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

In 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.