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. Approach 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. Main 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 degrees 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.

Implantable microcoils for intracortical magnetic stimulation

“…The properties of the induced electric fields from coils may remain more consistent over time because magnetic fields pass readily through the high-impedance glial encapsulation that can surround implants although encapsulation can markedly alter the strength as well as the spatial distribution of the electric fields arising from electrodes. In addition, the lack of direct metal-to-brain contact for coils eliminates many of the electrode-brain interface problems, for example, the variability of electrode impedance following implantation ( 9 , 15 ). …”

“…Maintaining response consistency over time with implanted electrodes has also been proven to be challenging ( 1 , 9 , 10 ). For example, electrodes implanted into the primary visual cortex (V1) of macaque monkeys each reliably elicited a visual percept (phosphene) shortly after implantation, but individual electrodes lost effectiveness within a few months ( 9 ). Although larger groupings of electrodes could be used to generate phosphenes, the need to couple electrodes together represents a significant loss in potential visual acuity.…”

Enhanced Control of Cortical Pyramidal Neurons With Micromagnetic Stimulation

“…Despite this potential and much ongoing effort however, several fundamental limitations associated with electric stimulation from implanted electrodes raise concerns about the long-term viability of this approach. For example, implantation into cortex induces a host of inflammatory responses; the resulting gliosis [3–8] can lead to encapsulation of the stimulating electrodes with a corresponding loss in effectiveness over time [3, 6]. Another limitation arises from the high sensitivity of axons of passage and other horizontally extending processes to electric stimulation – their inadvertent activation can greatly expand the spatial extent of the region influenced by stimulation and lead to a wide range of undesirable side effects [9, 10].…”

Properties of electrically evoked potentials activated by optic nerve stimulation with penetrating electrodes of different modes in rabbits

“…Visual prostheses have proved to be a promising way to restore partial functional vision for patients with RP. Three major types of visual prostheses have been investigated according to the stimulation locations: cortical prostheses [3][4][5][6][7], retinal prostheses using epi-and subretinal stimulation , and optic nerve (ON) prostheses [31][32][33][34][35][36][37][38][39][40][41]. The retinal prosthesis is the most developed type among the three, and the Argus II epiretinal prosthesis has been approved by the European CE and the US FDA for clinical use [23].…”