Neuronal feedback could change what we 'see'

March 30, 2016 by Jocelyn Duffy, Carnegie Mellon University
Carnegie Mellon neuroscientists believe that neuronal feedback could explain why we see optical illusions, like the Kanizsa triangle. Credit: Carnegie Mellon University

Ever see something that isn't really there? Could your mind be playing tricks on you? The "tricks" might be your brain reacting to feedback between neurons in different parts of the visual system, according to a study published in the Journal of Neuroscience by Carnegie Mellon University Assistant Professor of Biological Sciences Sandra J. Kuhlman and colleagues.

Understanding this feedback system could provide new insight into the 's neuronal circuitry and could have further implications for understanding how the interprets and understands sensory stimuli.

Many make you see something that's not there. Take the Kanizsa triangle: when you place three Pac-Man-like wedges in the right spot, you see a triangle, even though the edges of the triangle aren't drawn.

"We see with both our brain and our eyes. Your brain is making inferences that allow you to see the triangle. It's connecting the dots between the corners of the wedges," said Kuhlman, who is a member of Carnegie Mellon's BrainHub neuroscience initiative and the joint Carnegie Mellon/University of Pittsburgh Center for the Neural Basis of Cognition (CNBC). "Optical illusions illustrate some of the amazing things our visual system can do."

When we look at an object, about what we see travels through circuits of neurons beginning in the retina, through the thalamus and into the brain's . In the visual cortex, the information gets processed in multiple stages and is ultimately sent to the —the area of the brain that makes decisions, including how to respond to a given stimulus.

However, not all information stays on this forward moving path. At the secondary of processing in the visual cortex some neurons reverse course and send information back to the first stage of processing. Researchers at Carnegie Mellon wondered if this feedback could change how the neurons in the visual cortex respond to a stimulus and alter the messages being sent to the prefrontal cortex.

While there has been a good deal of research studying how information moves forward through the visual system, less has been done to study the impact of the information that moves backward. To find out if the information traveling from the secondary stage of processing back to the first stage impacted how information is encoded in the visual system, the researchers needed to quantify the magnitude of information that was being sent from the second stage back to the first stage. Using a mouse model, they recorded normal neuronal firing in the first stage of the visual cortex as the mouse looked at moving patterns that represented edges. They then silenced the neurons in the second stage using modified optogenetic technology. This halted the feedback of information from the second stage back to the first stage, and allowed the researchers to determine how much of the neuronal activity in the first stage of visual processing was the result of feedback.

Twenty percent of the in the visual cortex was the result of feedback, a concept Kuhlman calls reciprocal connectivity. This indicates that some of the information coming from the visual cortex is not a direct response to a visual stimuli, but is a response to how the stimuli was perceived by higher cortical areas.

The feedback, she says, might be what causes our brain to complete the undrawn lines in the Kanizsa triangle. But more importantly, it signifies that studying neuronal feedback is important to our understanding of how the brain works to process stimuli.

"This represents a new way to study visual perception and neural computation. If we want to truly understand the visual pathway, and cortical function in general, we have to understand these reciprocal connection," Kuhlman said.

Explore further: Thalamus found to add contextual information to visual signals

More information: D. E. Pafundo et al. Top-Down-Mediated Facilitation in the Visual Cortex Is Gated by Subcortical Neuromodulation, Journal of Neuroscience (2016). DOI: 10.1523/JNEUROSCI.2909-15.2016

Related Stories

Thalamus found to add contextual information to visual signals

December 23, 2015
The thalamus not only relays visual signals from the eye to the visual cortex as previously thought, but also conveys additional, contextual information. Integrating these different signals is essential to understand and ...

Study helps fill in gaps in our visual perception

January 21, 2016
A Dartmouth College study sheds light on how the brain fills in the gaps of how we visually perceive the world around us.

Study reveals cortical circuits that encode black and white

November 18, 2015
While some things may be 'as simple as black and white,' this has not been the case for the circuits in the brain that make it possible for you to distinguish black from white. The patterns of light and dark that fall on ...

Researchers track how brain routes visual signals

March 11, 2016
Understanding how the brain manages to process the deluge of information about the outside world has been a daunting challenge. In a recent study in the journal Cell Reports, Yale's Michael Higley and Jessica Cardin from ...

Waking up the visual system

October 3, 2014
The ways that neurons in the brain respond to a given stimulus depends on whether an organism is asleep, drowsy, awake, paying careful attention or ignoring the stimulus. However, while the properties of neural circuits in ...

Neuronal activity in the visual cortex controlled by both where the eyes are looking and what they see

September 20, 2013
Even though our eyes are constantly moving, the brain perceives the external world as stationary—a feat achieved by integrating images acquired by the retina with information about the direction of the gaze. An international ...

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.