VC/VS for Apathy in PD

Apathy is a disabling neuropsychiatric symptom marked by reduced goal-directed behavior, including diminished interest, motivation, emotional expression, and social engagement. Though not formally defined in the DSM-V, apathy is common in several neurological and psychiatric disorders and significantly affects quality of life. In Parkinson's Disease (PD), it affects about 40% of patients and is associated with increased caregiver burden, reduced functional ability, and nearly threefold higher mortality. PD affects over 680,000 Americans today and is projected to impact more than 1.2 million by 2030. It presents with both motor symptoms (e.g., bradykinesia, tremor, rigidity) and non-motor symptoms like depression, anxiety, and apathy. While motor symptoms are often managed with dopaminergic medications and deep brain stimulation (DBS) targeting motor regions (e.g., subthalamic nucleus, globus pallidus internal), apathy typically persists or worsens following these treatments. No FDA-approved or consistently effective treatments exist for apathy in PD. Dopamine agonists may help but have side effects that limit long-term use. SSRIs and cholinesterase inhibitors may be tried for co-occurring depression or cognitive decline, but they are not indicated for apathy and can worsen symptoms or cause adverse effects in PD. This protocol proposes targeting apathy in PD using DBS of the ventral capsule/ventral striatum (VC/VS), a region involved in reward processing and goal-directed behavior. VC/VS DBS is FDA-approved under a Humanitarian Device Exemption for OCD and has shown promise in treating depression, addiction, and other disorders involving motivational deficits. Neuroimaging and preclinical models strongly implicate this region in the regulation of goal-directed behavior, reward sensitivity, and cognitive control-mechanisms disrupted in apathy. Stimulating VC/VS may improve motivation through fibers connected to orbitofrontal and anterior cingulate cortices (reward