Neural correlates of impulse control disorder in Parkinson,s Disease: FMRI evidence from motor, inhibition and semantic domains.
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Parkinson's disease (PD) is the second most common neurodegenerative disorder associated with aging. Approximately 40% of the PD patients treated with dopaminergic medication will develop Impulse Control Disorder (ICD). PD patients with ICD engage in pathological behaviors akin to behavioral addictions, as a result of a malfunction of their reward system due to chronic exposure to dopaminergic medication. Cognitive neuroscience research has investigated cognitive impulsivity and reward mechanisms in PD patients with ICD. However, functional and molecular imaging evidence indicates abnormalities in regions and networks that are not associated with cognitive impulsivity, but with domains such as movement, inhibitory control, and semantic processing. These domains have either not been previously investigated in this population, or previous literature shows mixed results. This doctoral dissertation aims at examining the neural correlates of three different domains in a group of patients with PD and ICD, a group of patients with PD and no ICD, and a group of healthy control participants using functional magnetic resonance imaging (fMRI). The three domains examined in each Experiment are motor function through a sequential finger-tapping task (Experiment I), inhibitory control through measures of response inhibition (Experiment II), and semantic processing via an auditory processing task (Experiment III). We were particularly interested in group differences in the functional networks and regions implicated in these tasks. Our results revealed that, across the three examined domains (i.e., motor, response inhibition, semantic processing), PD patients with ICD showed differential functional coupling among regions relative to their control counterparts, which remarks the importance of neural networks in cognitive neuroscience. Although the domains examined here had not received special attention in PD patients with ICD, we show that these patients exhibit functional differences beyond the reward system circuitry.