Stimulus generalization of fear responses: effects of auditory cortex lesions in a computational model and in rats

The conditioning of fear responses to a simple acoustic stimulus (puretone) paired with footshock can be mediated by the transmission of auditoryinformation to the lateral nucleus of the amygdala from either the auditorythalamus or the auditory cortex. We examined the processing capacity of thethalamo-amygdala pathway by making lesions of the auditory cortex andtesting the extent to which conditioned fear responses generalized to tonesother than the one paired with footshock. Two studies were performed, onein an anatomically constrained computational model of the fear conditioningnetwork and the other in rats. Stimulus generalization was unaffected inboth. These findings support the validity of the model as an approach tostudying the neural basis of conditioned fear learning, and in additionsuggest that the thalamo-amygdala pathway, possibly by the use ofpopulation coding, is capable of performing at least crude stimulusdiscriminations.