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A Functional Magnetic Resonance Imaging Study

Thilo van Eimeren, MD; Oury Monchi, PhD; Benedicte Ballanger, PhD; Antonio P. Strafella, MD, PhD, FRCPC

Arch Neurol. 2009;66(7):877-883.

Objective  To examine the integrity of the default mode network in patients with Parkinson disease (PD). Previous functional neuroimaging experiments have studied executive deficits in patients with PD with regard to task-related brain activation. However, recent studies suggest that executive performance also relies on the integrity of the default mode network (ie, medial prefrontal cortex, posterior cingulate cortex, precuneus, and lateral parietal and medial temporal cortices), characterized by a deactivation of these cortical areas during the performance of executive tasks.

Design  We used functional magnetic resonance imaging to investigate cortical deactivations during a card-sorting task (retrieval and manipulation of short-term memory contents) compared with a simple sensory-motor matching task. In addition, a functional connectivity analysis was performed.

Setting  Tertiary outpatient clinic.

Participants  Seven patients with mild to moderate PD (not taking medication) and 7 healthy controls.

Main Outcome Measure  Cortical deactivations.

Results  Both groups showed comparable deactivation of the medial prefrontal cortex but different deactivation in the posterior cingulate cortex and the precuneus. Compared with controls, patients with PD not only showed less deactivation of the posterior cingulate cortex and the precuneus, they even demonstrated a reversed pattern of activation and deactivation. Connectivity analysis yielded that in contrast to healthy individuals, medial prefrontal cortex and the rostral ventromedial caudate nucleus were functionally disconnected in PD.

Conclusions  We describe specific malfunctioning of the default mode network during an executive task in PD. This finding is plausibly linked to dopamine depletion and may critically contribute to the understanding of executive deficits in PD.

Author Affiliations: Division of Brain, Imaging and Behaviour–Systems Neuroscience, Toronto Western Research Institute, and Movement Disorders Centre, Toronto Western Hospital, University Health Network (Drs van Eimeren, Ballanger, and Strafella), and PET Imaging Centre, Centre for Addiction and Mental Health (Drs van Eimeren, Ballanger, and Strafella), University of Toronto, Toronto, Ontario, and Centre de Recherche de l'Institut Universitaire de Gériatrie, Université de Montréal, Montréal, Québec (Dr Monchi), Canada.

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