Chromatic and Achromatic Spatial Resolution of Local Field Potentials in Awake Cortex

Abstract

Local field potentials (LFPs) have become an important measure of neuronal population activity in the brain and could provide robust signals to guide the implant of visual cortical prosthesis in the future. However, it remains unclear whether LFPs can detect weak cortical responses (e.g., cortical responses to equiluminant color) and whether they have enough visual spatial resolution to distinguish different chromatic and achromatic stimulus patterns. By recording from awake behaving macaques in primary visual cortex, here we demonstrate that LFPs respond robustly to pure chromatic stimuli and exhibit ∼2.5 times lower spatial resolution for chromatic than achromatic stimulus patterns, a value that resembles the ratio of achromatic/chromatic resolution measured with psychophysical experiments in humans. We also show that, although the spatial resolution of LFP decays with visual eccentricity as is also the case for single neurons, LFPs have higher spatial resolution and show weaker response suppression to low spatial frequencies than spiking multiunit activity. These results indicate that LFP recordings are an excellent approach to measure spatial resolution from local populations of neurons in visual cortex including those responsive to color.

Long-wavelength (reddish) hues induce unusually large gamma oscillations in the primate primary visual cortex

“…Color processing in V1 has mostly been studied by analyzing evoked spiking responses due to chromatic stimuli (reviewed in refs. 15 – 17 ), with only a few recent studies looking at LFP responses, although not at gamma oscillations ( 18 – 20 ). We show that the gamma band of V1 LFP is highly sensitive to hue and saturation and largely invariant to luminance, with power increases far exceeding those reported in previous studies that used achromatic stimuli.…”

Cortical Balance Between ON and OFF Visual Responses Is Modulated by the Spatial Properties of the Visual Stimulus

“…First, the dot product of the emission spectra of the red, green, and blue monitor phosphors and the Smith–Pokorny 2-degree cone fundamentals were measured with a Photo Research PR 650 SpectraScan spectroradiometer to determine the excitations for the long (L), medium (M), and short (S) wavelength-sensitive cones. Then, equiluminant stimuli were prepared in the same color space used by Derrington et al (1984) with the methods described by Zaidi and Halevy (1993) and Jansen et al (2015). This color space is described by two chromatic axes, popularly known as the RG or BY axes, and a luminance or light–dark (LD) axis.…”

Multiple-target tracking in human and machine vision

“…It is worth noting that the brain chooses an efficient strategy to track multiple targets considering its physical and cognitive limitations; these limitations are mostly related to the physiological properties and functions of neurons, which are tuned to specific features of visual scenes, visual spatial mapping, and varied emotional and intrinsic brain states [13][14][15][16][17]. Computers do not have similar computational limitations.…”