BINAURAL RESPONSE PATTERNS IN SUBDIVISIONS OF THE MEDIAL GENICULATE-BODY

Auditory evoked potentials (AEPs) to binaural click stimulation were e xamined in the ventral (MGv) and caudomedial (MGcm) subdivisions of th e medial geniculate body (MG) in guinea pigs. Binaural stimulation cau sed a decrease in amplitude for the response component recorded from t he MGv, but an increase in amplitude for the AEP component recorded fr om the MGcm. Findings suggest that the evoked responses recorded from MGv and MGcm are functionally distinct. The inhibitory binaural respon se (BR) pattern seen in MGv was similar to that of the middle latency response (MLR) component recorded over the temporal cortex, while the additive BR pattern typical of the MGcm was similar to that of the sur face midline MLR component. Furthermore, these data imply that the bin aural response patterns seen in the primary and non-primary auditory c ortex may be processed and encoded at the thalamic level. It is conclu ded that the distinct BR patterns noted for the two MG subdivisions re flect the predominant type of binaurally responsive neurons within the respective pathways.