Gustatory thalamus lesions eliminate successive negative contrast in rats.

Neurologically intact rats expecting to receive a high-value reward (1.0 M sucrose), licked less for an unexpected low-value reward (0.15% saccharin) than did control subjects that only received the saccharin solution. This reward comparison effect, termed successive negative contrast, was eliminated after bilateral electrolytic lesions of the gustatory thalamus. The results are discussed in terms of disrupted memory processes that may have rendered the lesioned rats incapable of computing the relative reward value of the available solution (0.15% saccharin) with respect to the memory of the preferred solution (1.0 M sucrose).