DETECTION OF STIMULUS DEVIANCE WITHIN PRIMATE PRIMARY AUDITORY-CORTEX- INTRACORTICAL MECHANISMS OF MISMATCH NEGATIVITY (MMN) GENERATION

Mismatch negativity (MMN) is a cognitive, auditory event-related poten tial (AEP) that reflects preattentive detection of stimulus deviance a nd indexes the operation of the auditory sensory ('echoic') memory sys tem. MMN is elicited most commonly in an auditory oddball paradigm in which a sequence of repetitive standard stimuli is interrupted infrequ ently and unexpectedly by a physically deviant 'oddball' stimulus. Ele ctro- and magnetoencephalographic dipole mapping studies have localize d the generators of MMN to supratemporal auditory cortex in the vicini ty of Heschl's gyrus, but have not determined the degree to which MMN reflects activation within primary auditory cortex (AI) itself. The pr esent study, using moveable multichannel electrodes inserted acutely i nto superior temporal plane, demonstrates a significant contribution o f AI to scalp-recorded MMN in the monkey, as reflected by greater resp onse of AI to loud or soft clicks presented as deviants than to the sa me stimuli presented as repetitive standards. The MMN-like activity wa s localized primarily to supragranular laminae within AI. Thus, standa rd and deviant stimuli elicited similar degrees of initial, thalamocor tical excitation. In contrast, responses within supragranular cortex w ere significantly larger to deviant stimuli than to standards. No MMN- like activity was detected in a limited number to passes that penetrat ed anterior and medial to AI. AI plays a well established role in the decoding of the acoustic properties of individual stimuli. The present study demonstrates that primary auditory cortex also plays an importa nt role in processing the relationships between stimuli, and thus part icipates in cognitive, as well as purely sensory, processing of audito ry information.