researchers show how vision relies on patterns of brain activity

August 4, 2016, Salk Institute
Salk scientists show how visual neurons encode temporal dynamic information. It was previously thought that visual neurons encode information by summing the number of action potentials within a static temporal window. This representation is fixed, like a photo of an animal seemingly about to collide with a car, above. The new research shows that neurons are more dynamic, and capture far more information tied to timing, enabling them to reveal critical contextual information (analogous to a short video showing the same animal turning back and avoiding a car collision, below).

Visual prosthetics, or bionic eyes, are soon becoming a reality, as researchers make strides in strategies to reactivate parts of the brain that process visual information in people affected by blindness.

Bursts in a neuron's electrical activity—the number of "spikes" that result when brain cells fire—make up the basic code for perception, according to traditional thought. But neurons constantly speed up and slow down their signals. A new study by Salk Institute scientists shows that being able to see the world relies on not just the number of spikes over a window of time but the timing of those spikes as well.

"In vision, it turns out there's a huge amount of information present in the patterns of neuron activity over time," says Salk Professor John Reynolds, the study's senior investigator and holder of the Fiona and Sanjay Jha Chair in Neuroscience. "Increased computing power and new theoretical advances have now enabled us to begin to explore these patterns." The study was published August 4, 2016 in the journal Neuron.

The human brain houses an extensive network of neurons that are responsible for seeing everything from simple shapes—with certain groups of neurons getting excited by a horizontal or a vertical edge, for example—to intricate stimuli, such as faces or specific places. Reynolds' team focused on a visual brain area called V4, located in the middle of the brain's visual system that recognizes contours. Neurons in V4 are sensitive to the contours that define the boundaries of objects and help us recognize a shape regardless of where it is in space. But Reynolds and postdoctoral researcher Anirvan Nandy discovered in 2013 that V4 was more complicated: some neurons in the area only care about contours within a designated spot in the visual field.

Credit: Salk Institute

Those findings led the team to wonder whether the activity code of V4 could be even more nuanced, taking in visual information not only in space but also in time. "We don't see the world around us as if we are looking at a series of photographs. We live—and see—in real time and our neurons capture that," says Nandy, lead author of the new paper.

The scientists collaborated with Salk theoretician and Monika Jadi to create in computer code what they called an "ideal observer." With access to only the brain data, the computer would decipher—or at least guess—the moving pictures that had been seen. One version of the ideal observer had access to the number of times the fired, whereas the other version had access to the full timing of the spikes. Indeed, the latter observer was able to guess the images more than twice as accurately compared with the more basic observer.

Better ways to record from and stimulate the brain, and better theoretical modeling efforts, have enabled these new findings. Now the group plans to not only observe V4 but to activate it using light through a cutting-edge technique called optogenetics. This, says Reynolds, is like taking the visual system for a spin. It will help them better understand the relationship between patterns of and how the perceives the world, potentially laying the groundwork for more advanced visual prosthetics.

Explore further: Neural connections mapped with unprecedented detail

More information: Neurons in Macaque Area V4 Are Tuned for Complex Spatio-Temporal Patterns, Neuron, dx.doi.org/10.1016/j.neuron.2016.07.026

Related Stories

Neural connections mapped with unprecedented detail

July 4, 2016
A team of neuroscientists at the Champalimaud Centre for the Unknown, in Lisbon, has been able to map single neural connections over long distances in the brain. "These are the first measurements of neural inputs between ...

The eyes are the window into the brain

July 27, 2016
Our eyes are constantly moving, whether we notice or not. They jump from one focus point to another and even when we seem to be focused on one point, the eyes continue to reflexively move. These types of eye movements are ...

Scientists help explain visual system's remarkable ability to recognize complex objects

July 2, 2013
How is it possible for a human eye to figure out letters that are twisted and looped in crazy directions, like those in the little security test internet users are often given on websites?

Scientists find neural match for complexity of visual world

November 5, 2015
The complexity of the neural activity we use to process visual images reflects the intricacy of those images, a team of New York University scientists has found. Their study offers new insights into how our brain extracts ...

Scientists discover the function and connections of three cell types in the brain

December 16, 2015
How the brain functions is still a black box: scientists aren't even sure how many kinds of nerve cells exist in the brain. To know how the brain works, they need to know not only what types of nerve cells exist, but also ...

Zebrafish reveal the ups and downs of vision

June 30, 2016
Researchers from the Centre for Developmental Neurobiology at King's College London have shed light on how we perceive and recognise specific visual stimuli.

Recommended for you

Therapeutic antibodies protected nerve–muscle connections in a mouse model of Lou Gehrig's disease

February 20, 2018
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, causes lethal respiratory paralysis within several years of diagnosis. There are no effective treatments to slow or halt this devastating disease. Mouse ...

Brain immune system is key to recovery from motor neuron degeneration

February 20, 2018
The selective demise of motor neurons is the hallmark of Lou Gehrig's disease, also known as amyotrophic lateral sclerosis (ALS). Yet neurologists have suspected there are other types of brain cells involved in the progression ...

Brain liquefaction after stroke is toxic to surviving brain: study

February 20, 2018
Scientists have known for years that the brain liquefies after a stroke. If cut off from blood and oxygen for a long enough period, a portion of the brain will die, slowly morphing from a hard, rubbery substance into liquid ...

Brain aging may begin earlier than expected

February 20, 2018
Physicists have devised a new method of investigating brain function, opening a new frontier in the diagnoses of neurodegenerative and ageing related diseases.

Every experience that the brain perceives is unique

February 20, 2018
Neuronal activity in the prefrontal cortex represents every experience as "novel." The neurons adapt their activity accordingly, even if the new experience is very similar to a previous one. That is the main finding of a ...

Electrical implant reduces 'invisible' symptoms of man's spinal cord injury

February 19, 2018
An experimental treatment that sends electrical currents through the spinal cord has improved "invisible" yet debilitating side effects for a B.C. man with a spinal cord injury.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.