Comparative effects of deep brain stimulation in subthalamic nucleus and globus pallidus interna on verbal fluency and working memory in adult populations with parkinson's disease: A systematic review.

Background: Deep Brain Stimulation (DBS) in the subthalamic nucleus and globus pallidus interna is a well-established treatment for motor symptoms in Parkinson's Disease (PD). However, the cognitive effects of DBS, particularly on verbal fluency and working memory, remain less clear.

Purpose: This systematic review explores the comparative effects of subthalamic nucleus and globus pallidus interna DBS on verbal fluency and working memory in adults with PD, addressing gaps in current cognitive outcome data.

Methods: A comprehensive search of EMBASE, MEDLINE, EMCARE, and PsycINFO was conducted. Studies were selected based on predefined criteria, focusing on randomised and non-randomised controlled trials involving adult PD patients treated with subthalamic nucleus or globus pallidus interna DBS. Data extraction and risk of bias assessments were performed.

Results: Eight studies were included, with varied findings. Most studies observed a decline in verbal fluency following DBS, with no significant differences between subthalamic nucleus and globus pallidus interna targets. Working memory outcomes were also mixed; however, one study showed a statistically significant result favouring globus pallidus interna DBS for working memory.

Conclusions: The cognitive effects of DBS appear variable and target-independent, highlighting the need for individualised treatment planning. While DBS effectively addresses motor symptoms, its cognitive impacts, especially on verbal fluency and working memory, require further exploration. These findings support a more personalised DBS approach, considering cognitive profiles, implantation laterality, and long-term outcomes.