Research ReportMeasuring Pavlovian fear with conditioned freezing and conditioned suppression reveals different roles for the basolateral amygdala

In Pavlovian fear conditioning, pairing a neutral cue with aversive foot shock endows a cue with fear-eliciting properties. Studies of Pavlovian fear conditioning measuring freezing have demonstrated the basolateral amygdala (BLA) to be critical to both fear learning and memory. The nucleus accumbens core (NAc), while not important to freezing, is important to the enhancement of instrumental responding by cues paired with food reward. In the present study we investigated the role of the BLA and the NAc in another property of fear cues, the ability to suppress instrumental responding for food rewards (conditioned suppression). Sham, BLA and NAc-lesioned rats received a fear discrimination procedure in which one visual cue (CS+) predicted foot shock while a second cue (CS−) did not. Conditioning took place over a baseline of instrumental responding, allowing for concurrent measure of freezing and instrumental suppression. NAc lesions left fear conditioning fully intact. BLA lesions impaired acquisition and discrimination of fear when assessed with conditioned freezing. However, BLA lesions only altered fear acquisition and left discrimination completely intact when assessed with conditioned suppression. These findings suggest a critical role for the BLA in fear when assessed with conditioned freezing but a diminished role when assessed with conditioned suppression.

Research Highlights► Normal rats readily acquire discrimination in both conditioned freezing and conditioned suppression. ► The nucleus accumbens core is not necessary for discrimination in either conditioned freezing or conditioned suppression. ► The basolateral amygdala is critical to acquisition and discrimination in conditioned freezing. ► The basolateral amygdala contributes to acquisition but is not necessary for discrimination in conditioned suppression.