2010-Жов-22, П'ятниця

Paris, 15 April 2010; Press information
How does the brain manage to integrate the different goals that we set ourselves? Where about in the brain is this information "processed"? How many simultaneous goals is the brain capable of registering? These are some of the many questions that researchers in the neurosciences have been trying to answer for a number of years. In a study which appeared this week in the journal Science, scientists from Inserm and the Ecole normale supérieure, Sylvain Charron and Etienne Koechlin, show that when a person sets two simultaneous goals, each of them is represented in a different hemisphere of the brain. However, the human brain seems unable to coordinate more than two goals. Man possesses a brain with two frontal lobes and these are significantly more developed than for other species of animal. It is known that the frontal lobes facilitate the capacity of an individual to act according to his own goals and reasons, thus equipping him with the capacity of autonomy, adaptation and remarkable mental flexibility. Frontal lobe function is however very fragile and is altered in the majority of the major neuropsychiatric disorders such as schizophrenia, autism, depression or dementias.
By using functional Magnetic Resonance Imaging on human subjects, Etienne Koechlin and Sylvain Charron observed that, when individuals were following a single goal – for example by pairing letters appearing successively on a screen in order to obtain a reward –, this task was coded, according to the expected reward, in two symmetric regions of the left and right medial frontal lobes simultaneously. By contrast, when the subjects were pursuing two tasks at the same time – for example pairing capital letters on the one hand and small letters on the other –, the two frontal lobes "distributed the work". The left region codes the rewards driving one task while the right region codes those associated with the other task. This all occurs as if each frontal lobe was pursuing its own goal!
How does the human brain coordinate the pursuit of goals which belong to different frontal lobes? The researchers have shown that the most anterior prefrontal regions, situated just behind the forehead, deal with coordinating the execution of these objectives. Hence, it is within these regions that the integrity of the will of the subject is ensured and the coherence of the associated behaviours.
Image credit : Etienne Koechlin, Inserm-ENS, Paris; France 2010

When a person pursues two independent goals A and B (Goal A/ Goal B), the two frontal lobes are activated and are the concurrent sites for the representation of these two goals and their associated actions (Action A/ Action B). The prefrontal regions (in orange), situated just behind the forehead, ensure coordination between the two goals (Goal switch), by dealing with the "processing" of one goal while the second is suspended. This "interhemispheric" division of work explains why the human species seems incapable of carrying out more than two tasks at the same time.

The researchers then deduced from their results than the human frontal function must be
incapable of managing more than two goals at the same time: beyond these, any additional goal must escape the control of the two frontal lobes. The researchers investigated this hypothesis by analysing the behaviour of subjects in an experiment which required them to pursue three goals at the same time: independently pairing letters of three different colours. They demonstrated that the reaction times and the errors committed by the subjects did indeed reflect an incapacity to pursue more than two goals at the same time, regardless of the difficulty of carrying out these tasks.
These results reveal a fundamental neurological component of human intentionality, its potential and its limits. They may well, now, be able to clarify and better target the causes of certain behavioural and mental functions observed in a number of neuropsychiatric human disorders. « The dual nature of the frontal function may explain many limitations in our capacity to reason, make decisions and adapt", explains Etienne Koechlin.

Sources: “Divided representation of concurrent goals in the human frontal lobes”; Sylvain Charron 1,2 and Etienne Koechlin 1,3,4; 1 Institut National de la Santé et de la Recherche Médicale U879, Bron, F-75654, France; 2 Ecole Polytechnique, Palaiseau, France.; 3 Ecole Normale Supérieure, Paris F-75230, Cedex 05, France.;4 CENIR, Université Pierre et Marie Curie, Paris, F-75651 Cedex 13, France.; Science, vol 328, 16 April 2010
Research contact: Etienne Koechlin; Inserm Research Director; Inserm Unit 960 "Laboratoire de Neurosciences Cognitives"; Ecole Normale Supérieure; Tel :++ (33) 1 44 32 26 40; E-mail: etienne.koechlin@upmc.fr
Posted Wednesday, July 15, 2009 — 12:35 PM

Training increases brain processing speed and improves our ability to multitask, new research from Vanderbilt University published in the June 15 issue of Neuron indicates.
“We found that a key limitation to efficient multitasking is the speed with which our prefrontal cortex processes information, and that this speed can be drastically increased through training and practice,” Paul E. Dux, a former research fellow at Vanderbilt, and now a faculty member at the University of Queensland in Brisbane, Australia, and co-author of the study, said. “Specifically, we found that with training, the ‘thinking’ regions of our brain become very fast at doing each task, thereby quickly freeing them up to take on other tasks.”
To understand what was occurring in the brain when multitasking efficiency improved, the researchers trained seven people daily for two weeks on two simple tasks — selecting an appropriate finger response to different images, and selecting an appropriate vocal response (syllables) to the presentation of different sounds. The tasks were done either separately or together (multitasking situation). Scans of the individuals’ brains were conducted three times over the two weeks using functional magnetic resonance imaging (fMRI) while they were performing the tasks.
Before practice, the participants showed strong dual-task interference—slowing down of one or both tasks when they attempted to perform them together. As a result of practice and training, however, the individuals became very quick not only at doing each of the two tasks separately, but also at doing them together. In other words, they became very efficient multitaskers.
The fMRI data indicate that these gains were the result of information being processed more quickly and efficiently through the prefrontal cortex.
“Our results imply that the fundamental reason we are lousy multitaskers is because our brains process each task slowly, creating a bottleneck at the central stage of decision making,” René Marois, associate professor of psychology at Vanderbilt University and co-author of the study, said. “Practice enables our brain to process each task more quickly through this bottleneck, speeding up performance overall.”
The researchers also found the subjects, while appearing to multitask simultaneously, were not actually doing so.
“Our findings also suggest that, even after extensive practice, our brain does not really do two tasks at once,” Dux said. “It is still processing one task at a time, but it does it so fast it gives us the illusion we are doing two tasks simultaneously.”
The researchers noted that though their results showed increased efficiency in the posterior prefrontal cortex, this effect and multitasking itself are likely not supported solely by this brain area.
“It is conceivable, for example, that more anterior regions of prefrontal cortex become involved as tasks become more abstract and require greater levels of cognitive control,” Marois said.
Dux completed this study while conducting post-doctoral research at Vanderbilt. Michael Tombu, Stephenie Harrison and Frank Tong, all of the Department of Psychology at Vanderbilt, and Baxter Rodgers of the Vanderbilt University Institute of Imaging Science and Department of Radiology and Radiological Sciences also co-authored the study. Marois, Tombu, Harrison and Tong are members of the Vanderbilt Vision Research Center and the Vanderbilt Center for Integrative and Cognitive Neurosciences.
The research was funded by the National Institute of Mental Health.
Media contact: Melanie Moran, (615) 322-NEWS


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