‘On’ and ‘Off’ Components in the Human Somatosensory Evoked Response

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Abstract
The somatosensory evoked response to vibrotactile stimuli was studied in 20 subjects. This type of response to stimuli of 1000 ms duration displays ‘on’ and ‘off’ components. The latter consists of a surface negative deflection of about 100–120 ms peak latency, followed by a slower positive wave. As in the averaged visual evoked response an afteractivity of frequency 8–10 Hz may follow the ‘on’ component. This activity may either mask the ‘off’ component, be initiated by the termination of the stimulus, or its rhythm can be interrupted by the stimulus end. In view of the similarity between the averaged evoked response to visual and vibrotactile stimuli, it is suggested that visual and somatosensory information may be processed according to a common pattern.