Elsevier

NeuroImage

Volume 38, Issue 3, 15 November 2007, Pages 549-556
NeuroImage

Striatal dopamine release in sequential learning

https://doi.org/10.1016/j.neuroimage.2007.07.052Get rights and content

Abstract

Sequential learning is an important aspect of cognitive processing. Neuropharmacological evidence acquired in laboratory animals suggests that striatal dopaminergic mechanisms may be important for processing of this form of learning. However, because experiments conducted on dopamine deficient patients have reported contradictory evidence, the role of dopamine and the striatum remains unclear in human sequential learning. We used a newly developed dynamic molecular imaging technique to determine whether striatal dopamine is released during performance of a sequential learning task. In this study we localized striatal regions where dopamine receptor ligand (11C-raclopride) was displaced from receptor sites, during performance of a motor sequence learning (serial reaction time) task. The results suggest that the task induces release of endogenous dopamine in the posterior two-third of dorsomedial aspect of left putamen and the anterior part of the body of caudate bilaterally. The activations of the left putamen and the right caudate coincided with the activations observed earlier during performance of a motor planning task. Since these activations are associated with the selection and execution of a response, the activation in the left caudate, which was not observed in motor planning, is probably associated with the detection of a change in the ‘context’, and in the formulation of a new ‘rule’. Thus, the results suggest that sequential learning involves two striatal dopaminergic mechanisms, one for the detection of a change in context, and the other for selection and execution of the response.

Section snippets

Materials and methods

The experiments were conducted on right-handed young healthy volunteers who had no history of a psychiatric or neurological disorder.

SRT experiment

In this experiment response accuracy during the control (98.6%) and test (99.2%) conditions was high and statistically similar. The response time however, was significantly quicker (p < 0.01) in the test (310 ± 26 ms) condition, in comparison with the control (405 ± 94 ms). Quicker response in the test suggested that the volunteers had learned the motor sequence (Fig. 1). Further, implicit nature of the task was confirmed by debriefing questionnaires. Six of the eight volunteers were not aware that

Discussion

To our knowledge, this is the first study that has demonstrated endogenous release of striatal dopamine during processing of a learning task. Further, by localizing areas of dopaminergic activity, the experiment provides a novel insight into the striatal and dopaminergic processing of human sequential learning. The finding that dopamine was released in the caudate and left putamen is consistent with the observation of neuroimaging experiments that have reported increased striatal activity

Acknowledgments

This work was supported by grants from the National Institutes of Health (1R21MH073624), Dana Foundation, and Shriners Hospital for Children (Grant 8580).

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