Cognitive dysfunction in non-demented Parkinson's disease patients: controlled and automatic behavior.

The evidence with regard to impaired automatic and controlled information processing in non-demented patients with Parkinson's disease (PD) is critically discussed. We use a comprehensive mental schema framework of executive functioning, that is the planning and regulation of behavior in complex everyday tasks (International Classification of Functioning - ICF - activity level). In this framework monitoring, inhibition, mental effort, planning, working memory and flexibility are important elements of controlled processing (supervisory attentional control) and controlled processing can only influence performance by modulating automatic processes. The striatum plays an important role in the interface between controlled and automatic processes. It is wel documented that PD patients show impairments applying and achieving automaticities. With sustained cortical control of task performance during both automatic and controlled processing, not showing the transition to striatal control, which is normal in the case of skill learning. In addition, PD patients have been shown to be limited in executive functioning. Many authors have interpreted this as evidence for impaired executive functions (ICF body level). But the question must be asked to what extent these limitations are an indirect effect of impaired automatic processing. To answer this question, studies on executive functioning are critically assessed with regard to the control they have provided for impaired automaticity. It is concluded that only for cognitive flexibility and working memory, the evidence for impairments is convincing because significant limitations have also been shown in tasks with very low automatic processing demands. Impairments in other executive functions, such as monitoring, inhibition and planning have not been convincingly shown in non-demented PD patients and are likely to be due to treatment strategies and factors such as fatigue.