DIFFERENTIAL ACTIVATION OF THE CAUDATE-NUCLEUS IN PRIMATES PERFORMINGSPATIAL AND NONSPATIAL WORKING-MEMORY TASKS

The caudate nucleus is part of an anatomical network subserving functi ons associated with the dorsolateral prefrontal cortex (DLPFC). The ai m of the present study was to investigate whether the metabolic activi ty in the striatum reflects specific changes in working memory tasks, which are known to be dependent on the DLPFC, and whether these change s reflect the topographic ordering of prefrontal connections within th e striatum. Local cerebral glucose utilization (LCGU) rates were asses sed in the striatum by the C-14-2-deoxyglucose method in monkeys that performed a spatial (delayed spatial alternation), a nonspatial (delay ed object alternation) visual working memory task, or tasks that did n ot involve working memory, i.e., a visual pattern discrimination or se nsorimotor paradigm. The results show a topographic segregation of act ivation related to spatial and nonspatial working memory, respectively . The delayed spatial alternation task increases LCGU rates bilaterall y by 33-43% in the head of the caudate nucleus, where efferents from t he dorsolateral prefrontal cortex project most densely. The delayed ob ject alternation task enhances LCGU rates bilaterally by 32-37% in the body of the caudate nucleus, which is innervated by the temporal cort ex. The visual pattern discrimination task similarly activated the bod y of the caudate, but in a smaller region and only in the right hemisp here. These findings provide the first evidence for metabolic activati on of the caudate nuclei in working memory, supporting the role of thi s nucleus as a node in a neural network mediating DLPFC-dependent work ing memory processes. The double dissociation of activation observed s uggests an anatomical and functional segregation of cortico-striatal c ircuits subserving spatial and nonspatial cognitive operations.