release the Mindflex, a game that used an EEG to steer a ball through an obstacle course. By far the best selling consumer based EEG to date.[64][66]
- In 2009 Uncle Milton Industries partnered with NeuroSky to release the StarWars Force Trainer, a game designed to create the illusion of possessing The Force.[64][67]
- In 2009 Emotiv released the EPOC, a 14 channel EEG device. The EPOC is the first commercial BCI to not use dry sensor technology, requiring users to apply a saline solution to their head.[68]
- In 2010, NeuroSky added a blink and electromyography function to the MindSet.[69]
- In 2011, NeuroSky released the MindWave, an EEG device designed for educational purposes and games.[70] The MindWave won the Guinness Book of World Records award for "Heaviest machine moved using a brain control interface".[71]
- In 2012, a Japanese gadget project, neurowear, released Necomimi: a headset with motorized cat ears. The headset is a NeuroSky MindWave unit with two motors on the headband where a cat's ears might be. Slipcovers shaped like cat ears sit over the motors so that as the device registers emotional states the ears move to relate. For example, when relaxed, the ears fall to the sides and perk up when excited again.
EEG electroencephalophone used during a music performance in which bathers from around the world were networked together as part of a collective musical performance, using their brainwaves to control sound, lighting, and the bath environment[citation needed]
See also[edit]
- 10-20 system (EEG)
- Binaural beats
- Brain-computer interface
- Brainwave synchronization
- CAET-Canadian association of EEG Technology
- Comparison of consumer brain-computer interface devices
- Direct brain interfaces
- EEG measures during anesthesia
- EEG microstates
- Electrocorticography
- Electromagnetic Weapon
- Electroneurogram
- Electropalatograph
- Emotiv Systems
- European data format
- Event-related potential
- Evoked potential
- FieldTrip
- God helmet
- Hemoencephalography
- Imagined Speech
- Induced activity
- Intracranial EEG
- Local field potentials
- Magnetoencephalography
- Mind machine
- Neural oscillations
- Neurofeedback
- Ongoing brain activity
- Spontaneous potential
- ^ a b c d e Niedermeyer E. and da Silva F.L. (2004). Electroencephalography: Basic Principles, Clinical Applications, and Related Fields. Lippincot Williams & Wilkins. ISBN 0-7817-5126-8.
- ^ Atlas of EEG & Seizure Semiology. B. Abou-Khalil; Musilus, K.E.; Elsevier, 2006.
- ^ Article must be purchased. Swartz, B.E; Goldensohn, ES (1998). "Timeline of the history of EEG and associated fields" (PDF). Electroencephalography and clinical Neurophysiology 106 (2): 173–176. doi:10.1016/S0013-4694(97)00113-2. PMID 9741779.
- ^ Pravdich-Neminsky, VV. (1913). "Ein Versuch der Registrierung der elektrischen Gehirnerscheinungen". Zbl Physiol 27: 951–960.
- ^ Haas, L F (2003). "Hans Berger (1873-1941), Richard Caton (1842-1926) and electroencephalography". Journal of Neurology, Neurosurgery & Psychiatry 74 (1): 9. doi:10.1136/jnnp.74.1.9. PMC 1738204. PMID 12486257.
- ^ Millet, David (2002). "The Origins of EEG". International Society for the History of the Neurosciences (ISHN).
- ^ Tatum, W. O., Husain, A. M., Benbadis, S. R. (2008) "Handbook of EEG Interpretation" Demos Medical Publishing.
- ^ a b Nunez PL, Srinivasan R (1981). Electric fields of the brain: The neurophysics of EEG. Oxford University Press.
- ^ Klein, S.; Thorne, B. M. (3 October 2006). Biological psychology. New York, N.Y.: Worth. ISBN 0-7167-9922-7.
- ^ Whittingstall, K; Logothetis, NK. (2009). "Frequency-band coupling in surface EEG reflects spiking activity in monkey visual cortex". Neuron 64 (2): 281–9. doi:10.1016/j.neuron.2009.08.016. PMID 19874794.
- ^ Vespa, P., Nenov, V., & Nuwer, M. (1999). Continuous EEG monitoring in the intensive care unit: early findings and clinical efficacy. J Clin Neurophysiol, 16: 1–13.
- ^ a b Hamalainen, M., Riitta, H., Ilmoniemi, R., Knuutila, J., & Lounasmaa, O. (1993). Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain. Reviews of Modern Physics, 65(2), 414-497.
- ^ O'Regan, S., Faul, S., & Marnane, W. (2010). "Automatic detection of EEG artefacts arising from head movements." Engineering in Medicine and Biology Society (EMBC), 2010 Annual International Conference of the IEEE, Buenos Aires, Argentina, August 31 - September 4, 2010, 6353-6356.
- ^ Murphy, K., & Brunberg, J. (1997). "Adult claustrophobia, anxiety and sedation in MRI." Magnetic Resonance Imaging, 15(1), 51-54.
- ^ Schenck, J. (1996). "The role of magnetic susceptibility in magnetic resonance imaging: MRI magnetic compatibility of the first and second kinds." Med. Phys., 23(6), 815-850
- ^ a b Yasuno et al. (2008). "The PET Radioligand [11C]MePPEP Binds Reversibly and with High Specific Signal to Cannabinoid CB1 Receptors in Nonhuman Primate Brain". Neuropsychopharmacology 33: 259–269.
- ^ Mulholland, T. (1973). "Objective EEG methods for studying covert shifts of visual attention." In F. J. McGuigan and J. Schoonover (Eds.), The Psychophysiology of thinking. Academic Press: New York, 109-151.
- ^ Hinterberger, T., Kübler, A., Kaiser, J., Neumann, N., & Birbaumer, N. (2003). A brain-computer interface (BCI) for the locked-in: comparison of different EEG classifications for the thought translation device. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology, 114(3), 416-25.
