IBOTENIC ACID LESIONS OF THE AMYGDALA BASOLATERAL COMPLEX OR CENTRAL NUCLEUS DIFFERENTIALLY EFFECT THE RESPONSE TO REDUCTIONS IN REWARD

The present study examined the role of the amygdala in the acquisition and expression of the Crespi effect (Crespi, L.P., Quantitative varia tion in incentive and performance in the white rat, Am. J. Psychol., 5 5 (1942) 467-517), also known as successive negative behavioral contra st. In Experiment One rats with bilateral amygdala cannulae were train ed to run a straight alley for either a large (ten pellet) or small (o ne pellet) food reward. After 8 days of training, half of the rats in each reward condition received vehicle or ibotenic acid administered b ilaterally into the amygdala. After 4 days of recovery from the induct ion of the lesions, training resumed. On Day 12 of training, the rewar d for rats in the large reward condition was shifted to one pellet and this reward level was maintained for the next 4 days of training. Bot h the lesioned and unlesioned shifted rats exhibited increased latenci es to the reduction. However, shifted lesioned rats displayed a more p ersistent increase in latencies than shifted unlesioned rats, exhibiti ng significantly longer latencies than those of unlesioned rats by Day 15. This finding suggests that large amygdala lesions may impair lear ning of the appetitive value of the small reward. Experiment Two exami ned the effects of discrete ibotenic acid lesions of either the centra l nucleus or basolateral/lateral complex of the amygdala. Lesions of t he central nucleus produced results similar to those of Experiment One . However, in Experiment Two the performance of shifted unlesioned and lesioned groups diverged significantly 1 day earlier, on Day 14. In c ontrast, lesions of the basolateral/lateral complex reduced the durati on of the contrast effect. Shifted lesioned rats exhibited significant ly lower latencies than shifted unlesioned rats by the first postshift day, Day 13. This finding suggests that the basolateral/lateral compl ex may be involved in learning about, or expressing the response to, t he aversiveness of reward reduction.