Progressive loss of the ascending dopaminergic projection in the basal ganglia is a fundamental pathological feature of Parkinson's disease. Studies in animals and humans have identified spatially segregated functional territories in the basal ganglia for the control of goal-directed and habitual actions. In patients with Parkinson's disease the loss of dopamine is predominantly in the posterior putamen, a region of the basal ganglia associated with the control of habitual behaviour. These patients may therefore be forced into a progressive reliance on the goal-directed mode of action control that is mediated by comparatively preserved processing in the rostromedial striatum. Thus, many of their behavioural difficulties may reflect a loss of normal automatic control owing to distorting output signals from habitual control circuits, which impede the expression of goal-directed action.
Bibliographical noteFunding Information:
This article arose as a result of a meeting (‘From movement to behaviour and emotions: role of the basal ganglia’) held in December 2008 at the Centro Internacional de Restauracion Neurologica (CIREN) in Havana, Cuba. The meeting was organized by the CIREN and the Neuroscience Department, CIMA, University of Navarra, Pamplona, Spain, and sponsored by private donations. Authors are grateful to J. Alvarez, President of CIREN, and D. Frontera and family for their support and contribution to the project’s success. P.R. was supported by a European Framework 7 grant and the Wellcome Trust, and J.A.O. by the University of Navarra–Union Temporal de Empresas (UTE) agreement during the preparation of this article. We thank B. Balleine for providing us with a high resolution copy of figure 3, and C. Juri and J. Arbizu for the PET images in figure 4.