- ^ Sereno, S. C., Rayner, K., & Posner, M. I. (1998). Establishing a time-line of word recognition: evidence from eye movements and event-related potentials. Neuroreport, 9(10), 2195-200. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/9694199
- ^ http://www.sciencedaily.com/releases/2013/03/130319102757.htm
- ^ Srinivasan, R. (1999). Methods to Improve the Spatial Resolution of EEG. International Journal, 1(1), 102-111.
- ^ Schlögl, A., Slater, M., & Pfurtscheller, G. (2002). Presence research and EEG Properties of EEG recordings. Proceedings of the 5th Annual International Workshop PRESENCE. Porto, Portugal, October 9–11.
- ^ Horovitz, S. G., Skudlarski, P., & Gore, J. C. (2002). Correlations and dissociations between BOLD signal and P300 amplitude in an auditory oddball task: a parametric approach to combining fMRI and ERP. Magnetic Resonance Imaging, 20, 319 -325.
- ^ Laufs H., Kleinschmidt A., Beyerle A., Eger E., Salek-haddadi A., Preibisch C., Krakow K. (2003). "EEG-correlated fMRI of human alpha activity". NeuroImage 19 (4): 1463–1476. doi:10.1016/S1053-8119(03)00286-6. PMID 12948703.
- ^ DiFrancesco, M., Holland, S., & Szaflarski, J. (2008). Simultaneous EEG/Functional Magnetic Resonance Imaging at 4 Tesla: Correlates of Brain Activity to Spontaneous Alpha Rhythm During Relaxation. J Clin Neurophysiol., 25(5), 255-264.
- ^ Huizenga, H. M., van Zuijen, T. L., Heslenfeld, D. J., & Molenaar, P. C. (2001). Simultaneous MEG and EEG source analysis. Physics in medicine and biology, 46(7), 1737-51. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/11474922
- ^ Schreckenberger M., Lange-Asschenfeldt C., Lange-Asschenfeld C., Lochmann M., Mann K., Siessmeier T., Buchholz H.-G. et al. (2004). "The thalamus as the generator and modulator of EEG alpha rhythm: a combined PET/EEG study with lorazepam challenge in humans". NeuroImage 22 (2): 637–44. doi:10.1016/j.neuroimage.2004.01.047. PMID 15193592.
- ^ Towle VL, Bolaños J, Suarez D, Tan K, Grzeszczuk R, Levin DN, Cakmur R, Frank SA, Spire JP. (1993). "The spatial location of EEG electrodes: locating the best-fitting sphere relative to cortical anatomy". Electroencephalogr Clin Neurophysiol 86 (1): 1–6. doi:10.1016/0013-4694(93)90061-Y. PMID 7678386.
- ^ &Na; (1994). "Guideline seven: a proposal for standard montages to be used in clinical EEG. American Electroencephalographic Society.". Journal of Clinical Neurophysiology 11 (1): 30–6. doi:10.1097/00004691-199401000-00008. PMID 8195424.
- ^ H. Aurlien, I.O. Gjerde, J. H. Aarseth, B. Karlsen, H. Skeidsvoll, N. E. Gilhus (March 2004). "EEG background activity described by a large computerized database.". Clinical Neurophysiology 115 (3): 665–673. doi:10.1016/j.clinph.2003.10.019. PMID 15036063.
- ^ Nunez P.L. and Pilgreen K.L. (1991). "The spline-Laplacian in clinical neurophysiology: a method to improve EEG spatial resolution". J Clin Neurophysiol 8 (4): 397–413. doi:10.1097/00004691-199110000-00005. PMID 1761706.
- ^ Anderson, J. (22 October 2004). Cognitive Psychology and Its Implications (HardcoverISBN 0-7167-0110-3. ) (6th ed.). New York, NY: Worth. p. 17.
- ^ Creutzfeldt OD, Watanabe S, Lux HD (1966). "Relations between EEG phenomena and potentials of single cortical cells. I. Evoked responses after thalamic and epicortical stimulation". Electroencephalogr Clin Neurophysiol 20 (1): 1–18. doi:10.1016/0013-4694(66)90136-2. PMID 4161317.
- ^ Hamalainen M, Hari R, Ilmoniemi RJ, Knuutila J, Lounasmaa OV (1993). "Magnetoencphalography - Theory, instrumentation, and applications to noninvasive studies of the working human brain". Reviews of Modern Physics 65 (2): 413–497. Bibcode:1993RvMP...65..413H. doi:10.1103/RevModPhys.65.413.
- ^ Buzsaki G (2006). Rhythms of the brain. Oxford University Press. ISBN 0-19-530106-4.
- ^ a b Kirmizialsan, E.; Bayraktaroglu, Z.; Gurvit, H.; Keskin, Y.; Emre, M.; Demiralp, T. (2006). "Comparative analysis of event-related potentials during Go/NoGo and CPT: Decomposition of electrophysiological markers of response inhibition and sustained attention". Brain Research 1104 (1): 114–128. doi:10.1016/j.brainres.2006.03.010. PMID 16824492.
- ^ Kisley, M. A.; Cornwell, Z. M. (2006). "Gamma and beta neural activity evoked during a sensory gating paradigm: Effects of auditory, somatosensory and cross-modal stimulation". Clinical Neurophysiology 117 (11): 2549–2563. doi:10.1016/j.clinph.2006.08.003. PMC 1773003. PMID 17008125.
- ^ Kanayama, N.; Sato, A.; Ohira, H. (2007). "Crossmodal effect with rubber hand illusion and gamma-band activity". Psychophysiology 44 (3): 392–402. doi:10.1111/j.1469-8986.2007.00511.x. PMID 17371495.
- ^ Gastaut, H. (1952). "Etude electrocorticographique de al reactivite des rhytmes rolandiques". Rev. Neurol 87 (2): 176–182. PMID 13014777.
- ^ a b Oberman, LM; Hubbard, EM; McCleery, JP; Altschuler, EL; Ramachandran, VS; Pineda, JA (2005). "EEG Evidence for mirror neuron dysfunction in autism spectrum disorders". Cognitive Brain Research 24 (2): 190–198. doi:10.1016/j.cogbrainres.2005.01.014. PMID 15993757.
