Overview: Red is not particularly strong in terms of the strength of gamma oscillations that occur in the brain.
sauce: ESI
Red lights stop drivers. The red color creates a signal and warning effect. But is this also reflected in the brain?
Researchers at the Ernst Strüngmann Institute for Neuroscience (ESI) are currently investigating this question. They wanted to know if red provokes brain waves more strongly than other colors.
A study titled “Human Visual Gamma to Color Stimuli” is published in the journal e-life.
The research by Benjamin J. Stauch, Alina Peter, Isabelle Ehrlich, Zora Nolte, and ESI Director Pascal Fries focuses on the early visual cortex, also known as V1. It is the largest visual area in the brain and receives input primarily from the retina.
When this region is stimulated by an intense, spatially uniform image, it produces brain waves (vibrations) at specific frequencies called the gamma band (30-80 Hz). However, not all images produce this effect to the same extent.
difficult to define colors
“Recently, many studies have attempted to investigate which specific inputs drive gamma waves,” explains Benjamin J. Stouch, the study’s lead author. “One visual input is like a colored surface, especially if they are red. Did.”
But how can we scientifically prove the effect of color? Or refute it? After all, it is difficult to objectively define color, and it is equally difficult to compare color across different studies.
All computer monitors reproduce colors differently, so red on one screen is not the same as red on another. Additionally, there are different ways to define colors. Based on the impact of a single monitor, perceptual judgment, or input on the human retina.
Color activates photoreceptor cells
Humans perceive color when photoreceptors, so-called cone cells, are activated in the retina. They respond to light stimuli and convert them into electrical signals that are transmitted to the brain.
Some types of cones are required for color recognition. Each type is specifically receptive to a particular range of wavelengths in red (L cones), green (M cones), or blue (S cones). The brain then compares how strongly each pyramidal cell responds to infer a color impression.
It works the same for all humans. Therefore, measuring how strongly different colors activate retinal cones makes it possible to objectively define color. Scientific studies with monkeys have shown that the early primate visual system has her two color axes based on these cones. The LM axis compares red and green, and the S-(L+M) axis compares yellow and purple.
“We believe that a color coordinate system based on these two axes is a good way to define color if researchers want to study the strength of gamma oscillations. You define color by how it activates,” says Benjamin J. Stouch.
He and his team wanted to measure a sample of more individuals (N = 30). Previous studies on color-associated gamma oscillations were primarily performed on small samples of small numbers of primates or human participants, as the spectrum of cone activation may be genetically distinct. from individual to individual
red and green have equal effect
In doing so, Benjamin J. Stauch and his team investigated whether red is a special color and whether this color causes stronger gamma oscillations than green of comparable color intensity (i.e., cone contrast). I investigated.
They also explored secondary questions. Can color-induced gamma oscillations be detected by magnetoencephalography (MEG), a method of measuring magnetic activity in the brain?
They conclude that red is not particularly strong with respect to the strength of red-induced gamma oscillations. Rather, red and green produce equally strong gamma oscillations in the early visual cortex at the same absolute LM cone contrast.
Furthermore, since color-induced gamma waves can be measured in MEG in humans with careful handling, the use of humans rather than non-human primates should be used in future studies to support the 3R principles of animal testing (reduction, substitution, refinement) can be followed.
A color that activates only the S cone (blue) generally appears to elicit only weak neural responses in the early visual cortex. This is to some extent expected because S cones are less common in the primate retina, evolutionarily ancient and sluggish.
Led by ESI scientists, the results of this study will help us understand how the early human visual cortex encodes images and may one day aid in the development of artificial vision. . These prostheses may seek to activate the visual cortex to induce vision-like perceptual effects in people with retinal damage. However, this goal is still a long way off.
See also
Much more needs to be understood about the specific responses of the visual cortex to visual input.
About this visual neuroscience research news
author: press office
sauce: ESI
contact: Press Office – ESI
image: Images credited to ESI/C.khan burger
Original research: open access.
“Human visual gamma for color stimuliBenjamin J. Stouch and others e-life
Overview
Human visual gamma for color stimuli
Strong gamma-band oscillations in the early visual cortex of primates can be induced by homogeneous color planes (Peter et al., 2019; Shirhatti and Ray, 2018). Particularly strong gamma oscillations have been reported for red stimuli compared to other hues.
However, the intensity of precortical color processing and the resulting input to V1 is often not fully controlled. Therefore, stronger responses to red may be due to differences in V1 input intensity.
We presented stimuli with equal luminance and cone contrast levels in a color coordinate system based on the response of the lateral geniculate nucleus, the main input source for region V1. Using these stimuli, we recorded magnetoencephalograms in 30 participants.
Contrary to previous reports, we found gamma oscillations in the early visual cortex that did not differ between red and green stimuli of equal LM cone contrast.
In particular, blue stimuli with contrast only in the S cone axis elicited very weak gamma responses, resulting in smaller event-related fields and poorer change detection performance.
The strength of the human color gamma response to stimuli on the LM axis can be well described by the contrast of the LM cones, showing no distinct red bias when the LM cone contrasts are properly equalized. I did.
