When multi-tasking, each half of the brain focuses on different goals

By Ed Yong | April 15, 2010 2:00 pm

MultitaskingIn the digital age, many of us are compulsive multi-taskers. As I type this, I’m listening to some gentle music and my laptop has several programs open including Adobe Reader, Word, Firefox and Tweetdeck. I’ve always wondered what goes on in my brain as I flit between these multiple tasks, and I now have some answers thanks to a new study by Parisian scientists Sylvain Charron and Etienne Koechlin.

They have found that the part of our brain that controls out motivation to pursue our goals can divide its attention between two tasks. The left half devotes itself to one task and the right half to the other. This division of labour allows us to multi-task, but it also puts an upper limit on our abilities.

Koechlin has previously suggested that the frontopolar cortex, an area at the very front of our brains, drives our ability to do more than one thing at a time. It allows us to simultaneously pursue two different goals, holding one in the ready while we work on the other. Just behind the frontopolar cortex lies the medial frontal cortex (MFC), an area that’s involved in motivation. It drives our pursuit of multiple goals, according to the rewards we expect from them. Koechlin wanted to understand how these two areas cope with multi-tasking.

To do that, he used a brain-scanning technique called functional magnetic resonance imaging (fMRI) to study the brain activity of 32 volunteers, as they carried out a challenging task. They saw a steady stream of letters, all from the word “tablet”. For every block of three letters, they had to say if the first one was a “t” and if the other two appeared in the same order that they would in “tablet” (e.g. TAB rather than TEB). If the letters were red, they would get a sizeable cash reward but if they were green, the reward would be smaller.

Based on this same set-up, they had to cope with two slightly different tests. In the “branching” tests, they had to deal with two separate streams of triplets, a primary one indicated by normal letters and a secondary one indicated by italics. The primary stream was continuous and the volunteers had to revert back to it every time they finished a secondary triplet. They had to hold the primary stream in mind so that they could return to it after their interruption. In the simpler “switching” tests, they started afresh with every new triplet, so they only had to cope with a single stream of information.

Multitasking-experimentCharron and Koechlin found that in the switching tests, when the volunteers were only faced with a single task, both halves of their MFC were active, particularly the dorsal anterior cingulated cortex (dACC) and the presupplementary motor area (PMA). The more money was at stake, the stronger the activity in these regions.

In the branching tests, both halves of the MFC were also active, but they were split between the two tasks. The right dACC took control of the secondary task; when the volunteers could earn more money from these triplets, only the right dACC became more active. The left half took control of the primary task; its activity matched the rewards associated with the primary triplets but not the secondary ones.

The frontopolar part of the brain also became active during the branching tests, which fits with its established role in multi-tasking. However, its attentions weren’t divided by the two tasks and it only became more active when both the primary and secondary rewards were higher. This suggests that the frontopolar cortex plays the role of coordinator. While each half of the MFC encodes the incentives of pursuing each separate goal, the frontopolar cortex encodes the incentives of pursuing both goals together.

It also suggests that we might not be able to cope with more than two tasks at the same time. Charron and Koechlin tested this with an even more fiendish “double branching” test, where the two streams of triplets in their original experiment were interrupted by a third stream. To succeed in this task, they had to retain three separate lanes of information at the same time. They couldn’t. When they tried to return to the first stream from the second, or the second from the third, their answers were no better than guesswork.

Despite what some psychologists have suggested, it seems that the human brain is capable of multi-tasking although to a far lesser extent than a computer can. While my laptop is running several different programs at once with nary a hint of discomfort, Charron and Koechkin’s work suggests that my brain can’t handle any more than two tasks at once.

Reference: Science http://dx.doi.org/10.1126/science.1183614

More on multi-tasking: Information overload? Heavy multimedia users are more easily distracted by irrelevant information


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Comments (13)

  1. dearieme

    You may find that, as you age, you become less tolerant of music while you are trying to work. Source: introspection.

  2. Ersen Alp

    By quantifying the responses of frontopolar cortex in terms of switching multitask goals and actions, real IQ levels of individuals can be predicted materialistically.

  3. SpaceManSpiff

    This would explain why listening to instrumental music can help me concentrate on a task: it safely occupies the secondary slot, preventing something that could become truly distracting from gaining my attention. It’s would also explain why the music can’t have recognizable lyrics — processing the language of a song would be a third task, which would compete with the primary task for mental space.

