title: Verbal Fluency in Parkinson's Patients with and without Bilateral Deep Brain Stimulation of the Subthalamic Nucleus: A Meta-analysis.
abstract: OBJECTIVE
  Patients with Parkinson's disease often experience significant decline in verbal fluency over time; however, deep brain stimulation of the subthalamic nucleus (STN-DBS) is also associated with post-surgical declines in verbal fluency. The purpose of this study was to determine if Parkinson's patients who have undergone bilateral STN-DBS have greater impairment in verbal fluency compared to Parkinson's patients treated by medication only.
  
  
  METHODS
  A literature search yielded over 140 articles and 10 articles met inclusion criteria. A total of 439 patients with Parkinson's disease who underwent bilateral STN-DBS and 392 non-surgical patients were included. Cohen's d, a measure of effect size, was calculated using a random effects model to compare post-treatment verbal fluency in patients with Parkinson's disease who underwent STN-DBS versus those in the non-surgical comparison group.
  
  
  RESULTS
  The random effects model demonstrated a medium effect size for letter fluency (d=-0.47) and a small effect size for category fluency (d=-0.31), indicating individuals with bilateral STN-DBS had significantly worse verbal fluency performance than the non-surgical comparison group.
  
  
  CONCLUSIONS
  Individuals with Parkinson's disease who have undergone bilateral STN-DBS experience greater deficits in letter and category verbal fluency compared to a non-surgical group.
authors.affiliation: Pacific University,Hillsboro,Oregon.
authors.forename: Kathryn A
authors.identifier: http://orcid.org/0000-0002-5057-5094
authors.initials: KA
authors.lastname: Wyman-Chick
mesh_terms: D016208:Databases, Factual / Q000706:statistics & numerical data; D046690:Deep Brain Stimulation / Q000379:methods*; D006801:Humans; D009483:Neuropsychological Tests; D010300:Parkinson Disease / Q000150:complications* / Q000628:therapy*; D013064:Speech Disorders / Q000209:etiology* / Q000628:therapy*; D020531:Subthalamic Nucleus / Q000502:physiology*
keywords: Category fluency; DBS; Disease comparison group; Letter fluency; Movement disorders; STN