title: Spatial and temporal characteristics of V1 microstimulation during chronic implantation of a microelectrode array in a behaving macaque.
abstract: OBJECTIVE
  It has been hypothesized that a vision prosthesis capable of evoking useful visual percepts can be based upon electrically stimulating the primary visual cortex (V1) of a blind human subject via penetrating microelectrode arrays. As a continuation of earlier work, we examined several spatial and temporal characteristics of V1 microstimulation.
  
  
  METHODS
  An array of 100 penetrating microelectrodes was chronically implanted in V1 of a behaving macaque monkey. Microstimulation thresholds were measured using a two-alternative forced choice detection task. Relative locations of electrically-evoked percepts were measured using a memory saccade-to-target task.
  
  
  RESULTS
  The principal finding was that two years after implantation we were able to evoke behavioural responses to electric stimulation across the spatial extent of the array using groups of contiguous electrodes. Consistent responses to stimulation were evoked at an average threshold current per electrode of 204 ± 49 µA (mean ± std) for groups of four electrodes and 91 ± 25 µA for groups of nine electrodes. Saccades to electrically-evoked percepts using groups of nine electrodes showed that the animal could discriminate spatially distinct percepts with groups having an average separation of 1.6 ± 0.3 mm (mean ± std) in cortex and 1.0° ± 0.2° in visual space. Significance. These results demonstrate chronic perceptual functionality and provide evidence for the feasibility of a cortically-based vision prosthesis for the blind using penetrating microelectrodes.
authors.affiliation: Department of Bioengineering, University of Utah, Salt Lake City, UT, USA.
authors.forename: T S
authors.initials: TS
authors.lastname: Davis
authors.forename: R A
authors.initials: RA
authors.lastname: Parker
authors.forename: P A
authors.initials: PA
authors.lastname: House
authors.forename: E
authors.initials: E
authors.lastname: Bagley
authors.forename: S
authors.initials: S
authors.lastname: Wendelken
authors.forename: R A
authors.initials: RA
authors.lastname: Normann
authors.forename: B
authors.initials: B
authors.lastname: Greger
mesh_terms: D000818:Animals; D002415:Cats; D003623:Dark Adaptation / Q000502:physiology; D017097:Electric Impedance; D004558:Electric Stimulation / Q000379:methods*; D004567:Electrodes, Implanted; D008253:Macaca mulatta; D008297:Male; D008839:Microelectrodes; D010775:Photic Stimulation; D012438:Saccades / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*; D057488:Visual Prosthesis