INFLUENCE OF SOMATOSENSORY INPUT ON PAROXYSMAL ACTIVITY IN BENIGN ROLANDIC EPILEPSY WITH EXTREME SOMATOSENSORY-EVOKED POTENTIALS

We studied six patients suffering from benign rolandic epilepsy of chi ldhood with central temporal spikes who presented so-called 'extreme s omatosensory evoked potentials (SEPs)' following peripheral somatosens ory stimulation. Stimuli were delivered to the fingers of one hand usi ng both a triggered tendon hammer and low-intensity electrical stimula tion. The electrical stimulation was delivered in sequences in differe nt conditions (i.e. random order 1, 3 and 10 Hz). Both tapping and ele ctrical stimulation produced scalp evoked potentials in all subjects, characterized by a spike followed by a slow wave, similar in morpholog y and scalp distribution to the spontaneously occurring spikes. This p aroxysmal activity was sensitive to stimulus rate; the number of evoke d spikes was inversely related to the frequency of stimulation, being maximal at 1 Hz and disappearing at high frequencies (10 Hz). Spontane ous spikes disappeared during high-frequency stimulation but were pres ent during low-frequency stimulation. Averaged SEPs at 3-Hz stimulatio n showed a late high-amplitude component, identical in morphology and distribution to the single evoked spike. We therefore conclude that, i n these subjects, the so-called 'extreme SEPs' are evoked spikes and t hat evoked and spontaneous spikes share common cortical sensorimotor g enerators. The evidence that these generators cart be influenced by af ferent input provides important information regarding the functional m echanisms involved in modulating cortical excitability in benign rolan dic epilepsy. Moreover, we suggest that peripheral electrical stimulat ion can be used as an additional activation test in this kind of epile psy.