Scientists are still a long way from determining whether people's"
voluntary" actions are governed by "free will" or
predetermined by brain chemistry. But at least they've reached the point where
they have unmasked some of the brain areas that subserve such actions.
So said Patrick Haggard, Ph.D., of University College London, England, and
Brian Knutson, Ph.D., of Stanford University—both cognitive
neuroscientists—at a session on "Willpower: What Really Governs
The session was part of a mini-convention titled "Frontiers in
Addiction Research," sponsored by the National Institute on Drug Abuse
(NIDA) in Washington, D.C., in November, just prior to the annual meeting of
the Society for Neuroscience.
The cognition preceding a person's voluntary actions can be divided into
phases, Haggard and Knutson explained to an audience largely made up of young
neuroscientists. There is the anticipation phase, and there is the actual
decision to act or not act phase.
As far as the anticipation phase is concerned, both the nucleus accumbens
and the caudate areas of the brain appear to be major players, Knutson said.
For example, he and his colleagues found that when subjects anticipated
enjoying erotic pictures, their mental state coincided with an increased
activation of the nucleus accumbens. In contrast, when subjects anticipated
punishment, their mental state coincided with a turning on of the caudate.
Thanks to functional magnetic resonance imaging, which has been available
since the mid-1990s, scientists can visualize changes in the brain activity of
individuals only seconds before their anticipations lead to an actual decision
to act or not act, Knutson continued.
He and his coworkers have found that nucleus accumbens activation precedes,
for example, the purchase of a desirable product or the decision to take a
risk, whereas activation of the prune-size insula area of the brain and the
deactivation of the mesial prefrontal cortex precedes, say, the rejection of
overpriced products or the decision to not take a risk.
Now, imagine that you are angry at your boss and are about to send him or
her a nasty e-mail, but decide at the last second not to click on the"
"Your dorsal-medial frontal cortex has undoubtedly kicked in,"
Haggard said. He further explained that he and a colleague found that a
specific area of the dorsal-medial frontal cortex is robustly switched on when
people prepare to act, but then decide not to.
Even though the brain activity leading up to people's actions can now be
studied scientifically, "we clearly need to move on to more naturalistic
and long-term studies," Haggard asserted.
Added Knutson: "We hope to get to the point where we have a model of
how the brain makes decisions and to find out whether people who are addicted
make decisions in the same way that nonaddicted persons do."
Meanwhile, Nora Volkow, M.D., director of NIDA, reported not long ago that
certain areas of the brain are already known to be compromised by drug
addiction. They are the anterior cingulate gyrus, which governs attention and
regulation of impulsivity; the orbital prefrontal cortex, which mediates the
assignment of value to environmental stimuli; and the dorsal lateral
prefrontal cortex, a major neural substrate of executive function and decision
making (Psychiatric News, July 6, 2007). ▪