Summary: A recent study indicates that unilateral deep brain stimulation (DBS) confined to the right hemisphere can improve motor symptoms in people with Parkinson’s disease while avoiding the notable declines in verbal fluency that are sometimes observed after DBS. By contrast, stimulation in the left hemisphere was linked to measurable declines in word retrieval and generation. These findings suggest that a unilateral approach—targeting the most affected side—may preserve certain cognitive abilities, such as speech, better than the traditional bilateral strategy.
The study, led by researchers at the University of Alabama at Birmingham and published in the Annals of Neurology, evaluated cognitive outcomes in patients who received unilateral subthalamic nucleus (STN) DBS. Results showed that right-sided implants were associated with either stable or mildly improved verbal fluency and faster response inhibition, whereas left-sided implants tended to produce declines in verbal fluency.
Key Facts:
- Right-side unilateral DBS improved motor symptoms and did not produce declines in verbal fluency in this cohort.
- Left-side unilateral DBS was associated with declines in verbal fluency and slower response inhibition.
- Unilateral DBS on the more affected hemisphere may be a viable alternative to routine bilateral stimulation, potentially reducing risks to verbal functions.
Source: University of Alabama at Birmingham
Background: Deep brain stimulation is an established therapy for reducing motor symptoms in movement disorders such as Parkinson’s disease. While generally safe and clinically effective, DBS has been linked in some cases to declines in verbal fluency—how quickly and effectively a person can retrieve and produce words. Because Parkinson’s motor symptoms often begin asymmetrically, clinicians at UAB Medicine have explored unilateral DBS—placing electrodes on the hemisphere most affected by motor impairment—as a less invasive and potentially cognitive-sparing option.
The investigation was supported by the National Institutes of Health (NIH) BRAIN Initiative and represents an effort to clarify how unilateral STN DBS impacts cognition over time. Victor Del Bene, Ph.D., a neuropsychologist in the UAB Department of Neurology and the study’s lead author, noted that participants who received right-sided implants exhibited mild improvements in verbal fluency during the follow-up interval, a contrast to declines typically reported after left-sided or bilateral procedures.
Harrison Walker, M.D., a professor in UAB’s Department of Neurology, explained that unilateral stimulation targeting the most affected hemisphere can significantly relieve motor symptoms for years and leaves open the option to perform DBS on the opposite side later if necessary. This strategy may reduce cognitive side effects for some patients compared with immediate bilateral implantation.
The authors report that left-hemisphere stimulation was linked to greater declines in response inhibition and verbal fluency, while no hemisphere-related differences were observed for immediate or delayed verbal recall attributable specifically to DBS. Overall delayed verbal recall showed a modest decline over time regardless of implantation side, while immediate recall remained stable.
The UAB team hopes these findings will encourage clinicians and centers treating Parkinson’s disease to consider unilateral DBS on the most affected side as a therapeutic option—particularly when preserving language-related cognitive functions is a priority. Unilateral right-hemisphere stimulation, in selected patients, may help avoid some of the language and executive deficits that can accompany bilateral DBS.
This research originated from an NIH BRAIN Initiative grant awarded to UAB in 2016 and involved collaboration among the UAB Departments of Neurology, Neurosurgery and Physical Therapy, along with the School of Public Health. The investigators plan to continue this line of work with a subsequent BRAIN Initiative award to refine patient selection and better understand long-term cognitive outcomes after unilateral DBS.
Funding: The BRAIN Initiative® is a registered trademark of the U.S. Department of Health and Human Services. The content of the study is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This research was supported by the NIH BRAIN Initiative under award number UH3-NS100553.
About this Parkinson’s disease and DBS research news
Author: Katherine Gaither
Source: University of Alabama at Birmingham
Contact: Katherine Gaither – University of Alabama at Birmingham
Image: The image is credited to Neuroscience News
Original Research: Open access. “Differential Cognitive Effects of Unilateral Subthalamic Nucleus Deep Brain Stimulation for Parkinson’s Disease” by Victor Del Bene et al., Annals of Neurology.
Abstract
Differential Cognitive Effects of Unilateral Subthalamic Nucleus Deep Brain Stimulation for Parkinson’s Disease
Objective
The study aimed to evaluate how unilateral subthalamic nucleus deep brain stimulation (STN DBS) affects cognition—particularly verbal fluency, memory, and response inhibition—in patients with advanced Parkinson’s disease, and whether directional versus ring stimulation produces different cognitive outcomes.
Methods
Researchers assessed 31 participants who underwent unilateral STN DBS: 17 received left-hemisphere implants and 14 received right-hemisphere implants. The study was part of an NIH-sponsored randomized, double-blind, crossover trial comparing directional stimulation to ring stimulation. All patients received electrodes on the hemisphere most affected by motor parkinsonism. Cognitive measures included tests of verbal fluency, auditory-verbal memory (immediate and delayed recall), and response inhibition. Mixed linear models were used to analyze the longitudinal effects of stimulation type and implant hemisphere on cognitive performance.
Results
Crossover analyses found no group-level cognitive differences between directional and ring stimulation modes. However, implant hemisphere influenced cognitive outcomes: patients with left STN implants had lower baseline verbal fluency than those with right implants. Verbal fluency declined after left-sided STN DBS but increased after right-sided STN DBS, and response inhibition was faster following right-sided stimulation. Across both groups, delayed recall declined modestly over time compared with baseline, while immediate recall remained stable.
Interpretation
The type of stimulation (directional versus ring) did not differentially affect cognition in this cohort. Consistent with prior studies of bilateral DBS, unilateral left STN stimulation was associated with worsened verbal fluency. In contrast, unilateral right STN stimulation improved performance on verbal fluency and response inhibition tasks. These results support the hypothesis that, for selected patients with predominantly right-hemisphere motor symptoms, unilateral right STN DBS might reduce the risk of verbal fluency decline compared with immediate bilateral intervention.