Association between age-related decline in brain dopamine activity and impairment in frontal and cingulate metabolism

Objective: Despite the well-documented loss of brain dopamine activity with age, little is known about its functional consequences in healthy individuals. This study investigates the relationship between measures of brain dopamine D-2 receptors (molecules that transmit dopamine signals) and regional brain glucose metabolism (a marker of brain function) in healthy individuals. Method: Thirty-seven healthy volunteers aged 24-86 years underwent positron emission tomography scans after injection of [C-11]raclopride to assess dopamine D-2 receptors and [(18)]fluorodeoxyglucose to assess regional brain glucose metabolism. Two methods used to assess the correlations between metabolism and dopamine D-2 receptors-pixel-by-pixel correlations and correlations in preselected regions of interest-were then compared. Results: D-2 receptors as well as frontal and cingulate metabolism declined with age. Regardless of the method used, significant correlations between metabolism and D-2 receptors were found in the frontal cortex (Brodmann's areas 6, 7, 8, 9, 10, 11, 44, 45, 47), anterior cingulate gyrus (areas 24, 32), temporal cortex (area 21), and caudate. These correlations remained significant after removing age effects (partial correlation). Conclusions: These results provide the first link between age-related declines in brain dopamine activity and frontal and cingulate metabolism, which supports the need to investigate the therapeutic utility of interventions that enhance dopamine function in the elderly. The fact that correlations remained significant after removing age effects suggests that dopamine may influence frontal, cingulate, and temporal metabolism regardless of age.