Electrical stimulation of cortical-caudate pairs during delayed successive visual discrimination in monkeys.

The anterodorsal head of the caudate nucleus is the recipient of efferent projections from the dorsolateral prefrontal cortex while the tail of the caudate receives fibers originating in inferotemporal cortex. In order to investigate whether anatomically related members of these two systems are also functionally related, monkeys were trained on a delayed successive visual discrimination task. Electrical stimulation was administered during varied portions of individual trials to determine when in each trial performance was most disturbed as a function of the structure stimulated. Comparisons of stimulation effects allowed for examination of both functional dissociation and functional equivalence. Performance was maximally impaired when a 2 sec train of stimulation was applied to the principal sulcus region of dorsolateral prefrontal cortex or to the anterodorsal head of the caudate nucleus early during the delay or was delivered to posterior inferotemporal cortex or the tail of the caudate during cue presentation. No significant differences were seen between stimulation performance curves drawn for two members of each anatomically related system. Thus it appears that the anatomical systems may be functionally dissociated while the anatomically related structures within these systems show a functional equivalence; however the nature of this equivalence is uncertain. The theoretical functional relationship of the cortical-caudate pairs is also considered.