Fast epileptic discharges associated with ictal negative motor phenomena

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.

Ictal positive and negative motor phenomena occurring during seizures affecting the rolandic area were studied in a patient having intracerebral recordings (stereo-electro-encephalography, SEEG) for drug resistant epilepsy.

During the video-SEEG and EMG recording, nine positive and 27 negative motor seizures were recorded. All were generated within the same area (right opercular central area, Brodmann Area 4). The 2 different types of clinical seizure were differentiable by their power/frequency spectrum: positive motor seizures were associated with a prominent alpha-beta band discharge while negative motor seizures were associated with a gamma band discharge (>45Hz).

We propose that within the primary motor cortex, high frequency sustained discharges may disrupt the ongoing excitatory drive to the peripheral motoneurons and produce negative motor signs, while sustained lower frequency discharges (alpha and beta bands) may activate the cortico-nuclear or cortico-spinal pathway and produce positive motor signs.

Both positive and negative ictal motor phenomena can be observed in the primary motor cortex depending on the properties of the epileptic discharge.