Are 2 Tasks the Limit of Multitasking?

Study Shows the Brain May Be Able to Do 2 Demanding Tasks at Once

By Denise Mann
WebMD Health News

Reviewed By Laura J. Martin, MD

April 15, 2010 -- Multitasking may seem like the only way to get ahead in today's fast-paced, 24/7 society, but new research shows that we can really only handle two complicated tasks at a time. The findings appear online in the April 15 issue of the journal Science.

Sylvain Charron, PhD, and Etienne Koechlin, PhD, of Institut National de la Santé et de la Recherche Médicale in Paris, used functional magnetic resonance imaging to monitor changes in the brains of 31 volunteers who completed one complex task at a time, and then again when they completed two tasks simultaneously. The tasks involved letter sequencing.

When the volunteers completed one task, sections of the frontal cortex on both sides of the brain lit up. However, when they were asked to temporarily stop one task and start another, the activity in the regions on the left lobe corresponded to the first task and the activity on the right lobe corresponded to the second task. This suggests that when we try to do two complex things at once, our brain divides, with each half devoting itself to one task. When researchers introduced a third task to their experiment, participants made even more errors.

As a result of these findings, we are "limited to driving the pursuit of two concurrent goals simultaneously," the researchers write.

Don't Text and Drive

"This was a fairly demanding task," points out Mark Mapstone, PhD, an assistant professor of cognitive behavioral neurology at the University of Rochester School of Medicine and Dentistry in Rochester, N.Y.

"A lot of things that we do during the day don't demand that much," he says. For example, "walking and chewing gum is not cognitively demanding."

That said, the findings "suggest that there are limitations and we can't handle an infinite number of things at once," he says. "It is not a good idea to drive and talk on cell phone at the same time."

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SOURCES: Charron, S. Science, April 15, 2010.

Mark Mapstone, PhD, assistant professor of cognitive behavioral neurology, University of Rochester School of Medicine and Dentistry, Rochester, N.Y.

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