- ^ Cahn, B.R.; Polich, J. (2006). "Meditation states and traits: EEG, ERP, and neuroimaging studies". Psychological Bulletin 132 (2): 180–211. doi:10.1037/0033-2909.132.2.180. PMID 16536641.
- ^ Niedermeyer, E (1997). "Alpha rhythms as physiological and abnormal phenomena". Int J Psychophysiol 26 (1–3): 31–49. doi:10.1016/S0167-8760(97)00754-X. PMID 9202993.
- ^ Feshchenko, VA; Reinsel, RA; Veselis, RA (2001). "Multiplicity of the alpha rhythm in normal humans". J Clin Neurophysiol 18 (4): 331–44. doi:10.1097/00004691-200107000-00005. PMID 11673699.
- ^ Pfurtscheller G, Lopes da Silva FH (1999). "Event-related EEG/MEG synchronization and desynchronization: basic principles". Clin Neurophysiol 110 (11): 1842–1857. doi:10.1016/S1388-2457(99)00141-8. PMID 10576479.
- ^ Barry, W; Jones, GM (1965). "INFLUENCE OF EYE LID MOVEMENT UPON ELECTRO-OCULOGRAPHIC RECORDING OF VERTICAL EYE MOVEMENTS". Aerospace medicine 36: 855–858. PMID 14332336.
- ^ Iwasaki, M.; Kellinghaus, C.; Alexopoulos, A.V.; Burgess, R.C.; Kumar, A.N.; Han, Y.H.; Lüders, H.O.; Leigh, R.J. (2005). "Effects of eyelid closure, blinks, and eye movements on the electroencephalogram". Clinical Neurophysiology 116 (4): 878–885. doi:10.1016/j.clinph.2004.11.001. PMID 15792897.
- ^ Lins, O.G.; Picton, T.W.; Berg, P.; Scherg, M. (1993). "Ocular artifacts in EEG and event-related potentials I: Scalp topography". Brain Topography 6 (1): 51–63. doi:10.1007/BF01234127. PMID 8260327.
- ^ a b c d Keren, A.S.; Yuval-Greenberg, S.; Deouell, L.Y. (2010). "Saccadic spike potentials in gamma-band EEG: Characterization, detection and suppression". Neuroimage 49 (3): 2248–2263. doi:10.1016/j.neuroimage.2009.10.057. PMID 19874901.
- ^ Yuval-Greenberg, S.; Tomer, O.; Keren, A.S.; Nelken, I.; Deouell, L.Y. (2008). "Transient Induced Gamma-Band Response in EEG as a Manifestation of Miniature Saccades". Neuron 58 (3): 429–441. doi:10.1016/j.neuron.2008.03.027. PMID 18466752.
- ^ Epstein, Charles M. (1983). Introduction to EEG and evoked potentials. J. B. Lippincot Co. ISBN 0-397-50598-1.
- ^ Jung, TP; Makeig, S; Humphries, C; Lee, TW; McKeown, MJ; Iragui, V; Sejnowski, TJ (2000). "Removing electroencephalographic artifacts by blind source separation". Psychophysiology 37 (2): 163–178. doi:10.1017/S0048577200980259. PMID 10731767.
- ^ Jung, T.P.; Makeig, S.; Westerfield, M.; Townsend, J.; Courchesne, E.; Sejnowski, T.J. (2000b). "Removal of eye activity artifacts from visual event-related potentials in normal and clinical subjects". Clinical Neurophysiology 111 (10): 1745–1758. doi:10.1016/S1388-2457(00)00386-2. PMID 11018488.
- ^ Joyce, Carrie A.; Gorodnitsky, Irina F.; Kutas, Marta (2004). "Automatic removal of eye movement and blink artifacts from EEG data using blind component separation". Psychophysiology 41 (2): 313–325. doi:10.1111/j.1469-8986.2003.00141.x. PMID 15032997.
- ^ Shackman, AJ; McMenamin, BW; Maxwell, JS; Greischar, LL; Davidson, RJ (2010). "Identifying robust and sensitive frequency bands for interrogating neural oscillations". NeuroImage 51 (4): 1319–1333. doi:10.1016/j.neuroimage.2010.03.037. PMC 2871966. PMID 20304076.
- ^ Nolan, H.; Whelan, R.; Reilly, R.B. (2010). "FASTER: Fully Automated Statistical Thresholding for EEG artifact Rejection". Journal of Neuroscience Methods 192 (1): 152–162. doi:10.1016/j.jneumeth.2010.07.015. PMID 20654646.
- ^ Montez T, Poil S-S, Jones BF, Manshanden I, Verbunt JPA, van Dijk BW, Brussaard AB, van Ooyen A, Stam CJ, Scheltens P, Linkenkaer-Hansen K (2009). "Altered temporal correlations in parietal alpha and prefrontal theta oscillations in early-stage Alzheimer disease". PNAS 106 (5): 1614–1619. Bibcode:2009PNAS..106.1614M. doi:10.1073/pnas.0811699106. PMC 2635782. PMID 19164579.
- ^ Keiper, Adam. "The Age of Neuroelectronics". The New Atlantis.
- ^ Mind over matter: Brain waves control Asimo 1 Apr 2009, Japan Times
- ^ This brain test maps the truth 21 Jul 2008, 0348 hrs IST, Nitasha Natu,TNN
- ^ "Puranik, D.A., Joseph, S.K., Daundkar, B.B., Garad, M.V. (2009). Brain Signature profiling in India. Its status as an aid in investigation and as corroborative evidence – as seen from judgments. Proceedings of XX All India Forensic Science Conference, 815 – 822, November 15 – 17, Jaipur.".
- ^ MURI: Synthetic Telepathy. Cnslab.ss.uci.edu. Retrieved 2011-07-19.
- ^ "Mind Games". The Economist. 2007-03-23.
- ^ a b c Li, Shan (2010-08-08). "Mind reading is on the market". Los Angeles Times.
- ^ "Brains-on with NeuroSky and Square Enix's Judecca mind-control game". Engadget. Retrieved 2010-12-02.
