A noise, a presence, a telephone ringing…, how does the brain make a selection between what deserves to be interested in it and what should be ignored? A team of researchers located, visualized and timed this selective sorting system using intracranial recordings.
Staying focused is an eminently complex process because the brain is constantly disturbed by stimulation, noise, presence, image, call… Staying attentive therefore requires constantly sorting out this multitude of stimuli to focus only on the most relevant information for the current task. How the brain make this sorting out between what deserves to stop there and what should be ignored? This is the question posed by the team of Jean-Philippe Lachaux, unit 1028 Inserm/CNRS/Claude Bernard University/Jean Monnet University, Lyon Neuroscience Research Center, team DYCOGLyon, in collaboration with that of Marcela Perrone, Psychology and Neurocognition Laboratory (UMR 5105 CNRS/Grenoble Alpes University).
The localized selective sorting system
To locate and characterize this evaluation mechanism, Researchers used intracerebral recordings by electrodes implanted in 85 patients epileptic. ” We knew thanks to previous work that an area of the prefrontal cortex is specialized in keeping in memory what we are trying to do: our current intention. It is she who allows you to complete a job or a discussion started a few moments earlier. We assumed that the system selective sorting stimulations, which directly influences this function, had to be localized nearby. However, about fifty electrodes were implanted in the prefrontal cortex of each patient, which allowed us to analyze the neural signals in this particular region at the scale of milliseconds”explains Jean-Philippe Lachaux.
The brain decides in less than a quarter of a second
To study this sorting system, the researchers asked participants to read a text displayed as successive words in gray on a screen, interspersed with others in white unrelated to the story. This forced individuals to focus only on the gray terms to understand the meaning of the text. ” With each new word, there was decision-making according to the color : read it or not. Thanks to this exercise we were able to search for an area of the prefrontal cortex who reacted whenever a new word appeared on the screen. And we found it. A signal was systematically lit 200 ms after the display of the word and just before the dissociation between reading or not reading the word. And this at a single place, identical in all participants and in the immediate vicinity of the region of the intention of the moment as suspecteddescribes 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 or in other words, our attentional system makes several decisions per second. So many opportunities to take the wrong one and get distracted by unimportant content! ».
By revealing for the first time the location and operation of this sorting mechanism in the human brain, researchers are opening up the carries to new avenues of research. ” This region of the brain could very well be involved in the attentional problems observed in certain individuals. It will also be possible to model the attentional system to learn how to measure a person’s level of attention from an electrical recording on the surface of the brain.”concludes Jean-Philippe Lachaux.
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