title: Spatiotemporal interactions in the visual cortex following paired electrical stimulation of the retina.
abstract: OBJECTIVE
  Retinal prostheses use spatiotemporal patterns of electrical stimulation across multiple electrodes to provide visual percepts to blind patients. It is generally assumed that percepts produced by individual electrodes are independent of one another, which may not be the case. In this study, we aimed to quantify interactions between pairs of electrical stimuli delivered to the retina.
  
  
  METHODS
  Normally sighted cats were implanted with a suprachoroidal electrode array. The retina was stimulated with a paired-pulse paradigm that consisted of a conditioning stimulus followed by a test stimulus, while recording multiunit activity in the visual cortex. Conditioning current, and spatial and temporal separation between the conditioning and test stimuli were varied. Cortical interactions were quantified by changes in multiunit activity elicited by stimulation with the paired-pulse paradigm, compared to stimulation of the test stimulus alone (control).
  
  
  RESULTS
  Interactions varied as a function of conditioning current and temporal separation between the two stimulating pulses. Cortical activity increased compared to the control condition at an interstimulus delay of 1.025 ms and was significantly suppressed for delays between 20 and 90 ms, returning to near control levels for longer delays. The level of interactions increased when the conditioning current was increased. Interactions were found to be similar for electrode separations up to 3 mm.
  
  
  CONCLUSIONS
  Interactions between sequential stimulation of pairs of electrodes in a suprachoroidal retinal prosthesis occur for delays up to 100 ms and electrode separations of several millimeters. Knowledge of these spatiotemporal interactions is essential for developing effective patterns of stimulation for retinal prostheses.
authors.affiliation: Bionics Institute, Victoria, Australia Department of Electronic Engineering, La Trobe University, Victoria, Australia.
authors.forename: Rosemary
authors.initials: R
authors.lastname: Cicione
authors.affiliation: Bionics Institute, Victoria, Australia Medical Bionics Department, University of Melbourne, Victoria, Australia.
authors.forename: James B
authors.initials: JB
authors.lastname: Fallon
authors.affiliation: Bionics Institute, Victoria, Australia Department of Electronic Engineering, La Trobe University, Victoria, Australia.
authors.forename: Graeme D
authors.initials: GD
authors.lastname: Rathbone
authors.affiliation: Bionics Institute, Victoria, Australia.
authors.forename: Chris E
authors.initials: CE
authors.lastname: Williams
authors.affiliation: Bionics Institute, Victoria, Australia Medical Bionics Department, University of Melbourne, Victoria, Australia.
authors.forename: Mohit N
authors.initials: MN
authors.lastname: Shivdasani
mesh_terms: D000818:Animals; D002415:Cats; D004558:Electric Stimulation / Q000379:methods; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology; D023421:Models, Animal; D012160:Retina / Q000502:physiology* / Q000601:surgery; D012684:Sensory Thresholds / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D057488:Visual Prosthesis
keywords: electrical stimulation; interactions; multiunit activity; retinal prosthesis; visual cortex