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 childhood with central temporal spikes who presented socalled
‘extreme somatosensory evoked potentials (SEPs)’
following peripheral somatosensory stimulation. Stimuli were
delivered to the fingers of one hand using both a triggered
tendon hammer and low-intensity electrical stimulation. The
electrical stimulation was delivered in sequences in
different conditions (i.e. random order, 1, 3 and 10 Hz). Both
tapping and electrical stimulation produced scalp evoked
potentials in all subjects, characterized by a spike followed
by a slow wave, similar in morphology and scalp distribution
to the spontaneously occurring spikes. This paroxysmal
activity was sensitive to stimulus rate; the number of evoked
spikes was inversely related to the frequency of stimulation,
being maximal at 1 Hz and disappearing at high frequencies (10 Hz). Spontaneous spikes disappeared during
high-frequency stimulation but were present during lowfrequency
stimulation. Averaged SEPs at 3-Hz stimulation
showed a late high-amplitude component, identical in
morphology and distribution to the single evoked spike. We
therefore conclude that, in these subjects, the so-called
‘extreme SEPs’ are evoked spikes and that evoked and
spontaneous spikes share common cortical sensorimotor
generators. The evidence that these generators can be influenced
by afferent input provides important information
regarding the functional mechanisms involved in modulating
cortical excitability in benign rolandic epilepsy. Moreover,
we suggest that peripheral electrical stimulation can be used
as an additional activation test in this kind of epilepsy