Facilitated extinction of appetitive instrumental conditioning following excitotoxic lesions of the core or the medial shell subregion of the nucleus accumbens in rats.

The nucleus accumbens has been implicated in the control of goal-directed behaviour, including instrumental conditioning. Here, we evaluated the effect of N-methyl-D: -aspartate (NMDA)-induced excitotoxic lesions restricted to either the core or the medial shell subregions of the nucleus accumbens (NAC) on extinction in rats using a trial discrete fixed ratio-5 (FR-5) appetitive operant procedure. Neither core nor shell lesions of the NAC affected the acquisition of instrumental responding. Both lesions facilitated the cessation of responding when the instrumental act no longer yielded reinforcement. Our results suggest that both the NAC core and medial shell contribute to the control of extinction learning of appetitively motivated instrumental behaviour.