Psychiatric complications in Parkinson's disease.

Parkinson's disease (PD) is caused by an abnormal degeneration of the dopamine (DA) producing cells in the substantia nigra (SN) and ventral tegmentum area (VTA) in combination with a varying decay of the noradrenergic (locus coeruleus), cholinergic forebrain (nucleus basalis of Meynert) and serotoninergic (dorsal raphe nuclei) systems, leading to a multitude of motor and non-motor behavioral disturbances, known as parkinsonism. Normally, main dopamine depletion is restricted to the SN region with manifest (non)motor behavioral abnormalities caused by the inability to spontaneously switch between intern-cued cortical behavioral programmes. Clinical symptoms comprise motoric abnormalities, though subtle cognitive disturbances as well as psychological dysfunction with loss of mental flexibility and reactive depressive symptoms might be seen. These symptoms might be compensated in part by externally-cued behavior.