The anatomical, functional, genetic and behavioural data support the dual syndrome hypothesis for Parkinson’s disease cognition, with (i) an executive syndrome that is frontally mediated, dopamine-dependant and modulated by COMT genotype; versus (ii) a temporo-parietal system subject to MAPT and APOE, but not dopaminergic modulation, that is required for visuospatial and memory tasks. Here, COMT is linked to Parkinson disease.