title: A computational model of direct brain excitation induced by electroconvulsive therapy: comparison among three conventional electrode placements.
abstract: BACKGROUND
  Electroconvulsive therapy (ECT) is a highly effective treatment for severe depressive disorder. Efficacy and cognitive outcomes have been shown to depend on variations in electrode placement and other stimulus parameters, presumably because of differences in the pattern of neuronal activation. This latter effect, however, is poorly understood.
  
  
  OBJECTIVE
  In this study, we present an anatomically accurate human head computational model to stimulate neuronal excitation during ECT, to better understand the effects of varying electrode placement and stimulus parameters.
  
  
  METHODS
  Electric field and current density throughout the head, as well as direct neural activation within the brain, were computed using the finite element method. Regions representing passive volume conductors (skin, skull, cerebrospinal fluid) were extracellularly coupled to an excitable neural continuum region representing the brain. The skull was modeled with anistropic electrical conductivity.
  
  
  RESULTS
  Simulation results indicated that direct activation of the brain occurred immediately beneath the electrodes on the scalp, consistent with existing imaging studies. In addition, we found that the brainstem was also activated using a right unilateral electrode configuration. Simulation also demonstrated that a reduction in stimulus amplitude or pulse width led to a reduction in the spatial extent of brain activation.
  
  
  CONCLUSIONS
  The novel model described in this study was able to simulate direct excitation of the brain during ECT, was useful in characterizing differences in neuronal activation as electrode placement, pulse width, and amplitude were altered, and is proposed as a tool for further exploring the effects of variations in ECT stimulation approaches. Results from the simulations assist in understanding recently described clinical phenomena, in particular, the reduction in cognitive side effects with ultrabrief pulse width stimulation, and greater effects of the ECT stimulus on cardiovascular function with unilateral electrode placement.
authors.affiliation: Graduate School of Biomedical Engineering, Faculty of Engineering, University of New South Wales, Sydney, Australia.
authors.forename: Siwei
authors.initials: S
authors.lastname: Bai
authors.affiliation: School of Psychiatry, University of New South Wales, Sydney, Australia; Department of Psychiatry, St George Hospital, Sydney, Australia; Black Dog Institute, Sydney, Australia.
authors.forename: Colleen
authors.initials: C
authors.lastname: Loo
authors.affiliation: Graduate School of Biomedical Engineering, Faculty of Engineering, University of New South Wales, Sydney, Australia.
authors.forename: Amr
authors.initials: A
authors.lastname: Al Abed
authors.affiliation: Graduate School of Biomedical Engineering, Faculty of Engineering, University of New South Wales, Sydney, Australia. Electronic address: s.dokos@unsw.edu.au.
authors.forename: Socrates
authors.initials: S
authors.lastname: Dokos
mesh_terms: D001921:Brain / Q000502:physiology*; D003198:Computer Simulation; D004565:Electroconvulsive Therapy / Q000295:instrumentation* / Q000379:methods*; D004566:Electrodes; D005071:Evoked Potentials / Q000502:physiology*; D006801:Humans; D008959:Models, Neurological