Spatial Resolution of Local Field Potential Signals in Macaque V4

TL;DR

This study demonstrates that local field potentials and multiunit activity in macaque V4 can discriminate spatial positions effectively, informing cortical visual prosthesis development with potential for more compact implants.

Contribution

It shows that ensembles of LFPs and MUA in V4 can discriminate spatial positions, with optimized electrode selection improving performance, advancing visual prosthesis design.

Findings

LFP and MUA responses enable fine and coarse spatial discrimination.

Noise correlations in LFPs carry significant positional information.

Optimized electrode selection enhances discrimination accuracy.

Abstract

A main challenge for the development of cortical visual prostheses is to spatially localize individual spots of light, called phosphenes, by assigning appropriate stimulating parameters to implanted electrodes. Imitating the natural responses to phosphene-like stimuli at different positions can help in designing a systematic procedure to determine these parameters. The key characteristic of such a system is the ability to discriminate between responses to different positions in the visual field. While most previous prosthetic devices have targeted the primary visual cortex, the extrastriate cortex has the advantage of covering a large part of the visual field with a smaller amount of cortical tissue, providing the possibility of a more compact implant. Here, we studied how well ensembles of Multiunit activity (MUA) and Local Field Potentials (LFPs) responses from extrastriate cortical visual area V4 of a behaving macaque monkey can discriminate between two-dimensional spatial positions. We found that despite the large receptive field sizes in V4, the combined responses from multiple sites, whether MUA or LFP, has the capability for fine and coarse discrimination of positions. We identified a selection procedure that could significantly increase the discrimination performance while reducing the required number of electrodes. Analysis of noise correlation in MUA and LFP responses showed that noise correlations in LFP responses carry more information about the spatial positions. Overall, these findings suggest that spatial positions could be localized with patterned stimulation in extrastriate area V4.