Abstract
Working memory is a limited capacity system that integrates and manipulates information across brief periods of time, engaging a network of prefrontal, parietal and subcortical brain regions. Genetic control of these heritable brain processes have been suggested by functional genetic variations influencing dopamine signalling, which affect prefrontal activity during complex working memory tasks. However, less is known about genetic control over component working memory cortical-subcortical networks in humans, and the pharmacogenetic implications of dopamine-related genes on cognition in patients receiving anti-dopaminergic drugs. Here, we examined predictions from basic models of dopaminergic signalling in cortical and cortical-subcortical circuitries implicated in dissociable working memory maintenance and manipulation processes. We also examined pharmacogenetic effects on cognition in the context of anti-dopaminergic drug therapy. Using dynamic causal models of functional magnetic resonance imaging in normal subjects (n = 46), we identified differentiated effects of functional polymorphisms in COMT, DRD2 and AKT1 genes on prefrontal-parietal and prefrontal-striatal circuits engaged during maintenance and manipulation, respectively. Cortical synaptic dopamine monitored by the COMT Val158Met polymorphism influenced prefrontal control of both parietal processing in working memory maintenance and striatal processing in working memory manipulation. DRD2 and AKT1 polymorphisms implicated in DRD2 signalling influenced only the prefrontal-striatal network associated with manipulation. In the context of anti-psychotic drugs, the DRD2 and AKT1 polymorphisms altered dose-response effects of anti-psychotic drugs on cognition in schizophrenia (n = 111). Thus, we suggest that genetic modulation of DRD2-AKT1-related prefrontal-subcortical circuits could at least in part influence cognitive dysfunction in psychosis and its treatment.
Highlights
Working memory, a limited capacity system that integrates and manipulates information across brief periods of time, critically engages a network of prefrontal, parietal and subcortical regions, and underlies important aspects of general intellectual function (Duncan et al, 2000; Gray et al, 2003)
In the functional MRI study of healthy subjects (n = 46), no demographic differences were found across COMT Val/Met, AKT1 rs1130233 and dopamine receptor D2 (DRD2) rs1076560 genotypes in terms of gender, age or IQ (n = 46, P 4 0.14)
The optimal model engaged working memory information input to the dorsolateral prefrontal cortex, and task-related changes in prefrontal-to-parietal and parietal-to-thalamic neural connections (Fig. 2)
Summary
A limited capacity system that integrates and manipulates information across brief periods of time, critically engages a network of prefrontal, parietal and subcortical regions, and underlies important aspects of general intellectual function (Duncan et al, 2000; Gray et al, 2003). Working memory is dysfunctional in schizophrenia (Weinberger et al, 1986) and is related to its genetics from family and twin studies (Goldberg et al, 1993; Cannon et al, 2000; Egan et al, 2001a; Callicott et al, 2003; Toulopoulou et al, 2010). Executive sub-processes of working memory engaging manipulation rather than simple maintenance of information appears more vulnerable in neuropsychiatric disease states (Goldberg et al, 1993; Silver et al, 2003; Tan et al, 2005) and is associated with dysfunction in dorsolateral prefrontal cortex (Weinberger et al, 1986; Barch et al, 2001; Cannon et al, 2005; Tan et al, 2005). To the extent genetic variation affects working memory brain circuit function, it will be important to know how this might extend to illness-related cognitive dysfunction and treatment
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