- ^ "New games powered by brain waves". Physorg.com. Retrieved 2010-12-02.
- ^ Snider, Mike (2009-01-07). "Toy trains 'Star Wars' fans to use The Force". USA Today. Retrieved 2010-05-01.
- ^ "Emotiv Systems Homepage". Emotiv.com. Retrieved 2009-12-29.
- ^ "News - NeuroSky Upgrades SDK, Allows For Eye Blink, Brainwave-Powered Games". Gamasutra. 2010-06-30. Retrieved 2010-12-02.
- ^ Fiolet, Eliane. "NeuroSky MindWave Brings Brain-Computer Interface to Education". www.ubergizmo.com. Ubergizmo.
- ^ "NeuroSky MindWave Sets Guinness World Record for "Largest Object Moved Using a Brain-Computer Interface"". NeuroGadget.com. NeuroGadget.
External links[edit]
Look up electroencephalography, electroencephalogram, electroencephalograph, or brainwave in Wiktionary, the free dictionary. |
- A tutorial on simulating and estimating EEG sources in Matlab
- A tutorial on analysis of ongoing, evoked, and induced neuronal activity: Power spectra, wavelet analysis, and coherence
- Scholarpedia EEG
- FASTER A fully automated, unsupervised method for processing of high density EEG data. FASTER has been peer-reviewed, it is free and the software is open source. The FASTER software is available here.
- Video demonstration of placement of electrodes
- OpenEEG The OpenEEG project makes hardware plans and software for do-it-yourself EEG devices in an Open Source manner. The hardware is aimed toward amateurs who would like to experiment with EEG.
- [1] Canadian association of EEG techs (CAET)


text:
All my other RPs are taking off. C'mon, this one needs some love too! D=
So myself and one other person have decided this sounds like it'd be fun and have come up with an idea to bring the two worlds together.
So for those familiar with the events at the end of the Shaman King anime, we decided that the events would go awry and Zeke would achieve his only Shaman world as well as the King of Spirits. As a last ditch attempt to save Yoh and the gang, the King would make a portal before he is absorbed by Zeke and the gang would be send to the Fire Emblem universe. But on the way to the new world, Yoh and his friends get separated, ending up in different areas, each knowing nothing of their friends's fate. We're thinking to have the others end up captured and Yoh needs to make new friends to team up with and save them.
For characters, anyone is available from both genres and for Fire Emblem, you can choose from any of the games. Made ups from each universe are allowed too though there a lot of characters to choose from so hopefully people will be still play them too.
"Listen to me. I haven't even shown you anything yet. Don't die old man!" -Rin Okumura
All my other RPs are taking off. C'mon, this one needs some love too! D=
"Listen to me. I haven't even shown you anything yet. Don't die old man!" -Rin Okumura
well it might got a little bump XD
-a warrior is guided, driven by heart and mind, a solider goes to war and dies.
-greatness comes to those who take it.
manga typesetter and cleaner
my first DBMA Gathering: http://www.youtube.com/watch?v=L1RzBzl_O3o
if you say that a women belongs into tha kitchen i feel sorry for ya. -.-
why? O.o
couse you dont know what to do with her in bed.
I express interest but in all honesty I doubt this will pick up.

subset: commoncrawl


text:
Pierce County prosecutors and state tax collectors sent county Assessor-Treasurer Dale Washam a stern message Monday: Do your job.
Washam replied that he never stopped doing it, and accused local leaders of abusing legal process. But internal documents from his office and his own prior statements tell a different story.
The clash could come to a head Thursday in Superior Court, when a judge will hear the county argue for a writ of mandate, filed by prosecutors Monday, that would compel Washam's office to continue inspecting new construction in the county and report the associated values by Aug. 31.
That's a state deadline, written into law, applicable to all county assessors.
The county's writ would leave Washam two options: He could argue against it in court, or simply continue to inspect new construction according to his duties under law.
Prosecutor Mark Lindquist hopes for the second option.
"If in fact he does it, we'll call that a victory for Pierce County taxpayers," Lindquist said Monday. "He can end this any time by just agreeing to do his job."
If Washam tries to fight the writ, he'll face opposition from the state as well as county leaders. Monday, the state Department of Revenue underlined the county's concerns and ordered Washam to continue inspections of new construction.
Technically, Washam's staff member still were working on new construction Monday – but the threat of stopping that work has been in play since mid-June, alarming county leaders who are beginning to build next year's budget.
New construction, meaning new homes and improvements, adds new money to budgets, for the county as well as cities, schools, fire districts and other local government agencies.
Fairness is another factor. Not inspecting new construction means property owners who build homes or additions become "free riders," going for a year or more without paying taxes while existing property owners pay the full freight.
The standoff between the assessor and county leaders stems from an order Washam gave to his staff in June. Through a subordinate, he ordered property appraisers to stop inspections of new construction July 1, and return to continuing physical inspections of existing properties.
Inspecting existing properties is Washam's signature issue. He believes past property assessments were tainted by his predecessor's use of computer models. He wants to correct them all, though state records show the values met or exceeded international standards of accuracy.
What's more, Washam has already met his quota of existing inspections for the year. He reported his success to the Revenue Department last month.
The trouble is Washam wants to keep going. He's placing a longer deadline in front of a shorter one. He wants to finish next year's physical inspections, which aren't due until May 31, 2013.
Monday's order from the Revenue Department tells Washam to deal with new construction first, and stick to a plan he agreed to follow in 2009. That plan includes a stipulation to complete all new construction inspections each year.
"It is our understanding that you intend to divert residential appraisal staff from assessing new construction to inspection of existing property," states the letter, written by Kathy Beith, assistant director of the agency's property tax division.
"If this occurs and you do not assess all taxable new construction, you will not be in compliance with your approved revaluation plan."
Washam did not respond to questions The News Tribune sent to his office Monday. He spoke briefly to a KOMO-TV reporter who asked about the new construction issue.
"We were on point to be done at all times," Washam said.
That's not what he said last month. In a June 13 e-mail to appraisers, Washam's chief deputy, Albert Ugas, told staff members to stop inspecting new construction July 1 a month before the state deadline.
