Dopamine And Learning

Animal research shows that dopamine is involved in the acquisition of operant tasks, avoidance learning, and intracranial self-stimulation. It is thought that dopamine in mesolimbic regions (most notably the nucleus accumbens) is involved in both the acquisition and the maintenance of these behaviors. This conclusion was based primarily on results from studies using dopamine-depleting agents and dopaminergic drugs to evaluate their effects on acquisition or maintenance of reinforced behaviors. The results of acquisition studies showed that administration of dopamine antagonists or the dopamine-depleting agent, 6-hydroxydopa-mine, prevented the acquisition of these tasks. Reinterpretation of studies evaluating the effects of these agents on the maintenance of such behaviors has not been so clear-cut. For example, the acute administration of a dopaminergic antagonist after acquisition of an operant task often has no effect or increases the level of operant responding. This has been interpreted to be the result of a decrease in the perceived "salience" of the reward, whereas chronic administration of these agents blocks these behaviors. Recent in vivo voltam-metry studies, which directly measure fast changes in dopamine release at the level of the synapse, carried out by Garris, Wightman, and colleagues have shown that evoked dopamine release in the nucleus accumbens is associated with the acquisition but not the maintenance of reinforced behavior, at least in the case of intracranial stimulation.

memory modulation in humans, although one study has also shown that the administration of the D2-like antagonist sulpride produced a dose-dependent impairment in spatial working memory.

Studies examining the performance of PD patients on working memory tasks also support the idea that dopamine may be involved in working memory in humans as well as in experimental animals. Imaging studies in PD patients have shown reduced fluorodopa uptake in the caudate nucleus and frontal cortex, which correlates with deficits in working memory as well as attention.

Some studies have also evaluated the effects of dopamine receptors in the ventral hippocampus on working memory tasks in rats. These studies suggest that D2-like but not D1-like receptors in the ventral hippocampus modulate spatial working memory.

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