Interstimulus interval has no effect on a mid-latency scalp potential generated by innocuous-related activity in the...

The sural nerve-evoked somatosensory evoked potential (SEP) scalp topography was separated into stable periods, where a stable period refers to consecutive time points with the same topographic pattern. The stimulus intensity-amplitude function, conduction velocity measurements, and a dipole source localization analysis of one of these stable periods, SP1 (60-90 ms post-stimulus), strongly suggests that it is generated by the response of neurons in the primary somatosensory cortex (SI) to inputs arising from the innocuous A beta peripheral afferents. Interstimulus intervals (ISI) ranging between 2.5 s and 10.0 s had no effect on SP1 amplitude. This contrasts with an earlier report from this laboratory demonstrating that subjective magnitude ratings and the amplitude of another stable period that appears at about 160-180 ms post-stimulus and that is also generated in SI, increase with decreasing ISI. Thus, ISI appears to affect perception and the late but not the mid-latency responses in SI.