Supplementary file 1 - Video-EEG technical protocol
The EEG record followed the recommendations of the IFCN [15], ILAE [16], ACNS [17, 18] and LPCE [19]. Video-EEG was performed bya Nihon-Kohden device (Neurofax EEG-1200) with a sampling frequency of 1000 Hz. We used the international 10/10 electrodes placement system and recorded at least 64 EEG channels. An electrode cap adapted to the patient head size was used and the correct position of the electrodes was confirmed. Two electrooculogram and one chin electromyogram channels were also recordedby silver chloride electrodes. If involuntary movements were observed additional EMG electrodes were placed allowing EMG/EEG synchronized recording.The electrode impedance was less than 5 KOhms at the beginning of the record and was revaluated whenever a compatible artifact was detected. The total recording period was at least 35 minutes of wakefulness, including activation tests. Sleep was recorded whenever possible at the end of the exam. The maximum duration of the test was 60 minutes. The acquisition parameters were: sensitivity at 10 µV/mm; time constant at 0,3s; high frequency filter at 70 Hz; low pass filter < 1 Hz. 50Hz filter was used when other attempts to eliminate electric artifact failed. The record included 3 different montages (bipolar longitudinal, bipolar transverse and referential). All attempts to fix EEG artefacts by the technical team were annotated in the record itself. Except in the final phase of the record, the technician tried to keep the patient awake or in his level of maximum alert. Changes in consciousness level were also recorded. For patients in stupor/coma, the auditory and somatosensory stimulation was used systematically (and recorded). In the event of repetitive epileptiform or periodic discharges, delta rhythmic activity and spacio-temporal evolution of a rhythmic or periodic activity even in the absence of obvious behavioural manifestations, the EEG technician called medical staff who look for subtle clinical epileptiform manifestations and assess systematically the consciousness level, orientation, response to simple motor orders (open and close your eyes, open and close both hands), naming of objects (pen, clock), numbers count in descending order, verbal memory and muscle strength of the upper limbs during the event.
All records were performed by EEG technicians with experience in video-EEG and EEG records in acute brain lesion patients, under medical supervision, using the following technical protocol:
I. In the longitudinal bipolar montage:
1st Lying patient with eyes closed: 5 minutes
2nd Opening eyelids for 5 seconds and ocular fixation on one point, then closing eyelids 25 seconds (opening/closing of the eyelids was done manually by the technician for an uncooperative patient). Twice repeated.
3rd Lying patient with eyes closed: 5 minutes
4th Hyperventilation for 3 minutes (the patient’s effort was graduated: weak, medium, good, excellent). It was not made in the presence of contraindications.
II. In bipolar transverse montage:
5th Lying patient with eyes closed: 5 minutes
6th Opening eyelids for 5 seconds and ocular fixation on one point, then closing eyelids 25 seconds (opening/closing of the eyelids was done manually by the technician for an uncooperative patient). Twice repeated.
III. In “average” montage:
7th Lying patient with eyes closed: 5 minutes
8th Intermittent photic stimulation performed with eyes open and closed with a photic stimulator at 30 cm in front of the eyes and using stimulation frequencies between 1 and 30 Hz, with 10 seconds range between stimuli.
9th Lying patient with eyes closed: 5 minutes
10th Lying patient with eyes closed until the end of the exam. Sleep was allowed in this period. It can be registered in the transverse bipolar montage.
Whenever myoclonus was observed during the neurological examination, synchronized EMG record of the involuntary movement was added to the exam. The EEG record includein that situation not only eye-lid opening and closure, hyperventilation, photic stimulation but also manoeuvres to elicit myoclonus, as previously observed in the neurological evaluation to allow“jerk-lock back averaging” analysis.
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