The neurobiology and neural circuitry of cognitive changes in Parkinson's disease revealed by functional neuroimaging.

Patients with Parkinson's disease (PD) often develop a spectrum of cognitive symptoms that can evolve into dementia. Dopamine (DA) replacement medications, though improving motor symptoms, can exert both positive and negative effects on cognitive ability, depending on the severity of the disease and the specific skill being tested. By considering the behavioral and clinical aspects of disease- and treatment-mediated changes in cognition alongside the pathophysiology of PD, an understanding of the factors that govern the heterogeneous expression of cognitive impairment in PD is beginning to emerge. Here, we review the neuroimaging studies revealing the neural correlates of cognitive changes after DA loss and DA replacement as well as those that may accompany the conversion from milder stages of cognitive impairment to frank dementia.