• Thilo van Eimeren, Oury Monchi, Benedicte Ballanger, and Antonio P Strafella.
• Division of Brain, Imaging and Behaviour-Systems Neuroscience, Toronto Western Research Institute, and Movement Disorders Centre, Toronto Western Hospital, University Health Network, University of Toronto, Toronto, Ontario M5T 1R8, Canada.
• Arch. Neurol. 2009 Jul 1; 66 (7): 877-83.

ObjectiveTo 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.DesignWe 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.SettingTertiary outpatient clinic.ParticipantsSeven patients with mild to moderate PD (not taking medication) and 7 healthy controls.Main Outcome MeasureCortical deactivations.ResultsBoth 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.ConclusionsWe 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.

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