title: A gamma band specific role of the subthalamic nucleus in switching during verbal fluency tasks in Parkinson's disease.
abstract: OBJECTIVE
  Decline in verbal fluency is the most consistent and persistent cognitive impairment documented after deep brain stimulation of the subthalamic nucleus in Parkinson's disease. The mechanisms of this deficit are unclear. We aimed to identify and characterise verbal fluency related processing within the subthalamic nucleus through analysis of local field potentials.
  
  
  METHODS
  Local field potentials were recorded from deep brain stimulation electrodes implanted in the subthalamic nuclei of 8 patients (16 sides) with Parkinson's disease, when patients were on medication. Patients performed phonemic and semantic verbal fluency tasks and a control word repetition task to control for the motor output involved in response generation.
  
  
  RESULTS
  Significant increases in local field potential Power (p ≤ 0.05) were seen across a broad gamma frequency band (30-95 Hz) during both verbal fluency tasks, after controlling for motor output. Increases in gamma local field potential Power of +7.5% ± 2.3% (SEM) in the semantic fluency task and +6.9% ± 2.0% in the phonemic fluency task were derived when averaging across all electrode contact pairs. Gamma changes recorded from contacts lying in the left hemisphere (dominant in verbal fluency) correlated with average number of correct responses generated (r=0.81 p=0.015) and measures of 'switching' (r=0.79 p=0.020) particularly strongly in the semantic fluency task.
  
  
  CONCLUSIONS
  Frequency specific power changes observed during task performance are consistent with involvement of the subthalamic nucleus in switching during verbal fluency. Antagonism of such task-related activity with high frequency stimulation of this nucleus may explain the impairments reported.
authors.affiliation: Sobell Department of Motor Neuroscience & Movement Disorders, UCL Institute of Neurology & The National Hospital for Neurology and Neurosurgery, WC1N 3BG, UK.
authors.forename: Anam
authors.initials: A
authors.lastname: Anzak
authors.forename: Louise
authors.initials: L
authors.lastname: Gaynor
authors.forename: Mazda
authors.initials: M
authors.lastname: Beigi
authors.forename: Patricia
authors.initials: P
authors.lastname: Limousin
authors.forename: Marwan
authors.initials: M
authors.lastname: Hariz
authors.forename: Ludvic
authors.initials: L
authors.lastname: Zrinzo
authors.forename: Thomas
authors.initials: T
authors.lastname: Foltynie
authors.forename: Peter
authors.initials: P
authors.lastname: Brown
authors.forename: Marjan
authors.initials: M
authors.lastname: Jahanshahi
mesh_terms: D046690:Deep Brain Stimulation / Q000009:adverse effects*; D056344:Executive Function / Q000502:physiology; D005260:Female; D005625:Frontal Lobe / Q000166:cytology / Q000502:physiology; D006801:Humans; D007807:Language Tests; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D010300:Parkinson Disease / Q000503:physiopathology* / Q000628:therapy; D010700:Phonetics; D012660:Semantics; D013064:Speech Disorders / Q000209:etiology* / Q000503:physiopathology*; D020531:Subthalamic Nucleus / Q000166:cytology / Q000503:physiopathology*