Background: Cognitive abilities decline with age with large individual variability. Genetic variations have been suggested to be an important source for some of this heterogeneity. Among these variations, those related to the dopaminergic system, particularly the valine(158)methionine polymorphism in catechol-O-methyltransferase (COMTval(158)met), have been implicated in modulating age-related changes in executive function.
Methods: We studied 75 subjects (age 21-90 years) using functional neuroimaging while they performed a low-level working memory (WM) task to explore the effects of aging, of the COMTval(158)met polymorphism, and their interactions on the physiological patterns of interconnected cortical activity engaged by WM.
Results: Our results show that val homozygotes and older subjects showed increased activity in dorsolateral prefrontal cortex (DLPFC) and decreased activity in ventrolateral prefrontal cortex (VLPFC) relative to met homozygotes and younger subjects, respectively. Interestingly, there were also independent effects of the COMTval(158)met polymorphism and age on the strength of connectivity between brain regions within the left prefrontal-parietal network; val homozygotes and older subjects showed greater connectivity between the DLPFC and other brain regions within the network and met homozygotes showed greater connectivity between the VLPFC and other brain regions within the network. Furthermore, the greater functional connectivity strength of DLPFC in val homozygotes relative to met homozygotes was much more pronounced in older adults
Conclusions: Our findings suggest that the COMTval(158)met polymorphism modulates both the activity and functional connectivity of brain regions within WM networks and most importantly that this effect is exaggerated with increasing age, contributing to the variability in age-related decline in executive cognition.