Abstract
The bilateral effects of deep brain stimulation (DBS) on motor and non-motor symptoms of Parkinson’s disease (PD) have been extensively studied and reviewed. However, the unilateral effects—in particular, the potential lateralized effects of left- versus right-sided DBS—have not been adequately recognized or studied. Here we summarized the current evidence and controversies in the literature regarding the lateralized effects of DBS on motor and non-motor outcomes in PD patients. Publications in English language before February 2021 were obtained from the PubMed database and included if they directly compared the effects of unilateral versus contralateral side DBS on motor or non-motor outcomes in PD. The current literature is overall of low-quality and is biased by various confounders. Researchers have investigated mainly PD patients receiving subthalamic nucleus (STN) DBS while the potential lateralized effects of globus pallidus interna (GPi) DBS have not been adequately studied. Evidence suggests potential lateralized effects of STN DBS on axial motor symptoms and deleterious effects of left-sided DBS on language-related functions, in particular, the verbal fluency, in PD. The lateralized DBS effects on appendicular motor symptoms as well as other neurocognitive and neuropsychiatric domains remain inconclusive. Future studies should control for varying methodological approaches as well as clinical and DBS management heterogeneities, including symptom laterality, stimulation parameters, location of active contacts, and lead trajectories. This would contribute to improved treatment strategies such as personalized target selection, surgical planning, and postoperative management that ultimately benefit patients.
Highlights
Ethical approval and patient consent were not required for this study
Publications in English language before February 2021 were initially searched in PubMed
Of the 243 publications, 225 articles were excluded after title and abstract screening
Summary
Cerebral lateralization refers to the functional specialization of the two cerebral hemispheres[1]. It is postulated that the functions of basal ganglia are hemisphere-specific as well. Both neurobiological[4,5] and structural[6] basis as well as the electrophysiological pattern asymmetry[7] suggest the functional laterality of basal ganglia. Interventions to left versus right basal ganglia may demonstrate distinctive effects on motor and cognitive features. The unilateral effects—in particular, the potential lateralized effects of left- versus right-sided DBS, given the postulated functional lateralization of basal ganglia— have not been adequately recognized or studied. We focus on the evidence and controversies regarding the potential lateralized effects of DBS on motor and non-motor symptoms in PD. We highlight limitations of the current literature and potential factors that may influence the interpretation of the evidence
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