How does the brain turn waves of light into experiences of color? (2024)
Perceiving something -- anything -- in your surroundings is to become aware of what your senses are detecting. Today, Columbia University neuroscientists identify, for the first time, brain-cell circuitry in fruit flies that converts raw sensory signals into color perceptions that can guide behavior.
Their findings were pulbished in the journal Nature Neuroscience.
"Many of us take for granted the rich colors we see every day -- the red of a ripe strawberry or the deep brown in a child's eyes. But those colors do not exist outside of our brains," said Rudy Behnia, PhD, a principal investigator at Columbia's Zuckerman Institute and the corresponding author on the paper. Rather, she explained, colors are perceptions the brain constructs as it makes sense of the longer and shorter wavelengths of light detected by the eyes.
"Turning sensory signals into perceptions about the world is how the brain helps organisms survive and thrive," Dr. Behnia said.
"To ask how we perceive the world seems like a simple question, but answering it is a challenge," added Dr. Behnia "My hope is that our efforts to uncover neural principles underlying color perception will help us better understand how brains extract the features in the environment that are important for making it through each day."
In their new paper, the research team reports discovering specific networks of neurons, a type of brain cell, in fruit flies that respond selectively to various hues. Hue denotes the perceived colors associated with specific wavelengths, or combinations of wavelengths of light, which themselves are not inherently colorful. These hue-selective neurons lie within the optic lobe, the brain area responsible for vision.
Among the hues these neurons respond to are those that people would perceive as violet and others that correspond to ultraviolet wavelengths (not detectable by humans). Detecting UV hues is important for the survival of some creatures, such as bees and perhaps fruit flies; many plants, for example, possess ultraviolet patterns that can help guide insects to pollen.
Scientists had previously reported finding neurons in animals' brains that respond selectively to different colors or hues, say, red or green. But no one had been able to trace the neural mechanisms making this hue selectivity possible.
This is where the recent availability of a fly-brain connectome has proven helpful. This intricate map details how some 130,000 neurons and 50 million synapses in a fruit-fly's poppy seed-sized brain are interconnected, said Dr. Behnia, who is also an assistant professor of neuroscience at Columbia's Vagelos College of Physicians and Surgeons.
With the connectome serving as a reference -- akin to a picture on a puzzle box serving as a guide for how a thousand pieces fit together -- the researchers used their observations of brain cells to develop a diagram they suspected represents the neuronal circuitry behind hue selectivity. The scientists then portrayed these circuits as mathematical models to simulate and probe the circuits' activities and capabilities.
"The mathematical models serve as tools that enable us to better understand something as messy and complex as all of these brain cells and their interconnections," said Matthias Christenson, PhD, a co-first author on the paper and a former member of Dr. Behnia's lab. "With the models, we can work to make sense of all of this complexity." Also contributing crucially to the modeling work was Dr. Larry Abbott, William Bloor Professor of Theoretical Neuroscience, Professor of Physiology and Cellular Biophysics and a principal investigator at the Zuckerman Institute.
Not only did the modeling reveal that these circuits can host activity required for hue selectivity, it also pointed to a type of cell-to-cell interconnectivity, known as recurrence, without which hue-selectivity cannot happen. In a neural circuitry with recurrence, outputs of the circuit circle back in to become inputs. And that suggested yet another experiment, said Álvaro Sanz-Diez, PhD, a postdoctoral researcher in Dr. Behnia's lab and the other co-first author of the Nature Neuroscience paper.
"When we used a genetic technique to disrupt part of this recurrent connectivity in the brains of fruit flies, the neurons that previously showed hue-selective activity lost that property," said Dr. Sanz-Diez. "This reinforced our confidence that we really had discovered brain circuitry involved in color perception."
"Now we know a little more about how the brain's wiring makes it possible to build a perceptual representation of color," said Dr. Behnia. "My hope is that our new findings can help explain how brains produce all kinds of perceptions, among them color, sound and taste."
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes.
https://en.wikipedia.org › wiki › Photoreceptor_cell
react to different wavelengths, or colors, of light. When light hits the rods and cones, they send electrical signals to let the brain know.They do that through the optic nerve. Like roads and highways, nerves carry signals around the brain and body.
The brain uses light signals detected by the retina's cone photoreceptors as the building blocks for color perception. Three types of cone photoreceptors detect light over a range of wavelengths. The brain mixes and categorizes these signals to perceive color in a process that is not well understood.
When light hits an object, some of the spectrum is absorbed and some is reflected. Our eyes perceive colors according to the wavelengths of the reflected light. We also know that how we see color will be different depending on the time of day, lighting in the room, and many other factors.
Cones are responsible for the color perception in our eyes. Rods help in sharpness of the image. Cones are sensitive to bright light whereas rods are sensitive to dim light.
Myelin gives the white matter its color. It also protects the nerve fibers from injury. It improves the speed and transmission of electrical nerve signals along extensions of the nerve cells called axons.
The human eye and brain together translate light into color. Light receptors within the eye transmit messages to the brain, which produces the familiar sensations of color. Newton observed that color is not inherent in objects. Rather, the surface of an object reflects some colors and absorbs all the others.
As a light wave's length increases, its energy decreases. This means the light waves that make up violets, indigo and blue have higher energy levels than the yellow, orange and red.
Light is made up of different wavelengths, or colors, and white light is a combination of all of them. When a ray of white sunlight hits a patch of beach ball, the paint absorbs most of the wavelengths.It reflects the rest. For example, if the patch is blue, it reflects the blue wavelengths and absorbs all the others.
Light is made up of wavelengths of light, and each wavelength is a particular colour. The colour we see is a result of which wavelengths are reflected back to our eyes. The visible spectrum showing the wavelengths of each of the component colours. The spectrum ranges from dark red at 700 nm to violet at 400 nm.
Coloring activates your frontal lobe, which means that your brain is organizing and problem-solving. Regular coloring sessions allow you to relax from the day and focus on one thing.
“Every colour that people see is actually inside their head … and the stimulus of colour, of course, is light.” As light pours down on us from the sun, or from a lightbulb in our home, objects and surfaces absorb some wavelengths of light and reflect others.
Some theorists argue that an environment rich in the color orange increases the oxygen supply to the brain, stimulating mental activity while simultaneously loosening peoples' inhibitions. An increased oxygen supply also leads to feeling invigorated and getting ready to 'get things done.
These cones have light-sensitive pigments that enable us to recognize color. Found in the macula (the central part of the retina), each cone is sensitive to either red, green or blue light (long, medium or short wavelengths). The cones recognize these lights based on their wavelengths.
The human eye is much more sensitive to yellow-green or similar hues, particularly at night, and now most new emergency vehicles are at least partially painted a vivid yellowish green or white, often retaining some red highlights in the interest of tradition.
The 'colour' of an object is the wavelengths of light that it reflects. This is determined by the arrangement of electrons in the atoms of that substance that will absorb and re-emit photons of particular energies according to complicated quantum laws.
We cannot imagine an entirely new color, animal, plant, or rock. This is because our imagination is based on what we know. As we better understand a topic, we can imagine it more thoroughly. For example, imagine how a car engine works.
“Colour constancy is what the brain does to compensate for different colours of … light shining on objects,” says Hurlbert. “When the light shining on objects changes,” from blue to white, for example, “the light reflected from the objects changes.”
White matter, which lies beneath the gray matter cortex, is composed of millions of bundles of axons (nerve fibers) that connect neurons in different brain regions into functional circuits. The white color derives from the electrical insulation (myelin) that coats axons (see the figure).
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