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 (pure tone) paired with footshock can be mediated by the transmission of auditory information to the lateral nucleus of the amygdala from either the auditory thalamus or the auditory cortex. We examined the processing capacity of the thalamo-amygdala pathway by making lesions of the auditory cortex and testing the extent to which conditioned fear responses generalized to tones other than the one paired with footshock. Two studies were performed, one in an anatomically constrained computational model of the fear conditioning network and the other in rats. Stimulus generalization was unaffected in both. These findings support the validity of the model as an approach to studying the neural basis of conditioned fear learning, and in addition suggest that the thalamo-amygdala pathway, possibly by the use of population coding, is capable of performing at least crude stimulus discriminations.