Just Do It?

21 August 2007 (All day)

There's one more doughnut in the box. Do you reach for it or not? The answer may depend on a brain region just behind your eyes called the dorsal frontomedial cortex. New experiments point to it, and two smaller regions, as the sources of our self-control.

The question of free will--whether and how we consciously control our actions--has puzzled philosophers for centuries. Twenty-five years ago, the question got a bit stranger when psychologists found that electrical signals in the brain that direct movement of a finger or limb occur about a half a second before a person is aware of making a decision to move. In other words, our brains seem to make decisions before we are consciously aware of doing so.

That result raised the question of why we should be aware of our actions at all. If our conscious minds don't control our actions, why did consciousness evolve? Benjamin Libet, a psychologist at the University of California, San Francisco, who did the original experiments, suggested that perhaps our conscious mind has the ability to veto actions--to stop ourselves from doing things that our brains have sent a message to do.

Psychologists Marcel Brass of Ghent University in Belgium and Patrick Haggard of University College London attempted to measure what happens in the brain when we stop ourselves from doing something. They had subjects press a button some time during a 10-second period. In some of the trials, they asked the participants to decide to press the button but then stop themselves at the last moment. The subjects performed the experiment in a magnetic resonance imaging (MRI) machine, so that the scientists could watch blood flow to different parts of the brain.

As the researchers report in today's Journal of Neuroscience, when the subjects stopped themselves from pushing the button, blood flow increased to the dorsal frontomedial cortex and two smaller regions, indicating that they were active. Those regions were quiet during trials in which subjects actually pushed the button. These brain areas may be the source of our ability to stop ourselves from doing things, the researchers say. The insight might lead to a better understanding of conditions such as attention deficit disorder that involve impulsivity and a lack of self-control.

Neuroscientist Richard Passingham of the University of Oxford in the U.K. says that the work provides a clue to the brain's ability to veto an action. The area the researchers identified has been fingered in other studies as playing a role in self-reflection, he notes, which may be related to inhibition. But he and Brass agree that the experiments don't solve the old puzzle of so-called free will. The MRI scans are not precise enough to tell whether the veto decision happens before the subject is conscious of it.

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