On June 14, in a memo to the county's Budget and Finance Department, Washam said his office would be unable to complete new construction inspections.
On June 27, a County Council subcommittee voted to funnel $20,000 in emergency funding to Washam's budget to assist with new construction inspections. Washam then ordered his staff to work new construction for one more week.
The record appears in an e-mail from Gary Foreman, an appraisal supervisor.
"As a result of a meeting and decision this afternoon, Mr. Washam gave orders to continue the pickup of new construction another week, through July 6," Foreman wrote.
Washam also spoke to county staff members about halting new construction inspections. In late June, after the council's decision to spend $20,000, Washam spoke to Gary Robinson, who heads the county Budget and Finance Department.
According to Robinson, Washam said $20,000 wouldn't be enough to finish the new construction work. Robinson asked how much Washam needed.
"At the end of the conversation, he indicated $150,000," Robinson said. "He initially gave me a range of $140,000 to $160,000."
Whether Washam will appear in court Thursday is unclear. If he doesn't, one likely outcome is approval of the county's writ: an order with legal force he'll be obligated to follow.
"If he doesn't show up, that court order becomes binding, and we have an insurance policy," Lindquist said.


text:
version: UK | USA | International
Sort: publication date | titles A - Z
The period following the death of a loved one can be a time of great turmoil. This sensitive book acts as a supportive road map through the initial period of loss, and through the weeks and months that follow.
June 2013, Paperback: £12.99/ $19.95Keywords: Alzheimer's disease, bereavement, cancer, carers, children, counselling, death, dementia, depression, families, grief, health care, intellectual disabilities, suicide
This comprehensive guide for practitioners working in end of life care covers everything from the different roles in the multi-disciplinary care team, the stages that a patient at the end of their life experiences and the professional help needed at each stage and gives a complete grounding of the current climate and philosophy in end of life care. more »
November 2013, Paperback: £19.99/ $29.95Keywords: adults, Alzheimer's disease, art therapy, arts therapies, cancer, creative therapies, creativity, death, dementia, dramatherapy, music therapy, older people, pain management, palliative care
Personalisation builds on person-centred care to focus on how people with dementia can have more choice and control in their lives, and be supported to be part of their community. This practical guide explains how to deliver personalised services and support for people with dementia through simple, evidence-based person-centred practices and tools. more »
October 2013, Paperback: £25.00/ $39.95Keywords: adults, Alzheimer's disease, carers, communication, community care, dementia, domicilary care, health care, nursing, older people, palliative care, person-centred, personalisation, residential care, social care, social work
The period following the death of a loved one can be a time of great turmoil. This sensitive book acts as a helpful and supportive road map through the initial period of loss, and the weeks and months that follow. As well as the emotional and spiritual aspects of bereavement, it covers important practical considerations, which are often overlooked. more »
June 2013, Paperback: £12.99/ $19.95Keywords: Alzheimer's disease, bereavement, cancer, carers, children, counselling, death, dementia, depression, families, grief, health care, intellectual disabilities, suicide
With a practical focus, this book will equip readers with the skills, knowledge and confidence necessary to lead person-centred dementia care. The areas explored are relevant across a range of care settings, and to all those in, or starting, either a managerial or non-managerial leadership role within a dementia care service. more »
2012, Paperback: £16.99/ $29.95Keywords: adults, Alzheimer's disease, carers, communication, dementia, employment, health care, nursing, older people, person-centred, residential care, social care
Focusing on theoretical, policy and practice issues predicted to become increasingly important, this book looks at dementia care across the globe, including how policy is developed, and the range of approaches that can be taken, with insight from clinicians, policy influencers and researchers who discuss case studies and effective strategies. more »
2012, Paperback: £24.99/ $42.50Keywords: adults, Alzheimer's disease, community care, dementia, health care, nursing, older people, person-centred, residential care, social care, social policy, social work
This fourth edition contains all the latest research on the use of the PAL Instrument, new information on using the PAL Checklist to carry out sensory interventions and information about how a new online PAL tool supports the book. It features photocopiable activity checklists and plans that help to match users' abilities with activities. more »
2011, Paperback: £26.99/ $45.00Keywords: adults, Alzheimer's disease, carers, cognitive behavioural therapy, dementia, disability, nursing, occupational therapy, older people, person-centred, social care
Introducing the concept of PIE (Planning, Implementation and Evaluation), this resource will enable professionals working with older people to initiate and run successful activity-based programmes, either individually or in groups. The authors guide the reader through the processes, and provide step-by-step instructions for a range of activities. more »
2011, Paperback: £19.99/ $32.95Keywords: adults, Alzheimer's disease, art therapy, carers, dance and movement therapy, dementia, dramatherapy, occupational therapy, older people
The author shows beyond question that neglectful care is a systemic blight, rather than mere local blemish, within our health services. He analyses the causes and factors involved, reveals the widespread denial and lack of accountability from those responsible, and spells out implications of this failure to care for the vulnerable with humanity. more »
2011, Paperback: £19.99/ $39.95Keywords: Alzheimer's disease, cancer, dementia, disability, disability law, health care, mental health, nursing, occupational therapy, older people, palliative care, pastoral care, practical theology, risk assessment, social care, social policy, trauma
This book outlines some of the key issues in risk perception, assessment and management in dementia care in a way that is both practical and accessible to a wide range of practitioners. It develops an approach to risk that promotes choice for people with dementia whilst also acknowledging the complex challenges care providers face. more »
2011, Paperback: £16.99/ $32.95Keywords: adult protection, adults, Alzheimer's disease, carers, dementia, nursing, older people, palliative care, person-centred, risk assessment, social care
Reminiscence is a valuable tool for the professional carer as well as those looking after a family member or friend. It enhances and enriches the care relationship, and benefits both the person being cared for and the carer. This fully-updated fourth edition is full of practical information on planning and running successful reminiscence work. more »
