Abstracts

Focal motor negative phenomena have been described in seizures primarily involving negative motor areas (opercular pre-motor and medial pre-motor regions) and the rolandic region (post-central or pre-central). The localizing value of such signs and the mechanisms by which an epileptic discharge may generate negative phenomena remain debated. Our objective is to study the localizing value of ictal facial paralysis and possible mechanisms of ictal negative motor phenomena. A 32-year-old right-handed woman underwent a presurgical evaluation for medically intractable epilepsy by Stereo-Electro-Encephalography (SEEG). During the video-SEEG and EMG recording both negative and positive motor seizures were observed. We compare the spatial and temporal characteristics of the epileptic discharges associated with positive and negative motor signs. Nine positive and 27 negative motor seizures were recorded. All were generated within the same area (right opercular central area, Brodmann Area 4). All the seizures started with a slow and sharp wave followed by a rhythmic discharge. The 2 different types of clinical seizure were differentiable by their power/frequency spectrum: positive motor seizures were associated with an alpha-beta band discharge while negative motor seizures were associated with a gamma band discharge. Both negative and positive ictal motor phenomena may be produced in the primary motor cortex. We propose that within the primary motor cortex, high frequency sustained discharges ([gt]40 Hz) may disrupt the ongoing excitatory drive to the peripheral motoneurons while sustained lower frequency discharges ([lt]40 Hz) may activate the cortico-nuclear or cortico-spinal pathway and produce positive motor signs.