Choice reflexes in the rodent habit system
published: July 28, 2015, recorded: June 2015, views: 1552
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We examined the neural mechanisms by which rats rapidly adjust choices following reward omission. Animals often employ a ‘lose-switch’ strategy in which they switch responses following reward omission. We surprisingly found that such responding was greatly reduced following lesions of the dorsolateral striatum (DLS), a brain region hypothesized to be involved in the gradual formation of habits. Moreover, we found that a modified Q-learning model better fit behavioural data from the DLS-lesioned animals than controls or animals with lesions of dorsomedial striatum (DMS), a region associated with ‘goal-directed’ responding. The model-based analysis revealed that animals with striatal lesions, particularly of the DLS, had blunted reward sensitivity and less stochasticity in the choice mechanism. Subsequent experiments showed that lose-switch responding was reduced by systemic administration of amphetamine, or by infusion of agonists for D2 type dopamine receptors in the DLS (but not into DMS). These data reveal that the DLS is able to drive rapid switches following reward omission (< 15 seconds) via inactivation of D2 receptors by periods of low dopamine (negative reward prediction error signal). We propose that this serves as a ‘choice reflex’ following errors that prevents animals from repeating mistakes while other behavioural control systems update expected action/state values.
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