Basal Impulses: findings from the last twenty years on impulsivity and reward pathways using deep brain stimulation.

Background Deep brain stimulation (DBS) is an important treatment modality for movement disorders. Its role in tasks and processes of higher cortical function continues to increase in importance and relevance. This review investigates the impact of DBS on measures of impulsivity. Methods A total of 45 studies were collated from PubMed (30 prospective, 8 animal, 4 questionnairebased, and 3 computational models), excluding case reports and review articles. Two areas extensively studied are the subthalamic nucleus (STN) and nucleus accumbens (NAc). Results While both are part of the basal ganglia, the STN and NAc have extensive connections to the prefrontal cortex, cingulate cortex, and limbic system. Therefore understanding cause and treatment of impulsivity requires understanding motor pathways, learning, memory, and emotional processing. DBS of the STN and NAc shell can increase objective measures of impulsivity, as measured by reaction times or reward-based learning, independent from patient insight. The ability for DBS to treat impulse control disorders, and also cause and/or worsen impulsivity in Parkinson's disease, may be explained by the affected closely-related neuroanatomical areas with discrete and sometimes opposing functions. Conclusions As newer, more refined DBS technology emerges, large-scale prospective studies specifically aimed at treatment of impulsivity disorders are needed.