"The results of this study suggest that the anterior prefrontal cortex, the area of the brain that is most developed in humans, mediates the ability to depart temporarily from a main task in order to explore alternative tasks before returning to the main task at the departed point," says Jordan Grafman, Ph.D., Chief of the Cognitive Neuroscience Section at the NINDS and a co-author of the study.

"We believe that this finding is important because branching processes appear to play a key role in human cognition," says Etienne Koechlin, Ph.D., also of the NINDS Cognitive Neuroscience Section and a co-author of the study. "In everyday life, we often need to interrupt an ongoing task to respond to external events and we all experience how demanding it is to react to these events while keeping our minds on the original task."

According to previous studies, humans may be the only species capable of performing branching, which involves keeping a goal in mind over time (working memory) while at the same time being able to change focus among tasks (attentional resource allocation). For example, people who are interrupted by a phone call while reading must be able to keep in mind the memory of what they were reading just before talking on the phone. Once the phone call is over, they should be able to return to the last sentence read and continue reading.

The investigators used functional magnetic resonance imaging (fMRI), which measures changes in blood flow to the brain, to view the brains of volunteers while they performed branching tasks. When a particular part of the brain is being used, there is an increase in blood flow to that area. The increase in blood flow means that there is an increase in the amount of oxygen-carrying hemoglobin in the blood. fMRI can measure the presence (or absence) of oxygenated hemoglobin and use that information to create an image of the brain at work on a screen. The image of the brain shows activation in the areas receiving increased blood flow. The region of the brain that is involved in multitasking is called the fronto-polar prefrontal cortex (FPPC).

Tasks performed by the volunteers involved exercises to test working memory, attentional focus, and a combination of the two. All of the subjects, who were healthy, normal volunteers, participated in all of the task groups. The task groups consisted of a control task, a delayed-response task, a dual-task, and a branching conditions task. Dual-task involves changing focus between alternative goals successively. The investigators predicted that subject performance on the individual delayed-response task and dual-task conditions would not activate the FPPC. They did predict that the branching task which involves problem solving and planning would stimulate activity in the FPPC. According to the fMRI data, their predictions were correct. The FPPC was activated only during those tasks that involved an interaction between working memory and attentional focus decisions.

The FPPC is the region of the brain that controls complex problem solving and is especially well developed in humans as compared to other primates. The study showed that the FPPC selectively mediates the human ability to multi-task.

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