D1 and D2 dopamine receptors (D1DRs and D2DRs) may contribute differently to various aspects of memory and cognition. The D1DR system has been linked to functions supported by the prefrontal cortex. By contrast, the role of the D2DR system is less clear, although it has been hypothesized that D2DRs make a specific contribution to hippocampus-based cognitive functions. Here we present results from 181 healthy adults between 64 and 68 y of age who underwent comprehensive assessment of episodic memory, working memory, and processing speed, along with MRI and D2DR assessment with [ 11 C]raclopride and PET. Caudate D2DR availability was positively associated with episodic memory but not with working memory or speed. Whole-brain analyses further revealed a relation between hippocampal D2DR availability and episodic memory. Hippocampal and caudate D2DR availability were interrelated, and functional MRIbased resting-state functional connectivity between the ventral caudate and medial temporal cortex increased as a function of caudate D2DR availability. Collectively, these findings indicate that D2DRs make a specific contribution to hippocampus-based cognition by influencing striatal and hippocampal regions, and their interactions.dopamine | memory | hippocampus D opamine (DA) plays a key role in several cognitive processes (1-4). Reductions of D1 and D2 DA receptors (D1DRs and D2DRs) in aging (5-7) have been linked to agerelated cognitive deficits (8, 9). The D1DR system has been related to functions supported by the prefrontal cortex (PFC), such as working memory and executive functions (10-12), which may reflect the relatively high density of D1DRs in the PFC (13). However, the role of D2DRs is far less clear. D2DRs are present in the PFC at very low densities (13), and evidence supporting a role for the D2DR system in working memory and executive functions is elusive (10). Pharmacological (14, 15) and PET studies assessing striatal D2DR availability (or binding potential to nondisplacable tissue uptake; BP ND ) with [ 11 C]raclopride (16, 17) have yielded mixed findings in relation to cognition. It has been hypothesized that D2DRs make a specific contribution to hippocampus-based cognitive functions (10,18,19). Supporting these claims, positive links between D2DR BP ND and episodic memory are commonly observed (20-23). PET imaging of hippocampal D2DR BP ND also provides support for this hypothesis, although some studies indicate that hippocampal D2DRs may be related to both episodic memory and PFC-based executive functions (22, 23), including verbal working memory (24). Medial temporal lobe regions have been implicated in working memory (25,26), and D2DR-mediated modulation may be exerted via hippocampal-cortical pathways (27). In addition, a [ 11 C]raclopride task-activation PET study demonstrated contributions of striatal D2DRs to a verbal working-memory task (11).Taken together, the specific role of the D2DR system in cognition remains unclear, likely due to the fact that past studies included small and age-hetero...