Ventral striatal and caudate contributions to episodic retrieval

Striatal activity during episodic memory retrieval is a robust phenomenon observed across various stimulus types and experimental paradigms. Previous research suggests that the ventral striatum and the caudate contribute differentially to retrieval processes: ventral striatal activity is posited to vary with the intrinsic reward of successful retrieval, whereas caudate activity is attributed to effortful cognitive control. The present fMRI study aimed to test the overarching hypothesis that these striatal subregions make distinct contributions to episodic retrieval and to further specify their functional roles. To this end, we employed a word-picture paired-associates learning paradigm in which words served as cues in two consecutive cued-recall tests that were separated by 24 hrs. Participants indicated the specificity of their associative memories, enabling characterization of striatal response profiles as a function of associative memory specificity and treatment of memory specificity as a proxy for the intrinsic reward associated with retrieval success. Rather than being not readily compatible with a role of the caudate in effortful post-retrieval control, the results suggest that elevated caudate activity during successful recall reflects pre-retrieval control or involuntary orienting to salient mnemonic information. In contrast, rather than reflect intrinsic reward itself, ventral striatal activity varied with the discrepancy between expected and actual intrinsic reward elicited by retrieval outcomes-that is, a metacognitive reward prediction error. Moreover, ventral striatum signaled the relevance of retrieved information and modulated its re-encoding to facilitate future retrievals.