Cortical responses to changes in auditory stimuli. Magnetoencephalographic studies.

Any infrequent change ("deviant") in the parameters of a repetitive auditory stimulus ("standard") elicits both in electro- and magnetoencephalogram a specific "mismatch response". Identical infrequent stimuli do not elicit it; the presence of standards is necessary. Magnetic measurements have shown that the mismatch response has its neural source at the supratemporal auditory cortex. This source is about 10 mm anterior to the source of the N100m deflection, suggesting that these two waves are generated at different cytoarchitectonic areas. It is suggested here that the mismatch response reflects the activity in "change detectors", whereas activity in auditory feature maps underlies the N100m deflection. A model is proposed where the activity from feature maps converges on change detectors; the presence of a mismatch response is suggested to indicate that feature maps have been previously activated.