Spatial resolution of local field potential signals in macaque V4

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. reconstruction of the natural responses of visual cortex to phosphene-like stimuli at different positions in the visual field can assist at designing a systematic procedure to control the position of multiple phosphenes by tuning the stimulation parameters. The key characteristic of such a system then, would be its capability to discriminate between responses to phosphene-like visual stimuli at different spatial positions.Multielectrode recordings are necessary to obtain both the spatial and temporal sampling properties required for the representation of position [13,14]. However, the majority of previous multielectrode recordings and stimulation studies in the visual cortex of monkeys have been performed in V1 [6,8,[15][16][17][18][19][20][21][22][23], which is quite large relative to standard recording arrays. Therefore, a multielectrode array in V1 can often sample only a tiny region of visual space. In contrast, extrastriate visual areas generally contain retinotopic maps that are physically smaller, while the receptive fields are much larger than those in the primary visual cortex (V1) [24][25][26]. This provides the opportunity to sample a larger region of visual space, albeit with reduced spatial resolution, using standard devices such as Utah arrays [27,28]. In particular, extrastriate area V4 offers an opportunity to recover the location of static visual stimuli, as it contains a retinotopic map of visual spa...

Sufficient sampling for kriging prediction of cortical potential in rat, monkey, and human µECoG

“…Another functional utility of redundant electrode signals was recently studied through the use of shared trial-to-trial variability in discriminating visual stimuli from V4 activity in NHP. Rather than being a nuisance, shared variability in LFP contributed substantially to decoding accuracy [76]. The logic of avoiding redundancy by setting electrode spacing based on spatial cycle limits was also challenged through a detection theory model that elucidated the impact of redundancy in both event-related signals of interest and background processes.…”