title: Electric field and stimulating influence generated by deep brain stimulation of the subthalamic nucleus.
abstract: OBJECTIVE
  The goal of this project was to develop a quantitative understanding of the volume of axonal tissue directly activated by deep brain stimulation (DBS) of the subthalamic nucleus (STN).
  
  
  METHODS
  The 3-dimensionally inhomogeneous and anisotropic tissue medium surrounding DBS electrodes complicates our understanding of the electric field and tissue response generated by the stimulation. We developed finite element computer models to address the effects of DBS in a homogeneous isotropic medium, and a medium with tissue conductivity properties derived from human diffusion tensor magnetic resonance data. The second difference of the potential distribution generated in the tissue medium was used as a predictor of the volume of tissue supra-threshold for axonal activation.
  
  
  RESULTS
  The model predicts that clinically effective stimulation parameters (-3 V; 0.1 ms; 150 Hz) result in activation of large diameter (5.7 microm) myelinated axons over a volume that spreads outside the borders of the STN. The shape of the activation volume was dependent on the strong dorsal-ventral anisotropy of the internal capsule, and the moderate anterior-posterior anisotropy of the region around zona incerta.
  
  
  CONCLUSIONS
  Small deviations ( approximately 1 mm) in the electrode position within STN can substantially alter the shape of the activation volume as well as its spread to neighboring structures.
  
  
  CONCLUSIONS
  STN DBS represents an effective treatment for medically refractory movement disorders such as Parkinson's disease. However, stimulation induced side effects such as tetanic muscle contraction, speech disturbance and ocular deviation are not uncommon. Quantitative characterization of the spread of stimulation will aid in the development of techniques to maximize the efficacy of DBS.
authors.affiliation: Department of Neurology, Emory University School of Medicine, Atlanta, GA, USA. mcintyre@bme.ri.ccf.org
authors.forename: Cameron C
authors.initials: CC
authors.lastname: McIntyre
authors.forename: Susumu
authors.initials: S
authors.lastname: Mori
authors.forename: David L
authors.initials: DL
authors.lastname: Sherman
authors.forename: Nitish V
authors.initials: NV
authors.lastname: Thakor
authors.forename: Jerrold L
authors.initials: JL
authors.lastname: Vitek
mesh_terms: D016477:Artifacts; D016022:Case-Control Studies; D002648:Child; D003198:Computer Simulation; D004410:Dyslexia / Q000503:physiopathology*; D004569:Electroencephalography; D004585:Electrooculography; D005123:Eye / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008959:Models, Neurological; D025341:Principal Component Analysis