it. This can lead to sleep apnea. Parasomnias The occurrence of parasomnias is very common in the last stage of NREM sleep. Parasomnias are sleep behaviors that affect the function, quality, or timing of sleep, caused by a physiological activation in which the brain is caught between the stages of falling asleep and waking. The autonomous nervous system, cognitive process, and motor system are activated during sleep or while the person wakes up from sleep. Some examples of parasomnias are somnambulism (sleep walking), somniloquy (sleep talking), sleep eating, nightmares or night terrors, sleep paralysis, and sexsomnia (or "sleep sex"). Many of these have a genetic component, and can be quite damaging to the person with the behavior or their bed partner. Parasomnias are most common in children, but most children have been found to outgrow them with age. However, if not outgrown, they can cause other serious problems with everyday life. Polysomnography Polysomnography (PSG) is a test used in the study of sleep; the test result is called a polysomnogram. Below are images of the NREM stages 1, 2 and 3. The figures represent 30-second epochs (30 seconds of data). They represent data from both eyes, EEG, chin, microphone, EKG, legs, nasal/oral air flow, thermistor, thoracic effort, abdominal effort, oximetry, and body position, in that order. EEG is highlighted by the red box. Sleep spindles in the stage 2 figure are underlined in red. Stage N1: Stage N2: Stage N3: Slow-wave sleep Slow-wave sleep (SWS) is made up of the deepest stage of NREM, and is often referred to as deep sleep. The highest arousal thresholds (e.g. difficulty of awakening, such as by a sound of a particular volume) are observed in stage 3. A person will typically feel groggy when awakened from this stage, and indeed, cognitive tests administered after awakening from stage 3 indicate that mental performance is somewhat impaired for periods up to 30 minutes or so, relative to awakenings from other stages. This phenomenon has been called "sleep inertia." After sleep deprivation there is usually a sharp rebound of SWS, suggesting there is a "need" for this stage. Slow Wave Sleep (SWS) is a highly active state unlike a state of brain quiescence as previously thought. Brain imaging data has shown that during NREM sleep the regional brain activity is influenced by the waking experience just passed. A study was done involving an experimental and a