INCREASED FIRING OF NEURONS IN THE POSTERIOR HYPOTHALAMUS WHICH PRECEDE CLASSICALLY-CONDITIONED PUPILLARY DILATIONS

Paralyzed cats were used as subjects in a classical conditioning exper iment where each subject was exposed to 40 explicitly unpaired 1-s bur sts of white noise and 0.5-s paw shocks. This training was followed by 60 trials of the two stimuli paired, where the white noise immediatel y preceded the paw shock. Following this training, the subjects were r e-exposed to 40 trials of the explicitly unpaired procedure. The pupil was monitored as the behavior and electrodes implanted in the thalamu s, the dorsal hypothalamus and the posterior hypothalamus recorded the activity of clusters of cells. Only the cells in the posterior hypoth alamus showed robust changes in firing rates that preceded the pupilla ry behavior, both (a) on any particular trial and (b) as the learned a ssociation was being demonstrated behaviorally across trials.