SHORT-LATENCY MEDIAN NERVE SOMATOSENSORY-EVOKED POTENTIAL (SEP) - INCREASE IN STIMULATION FREQUENCY FROM 3 TO 30 HZ

Somatosensory evoked potentials were obtained by electrical stimulatio n of the median nerve in 10 normal subjects at 3 and 30 Hz. At the hig her rate of stimulation, a reduction was observed in amplitudes and pr olongation of latencies of the N9,N/P13 and N20 components as well as increase of the interpeak latency N9-N/P13. A significant increase bet ween the onsets of the N11 and N20 components was also seen; however, no significant increase of the N/P13-N20 interpeak latency was observe d. Analysis suggested that an important reason for this last finding w as related to the fact that in some cases different fast frequency com ponents (FFC) determined the N20 peak in the different situations. It was further observed that, in those cases in which at least 3 peaks in the fast frequency components were detected (7/10), a significantly d ifferent increase in latency between the first and the third peaks was noted. A possible thalamo-cortical generation of the FFC is discussed .