Thalamic unit activity and delayed alternation performance in the monkey.

Single unit activity was recorded from the thalamus of rhesus monkeys while they performed a delayed-alternation bar-pressing task. Nine units in the dorsomedial nucleus of the thalamus were activated prior to the lever presses of the contralateral hand, as indicated by an EMG of the triceps brachii muscle. In this same region, no units were found that became active during the delay period. In contrast, three units in the ventralis lateralis nucleus of the thalamus were activated simultaneously with lever presses. The results indicate that the dorsomedial nucleus may be involved with the initiation of lever pressing responses in the delayed alternation task. The thalamic units studied here were compared with those observed previously in the prefrontal cortex and the caudate nucleus.