Contribution of motor cortex in generation of evoked spikes in patients with benign rolandic epilepsy

Objectives: Among the different kinds of rolandic epilepsy there is a form of benign epilepsy with centrotemporal spikes (BECT) presenting the peculiar characteristic of evoking rolandic paroxysmal activity, characterized by a spike followed by a slow wave, using electrical stimulation of the fingers. Methods: We evaluated 7 patients suffering from BECT presenting evoked scalp activity by electrical stimulation of the fingers of the hand. Electrical stimulation was performed using a pair of ring electrodes applied to the thumb. The motor evoked potentials (MEPs) were elicited in hand muscles by transcranial magnetic stimulation (TMS) and were conditioned by the same electrical digital stimulation producing the evoked spikes at interstimulus intervals ranging from 10 to 200 ms. Results: Digital stimulation in epileptic patients produced an increase in MEP amplitude substantially above the normal ranges. MEP facilitation showed a time course overlapping the ascending phase and peak of the evoked spike, whereas no significant MEP changes were found during the early positive peak and the descending phase of the spike, or during the following slow wave. Conclusions: Several considerations support the hypothesis that the short-lasting M1 facilitation is related to the spread of an abnormal hypersynchronous discharge of the S1 neurones to functionally related motor areas via cortico-cortical connections.