Dopamine Release in the Human Striatum: Motor and Cognitive Tasks Revisited

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Abstract
Striatal dopamine (DA) release has been shown during behavioural tasks, but the relative contribution of motor, reward, and cognitive components is unclear. Dopamine release was quantified using [11C]-raclopride in two studies using a triple-scan approach, comprising active task, motor control, and rest. In the first, bolus radiotracer was delivered during a sequential motor learning paradigm; in the second, a spatial planning task, bolus plus constant infusion was applied. [11C]-raclopride binding potentials (BPNDs) in striatal functional subdivisions were compared across conditions. [11C]-raclopride BPND was significantly reduced in active task compared with rest in both the sensorimotor and associative striatum in both studies, because of differences between rest and motor control conditions. In both regions, the motor control BPND fell between the rest and active task in the planning study, but the difference between motor control and active task conditions was not significant. No such changes were observed in the limbic striatum. Using rigorous methodology, this study validates earlier evidence that striatal DA release occurs during behavioural challenges. Increased DA release during movement was reliably detected in the sensorimotor and associative striatum, supporting use of the functional subdivision model in humans. No additional DA release was observed specific to the cognitive component of either task.