Differential changes in frontal and sub-temporal components of mismatch negativity

Novel evidence is reported showing changes in the mismatch negativity (MMN) event-related potential (ERP) that followed a different time course in fro ntal and sub-temporal (mastoid) electrodes. MMN recorded in frontal electro de sites, assumed to originate predominantly in the superior temporal gyrus , showed amplitude enhancement from the first to the second recording block . In-contrast, the amplitude of the sub-temporal, mastoid component (termed mismatch positivity, MMP) diminished. In addition to these changes in the MMN elicited by tone duration deviants, there were also significant changes in the ERP to the standard stimulus. The positivity in the standard ERP be tween 50 and 150 ms increased in bilateral mastoid electrodes but showed no reliable change in frontal electrodes. This suggests that more than one ge nerator underpins the two mismatch components, and that the sub-temporal mi smatch component does not only represent a polarity reversal of the main MM N component in the superior temporal gyrus. (C) 1999 Elsevier Science B.V. All rights reserved.