How does our brain sort information to stay focused?

A noise, a presence, a ringing telephone …, how does the brain make a selection between what deserves attention and what should be ignored? A team of researchers located, visualized and timed this selective sorting system using intracranial recordings.

Staying focused is an extremely complex process because the brain is constantly disturbed by stimulation, a noise, a presence, an image, a call … Staying attentive therefore requires constantly sorting out this multitude of stimuli to focus only on the information most relevant to the task at hand. How the brain does this sort between what deserves to stop there and what should be ignored? This is the question posed by Jean-Philippe Lachaux's team, unit 1028 Inserm / CNRS / Claude Bernard University / Jean Monnet University, Lyon Neuroscience Research Center, team DYCOG, Lyon, in collaboration with that of Marcela Perrone, Laboratory of Psychology and Neurocognition (UMR 5105 CNRS / Université Grenoble Alpes).

The localized selective sorting system

To locate and characterize this evaluation mechanism, Researchers used intracerebral recordings by electrodes implanted in 85 patients epileptics. " We knew from previous work that an area of ​​the prefrontal cortex is specialized in keeping in memory what we are trying to do: our intention of the moment. It is this which allows to complete a work or a discussion started a few moments earlier. We have assumed that the system of sorting stimulation, which directly influences this function, had to be located nearby. However, around fifty electrodes were implanted in the prefrontal cortex of each patient, this allowed us to analyze the neural signals in this particular region on a millisecond scale ”, explains Jean-Philippe Lachaux.

To study this sorting system, the researchers asked the participants to read a text displayed in the form of successive words in gray on a screen, interspersed with others in white unrelated to the story. This forced people to focus only on gray terms to understand the meaning of the text. " With each new word, there was a decision-making according to the color : read it or not. Thanks to this exercise we were able to find an area of ​​the prefrontal cortex which reacted each time a new word appeared on the screen. And we found it. A signal was systematically lit 200 ms after the word was displayed and just before the dissociation between reading or not the word. And this in one place, identical for all participants and in the immediate vicinity of the region of the intention of the moment as suspected, describes Jean-Philippe Lachaux. This means that the brain decides in less than a quarter of a second whether the object or the image it has under the eyes worth paying attention to it or in other words our attention system makes multiple decisions per second. So many opportunities to take the wrong one and get distracted by irrelevant content! ".

By revealing for the first time the location and functioning of this sorting mechanism in the human brain, researchers are opening up the door to new lines of research. " This region of the brain could well be involved in the attention problems observed in certain individuals. It will also be possible to model the attention system to learn how to measure a person's attention level from an electrical recording on the surface of the brain. ”, concludes Jean-Philippe Lachaux.

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