title: Measurement of evoked potentials during thalamic deep brain stimulation.
abstract: BACKGROUND
  Deep brain stimulation (DBS) treats the symptoms of several movement disorders, but optimal selection of stimulation parameters remains a challenge. The evoked compound action potential (ECAP) reflects synchronized neural activation near the DBS lead, and may be useful for feedback control and automatic adjustment of stimulation parameters in closed-loop DBS systems.
  
  
  OBJECTIVE
  Determine the feasibility of recording ECAPs in the clinical setting, understand the neural origin of the ECAP and sources of any stimulus artifact, and correlate ECAP characteristics with motor symptoms.
  
  
  METHODS
  The ECAP and tremor response were measured simultaneously during intraoperative studies of thalamic DBS, conducted in patients who were either undergoing surgery for initial lead implantation or replacement of their internal pulse generator.
  
  
  RESULTS
  There was large subject-to-subject variation in stimulus artifact amplitude, which model-based analysis suggested may have been caused by glial encapsulation of the lead, resulting in imbalances in the tissue impedance between the contacts. ECAP recordings obtained from both acute and chronically implanted electrodes revealed that specific phase characteristics of the signal varied systematically with stimulation parameters. Further, a trend was observed in some patients between the energy of the initial negative and positive ECAP phases, as well as secondary phases, and changes in tremor from baseline. A computational model of thalamic DBS indicated that direct cerebellothalamic fiber activation dominated the clinically measured ECAP, suggesting that excitation of these fibers is critical in DBS therapy.
  
  
  CONCLUSIONS
  This work demonstrated that ECAPs can be recorded in the clinical setting and may provide a surrogate feedback control signal for automatic adjustment of stimulation parameters to reduce tremor amplitude.
authors.affiliation: Department of Biomedical Engineering, Duke University, Durham, NC, USA.
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Kent
authors.affiliation: Department of Biomedical Engineering, Duke University, Durham, NC, USA.
authors.forename: Brandon D
authors.initials: BD
authors.lastname: Swan
authors.affiliation: Department of Biomedical Engineering, Duke University, Durham, NC, USA.
authors.forename: David T
authors.initials: DT
authors.lastname: Brocker
authors.affiliation: Department of Neurobiology, Duke University Medical Center, Durham, NC, USA; Department of Surgery, Duke University Medical Center, Durham, NC, USA.
authors.forename: Dennis A
authors.initials: DA
authors.lastname: Turner
authors.affiliation: Department of Neurosurgery, Emory University, Atlanta, GA, USA; Department of Neurology, Emory University, Atlanta, GA, USA; Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Gross
authors.affiliation: Department of Biomedical Engineering, Duke University, Durham, NC, USA; Department of Neurobiology, Duke University Medical Center, Durham, NC, USA; Department of Surgery, Duke University Medical Center, Durham, NC, USA; Department of Electrical and Computer Engineering, Duke University, Durham, NC, USA. Electronic address: warren.grill@duke.edu.
authors.forename: Warren M
authors.initials: WM
authors.lastname: Grill
mesh_terms: D000368:Aged; D016477:Artifacts; D002531:Cerebellum / Q000502:physiology*; D003198:Computer Simulation; D046690:Deep Brain Stimulation / Q000379:methods*; D004567:Electrodes, Implanted; D005071:Evoked Potentials / Q000502:physiology*; D025461:Feedback, Physiological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000502:physiology; D013788:Thalamus / Q000502:physiology*; D014202:Tremor / Q000503:physiopathology / Q000628:therapy*
keywords: Computer simulation; Evoked compound action potential; Movement disorders; Neural recording; Stimulus artifact