Effects of excitotoxic lesions of the rat ventral striatum on the perception of reward cost

This study examined the possibility that lesions of the nucleus accumbens i n rats impair the perception of the "cost of reward", as defined by the num ber of operant responses needed to obtain a food pellet. In a first experim ent, visual cues indicated the cost of reward under a multiple-ratio schedu le of reinforcement. In a second experiment, the number of lever presses re quired for each reward incremented with each trial in a progressive-ratio s chedule of reinforcement. Lesions of the nucleus accumbens altered the beha vioral response to the increasing cost of reward when there was an absence of external cues. There was no change in the ability of the lesioned rats t o respond to visual cues that indicated reward availability. The results ar e considered in terms of the traditional idea of the nucleus accumbens as a limbic-motor interface: it is suggested that, if the nucleus accumbens ser ves such a function, it is limited to only some contexts.