Effects of ventral striatal lesions on first- and second-order appetitive conditioning.

Rats with bilateral lesions of the ventral striatal nucleus accumbens failed to acquire Pavlovian second-order conditioning to auditory stimuli paired with visual stimuli that had previously received first-order pairings with food. This deficit in second-order conditioning was specific to learning driven by incentive properties of the first-order cues, and was observed whether the first-order training had occurred prior to or after lesion surgery. Lesions also produced deficits in the display of conditioned responses to the first-order conditioned stimulus, but only when they were made after first-order training. These results suggest a specific role for the ventral striatum in acquiring and expressing incentive properties of conditioned stimuli through second-order conditioning, as well as a more general role in expressing previously acquired Pavlovian conditioned responses.