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Red has a signal and a warning effect. Is this specificity reflected in the brain?

Researchers at the Ernst Strongman Institute (ESI) of Neuroscience wanted to find out whether red stimulates brain waves more than other colors in a particular area. They published their findings in the journal eLife.

If the traffic light is red, we stop. Ripe cherries stand out on the tree because of their color. The signal and warning effect are attributed to the color red. But is this also reflected in the brain? Researchers at the Ernst Strongman Institute (ESI) of Neuroscience investigated this question. They wanted to know if the color red triggered brain waves in a particular area more than other colors. They published their results in eLife magazine.
in the search center Benjamin J. StaushAlina Peter, Isabelle Ehrlich, Zora Nolte and Pascal Fries, Director of ESI Standing for early visual cortex, also known as V1. It is the largest visual area of ​​the brain. It is the first to receive input from the retina. There, brain waves (oscillations) occur at a specific frequency, called the gamma band (30-80 Hz), when this band is stimulated by strong, spatially homogeneous images. But not all images produce this effect to the same extent!

Show color effect

“Recently, several research projects have revolved around the question of which particular input drives gamma waves,” explains Benjamin J. Stauch, the study’s first author. “One of the triggers appears to be colored surfaces. Especially when it’s red. Scientists interpreted this to mean that the red color is something special for the visual system due to evolution, because fruits, for example, are often red. ”
But how can the effect of color be scientifically proven? Or even refute? then: It is difficult to determine the color objectivelyAlso to compare colors between different studies. Each computer screen displays a slightly different color, so the red color on one screen will not be the same as on another. In addition, there are a variety of ways to determine color: based on a single screen or perceptual judgments, or based on what their access to the human retina does.

Colors activate light-sensing cells

Because humans perceive colors when certain light-sensitive cells in the retina, called cones, are activated. It reacts to light stimuli by converting them into electrical signals, which neurons then transmit to the brain. In order to be able to recognize colors, we need several types of cones. Each type of cone is particularly sensitive to a specific range of wavelengths: red (L cones), green (M cones) or blue (S cones). The brain compares how strongly the respective cones respond and uses this to determine the chromatic impression.
This works in a similar way for all people. So there would be a way to objectively identify colors by measuring how much they activate different retinal cones. Scientific studies in macaques have shown that the early primate visual system has two chromatic axes that depend on these cones: the LM axis, which compares red with green, and the S- (L + M) axis, which compares yellow with violet. “We believe that a color coordinate system based on these two color axes is the correct way to identify color when researchers want to explore the strength of gamma oscillations, because it quantifies colors directly in terms of how strong and in what way they do it.” Activating early optical systems, says Benjamin J. Stausch. Because previous work on color-related gamma oscillations has mostly been performed using small samples from a few primates or people, but cone activation spectra can vary from individual to individual for genetic reasons, he and his team measured in the now published paper. Larger sample of individuals (n = 30).

Same effect as red and green

They explore the question of whether red is really something special. That is, whether this color leads to stronger gamma oscillations than green with similar color strength (ie, cone anisotropy). A side question is: Can color-induced gamma oscillations also be detected by magnetic electroencephalography (MEG), that is, a way to measure the magnetic activities of the brain?
They concluded that red is not particularly strong in terms of the intensity of the gamma oscillations it gives off. Alternatively, with the same absolute LM cone contrast, red and green lead to equally strong gamma oscillations in the early visual cortex. Furthermore, through micromanipulation, color-induced gamma waves can be measured in human MEG, allowing future research to explore 3R principles of animal testing (reduce/reduce, replace/avoid, refine/improve) This could be followed by its action on humans rather than non-human primates.
Colors that activate only the S-cone (blue) are generally shown to elicit weak neural responses in the early visual cortex. This is somewhat to be expected since the S-cone is less common, older evolutionarily, and more sluggish in the primate retina.

Contribute to the development of optical prosthetics

The results of this study by ESI scientists, understanding how the early human visual cortex encodes images, could one day aid the development of visual prosthetics that attempt Activating the visual cortex to elicit vision-like perceptual effects in people with retinal damage. However, this goal remains elusive. More needs to be understood about the specific responses of the visual cortex to visual input.

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