Amygdaloid lesions and stimulus-reward associations in the rat.

Rats with amygdaloid lesions were trained on learning set tasks designed to tax stimulus-reward associations. Lesions centred in the medial and ventral half of the amygdala had no effect on the acquisition of two object discriminations but did impair successive reversals of the second discrimination. The same lesions had no effect, however, on the acquisition of a spatial win-stay lose-shift task which taxed one-trial place-reward associations. In a second experiment it was found that lesions in the central and basolateral regions of the amygdala disrupted performance of the same spatial win-stay lose-shift task although, as before, acquisition was unaffected. Taken together these findings support a role for the amygdala in stimulus-reward associations and indicate that it may be particularly important when differing values of reward must be distinguished.