Colour

The Neuroscience of Colour Perception

Introduction

Neuroscience is a rapidly-advancing field which concerns the sciences that deal with the structure or function of our nervous system and brain. New discoveries about how we live, what decision-making capabilities we have, and why we are unique are made every day by scientists. Therefore, it is often difficult to explain all the most significant neuroscientific discoveries, as they keep on changing! However, this article will go over basic neuroscience and specifically how the brain perceives color.

Fundamental Concepts of Neuroscience

It is important to appreciate some of the brain’s most fundamental concepts in order to fully grasp its specific processes. Starting with the brain itself, there are around 90 billion neurons (nerve cells which function to communicate information); however, we do not use all of them at once. Neurons work based on electrical principles in order to send electrical signals from wherever the body receives them, to the brain, and then back to the part of the body affected in order to produce an output reaction. According to the University of California at Santa Barbara, nerves can send signals to the brain at a rate of 115,197 feet/second (3560 meters/second) [1]! The function of our body’s nervous system is to keep our body in harmony with our other body systems, such as the immune or cardiovascular system.

Our neurons are specialized cells for the nervous system. Their function is to make sure messages are sent and received to and from the body and its brain. This signaling pathway is much more in-depth, however, the main idea is the body receives an “input” such as your finger touching a pin, which then causes an electrical signal to travel from your sensory neurons via interneurons in order to get to the brain. When the signal reaches the brain, it is then redirected to a specific lobe or part of the brain designated for interpreting the initial input in order to make a decision. Then, an electrical signal carrying the message is sent from the brain’s neurons via interneurons to the part of the skin containing motor neurons, which then results in an “output” action taking place. This is why if your finger touches the head of a bobby pin, you almost immediately retract your finger away.

One of the key concepts of neuron function is the action-potential. In order for the message to be sent to the other neuron, the action potential created must transform to a chemical signal which then crosses the gap between the neurons, referred to as the synapse. After the message crosses the synaptic gap, it is received by dendrites on the next neuron, which then carries the message through the cell body, then to the axon, and then the axon terminal till the synaptic gap is reached again. A key concept responsible for the astronomically fast rate at which electrical signals can travel in between neurons is the fatty myelin sheath wrapping the axon. This sheath allows the signal to skip the grooves on the parts of an axon tail in order to travel faster. With every message that is sent, the synapse gets stronger.

Credit to MIT News

Image of a Neural Network

In your nervous system, there are 3 main types of circuits interconnecting it. This consists of sensory, motor, and simple circuits. The purpose of sensory circuits is to keep your brain connected to your body’s sensory neurons and send information between your sensory receptors to your brain. The purpose of your motor circuits is to execute the “output” by utilizing your muscles, such as removing your hand when you accidentally rest it on a hot stove. The purpose of your simple circuits is to execute automatic reflexes.

General Introduction to the Brain’s Senses

The body’s senses are its way of helping us understand the world around us. Without our senses, we would not be able to comprehend basic events such as the weather outside, what our food smells like, or what our pencil looks like. It is important to recognize that the world itself does not actually contain smells or images; however, our brain helps us to interpret these atoms and molecules that make up nature and translate it into things we can perceive. Though pathways for taste, smell, sound, touch, and vision do have some significant differences with regards to specific cells or anatomy involved, one basic idea does remain concurrent – once a stimulus is recognized by the sensory organs in our body (such as the nose), an electrical signal is generated and travels through many cells and other neurons via transduction in order to reach the specialized area of the brain designed for interpreting it. The brain is as compartmentalized as a basic cell is, making it convenient for our body to observe parts of nature and make sense of them quickly and effectively.

Vision (Introduction)

Recently, a team of neuroscientists from the Massachusetts Institute of Technology (MIT) discovered that human’s brains can process images seen through our eyes in as little as 13 milliseconds [2] To help emphasize the complexity of the visual pathway, here are some quick facts about the eyes and brain [3]-

  1. Human’s eyes can distinguish around 10 million different colors
  2. Human eyes can detect a single flame from a candle from 1.7 miles (2,736 meters) away
  3. The iris of your eye contains 256 characteristics unique to you, compared to 40 from your fingerprint
  4. The eye is made up of rods (used to see and recognize shapes) and cones (used to detect and understand colors)
  5. The fastest contracting muscle in your body is the eye, contracting in less than 1/100th of a second
  6. The optic nerve contains more than 1 million nerve cells

As observed by reading the above, it is simple to see how intricate and purposeful everything in our visual pathway is. Now, onto the actual processes that allow our brain to see and make sense of everything we observe.

