Neural correlates of stimulus-reward association in the rat mediodorsal thalamus.

Neural activity was recorded from the mediodorsal thalamic nucleus of behaving rats during the discrimination of olfactory cues associated with or without a reward. Approximately 10% of mediodorsal thalamic neurons showed significant responses during the presentation of cues. Most of these neurons responded strongly to cues associated with a reward. These neurons also differentiated between cues, even in the same reinforcement (reward/nonreward) group. All of the neurons tested in extinction, relearning, and/or new-learning trials changed their responses flexibly according to the reward contingency. These neurons were located primarily in the central and medial segments of the mediodorsal thalamus. These results suggest that these mediodorsal thalamic neurons are the neural substrates for association learning of olfactory stimuli with rewards.