Nucleus accumbens inhibits specific motor but not nonspecific classically conditioned responses.

A classical leg flexion conditioning paradigm was used to elicit specific motor responses, as well as nonspecific responses requiring less involvement of the motor system, in cats. Stimulating and lesioning the nucleus accumbens differentially affected these two types of responses. The specific conditioned responses, leg flexion and vocalization, were suppressed by stimulation and enhanced by lesions of the nucleus accumbens. The nonspecific responses, changes in respiration rate and amplitude, and in heart rate, were affected inconsistently or not at all. This suggests a role for the nucleus accumbens in the inhibition of motor components of learned emotional responses, and is consistent with hypotheses holding that the nucleus accumbens gates the access of the limbic system to motor systems.