Brain Circuit for Color Perception Identified

Summary: Researchers have identified the specific brain circuits in fruit flies responsible for color perception. These neurons within the optic lobe respond selectively to various hues, including those perceived as violet and ultraviolet by humans.

This groundbreaking discovery provides insight into how brains transform raw sensory signals into meaningful perceptions and could help us better understand the neural mechanisms underlying color vision in other animals, including humans.

Key Facts:

  • Specific neurons in the fruit fly optic lobe respond selectively to different colors.
  • The discovery of these circuits was made possible by the availability of a detailed fruit fly brain connectome.
  • This research sheds light on how brains transform sensory signals into perceptions of the world.

Source: Columbia University

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 published in the journal Nature Neuroscience.

This shows a rainbow colored eye.
Scientists had previously reported finding neurons in animals’ brains that respond selectively to different colors or hues, say, red or green. Credit: Neuroscience News

“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.”

About this color perception and visual neuroscience research news

Author: Ivan Amato
Source: Columbia University
Contact: Ivan Amato – Columbia University
Image: The image is credited to Neuroscience News

Original Research: Open access.
Hue selectivity from recurrent circuitry in Drosophila” by Rudy Behnia et al. Nature Neuroscience


Hue selectivity from recurrent circuitry in Drosophila

In the perception of color, wavelengths of light reflected off objects are transformed into the derived quantities of brightness, saturation and hue.

Neurons responding selectively to hue have been reported in primate cortex, but it is unknown how their narrow tuning in color space is produced by upstream circuit mechanisms.

We report the discovery of neurons in the Drosophila optic lobe with hue-selective properties, which enables circuit-level analysis of color processing.

From our analysis of an electron microscopy volume of a whole Drosophila brain, we construct a connectomics-constrained circuit model that accounts for this hue selectivity.

Our model predicts that recurrent connections in the circuit are critical for generating hue selectivity.

Experiments using genetic manipulations to perturb recurrence in adult flies confirm this prediction.

Our findings reveal a circuit basis for hue selectivity in color vision.

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