Apathy in Parkinson's Disease.

The normal maintenance of human motivation depends on the integrity of subcortical structures that link the medial and lateral prefrontal cortex with the limbic system. Apathy is highly prevalent in Parkinson's disease and causes major impact on the quality of life of patients and caregivers, comparable to depression or cognitive impairment. The clinical differentiation of apathy from the emotional symptoms of depression, and from difficulties in planning or organizing mental programs as a consequence of executive dysfunction, may guide a rationale for individualized treatment approach of apathetic symptoms, which is presently lacking. To review the different apathetic syndromes that can be diagnosed in clinical practice by appropriate scales, as well as the brain systems that subserve each syndrome, helps to explain how dopaminergic, antidepressant, or cholinergic medications may lead to individual improvements in apathy.