Figure 3From: Effects of lesions of the nucleus accumbens core on choice between small certain rewards and large uncertain rewards in ratsChoice with probabilistic reinforcement. (a) Preoperative patterns of choice. There were no differences between the groups preoperatively. (b) The first three postoperative sessions. Transiently, AcbC-lesioned rats exhibited relative indifference between the two alternatives; their preference did not differ significantly from 50% at any large-reinforcer probability. As a result, AcbC-lesioned rats preferred the large, unlikely reinforcer more than shams did when its probability was 0.0625 and 0.125 (## p < .01, lesion × probability interaction; * p < .05, ** p < .01, comparison to shams at individual probabilities). However, both groups were influenced by the large-reinforcer probability (p ≤ .004). (c) The last three postoperative sessions on the same basic task. By this point, AcbC-lesioned rats preferred the large reinforcer less when its probability was 0.5 or 1 (## p < .01, interaction; * p < .05, simple effects). Again, both groups were influenced by the large-reinforcer probability (p < .001). (d) When the 4-pellet reinforcer and the 1-pellet reinforcer were both certain, all groups preferred the 4-pellet reinforcer, and when the 4-pellet reinforcer was always very unlikely (delivered with a probability of 0.0625) and the 1-pellet reinforcer was certain, all groups preferred the 1-pellet reinforcer, with no differences between AcbC-lesioned and sham-operated rats. This indicates that both groups discriminated the reinforcers themselves and discriminated their probability of delivery. (e) Choice following further training in which the large-reinforcer probability increased, rather than decreased, across each session. The pattern of choice is similar to c, in that AcbC-lesioned rats were risk-averse compared to shams, i.e. less likely to choose the large, unlikely reinforcer (### p < .001, interaction; * p < .05 and *** p < .001, simple effects). The similarity to c, despite the reversed task order, also indicates that subjects' choice reflected the probabilities in force rather than the order within a session.Back to article page