Clinical Outcomes and Pathophysiological Correlates of Deep Brain Stimulation in Parkinson’s Disease: A Systematic Review

Background: Parkinson's disease (PD) is a progressive neurodegenerative disorder that causes motor and non-motor symptoms due to the loss of dopaminergic neurons and problems with the basal ganglia circuitry. Deep brain stimulation (DBS) is now a well-known surgical treatment for people with advanced PD who have motor problems that don't respond to medical treatment. To get the most out of DBS therapy and choose the best patients, it is important to know how it works and what the clinical outcomes are. Objective: To look at all the evidence, we have so far about the clinical outcomes and pathophysiological correlates of DBS in Parkinson's disease, focusing on improvements in motor and non-motor functions, target-specific effects, and the neurophysiological mechanisms behind them. Methods: We looked through the PubMed, Scopus, and Web of Science databases for all studies published between 2010 and 2025. Randomized controlled trials, cohort studies, and mechanistic investigations that looked at DBS outcomes in PD were all eligible studies. We got information about the stimulation targets (subthalamic nucleus (STN), globus pallidus internus (GPi]), clinical effectiveness, problems, and neurophysiological results. The PRISMA 2020 guidelines were used to look at the risk of bias and the quality of the study. Results: 78 studies met the requirements for inclusion. DBS significantly improved Unified Parkinson's Disease Rating Scale (UPDRS) motor scores (by an average of 45–60%), cut the need for medication by 30–50%, and raised quality of life scores. STN stimulation helped with motor function more, but it also caused more neuropsychiatric side effects. GPi DBS, on the other hand, helped with mood and cognitive stability more. Pathophysiological studies showed that DBS changes abnormal oscillatory activity in the basal ganglia-thalamo-cortical loop, brings beta-band synchronization back to normal, and makes cortical excitability patterns normal again. Conclusion: DBS improves motor and functional abilities in advanced PD in a big way and for a long time by changing dysfunctional neuronal networks. The therapeutic response changes depending on the stimulation target and the patient's profile. This shows how important it is to use personalized approaches and do more research on adaptive and closed-loop DBS systems.