Effect of appetitive Pavlovian conditioning on the N150 of the amygdalar Auditory Evoked Potential in the rat

A large, negative wave which reaches its peak amplitude around 150 ms after stimulus onset, can be found in the Auditory Evoked Potential (AEP) recorded from the lateral amygdala in the rat. Previous studies in our laboratory have repeatedly shown that this N150 component increases during various aversive conditioning protocols and that this increase is attributable to both increases in emotional arousal that are inherent to aversive conditioning and to the formation of an association between the conditioned stimulus (CS) and the aversive unconditioned stimulus (US). Currently it is not known whether the N150 is also enhanced in conditioning procedures with positive reinforcement. To address this issue, we used a Pavlovian conditioning protocol in which an auditory CS signaled the delivery of a food US in food-deprived rats. AEPs evoked by the CS were recorded from the lateral amygdala while the animals were subjected to this appetitive conditioning procedure. Heart rate and N150 amplitude did not increase during conditioning relative to pre-conditioning baselines. In contrast, heart rate and N150 amplitude increases were present during an aversive conditioning protocol (tone–shock pairings) that was carried out after the appetitive conditioning. The present results suggest that the enhancement of the amygdalar N150 is specific for learning experiences that are accompanied by autonomic arousal and that this arousal is a prerequisite for the enhancement of the N150.