Frequency change detection in human auditory cortex

We offer a model of how human cortex detects changes in the auditory enviro nment. Auditory change detection has recently been the object of intense in vestigation via the mismatch negativity (MMN). MMN is a preattentive respon se to sudden changes in stimulation, measured noninvasively in the electroe ncephalogram (EEG) and the magnetoencephalogram (MEG). It is elicited in th e oddball paradigm, where infrequent deviant tones intersperse a series of repetitive standard tones. However, little apart from the participation of tonotopically organized auditory cortex is known about the neural mechanism s underlying change detection and the MMN. In the present study, we investi gate how poststimulus inhibition might account for MMN and compare the effe cts of adaptation with those of lateral inhibition in a model describing to notopically organized cortex. To test the predictions of our model, we perf ormed MEG and EEG measurements on human subjects and used both small(<1/3 o ctave) and large- (>5 octaves) frequency differences between the standard a nd deviant tones. The experimental results bear out the prediction that MMN is due to both adaptation and lateral inhibition. Finally, we suggest that MMN might serve as a probe of what stimulus features are mapped by human a uditory cortex.