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We assess the relationship of age-related losses in striatal D1 receptor densities to age-related reductions in functional connectivity between spatially distinct cortical regions in healthy human participants. Previous neuroimaging studies have reported age-related differences in functional connectivity of the frontoparietal working memory network and the default mode network during task performance. We used functional magnetic resonance imaging and seed-based connectivity (right dorsolateral and medial prefrontal cortex) to extend these findings: Anterior-posterior connectivity of both these functional networks was reduced in older (65-75 years, n = 18) compared with younger (20-30 years, n = 19) adults, whereas bilateral connectivity in prefrontal cortex was increased in older adults. Positron emission tomography with the D1 receptor ligand (11)CSCH23390 was used to assess caudate D1 receptor density in the same sample. Older adults showed significantly reduced caudate D1 receptor density compared to the younger adults. Of key interest, partial correlations showed that individual differences in caudate D1 receptor density were positively associated with individual differences in dorsolateral prefrontal connectivity to right parietal cortex (BA40) and negatively with medial prefrontal connectivity to right parietal cortex (BA40 and postcentral gyrus), after controlling for age. We found no correlation of caudate D1 receptor density with anterior-posterior coupling within the default mode network or with bilateral frontal connectivity. These results are consistent with animal work that has identified a role for caudate D1 receptors in mediating information transfer between prefrontal areas and parietal cortex.
Rieckmann et al. (Wed,) studied this question.