Somatosensory evoked potentials following stimulation of the lower limb in cortical reflex myoclonus

Generating mechanisms of giant somatosensory evoked potentials (SEPs) following stimulation of the posterior tibial nerve as well as the big toe were investigated in three patients with cortical reflex myoclonus. Scalp distributions of recognisable components were very similar to those in normal subjects, except that their amplitude was much larger. The tibial nerve SEPs were remarkably attenuated by interfering tactile stimulation. Therefore, the giant SEPs observed in the present cases seem to be, at least partially, due to input from cutaneous nerve fibres on the background of extremely enhanced excitability in area 3b of the primary sensory cortex where normal SEPs are generated.