2011, Paperback: £19.99/ $34.95Keywords: adults, Alzheimer's disease, arts therapies, bereavement, carers, counselling, creative therapies, dementia, depression, grief, older people, palliative care, social work
Alcohol misuse is becoming an increasingly significant issue for people aged 55 and over. This practical guide explores the factors that differentiate older drinkers, and introduces an innovative person-centred model that will help counsellors and other healthcare professionals to them the help and support they need. more »
2011, Paperback: £20.99/ $34.95Keywords: addiction, adult protection, adults, alcohol, Alzheimer's disease, anxiety, carers, communication, community care, counselling, dementia, depression, occupational therapy, older people, pastoral care, person-centred, psychiatry, psychology, psychotherapy, residential care, self esteem, social care, social work, substance abuse, supervision, supported living
This book clearly explains what happens to communication as dementia progresses. Advocating a person-centred approach to dementia care, the author describes methods of verbal and non-verbal communication, techniques for communicating with people who cannot speak or move easily, and strategies for communicating more effectively. more »
2011, Paperback: £12.99/ $18.95Keywords: adults, Alzheimer's disease, carers, communication, dementia, nursing, older people, person-centred, residential care
This book provides night staff, their managers and anyone else with an interest in care homes with the information and practical skills they need to deliver appropriate care at night. The authors look at nutrition and hydration, continence, challenging behaviour, medication, night time checking, pain management and end of life care. more »
2010, Paperback: £19.99/ $32.95Keywords: adult protection, adults, Alzheimer's disease, dementia, drugs, elder abuse, employment, older people, palliative care, person-centred
This book looks at how to assess social skills and the qualities needed in a friend. Sharing interests can provide companionship and promote self-esteem, but some relationships and friendships can become negative or burdensome, and this book offers useful guidance on supporting service users in managing these relationships. more »
2010, Paperback: £14.99/ $24.95Keywords: adult protection, adults, advocacy, Alzheimer's disease, carers, communication, community care, dementia, disability, elder abuse, emotions, health care, intellectual disabilities, nonverbal learning disabilities, nursing, older people, person-centred, relationships, residential care, risk assessment, social care, social work, supported living
In this book, thirty carers from different backgrounds and circumstances share their experiences of caring for a parent, partner or friend with dementia. This unique collection of personal accounts will be an engaging read for anyone affected by dementia in a personal or professional context, including social workers, practitioners and care staff. more »
2009, Paperback: £14.99/ $24.95Keywords: Alzheimer's disease, dementia, families, health care, older people, social care
(29 titles match the current selection)


text:
Earn 2,000 Sony Rewards points on this purchase.
No interest financing available.
Explore your payment options >
Enjoy unlimited creativity and image control thanks to Intelligent Preview which allows you to adjust exposure and white balance. You can also fine-tune contrast, saturation, sharpness and brightness to achieve the precise tonalities and artistic effects your creativity requires.
Brilliantly capture your subject and expand your creativity with an unlimited range of accessories. From lenses and flashes to filters and grips, the A850 offers solutions to satisfy even the most demanding photographer.
Zeiss and G Badges
The finest build quality to match the finest in imaging. The α A850 is constructed of a rugged and lightweight magnesium-alloy body for durability, while the moisture and dust-resistant design make this DSLR camera safe to use in a variety of environments.
With an image precapture, you can display the effect of adjustments to exposure, white balance and Dynamic Range Optimizer on the LCD allowing you to fine tune your shots in advance.
DRO analyzes the scene and automatically adjusts the balance of highlight and shadow to assure optimum exposure balance, with richer image highlight and shadow detail.
Adjust contrast, saturation, sharpness, brightenss and zone matching in up to 13 Image Styles to achieve the precise tonalities and artistic effects your creativity requires.
Ruggedly constructed for years of service, the body is constructed of strong and remarkably light magnesium-alloy. Balance and handling are superb with intuitive ergonomics.
The high-precision shutter unit is built to withstand the demands of 1/8000 sec shutter speeds, 3fps continuous shooting, and is rated for 100,000 release cycles.
Controls, terminals, viewfinder and other sensitive components are protected by dust and moisture resistant seals for long term reliability in a wide range of environments.
Offering a lens for virtually every need, Sony's α (alpha) system includes top-quality G series and Carl Zeiss? lenses crafted to the highest standards of optical precision as well as a wide-ranging selection of other high performance lenses.
At the top of the α (alpha) lighting system, the new HVL-F58AM flash allows the head to pivot 90 left or right maintaining correct camera/flash orientation during both horizontal and vertical shooting.
HVL-F58AM can control sophisticated multi-flash off-camera setups, comprising up to 3 flash groups, with flash ratio balance among groups to achieve creative lighting results.
PhotoTV HD is a new way to view photos which brings out radiant beauty in every detail, filling the room with luminous, high-resolution images that more closely matches the natural look of printed photographs.
Packed with innovative features to get the best shot, the rugged Sony α850 DSLR camera features a 35mm full frame 24.6 megapixel Exmor™ CMOS image sensor that provides a larger capture area, improved wide angle performance, and tighter depth of field control. The α850 also incorporates SteadyShot INSIDE™ in-camera image stabilizer which actually shifts the image sensor to compensate for camera shake without sacrificing image quality. Additional features include Dual BIONZ™ imaging processors for continuous shooting at up to 3 fps, an ultra-bright glass pentaprism viewfinder, 3.0" Xtra Fine LCD™ display and HDMI™ output.
The A850 features a 35mm full frame Exmor™ CMOS image sensor that is approximately 2.35x larger than the APS-C sized sensors found in many DSLR cameras. The result is a larger capture area, improved wide angle performance, and tighter depth of field control. In addition, its 24.6MP resolution maximizes the resolving power of your existing lenses and delivers sharper, higher contrast photos.
A large, ultra bright glass pentaprism viewfinder provides you with amazing clarity and high optical performance for tighter focus control. In addition, it offers viewfinder magnification of 0.74x, allowing you to see an image nearer to its actual size, as well as 98% field coverage for detailed framing work.
