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The medial frontal cortex is a part of the front of the
brain above the eyes, and is thought to control the pursuit of rewards for
successfully carrying out a task. Scientists at the National Institute for
Health and Medical Research (INSERM) in Paris wondered what happens when a
person is asked to do two jobs at once. To find out, they used functional
magnetic resonance imaging (fMRI) to monitor the brain activity of 16 male
and 16 female volunteers, all aged 19 to 32, and all right-handed, as they
simultaneously performed two related tasks. The volunteers were offered a
monetary reward that reduced if they made errors.
The tasks were to match upper case letters and to match lower case letters,
switching back and forth between the two tasks. Rewards for each task were
calculated separately and depended on the numbers matched without error. The
researchers, neuroscientists Sylvain Charron and Etienne Koechlin, found
that when the volunteers tackled only one task, both halves of the medial
frontal cortex worked on it, but when they tackled both tasks
simultaneously, the left side of the frontal cortex corresponded to one of
the tasks and the right side corresponded to the other, with the two sides
working independently. Results improved as the monetary reward increased,
and there was no significant difference in the results of the men and women
volunteers.
Professor Koechlin said the results suggest the brain could only effectively
handle two tasks simultaneously because it has only two hemispheres. To test
this, the scientists took a further 16 volunteers and added a third task to
the previous two: matching letters of the same color. This group
consistently forgot one of the three jobs, and also made triple the errors
of the dual-tasking subjects. This means that, as Koechlin explained, if you
try to tackle three jobs at once, the frontal cortex will always neglect one
of them.
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