Disruption of auditory but not visual learning by destruction of intrinsic neurons in the rat medial geniculate body.

The contribution of intrinsic neurons in the medial geniculate body (MG) of the rat to the classical conditioning of emotional responses to acoustic stimuli was examined. Injection of ibotenic acid, which destroys cell bodies but not axons of passage, into the MG disrupted the conditioned changes in mean arterial pressure and emotional behavior elicited by a tone previously associated with footshock. Unconditioned responses elicited by the tone and by the footshock were unaffected. Moreover, the same animals readily learned to associate a visual stimulus with footshock. Thus, destruction of intrinsic neurons in the MG selectively disrupts the conditioning of emotional responses to acoustic stimuli. The MG appears to be the afferent link in a modality specific emotional learning pathway.