AbstractEfficient task performance requires co-ordination of internal cognitive processes by implementing control policies adapted to the dynamic structure of task demands. The cognitive and neural basis of control policy implementation remains poorly characterized, in part because it is typically confounded with implementing new stimulus-response rules. To disambiguate these processes, we asked participants to perform multiple novel variants of a working memory control task. Each variant had a unique, novel sequential trial structure, but all shared common stimulusresponse rules, enabling us to test control policy implementation separate from rule learning. Behaviorally, we found evidence for two adaptive processes tied to control policy implementation. One process was reflected in slower responses on the first trial with a novel sequential trial structure, followed by rapid speeding on subsequent trials. A second process was reflected in the diminishing size of the first trial cost as participants accommodated different variants of the task over many blocks. Using fMRI, we observed that the striatum and a cingulo-opercular cortical network increased activity to the first trial, tracking the fast adjustment. This pattern of activity dissociated these regions from a fronto-parietal network including dorsolateral PFC, inferior frontal junction, inferior parietal sulcus, and rostrolateral PFC, which showed a slower decline in activity across trials, mirroring findings in rule implementation studies, but in the absence of rule implementation demands. Our results reveal two adaptive processes underlying the implementation of efficient, generalizable control policies, and suggest a broader account of the role of a cortico-striatal network in control policy implementation.Significance statementRapid adaptation to novel tasks is a hallmark of human behavior. Understanding how human brains achieve this is of critical importance in neuroscience. Here we broaden the scope of this problem, going beyond task rules to more broadly consider the cognitive control demands produced by novel task dynamics. We propose that humans rely on two adaptive processes to rapidly implement efficient, generalizable control policies as task dynamics change, even when task rules remain unchanged. One process unfolds rapidly and underlies efficient adaptation. A second process unfolds slowly with experience across task conditions and underlies generalization of control policies. Using fMRI, we identify cingulo-opercular cortex, fronto-parietal cortex and striatum as dissociable components of a cortico-striatal network that contribute to control implementation.
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