Distinct representation of cognitive flexibility and habitual stability in the primate putamen, caudate, and ventral striatum
Recent primate studies have demonstrated a functional distinction along the rostral--caudal axis of the striatum, which has challenged the conventional view that flexible adaptation and habitual action differ in processing along the medial--lateral axis. We found that neurons in the rostral putamen, caudate, and ventral striatum encode values flexibly updated for adaptive choices, rather than values stably sustained for visual habit. In the reversal value learning, rostral striatal neurons dynamically updated their value discrimination responses after value reversals, whereas, in the stable value retrieval, most did not encode the value. Notably, caudate neurons were faster to update values after reversal trials than ventral striatum neurons. Slow-learning neurons were identified selectively in the ventral striatum. In each trial, their learning speeds were similar during initial learning, suggesting a parallel value update in each striatal region. Our findings thus indicate that the rostral striatum prioritizes cognitive flexibility over habitual stability.