  4. david

    I wonder what happens if the speed of the neurological feedback between the two halves varies by multiples in an individual. My experience shows that multi-tasking is more complicated than binary and depends on the type of tasks. Some tree branches appear binary but some not at all. Binary is the default program. And for a person to go beyond two to say five or six takes practice, a great familiarity with what you are doing. I have in mind jury trial practice and other things. Those five or six could still possibly be relegated and trained to switch within two somehow. In types of tasks, is emoting a task? Seems in my experience it is in the middle, and in control. I would go so far as to say if one is going to learn a difficult task, or more than one, it must be connected with emotion, the beginning point. Nice thought, nice people, but the assumption that the test subjects are representative of all needs only one exception to change the conclusion, which the scientists are certain to be aware of.

  5. NPR reported a story that challenges the idea we can multi-task while driving. They had a concert pianist come in to the studio and play mundane pieces while they asked questions. As the questions became more complex (i.e. math that required subtraction), the ‘memory ‘ in his fingers began to falter. To see the story go to http://www.npr.org/templates/story/story.php?storyId=95702512

    The ultimate conclusion for me was that my teen almost-driver needs to listen to this story (not while driving) and understand fully what she is asking her brain to process if she does anything else but concentrate on the road. Fortunately, she usually can’t even FIND the phone in her backpack, so I can relax a little bit.

    My parents always said I could grow up to be a “jack of all trades, master of none”, but I didn’t think it would actually be a job requirement for my children.

  6. Gingerbaker

    They need to test some drummers. There are some extremely skilled drummers who have trained themselves to perform four completely independent rhythms using both feet and both hands simultaneously. Some can even sing a bit while doing this. It’s like they don’t have a corpus callosum.

    The “upper limit”, with training, might be a bit higher than this set of experiments suggests.

  7. dearieme

    Let’s not forget the old description: “a jazz band consists of six musicians and a drummer”.

  8. Briana

    The tasks the participants engaged in were not only new but required active attention, and so the definition of “no more than two at a time” may only apply to that. This article makes it sound like they were trying to apply this as a general rule.

    The piano study is stronger for the lack of ability to multitask during a habitual activity. Have there been any studies on doing several habitual activities at once, where it is “safe” to multi-task because they require less processing each? I’m sure you could do more than two, considering I can watch mindless TV, paint, pet a cat, and drink coffee at the same time without any apparent problems aside from having only two hands (but with straws there are ways around that).

  9. Jo Lynn

    What Gingerbaker (Are you sitting in a white room with no curtains?) says about drummers is true, and on the piano one uses two hands and often a foot. There are many areas of intelligences and what he is describing would be spatial intelligence. The test in the article relied on visual discrimination. Each person’s brain and physiology is so unique that one can generalize and that’s about it. Plus, what if one of the test subjects had a learning disability related to letter recognition? There are so many factors that could influence a person’s performance. Each person has strengths in different areas. From what I see with younger people today (I’m a teacher and parent) many young people are far more adept at multitasking than people in my generation because they grew up with so much stimuli. Dr. Andrew Weil was writing about stimulation from a health perspective and suggested that perhaps the stress modern people experience is partially from over stimulation. Meditation has been practiced for so long that perhaps we only think of it as modern stress.

  10. As a guitar-playing singer I am thinking about the chord I am playing, the rhythm I am stumming, the words I am singing, the pitch I am singing each syllable at, the chord coming up, perhaps the next section coming up, guaging the reaction of the audience, and, most importantly, trying to use as much of my brainspace that is left over to… …listen to it all – for critical feedback of my own playing and singing and to know what the other musicians are doing, but, even more importantly, for enjoyment. In other words, I believe the brain can do a lot more than this study suggests.

  11. I see a number of issues with this study that make me skeptical:

    – This is not multi-tasking as much as it’s a working memory task(s) with reward and interference thrown in

    – fMRI is not precise enough to extract these kinds of precise conclusions — was the splitting related to “multi-tasking”? Strategies for dealing with the kind of interference? A lot of things are going on in the brain when fMRI is being recorded and averaging over all that is not necessarily meaningful to the hypothesis

    – It may well be nothing more than a practice issue, as others have identified. Other research has shown that people can be trained to do 4 things at once — true multi-tasking — and do them better than when concentrating on them, as long as it’s become automatic (like drumming 😉 But they do have to be trained on all of them. Working memory practice software also shows that people can improve their working memory significantly with practice.

    PLEASE don’t conclude “my brain can’t handle any more than two tasks at once.” That’s completely inaccurate as your brain is ALWAYS doing more than one thing. It’s only your conscious awareness that’s limited by its input and output streams.

  12. When most people refer to multitasking they mean simultaneously performing two or more things that require mental effort and attention. When we speak of multitasking, what we really mean is that we are switchtasking: switching rapidly between one task and another. Yet, each time we switch, no matter how quickly that switch takes place in our mind, there is a cost associated with it. It’s an economic term called switching cost—and the switching cost is high.

  13. Ms. Bellcourt loves to dance


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