INVOLVEMENT OF THE VENTROLATERAL THALAMIC NUCLEUS IN RABBIT CLASSICALEYEBLINK CONDITIONING

The involvement of the ventrolateral nucleus of the thalamus in relayi ng learning-related activity to higher brain structures during classic al conditioning of the rabbit eyelid response was examined in two expe riments. In the first study, multiple-unit ventrolateral thalamic nucl eus activity was monitored before and after lesions of either the cere bellar interpositus nucleus or red nucleus were given. Before the lesi ons were given,conditioned response-related activity was observed in t he ventrolateral thalamic nucleus. Lesions of the interpositus nucleus , but not the red nucleus, disrupted the conditioning-related activity in the ventrolateral thalamic nucleus, thus suggesting that an effere nt copy of conditioned response-related activity is projected directly from the interpositus nucleus to higher brain areas by way of the ven trolateral thalamic nucleus. In the second study, multiple unit activi ty in the hippocampus was monitored before and after lesions were plac ed in the ventrolateral thalamic nucleus or red nucleus. Conditioning- related activity in the hippocampus was not affected by either lesion, thus suggesting that maintenance of training. related activity in the hippocampus is not critically dependent on cerebellar information rel ayed through the ventrolateral thalamic nucleus or red nucleus.