Pleasure-attenuation of startle is disrupted by lesions of the nucleus accumbens.

The nucleus accumbens (NAC) and the amygdala have been implicated in processes by which reinforcers control instrumental behaviour. Reinforcement has both motivational and motor components, and it is necessary to differentiate between these two aspects. The acoustic startle response (ASR) is attenuated in the presence of a secondary reinforcer. In contrast to other paradigms used for investigating mechanisms of reward, the "pleasure-attenuated startle" (PAS) paradigm indicates the rewarding properties of a treatment by an attenuation rather than by reinforcement of a response, thus allowing determination of the motivational impact of a treatment independent from its motor stimulating effects. Here, we report that the ASR was attenuated in the presence of a positive conditioned stimulus in shamoperated animals and in rats with lesions of the amygdala, but not in animals bearing 6-hydroxydopamine lesions of the NAC. These findings suggest that the catecholaminergic innervation of the NAC is important for behavioural control by conditioned reward.