RATE EFFECT AND MISMATCH RESPONSES IN THE SOMATOSENSORY SYSTEM - ERP-RECORDINGS IN HUMANS

In the first experiment, somatosensory event-related potentials (SERPs ) were recorded to tactile pulses and vibration bursts applied to the left middle finger in trains of 4-8 stimuli with 1 s intervals. In add ition to the negative N140 deflection, also the positive P50, P100 and P300 waves attenuated in amplitude with stimulus repetition. These de creases were immediate, there being no marked further amplitude attenu ation after the second stimulus. The locus of this rate effect appears not to be the primary SI or SII, but rather prefrontal cortices or so me deeper structures. In the second experiment, vibratory stimuli of d ifferent frequencies or at different skin sites were presented using t he oddball paradigm. When the deviant stimulus was a high-frequency vi bration burst, it elicited a distinct N250 deflection, probably analog ous to the auditory N2b. When the deviation was a change in the stimul ation site, no N250 deflection but instead an extra negativity between 100-200 ms latency, probably analogous to the auditory mismatch negat ivity, was observed. (C) 1997 Elsevier Science B.V.