Somatosensory automatic responses to deviant stimuli.

We studied event-related potentials (ERPs) produced in response to deviant stimuli in a sequence of somatosensory stimuli which were measured under stimulus-ignoring conditions. A change in the repetitive somatosensory input elicited not only a frontal negativity which was similar to the somatosensory mismatch negativity very recently reported by Kekoni et al. [J. Kekoni, H. Hämäläinen, M. Saarinen, J. Gröhn, K. Reinikainen, A. Lehtokoski, R. Näätänen, Rate effect and mismatch responses in the somatosensory system: ERP-recordings in humans, Biol. Psychol. 46 (1997) 125-142] but also a positive deflection ranging in latency from 100 to 200 ms. This somatosensory change-related positivity was reduced with prolongation of the interstimulus interval (ISI) and was different from the responses to the deviant stimuli when they were presented alone. These findings suggest that the somatosensory change-related positivity is probably generated not by activation of new afferent elements but by a detection of change in a process of comparison with sensory memory.