Vision (Anatomy & Overview)

In order for our brain to understand and comprehend information received through our eyes, the cerebral cortex in our brain must be utilized. The cerebral cortex is densely populated with neuron circuits as mentioned before and divided into 4 main lobes. Briefly, it is responsible for “processing and interpreting input from various sources and maintaining cognitive function. Sensory functions interpreted by the cerebral cortex include hearing, touch, and vision. Cognitive functions include thinking, perceiving, and understanding language. [4]”

In order to understand the brain’s visual pathway, it is crucial to comprehend some basic anatomy. When a light is shone into your eye, the light passes through the cornea, finds an entrance in your pupil, and is then regulated by the iris in order to effectively manage the amount of light allowed to enter the eye (this is done by changing the pupil’s size). Next, your eye’s lens allows the light to focus on the retina. In the brain, when objects are seen on the left from your eyes, their image is projected onto the opposite right side and vice versa.This completes the projecting aspect, however, to fully make sense of an image, the signal must then travel via optic nerves to other highly specialized parts of the brain in order to comprehend what one is seeing. [5].

The retina contains photoreceptors, interneurons, and ganglion cells in order to function. When light enters the cornea and the lens, it then passes through the ganglion cells and interneurons before finally reaching the photoreceptors. The functions of the interneurons and ganglion cells (both are not sensitive to light) is mainly to transmit the light information to the photoreceptors and vice versa. The light-sensitive photoreceptors, the rods and cones, however, do have unique purposes. Rods allow you to see extremely sensitive things such as objects in dim lights, while cones are responsible for finer details and color.The cones the human eye contains are responsible for seeing shades of red, green, or blue [5].

At the center of the retina, the fovea is contained. In this area, the most cones are packed making it extremely sensitive to fine details other parts of the eye cannot recognize.

Credit to https://boozmanhof.com/diagram-of-the-eye/

Image is a simple diagram of the human eye

How is Vision Processed?

The brain’s visual pathway is very complex, however, it is extremely logical. Any time you are at a table or looking at something, you are utilizing the rods and cones in your eye to recognize shapes and colors. This brain’s visual process begins by light hitting a specific area of the ganglion cells’ activation area. If light hits the area surrounding the activation region, it is inhibited. However, if light manages to pass through and affect the entire activation region, the ganglion cell responds weakly. This process of distinguishing light levels is one of the first methods our visual pathways can utilize the concept of contrast in order to fully comprehend and display an image correctly [5].

After this takes place, optic nerves located in the visual pathway communicate neural signals from the ganglion cells to the back of the brain where no photoreceptors are. The lack of photoreceptors in this area is what is referred to as our “blind-spots” in the eyes. Though the human brain does try to fill in this empty spot with some information, it is still not completely accurate, as the information is coming from our other eye. At the optic chiasm, the signals from the eyes along to the brain cross over to reach their respective sides of the brain. The signal then continues towards the left/right sides of the brain in order to finally reach the primary visual cortex in the back of your head to make sense of the image [5].

Credit to [5]

Image of the Brain’s Visual Pathway

Now that the image can be processed, the rods and cones in your brain can effectively work together in order to help you perceive color. The visual pathway is one of the most complex projects constantly taking place in your brain. After understanding the steps needed for your brain to almost instantly recognize images as you read this article, hopefully you have gained a new appreciation for the greatest supercomputer, the human brain!

References

  1. http://scienceline.ucsb.edu/getkey.php?key=1950
  2. https://news.mit.edu/2014/in-the-blink-of-an-eye-0116
  3. https://versanthealth.com/blog/15-facts-about-all-things-eyes/
  4. https://www.thoughtco.com/cerebral-cortex-lobes-anatomy-373197
  5. https://www.brainfacts.org/

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