Averaged Evoked Responses To Tapping: A One-Subject Scalp Study of Large Signals


  • This work was aided in part by NIH training grant 61366. The encouragement of Dr. Dudley F. Peeler, the advice and assistance of Mr. T. Bouchlas, biomedical engineer, and the cooperation of our subject are gratefully acknowledged.

Address requests for reprints to: Dr. Holton Stowell, Research Department, Central State Hospital, Milledgeville, Georgia 31062.


Somatosensory evoked responses (SERs) of unusual amplitude were averaged from the scalp of one subject, for inspection of the time-course of the early positive-negative waveform (P1 to NH). These early components had a peak-to-peak half period of 10–14 msec, for varied stimulus locations and intensities, while their amplitude and latencies varied monotonically with stimulus intensity and sensory level. The time-course of the P1 to NH components conformed with that observed for the postsynaptic soma-dendritic response to direct stimulation of sensory cortex (DCR) in other mammals. Inspection of the later waveform, up to 125 msec poststimulus-onset (PSO), revealed no negative later than the NH, which peaked at 43–45 msec for digital stimulation. Mechanical stimulation of the digits in the absence of the usual masking noise evoked a different waveform having significant earlier and later components.