title: The Effect of Electric Cross-Talk in Retinal Neurostimulation.
abstract: OBJECTIVE
  To investigate the efficacy of electric field shaping in modulating the extent and activation threshold in retinal neurostimulation. This study aims to quantify the interference of neighboring stimulation sites by assessing the shift in the activation threshold produced by a concomitant interfering stimulus.
  
  
  METHODS
  Electrical stimuli were applied to healthy retinae in a feline model (n = 4) using a 24-channel electrode array surgically implanted in the suprachoroidal space. A 96-channel penetrating electrode array was used for recording cortical responses to a number of stimulation paradigms. Data were analyzed offline. Concurrent monopolar and hexapolar stimuli were delivered at primary and interfering sites separated by up to 2.19 mm to evaluate electric cross-talk. The spike rate was fit to a sigmoidal curve to estimate the P50 threshold. The slope of the linear regression of the P50 value versus interfering current level was considered as a measure of cross-talk.
  
  
  RESULTS
  Concurrent monopolar stimulation produced a proportional drop in the P50 of approximately 20% of the interfering current level in presence of a primary monopolar and hexapolar stimulus. On the other hand, hexapolar interference did not alter activation thresholds at the primary site.
  
  
  CONCLUSIONS
  Hexapolar stimulation reduces electric cross-talk between neighboring sites and represents a technique to reduce interference between individual stimulation sites. In contrast, concurrent monopolar stimulation produces a reduction of the activation threshold of stimuli delivered nearby. Thus, a single source of subthreshold monopolar charge injection can provide benefit in the form of significant threshold reduction simultaneously at multiple stimulation sites.
authors.affiliation: Graduate School of Biomedical Engineering University of New South Wales, Sydney, Australia.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Matteucci
authors.affiliation: Graduate School of Biomedical Engineering University of New South Wales, Sydney, Australia.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Barriga-Rivera
authors.affiliation: Graduate School of Biomedical Engineering University of New South Wales, Sydney, Australia.
authors.forename: Calvin D
authors.initials: CD
authors.lastname: Eiber
authors.affiliation: Graduate School of Biomedical Engineering University of New South Wales, Sydney, Australia.
authors.forename: Nigel H
authors.initials: NH
authors.lastname: Lovell
authors.affiliation: School of Medicine, Western Sydney University, Sydney, Australia 3School of Medical Science, University of New South Wales, Sydney, Australia.
authors.forename: John W
authors.initials: JW
authors.lastname: Morley
authors.affiliation: Graduate School of Biomedical Engineering University of New South Wales, Sydney, Australia.
authors.forename: Gregg J
authors.initials: GJ
authors.lastname: Suaning
mesh_terms: D000818:Animals; D001766:Blindness / Q000503:physiopathology / Q000534:rehabilitation*; D002415:Cats; D004195:Disease Models, Animal; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D058542:Implantable Neurostimulators; D011474:Prosthesis Design; D012160:Retina / Q000503:physiopathology; D057488:Visual Prosthesis