Pain pathways involved in fear conditioning measured with fear-potentiatedstartle: Lesion studies

It is well established that the basolateral amygdala is critically involved in the association between an unconditioned stimulus (US), such as a foot shock, and a conditioned stimulus (CS), such as a light, during classic fea r conditioning. However, little is known about how the US (pain) inputs are relayed to the basolateral amygdala. The present studies were designed to define potential US pathways to the amygdala using lesion methods. Electrol ytic lesions before or after training were placed in caudal granular/dysgra nular insular cortex (IC) alone or in conjunction with the posterior intral aminar nuclei of the thalamus (PoT/PIL), and the effects on fear conditioni ng were examined. Pretraining lesions of both IC and PoT/PIL, but not lesio ns of le alone, blocked the acquisition of fear-potentiated startle. Howeve r, post-training combined lesions of IC and PoT/PIL did not prevent express ion of conditioned fear. Given that previous studies have shown that lesion s of PoT/PIL alone had no effect on acquisition of conditioned fear, these results suggest that two parallel cortical (insula-amygdala) and subcortica l (PoT/PIL-amygdala) pathways are involved in relaying shock information to the basolateral amygdala during fear conditioning.