title: The effects of subthalamic and pallidal deep brain stimulation on postural responses in patients with Parkinson disease.
abstract: OBJECTIVE
  The effect of deep brain stimulation (DBS) for Parkinson disease (PD) on balance is unclear. The goal of this study was to investigate how automatic postural responses (APRs) were affected in patients randomized to either subthalamic nucleus (STN) or globus pallidus internus (GPi) surgery.
  
  
  METHODS
  The authors tested 24 patients with PD who underwent bilateral DBS, 9 control patients with PD who did not undergo DBS, and 17 age-matched control volunteers. The electrode placement site was randomized and blinded to the patients and to the experimenters. Kinematic, kinetic, and electromyographic recordings of postural responses to backward disequilibrium via forward translations of the standing surface were recorded in the week prior to surgery while the patients were off (OFF) and on (ON) antiparkinsonian medication (levodopa), and then 6 months after surgery in 4 conditions: 1) off medication with DBS switched off (OFF/OFF); 2) off medication with DBS on (DBS); 3) on medication with DBS off (DOPA); and 4) with both medication and DBS on (DBS+DOPA). Stability of the automatic postural response (APR) was measured as the difference between the displacement of the center of pressure and the projected location of the center of body mass.
  
  
  RESULTS
  Patients with PD had worse APR stability than controls. Turning the DBS on at either site improved APR stability compared with the postoperative OFF condition by lengthening the tibialis response, whereas medication did not show an appreciable effect. The STN group had worse APR stability in their best functional state (DBS+DOPA) 6 months after the DBS procedure compared with their best functional state (ON levodopa) before the DBS procedure. In contrast, the GPi group and the PD control group showed no change over 6 months. The APR stability impairment in the STN group was associated with smaller tibialis response amplitudes, but there was no change in response latency or coactivation with gastrocnemius.
  
  
  CONCLUSIONS
  Turning the DBS current on improved APR stability for both STN and GPi sites. However, there was a detrimental DBS procedural effect for the STN group, and this effect was greater than the benefit of the stimulating current, making overall APR stability functionally worse after surgery for the STN group.
authors.affiliation: Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA. stgeorgr@ohsu.edu
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: St George
authors.forename: Patricia
authors.initials: P
authors.lastname: Carlson-Kuhta
authors.forename: Kim J
authors.initials: KJ
authors.lastname: Burchiel
authors.forename: Penelope
authors.initials: P
authors.lastname: Hogarth
authors.forename: Nicholas
authors.initials: N
authors.lastname: Frank
authors.forename: Fay B
authors.initials: FB
authors.lastname: Horak
mesh_terms: D000368:Aged; D000978:Antiparkinson Agents / Q000627:therapeutic use; D001696:Biomechanical Phenomena / Q000502:physiology; D003131:Combined Modality Therapy; D046690:Deep Brain Stimulation / Q000379:methods*; D004292:Dominance, Cerebral / Q000502:physiology; D004311:Double-Blind Method; D004576:Electromyography; D005260:Female; D005500:Follow-Up Studies; D005917:Globus Pallidus / Q000503:physiopathology*; D006801:Humans; D007980:Levodopa / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000503:physiopathology / Q000628:therapy*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D020531:Subthalamic Nucleus / Q000503:physiopathology*
chemical_list: D000978:Antiparkinson Agents; D007980:Levodopa