The α850 provides direct HDMI™ output to your BRAVIA® HDTV and other compatible HDTV screens, so you can view and share photos in breathtaking clarity and detail Additionally, PhotoTV HD capable BRAVIA® HDTVs will automatically optimize display settings, such as sharpness, gradation, and color to display your images in a way that more closely matches the natural look of printed photographs
Sealed viewfinder optics and rubber gasket surrounds on all buttons, dials, and switches help resist the entry of dust and moisture into the camera, and allow for safe use in a wide range of environments.
The shutter mechanism in the A900 is designed to achieve shutter speeds up to 1/8000 seconds and proven for 100,000 cycle operation.
To recover details in dark or bright areas of the image, the A900 provides multiple levels of Dynamic Range Optimization: Standard mode, to improve shadow detail using standard gamma curves; Advanced Auto mode, allowing you to select any of 5 DRO correction levels, or DRO Advanced Bracketing, which automatically takes three shots at different DRO levels with a single shutter press.
The autofocus system in the α850 features a highly accurate F2.8 sensor for improved focus precision when using lenses faster than F2.8.
Viewfinder magnification of 0.74x lets you see your subjects nearer to actual size.
User-replaceable focusing screens for shooting specific subject types can be purchased as optional accessories.
Sony drew upon its extensive experience designing and building heavy professional broadcasting camcorders to develop a rubberized grip that allows you to hold the α850 with comfort and confidence.
Sony® Picture Motion Browser (PMB) software provides a simple and intuitive way to sort and archive your image collection, as well as perform common editing operations and output to data disc or the Web.
The α harnesses the power of Dual BIONZ™ image processing engines to deliver true-to-life images with ultra-low noise and continuous shooting at up to 3 fps.
Review your images in stunning detail on the 3.0" Xtra Fine™ LCD4 display (921k pixels). With photo-quality resolution of 270ppi (pixels per inch), you can identify any necessary focus or exposure corrections at the time of capture, rather than discovering them when you transfer your images to your PC.
The body of the A900 is entirely covered in a die-cast magnesium alloy shell, providing a rugged feel and surprisingly lightweight.
A supplied InfoLITHIUM® lithium-ion battery provides long-lasting performance, allowing you to capture approximately 880 images on a single charge7.
A 40-segment multi-pattern metering system provides superior exposure control accuracy in a wide range of lighting conditions.
In addition to digitizing analog signals, the full frame Exmor™ CMOS image sensor also performs both analog and digital noise reduction. This on-chip dual noise reduction process aids in the high speed transfer of noiseless digital signals.
In addition to full frame image capture, the α850 can also crop images to the APS-C size format, allowing the use of lenses designed specifically for APS-C sized image sensors.
AF Micro Adjustment allows you to fine tune focus for various lenses. The α850 can store adjusted focus values for up to thirty lenses.
The α850 allows you to bracket up to three exposures in 2.0EV-step increments.
Remote Camera Control allows you to control your α850 from your PC.
Building on years of expertise, Sony has developed the world's first body-integrated image stabilization solution for a full frame DSLR1. The SteadyShot INSIDE™ in-camera image stabilizer actually shifts the image sensor to compensate for camera shake without sacrificing image quality. The compensation effect is equal to as many as four shutter speed steps, giving you more creative freedom when shooting in low light. And, because it is integrated into the camera body, SteadyShot INSIDE technology works with all compatible α system lenses.
The Intelligent Preview function allows you to see the effects of manual adjustments to exposure value, shutter speed, aperture, Dynamic Range Optimizer and White Balance before you take the shot, so you can determine the optimum settings before you take the shot, instead of losing time to trial-and-error.
A high-performance autofocus system uses 9 focus points (center dual-cross type) and 10 assist points to deliver fast and precise focusing.
Changing lenses in a DSLR can allow dust to enter the camera -- so to help keep the CMOS imager cleaner for better pictures, the Sony® α; (alpha) DSLR-A900 utilizes both static-free anti-dust coating on the imager's filter and anti-dust vibration that automatically shakes the sensor to dislodge dust each time the camera is shut off.
The A900 features a dual card slots and accepts both CompactFlash® and Memory Stick Duo™ Media (sold separately).
Analog-to-digital signal conversion is performed by the full frame Exmor™ CMOS image sensor.
Updated Image Data Converter SR3 software improves your workflow with faster RAW file processing and improved image correction.
The α850 includes a built-in eyepiece shutter which can be shut to help shield against entering light and prevent exposure errors.
Mirror Lockup Mode raises the main mirror before exposure to reduce vibration at shutter release, resulting in better performance during long exposure shots of fireworks, stars, etc.
The Image Data Lightbox software included with your Sony®α DSLR helps you browse, rate, and compare your images, making it easier to select your favorites for further processing.
Concentrate on your shooting and make adjustments on the fly thanks to convenient button placement. The ISO and White Balance adjustment buttons are located on the top of the camera body near the shutter button for easy thumb operation.
We have detected that you do not have the Flash plug-in installed. Flash is a free plug-in that lets your browser display animations and enhanced content.
To begin automatically installing Flash, click the button below.
© 2009 Sony Electronics Inc. All rights reserved. Reproduction in whole or in part without written permission is prohibited. Sony, α, BIONZ, BRAVIA, Sync, Xtra Fine LCD Plus, SteadyShot INSIDE™, Memory Stick, Memory Stick Duo, Memory Stick PRO-HG Duo, InfoLITHIUM, HDNA, and Stamina, are trademarks of Sony. HDMI is a trademark of HDMI Licencing LLC. All other trademarks are trademarks of their respective owners. Non-metric weights and measurements are approximate and may vary.
Sony Rewards is a free loyalty program with many ways to earn, including earning at least 1 point per $1 spent when you shop at Sony Store. To earn points on your purchase, simply log in or join now to link your Sony Rewards account to a Sony Store account. Click here to learn more. You can also log in or enroll to earn points after completing your Sony Store online purchase.


text:
Best Commencement Speeches… Ever.
AIDemocracy would like to take the time to congratulate all the new and up and coming graduates of 2013.… [more]
Now Seeking: Network Leaders and Team Members for 2013-14 Year
Are you a young global activist ready to make a significant impact on US global engagement? Are you excited… [more]
Announcing Global Leader!
