PMC5707211_01
A. Electrode placement as seen on reconstructed images of MRI of the brain. B. i. Generalized interictal epileptiform discharge on mastoid average reference montage. The activity is maximum in amplitude over the left fronto-central region. ii. Generalized interictal polyspike-and-wave discharges maximum in bilateral frontal regions, viewed on an anterior-posterior bipolar montage. iii. Scalp EEG recording of a habitual seizure. Clinical onset consisted of right non-versive head turn followed in less than a second by bilateral arm tonic then generalized clonic jerking. Electrographic onset consisted of evolving generalized polyspike activity maximum in the left frontal region. All traces shown use low frequency and high frequency filter settings of 1 and 70 Hz, respectively.
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Interictally, there were generalized and left frontal maximal spike-and-wave discharges with associated wide-spread involvement (Fig. 1-B). See (Fig. 1-A) for a reconstruction of implanted electrodes into the suspected regions of interest based on the non-invasive presurgical evaluation.
Functional map from cortical stimulation. Red: positive motor; Green: sensory; Yellow: Language. Orange: Stimulations that triggered consistent impairment of consciousness with trains greater than 2 seconds; Circle with central red dot: Frontal eye field; Blue: negative tongue motor; Purple: Non-epileptic experiential auditory deja vu; White: Tested up to 12 mA with no observable function identified. T = tongue, Th = throat, F = face, H = hand.
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Language and motor mapping results are summarized in (Fig. 2). We identified a region of a few centimeters square over the caudal superior and middle left frontal gyri as well as the caudal right middle frontal gyrus, in which transient IOC could be induced consistently by ECS at current intensities of 4-5 mA (Fig. 2). As a negative control, IOC was not observed in other brain regions tested as highlighted in (Fig. 2).
Evoked responses were seen with stimulation of contacts 39-G40 that correlated with impairment of consciousness (A-B). As a control, we show EEG activity during stimulation of negative motor areas contacts K6-K7 (C) and language contacts G6-G14 (D). (B-C-D) are shown using low-frequency filter 1 HZ and high-frequency filter 30 Hz. Plate A shows 15-second icEEG activity before filtering. The red and orange lines mark the onset and the end of stimulation trains respectively. The responses seen in B are not seizures or after-discharges because i. They were time-locked to stimulation [i.e., they are not self-sustained] ii. There was a return to pre-stimulation background activity when the electrical stimulation was turned off. iii. The spatial extent of the intra-stimulation discharges is not commonly encountered during electrical stimulation mapping. iv. Refer to plate A for demonstration of how the activity was time-locked to the electrical stimulation and had no effect on background activity, similar in this way to photic driving or certain types of photoparoxysmal responses, and the thalamo-cortical evoked responses reported by Velasco et al..
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The IOC correlated with wide-spread evoked responses of admixed frequencies over the fronto-parietal convexities bilaterally, and in the mesial frontal and temporal structures that increased in amplitude, the longer the train and abated at the end of the trains (Fig. 3). This was not seen in other stimulations specifically, over the language and negative motor areas (Fig. 3).