Progressive ratio performance in rats with gustatory thalamus lesions.

To determine whether damage of the gustatory thalamus (the parvicellular region of the ventroposteromedial nucleus) disrupts the perceived value of reinforcing stimuli, the performance of rats with bilateral, electrophysiologically guided, electrolytic lesions of the area was examined in Experiment 1 with a progressive-ratio schedule of reinforcement. Lesioned rats showed normal concentration-dependent changes in break point (an index of the amount of effort a subject will expend to obtain reinforcement) and in consummatory responding (licking) for the sucrose reward. In the reward comparison procedure of Experiment 2, however, the same lesioned rats failed to show morphine-induced suppression of alanine consumption. The results provide no support for the view that the thalamic taste area is involved in the perception of the absolute reinforcing value of gustatory stimuli.