Eeg 1100

Electrocorticograms (ECoGs) were recorded with a bandpass filter of 0.016–600 Hz and a sampling rate of 2,000 Hz in all patients (EEG-1100, Nihon Kohden, Tokyo, Japan) and analyzed off-line using Matlab software (Matlab version 7.12.0; the MathWorks Inc., MA). Cortical recordings from subdural electrodes were referenced to a scalp electrode placed on the skin over the mastoid process contralateral (patient 1R and 2–6) or ipsilateral (patient 1L) to the side of electrode implantation.
The median nerve contralateral to the side of electrode implantation was stimulated at the wrist (a square wave pulse of 0.3 ms duration at 0.3 Hz) (Electrical Stimulator SEN-7203, Nihon Kohden, Tokyo, Japan). The stimulus intensity was adjusted to 20% above the motor threshold. In all the patiens, SEPs were recorded before tapering the antiepileptic drugs in the first week of chronic electrode implantation. During recording, the patients were lying on the bed and requested not to perform any specific task under awake condition. At least 2 trials of 150 sweeps were averaged to confirm the reproducibility of responses. SEPs were obtained by off-line averaging ECoGs time-locked to the stimulus onset with a time window of 1,000 ms (from 300 ms before to 700 ms after the stimulus onset). The baseline was set for the first 200 ms: from 300 ms to 100 ms before the stimulus onset.

To examine cortical activity, intracranial EEGs were recorded using subdural platinum electrodes (2.3 mm diameter; Ad-tech). Depth platinum electrodes (0.8 mm diameter; Unique Medical) were also inserted to record subcortical activity (data not shown). Electrodes were referenced to electrodes (2.3 mm diameter; Ad-tech) that were embedded inside the scalp of the midline dorsal frontal region. Impedances were balanced and maintained below 5 kΩ. Data were amplified, filtered online (band pass: 0.5–300 Hz), and sampled at 1,000 Hz onto the hard disk drive of the EEG system (EEG-1100; Nihon Kohden). Online monitoring was conducted using a more restricted bandwidth of 0.5–120 Hz. Vertical and horizontal electrooculograms (EOGs) were simultaneously recorded using Ag/AgCl electrodes (Nihon Kohden). As in previous studies54 (link), off-line visual inspection confirmed that the EOGs did not contaminate the intracranial EEGs. An unobtrusive video recording of events was made using the EEG system built-in video camera, and off-line analysis of the videos confirmed that all participants were fully engaged in the tasks.