Abstract
Impulsivity and compulsivity are prominent non-motor problems in Parkinson’s disease (PD). Despite 20 years of research, there is still an ongoing debate as to whether subthalamic deep brain stimulation (STN DBS) for PD exacerbates or improves these symptoms. Here, we review how STN DBS affects clinical symptoms and neurocognitive aspects of impulsivity and compulsivity. When comparing patients post- to pre-surgery, in the majority of studies STN DBS for PD is associated with a decrease in clinically diagnosed impulse-control disorders and disorders of compulsivity. To avoid confounds, such as post-surgical decreases in dopaminergic medication doses, comparisons can also be made between DBS “On” versus “Off” conditions. These experimentally assayed effects of STN DBS with respect to neurocognitive aspects of impulsivity and compulsivity are more mixed. STN DBS improves behavioral flexibility without impairing negative feedback learning, delay discounting, or inhibitory control, as long as stimulation is restricted to the dorsal STN. However, STN DBS may drive impulsive actions when a subject is faced with competing choices. We discuss how motivated responses may be either enhanced or impaired by STN DBS depending on engagement of dorsal or ventral STN-mediated circuits. Future studies should combine structural and functional circuit measures with behavioral testing in PD patients on and off medication and stimulation. A more sophisticated understanding of how to modulate cortico-striatal-thalamo-cortical loops will increase the likelihood that these circuit manipulation techniques can successfully be applied to a wider range of neuropsychiatric disorders.
Highlights
Parkinson’s Disease (PD) is a neurodegenerative disorder affecting basal ganglia systems controlling motor and non-motor functions
We focused on changes in neurocognitive paradigms that reflect different aspects of impulsivity and compulsivity, and that can be quantified during experimental changes in stimulation delivery
We found 12 studies investigating the prevalence of Impulse control disorders (ICDs) in a total of 582 PD patients pre- and (6– 12 months) post subthalamic deep brain stimulation (STN DBS) (Ardouin et al, 1999; Lim et al, 2009; Lhommée et al, 2012; Shotbolt et al, 2012; Eusebio et al, 2013; Kim et al, 2013; Amami et al, 2015; Castrioto et al, 2015; Gee et al, 2015; Merola et al, 2017)
Summary
Parkinson’s Disease (PD) is a neurodegenerative disorder affecting basal ganglia systems controlling motor and non-motor functions. Impulsivity and compulsivity are prevalent non-motor features of PD associated with lack of self-control. In patients with PD, impulsive and compulsive symptoms can cause suffering and functional impairments, and are often unresponsive to, or even induced by, PD medications. The standard treatment for PD is dopamine replacement therapy (DRT), with either levodopa or dopamine agonists. These drugs are highly effective for motor symptoms such as rigidity, bradykinesia and resting tremor, they are associated with a 2- to 3.5-fold increased odds of developing impulsive or compulsive behaviors (Weintraub et al, 2009; Santangelo et al, 2013; Kim et al, 2015)
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