Differential roles of caudate nucleus and putamen during instrumental learning.

The dorsal striatum is crucial for the acquisition and consolidation of instrumental behaviour, but the underlying computations and internal dynamics remain elusive. To address this issue, we combined a model of key computations supporting decision-making during instrumental learning with human behavioural and functional magnetic resonance imaging (fMRI) data. The results showed that the associative and sensorimotor dorsal striatum host complementary computations that, we suggest, may differentially support goal-directed and habitual processes. The anterior caudate nucleus integrates information about performance and cognitive control demands, whereas the putamen tracks how likely the conditioning stimuli lead to correct response. Contrary to current models, the putamen is recruited during initial acquisition. As the exploratory phase proceeds, the relative contribution of the caudate nucleus becomes dominant over the putamen. During early consolidation, caudate nucleus and putamen settle to asymptotic values and share control. We then investigated how dorsal striatal computations may affect decision-making. We found that portion of reaction times' variance parallels the combined cost associated with the dorsal striatal computations. Overall, our findings provide a deeper insight into the functional heterogeneity within the dorsal striatum and suggest that the dynamic interplay between caudate nucleus and putamen, rather than their serial recruitment, underlies the acquisition and early consolidation of instrumental behaviours.