Visuotopic Mapping Through a Multichannel Stimulating Implant in Primate V1

Abstract

We report on our efforts to establish an animal model for the development and testing of a cortical visual prostheses. One-hundred-fifty-two electrodes were implanted in the primary visual cortex of a rhesus monkey. The electrodes were made from iridium with an activated iridium oxide film, which has a large charge capacity for a given surface area, and insulated with parylene-C. One-hundred-fourteen electrodes were functional after implantation. The activity of small (2-3) neuronal clusters was first recorded to map the visually responsive region corresponding to each electrode. The animal was then trained in a memory (delayed) saccade task, first with a visual target, then to a target defined by direct cortical stimulation with coordinates specified by the stimulating electrode's mapped receptive field. The SD of saccade endpoints was approximately 2.5 larger for electrically stimulated versus visual saccades; nevertheless, when trial-to-trial scatter was averaged out, the correlation between saccade end points and receptive field locations was highly significant and approached unity after several months of training. Five electrodes were left unused until the monkey was fully trained; when these were introduced, the receptive field-saccade correlations were high on the first day of use (R = 0.85, P = 0.03 for angle, R = 0.98, P < 0.001 for eccentricity), indicating that the monkey had not learned to perform the task empirically by memorizing reward zones. The results of this experiment suggest the potential for rigorous behavioral testing of cortical visual prostheses in the macaque.

Demonstration of artificial visual percepts generated through thalamic microstimulation

“…Results from that study suggest that evoked percepts were Ϸ0.6°in diameter for stimulation in the parafoveal area. Bradley et al (27) performed a study similar to the present one, using indwelling microelectrodes in macaque V1 and assessing perceptual characteristics by using a memory-saccade task. On average they found saccades to electrical targets had larger scatter than those to optical targets (2.4°vs.…”

Behavioral Time Course of Microstimulation in Cortical Area MT

“…Recent studies have begun to show how sensory areas encode natural stimuli (Butts et al 2007;David et al 2004;Felsen et al 2005;Lesica and Stanley 2004;Nemenman et al 2008;Sharpee et al 2004;Simoncelli and Olshausen 2001), and it is useful to know the extent to which microstimulation can be used to show the causality between sensory activity and perception on these fast timescales. Furthermore, microstimulation will be the basis for future advanced sensory neural prosthetics (Bradley et al 2005;Fernandez et al 2005;Girvin 1988;McIntyre and Grill 2000;Middlebrooks et al 2005;Normann et al 1999;Tehovnik and Slocum 2007;Troyk et al 2003). Thus it is imperative we understand the effects of microstimulation in the same temporal regimen as natural sensory inputs.…”

“…Electrical microstimulation of the brain is an important research tool for establishing causality between neural activity and behavior (for reviews, see Cohen and Newsome 2004;Romo and Salinas 1999) and serves as the basis for supplying sensory inputs in neural prosthetics (Bradley et al 2005;Fernandez et al 2005;Girvin 1988;McIntyre and Grill 2000;Middlebrooks et al 2005;Normann et al 1999;Tehovnik and Slocum 2007;Troyk et al 2003). Both of these applications rely on the assumption that microstimulation can generate percepts that are reasonably similar to those produced by naturally occurring stimuli.…”

Phosphene induction by microstimulation of macaque V1

“…This finding has lead to the suggestion that microstimulation of V1 in behaving monkeys could serve as a model for the implantation of a functional cortical visual prosthesis in clinically blind individuals (Troyk et al, 2003;Bartlett et al 2005;Bradley et al, 2005;DeYoe et al, 2005;Tehovnik et al, 2005a). For over ten years since Schmidt and colleagues (1996) first implanted a microelectrode array in one blind patient for the study of phosphenes, the creation of a functional cortical visual prosthesis for the blind has not been realized.…”