How Extraneous Neural Background Noise Interrupts Focused Attention

Scientists have long theorized that attention to a particular object can alter perception by amplifying certain neuronal activity and suppressing the activity of other neurons (brain “noise”).

Now, researchers from the Salk Institute have confirmed this theory by showing how too much background noise from neurons can interrupt focused attention and cause the brain to struggle to perceive objects. The findings could help improve designs for visual prosthetics.

“This study informs us about how information is encoded in the electrical circuits in the brain. When a stimulus appears before us, this activates a population of neurons that are selective for that stimulus. Layered on top of that stimulus-evoked response are large, low-frequency fluctuations in neural activity,”

says Salk Professor and senior author John Reynolds.

Visual Stimulus Orientation

Previous work from Reynolds’ laboratory found that when attention is directed to the stimulus, these low-frequency fluctuations are suppressed. Theoretical models of neural information processing suggested that such fluctuations should impair perception and that attention improves perception by filtering these fluctuations out.

To test this idea directly, the researchers turned to a cutting-edge technology called optogenetics, a technique that can affect the activity of neurons by shining lasers onto light-activated proteins. The team used a low-frequency laser stimulation protocol directed at a visual brain region in animals to create low-frequency response fluctuations—the very neural fluctuations that attention suppresses.

Surface Optogenetics and electrophysiology through an artificial dura.
Surface Optogenetics and electrophysiology through an artificial dura.
Credit: Anirvan Nandy et al, CC-BY

They measured the impact of this on the animal’s ability to detect a small change in the orientation of a visual stimulus presented on a computer screen.

Induced Low-frequency Correlations

As predicted by the theory, the added noise impaired perception.

Then, they repeated the experiment, but using a different laser protocol to induce fluctuations over a high-frequency range that attention does not suppress. Consistent with the theory, this had no impact on perception.

“This is the first time this theoretical idea that increased background noise can hurt perception has been tested. We’ve confirmed that attention does operate largely by suppressing this coordinated neuron firing activity,”

says first and corresponding author Anirvan Nandy, assistant professor at the Yale University School of Medicine and former Salk researcher.

“This work opens a window into the neural code, and will become part of our understanding of the neural mechanisms underlying perception. A deeper understanding of the neural language of perception will be critical in building visual prosthetics,”

adds Reynolds.

Next, the scientists plan to examine the different types of cells that make up the visual circuit in the brain in order to better understand the neurological underpinnings of attention and perception.

Anirvan Nandy, Jonathan J Nassi, Monika P Jadi, John Reynolds
Optogenetically induced low-frequency correlations impair perception
eLife 2019;8:e35123 DOI: 10.7554/eLife.35123

Top Image: Anirvan Nandy et al, CC-BY