Evoked potentials elicited by long vibrotactile stimuli in the human EEG.

Evoked potentials elicited by long vibrotactile stimuli were studied in six subjects. Stimuli were vibratory bursts (60 HZ, 600 ms, 680 micrometers) delivered to the back of the hand trains of four stimuli with an interstimulus-interval of 2 s. Stimulus trains were repeated once every minute. EEG was recorded from vertex and from ipsi- and contralateral parietal areas. First stimuli of the trains elicited a transient response followed by a large negative sustained potential which reached its peak amplitude about 700 ms after the stimulus onset and which was not restricted to the stimulus duration. The negative component of the transient on-response as well as the sustained potential was at the 1st stimulus of the train maximal in amplitude at the vertex, and no significant difference between the ipsi- and contralateral parietal areas was detected. Stimulus repetition in the train resulted in a marked decrease of the transient response, and in an almost complete disappearance of the sustained potential, which was only occasionally observed during repeated stimuli.