Are you ready to change the world? Join us in summer 2013! Global Leader is an intensive training… [more]
"Hold Your Reaction"
By Carla Issa, Hope not Hate fellow "I smelled smoke and saw everyone running." Just two days… [more]
Seeking Summer 2013 Interns: Issue Analysts, Social Media, Tech Team, Movement Builders, Global Citizenship, Campaigners
These are all virtual positions, which can be performed from anywhere. Are you ready to amplify… [more]
Voices From Our Network …
Bridging the Gap: Graduating in America
June 18, 2013 By AIDemocracy Leave a Comment
By Gao Qinglian Last Thursday, June 13th, I completed my two-year masters study at the University of Washington Evans School of Public Affairs. In Dean Sandra Archibald's opening address, she mentioned the strong Chinese representation in the school and how it was a sign of globalization. There … [Read More...]
This Is No Turkish Spring — It's Better
June 13, 2013 By AIDemocracy Leave a Comment
By Ramis Wadood. We've all been watching Turkey: what began as a small environmentalist protest in Gezi Park has expanded into a nationwide protest in over eighty cities. Five are dead, thousands have been injured and detained by police, and tens of thousands more continue to protest as I … [Read More...]
The Limits of Democracy
June 7, 2013 By tarariggs Leave a Comment
By Tara S Riggs Revolutions are a reaction to failed government policy and general disillusionment with one's government. If enough people share the sentiment, revolutionary sparks are ignited and as grass roots movements gain strength, collective groups attempt to overthrow the government. The … [Read More...]
Sometimes it All Comes Down to Opportunity
May 29, 2013 By AIDemocracy Leave a Comment
By: Maddie Reeves, Hope Not Hate Cultural Innovator As a high school student I am proof of the old saying, "knowledge is power." Everyday students around the world learn new things, and with this education, they grow as people and change. But education isn't always clear cut, and oftentimes … [Read More...]
Commencement: Don't Eat Fortune's Cookie
May 29, 2013 By AIDemocracy Leave a Comment
By Michael Lewis, American non-fiction and financial author, at Princeton University, 2012. Watch the video here. Thank you. President Tilghman. Trustees and Friends. Parents of the Class of 2012. Above all, Members of the Princeton Class of 2012. Give yourself a round of applause. The next time … [Read More...]
Commencement: Don't Settle.
May 28, 2013 By AIDemocracy Leave a Comment
By Steve Jobs, at Stanford University, 2005. Watch Steve's address here. I am honored to be with you today at your commencement from one of the finest universities in the world. I never graduated from college. Truth be told, this is the closest I've ever gotten to a college graduation. Today I … [Read More...]
Commencement: Get on the Rocketship
May 27, 2013 By AIDemocracy Leave a Comment
By Sheryl Sandberg, Harvard Business School, 2012. Watch the speech here. It's an honor to be here today to address HBS's distinguished faculty, proud parents, patient guests, and most important the class of 2012. Today was supposed to be a day of unbridled celebration, and I know … [Read More...]


text:
Only a 1 minute walk to the beach and village. Short ride to Ft. Lauderdale if you want more action. They have a nice hot tub that I used often, as it was a bit cooler than normal. The pool is also heated, so that helped too. I didn't find the staff freindly at all, probably because we weren't the... More
- Also Known As:
- Driftwood Beach Club Hotel
- Driftwood Beach Club Hotel Lauderdale By The Sea
- Driftwood Beach Club Lauderdale By The Sea, Florida
- Official Description (provided by the hotel):
- Welcome Home… to the Driftwood Beach Club! Conveniently located on the Atlantic Ocean in the heart of Lauderdale-By-The-Sea, we are one block north of Commercial Blvd on the east side of State Road A1A and are easily accessible from the Florida Turnpike, I-95 and U.S. 1. Lounge away poolside in our 55′×33′ swimming pool, the largest in Lauderdale-By-The-Sea, or enjoy our other amenities, including two gas barbecue grills, a new jacuzzi, a large garden patio and two shuffleboard courts directly on the ocean next to our private beach.Nearby, you can find everything for the perfect family vacation. We're just moments away from a variety of fine restaurants, boutiques, grocery stores, banks, car rentals, fishing pier, marina, tennis courts and a children's playground… all within walking distance. For your convenience, we offer daily maid service. Two private coin laundries are located on the property. ... more less


text:
IT Security
Welcome to the BrightTALK Summit series. Our summits are a collection of topical webcasts run over the course of one or two days focused on a variety of relevant and timely subjects that matter most to you. They are free to attend. Choose all or specific summit webcasts to attend live or on demand.
Live & upcoming summits
Previous summits
Today's accepted wisdom is that there are only two types of organizations, those that have been breached and know it and those that have been breached and don't. With this new vision comes the realization that building p..
Far from the emerging technologies of 2011 and 2012 Cloud and Virtualization have arrived, allowing the modern IT team to become nimble and efficient at utilizing computing and infrastructure resources to enable their bu..
There is little debate that cloud is becoming main stream, driving agility and a competitive advantage. But adopting and realizing the optimal benefits for your organization can be overwhelming. Join your peers in lear..
Cyber-attacks are increasing at an exceptional rate – From DDOS attacks by "Hacktivists" groups to individual phishing attacks and state-sponsored cyber-espionage, the threat landscape has never been so fierce. As ..
As auditors take on a more central and strategic role within organizations, there is increasing interaction between the internal audit team and stakeholders. Join this summit and learn from top thought leaders in the fie..
Applications have become paramount in increasing business productivity. They allow us to access a wide range of information from different devices, taking advantage of advanced functionalities such as cloud or mobile ser..
Effective risk management can make or break your organization's future. It is imperative to have a clear picture regarding the threats and vulnerabilities that may be lurking.
Join this summit to learn effective solut..
In our world of constantly increasing risks, the value of business continuity to an organization cannot be measured. Learn how to optimize your continuity plan and be better prepared for any unplanned risks that your org..