People perceive color when photoreceptor cells, the so-called cones, are activated in the retina. They react to light stimuli by converting them into electrical signals, which are then sent to the brain. The brain reacts with gamma oscillations to different degrees (upper row) if maximally colored colors are selected in the RGB color space. The bottom row reveals colors that trigger the retinal cones to the same level and produce equally strong gamma oscillations in the brain. Credit: © ESI/C. Kernberger
Red has a signaling and caution result. How is this color uniqueness shown in the brain?
Scientists at the Ernst Strüngmann Institute for Neuroscience have actually now examined the question of whether red triggers brain waves more highly than other colors.
Due to the fact that of their color, we right away identify ripe cherries on a tree. The color red is associated a signaling and warning impact. They wanted to know whether red triggers brain waves more strongly than other colors.
The new research study focuses on the early visual cortex, also understood as V1. It is the biggest visual location in the brain and the very first to get input from the retina. When this area is stimulated by spatially uniform and strong images, brain waves (oscillations) occur at a specific frequency called the gamma band (30-80 Hz). Not all images create this effect to the very same level. The research study, by Benjamin J. Stauch, Alina Peter, Isabelle Ehrlich, Zora Nolte, and ESI director Pascal Fries was released earlier this year in the journal eLife.
Colors trigger photoreceptor cells
Humans perceive color when photoreceptor cells, the so-called cones, are triggered in the retina. They react to light stimuli by transforming them into electrical signals, which are then transferred to the brain. To acknowledge colors, we need numerous types of cones. Each type is especially receptive to a particular range of wavelengths: red (L cones), green (M cones), or blue (S cones). The brain then compares how strongly the particular cones have responded and deduces a color impression.
It works likewise for all human beings. It would therefore be possible to define colors objectively by determining how highly they trigger the various retinal cones. Scientific studies with macaques have shown that the early primate visual system has 2 color axes based upon these cones: the L-M axis compares red to green, and the S– (L+M) axis is yellow to violet. “We think that a color coordinate system based on these two axes is the best one to define colors when researchers wish to check out the strength of gamma oscillations. It specifies colors according to how highly and in what way they activate the early visual system,” Benjamin J. Stauch says. Because previous deal with color-related gamma oscillations has mostly been kept up little samples of a couple of primates or human individuals , however the spectra of cone activation can vary genetically from individual to specific, he and his team wanted to determine a larger sample of people (N = 30).
Red and green have equivalent result
In doing so, Benjamin J. Stauch and his team examined whether the color red is something special and whether this color triggers stronger gamma oscillations than green of similar color intensity (i.e., cone contrast). And a side question was: Can color-induced gamma oscillations also be spotted by magnetoencephalography, a technique for determining the magnetic activities of the brain?
They conclude that the color red is not especially strong in terms of the strength of the gamma oscillations it causes. Rather, green and red produce similarly strong gamma oscillations in the early visual cortex at the very same absolute L-M cone contrast. Additionally, color-induced gamma waves can be measured in human magnetoencephalography when treated carefully, so future research study might follow the 3R principles for animal experiments (Reduce, Replace, Refine) by using people rather than nonhuman primates.
Colors that trigger just the S-cone (blue) normally appear to generate just weak neuronal responses in the early visual cortex. To some degree, this is to be expected, because the S-cone is less common in the primate retina, evolutionarily older, and more slow.
Advancement of visual prostheses
The results of this research study led by ESI researchers, comprehending how the early human visual cortex encodes images, might one day be used to assist establish visual prostheses. These prostheses might try to activate the visual cortex to induce vision-like perceptual results in individuals with damaged retinas. This goal is still a long method off. Prior to, a lot more needs to be understood about the particular responses of the visual cortex to visual input.
Referral: “Human visual gamma for color stimuli” by Benjamin J Stauch, Alina Peter, Isabelle Ehrlich, Zora Nolte and Pascal Fries, 9 May 2022, eLife.DOI: 10.7554/ eLife.75897.
Brain anatomy illustration.
Color is hard to define
” Recently, a lot of research study has attempted to explore which specific input drives gamma waves,” describes Benjamin J. Stauch, first author of the research study. “One visual input seems to be colored surface areas. Especially if they are red. Scientist translated this to indicate that red is evolutionarily unique to the visual system because, for instance, fruits are frequently red.”
However how can the effect of color be scientifically shown? Or refuted? After all, it is difficult to specify a color objectively, and it is similarly hard to compare colors in between different studies. Every computer screen reproduces a color differently, so red on one screen is not the like on another. Furthermore, there are a variety of methods to specify colors: based on a single display, affective judgments, or based on what their input does to the human retina.
The visual cortex is the primary cortical region of the brain that receives, integrates, and processes visual details relayed from the retinas. It is situated in the occipital lobe of the primary cortex, which is in the most posterior area of the brain.
The visual cortex is divided into five different areas, called V1 to V5, based on function and structure. Visual information from the retinas that are taking a trip to the visual cortex first passes through the thalamus, where it synapses in a nucleus called the lateral geniculate.
If maximally colored colors are picked in the RGB color area, the brain reacts with gamma oscillations to various degrees (upper row). The bottom row reveals colors that trigger the retinal cones to the exact same degree and create equally strong gamma oscillations in the brain. It is challenging to define a color objectively, and it is equally challenging to compare colors in between different studies. The brain then compares how highly the particular cones have actually responded and deduces a color impression.
“We think that a color coordinate system based on these two axes is the ideal one to specify colors when scientists want to explore the strength of gamma oscillations.
