title: Anatomic correlates of deep brain stimulation electrode impedance.
abstract: BACKGROUND
  The location of the optimal target for deep brain stimulation (DBS) of the subthalamic nucleus (STN) remains controversial. Electrode impedance affects tissue activation by DBS and has been found to vary by contact number, but no studies have examined association between impedance and anatomic location.
  
  
  OBJECTIVE
  To evaluate the relationship between electrode impedance and anatomic contact location, and to assess the clinical significance of impedance.
  
  
  METHODS
  We gathered retrospective impedance data from 101 electrodes in 73 patients with Parkinson's disease. We determined contact location using microelectrode recording (MER) and high-field 7T MRI, and assessed the relationship between impedance and contact location.
  
  
  RESULTS
  For contact location as assessed via MER, impedance was significantly higher for contacts in STN, at baseline (111 Ω vs STN border, p=0.03; 169 Ω vs white matter, p<0.001) and over time (90 Ω vs STN border, p<0.001; 54 Ω vs white matter, p<0.001). Over time, impedance was lowest in contacts situated at STN border (p=0.03). Impedance did not vary by contact location as assessed via imaging. Location determination was 75% consistent between MER and imaging. Impedance was inversely related to absolute symptom reduction during stimulation (-2.5 motor portion of the Unified Parkinson's Disease Rating Scale (mUPDRS) points per 1000 Ω, p=0.01).
  
  
  CONCLUSIONS
  In the vicinity of DBS electrodes chronically implanted in STN, impedance is lower at the rostral STN border and in white matter, than in STN. This finding suggests that current reaches white matter fibres more readily than neuronal cell bodies in STN, which may help explain anatomic variation in stimulation efficacy.
authors.affiliation: Department of Neurosurgery, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: David
authors.initials: D
authors.lastname: Satzer
authors.affiliation: Department of Neurosurgery, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Eric W
authors.initials: EW
authors.lastname: Maurer
authors.affiliation: Department of Neurosurgery, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: David
authors.initials: D
authors.lastname: Lanctin
authors.affiliation: Department of Biostatistics, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Weihua
authors.initials: W
authors.lastname: Guan
authors.affiliation: Department of Neurosurgery, University of Minnesota, Minneapolis, Minnesota, USA Department of Neurosurgery, University of Colorado, Denver, Colorado, USA.
authors.forename: Aviva
authors.initials: A
authors.lastname: Abosch
mesh_terms: D046690:Deep Brain Stimulation / Q000295:instrumentation*; D017097:Electric Impedance; D004566:Electrodes; D006801:Humans; D008279:Magnetic Resonance Imaging; D008839:Microelectrodes; D010300:Parkinson Disease / Q000503:physiopathology* / Q000628:therapy*
keywords: Anatomy; Electrical Stimulation; MRI; Movement Disorders; Parkinson's Disease