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Parkinson's disease (PD) is an important model for the role of dopamine in supporting human cognition. However, despite the uniformity of midbrain dopamine depletion only some patients experience cognitive impairment. The neurocognitive mechanisms of this heterogeneity remain unclear. A genetic polymorphism in the catechol O-methyltransferase (COMT) enzyme, predominantly thought to exert its cognitive effect through acting on prefrontal cortex (PFC) dopamine transmission, provides us with an experimental window onto dopamine's role in cognitive performance in PD. In a large cohort of PD patients (n=372), we examined the association between COMT genotype and two tasks known to implicate prefrontal dopamine (spatial working memory and attentional set-shifting) and on a task less sensitive to prefrontal dopamine (paired associates learning). Consistent with the known neuroanatomical locus of its effects, differences between the COMT genotype groups were observed on dopamine-dependant tasks, but not the paired associates learning task. However, COMT genotype had differential effects on the two prefrontal dopamine tasks. Putative prefrontal dopamine levels influenced spatial working memory in an 'Inverted-U'-shaped fashion, whereas a linear, dose-dependant pattern was observed for attentional set-shifting. Cumulatively, these results revise our understanding of when COMT genotype modulates cognitive functioning in PD patients by showing that the behavioural consequences of genetic variation vary according to task demands, presumably because set-shifting and working memory have different optimal dopamine levels.

Original publication

DOI

10.1016/j.neuropsychologia.2015.07.031

Type

Journal article

Journal

Neuropsychologia

Publication Date

10/2015

Volume

77

Pages

42 - 51

Keywords

COMT, Dopamine, Parkinson's disease, Set-shifting, Working memory, Adult, Aged, Association Learning, Attention, Catechol O-Methyltransferase, Dopamine, Executive Function, Female, Humans, Male, Memory, Short-Term, Middle Aged, Neuropsychological Tests, Parkinson Disease, Polymorphism, Genetic, Prefrontal Cortex, Spatial Memory