COMT and Parkinson disease: Functional MRI studies further support a role for COMT val158met in mediating executive function in PD, demonstrating that impaired performance on both planning and attentional control tasks in met homozygotes is associated with reduced BOLD activation in frontoparietal networks (77, 78), and revealing an interaction between genotype and dopaminergic medication (62), which has potential implications for planning treatment in PD patients with significant executive dysfunction.