PASADENA, Calif.—You're trying to decide what to eat for
dinner. Should it be the chicken and broccoli? The super-sized
fast-food burger? Skip it entirely and just get some Rocky
Making that choice, it turns out, is a complex neurological
exercise. But, according to researchers from the California
Institute of Technology (Caltech), it's one that can be influenced
by a simple shifting of attention toward the healthy side of life.
And that shift may provide strategies to help us all make healthier
choices—not just in terms of the foods we eat, but in other
areas, like whether or not we pick up a cigarette.
Their research is described in a paper published in the July 27
issue of the Journal of Neuroscience.
When you decide what to eat, not only does your brain need to
figure out how it feels about a food's taste versus its health
benefits versus its size or even its packaging, but it needs to
decide the importance of each of those attributes relative to the
others. And it needs to do all of this more-or-less
Antonio Rangel, professor of economics and neuroscience at
Caltech, has been studying this value-deriving and decision-making
process for years now. Along with Todd Hare—a former postdoc
at Caltech who is now an assistant professor of neuroeconomics at
the University of Zurich in Switzerland—he published a paper
in Science in 2009 describing differences in the brains of
people who are better at exercising self-control than others. What
they found was that while everyone uses the same area of the
brain—the ventral medial prefrontal cortex, or vmPFC—to
make value-laden decisions like what to munch on, there's a second
brain area—the dorsolateral prefrontal cortex, or
dlPFC—that seems to come to life when a person is using
self-control during the decision-making process.
In other words, when the dlPFC is active, it allows the vmPFC to
take into account health benefits as well as taste when it assigns
a value to a particular food.
The new study goes a step further, showing that there seem to be
ways to help kickstart the dlPFC through the use of what Hare calls
"external cues" that allow us to exhibit more self-control than we
might have otherwise.
The researchers came to their conclusions based on data from a
brain-imaging experiment conducted with 33 adult volunteers, none
of whom were following a specific diet or trying to lose weight for
any reason. Each of the volunteers was shown 180 different food
items—from chips and candy bars to apples and
broccoli—through a set of video goggles while in a functional
magnetic resonance imaging (fMRI) machine.
The hungry subjects—they were asked to fast for at least
three hours prior to the experiment—were given up to three
seconds to respond to each picture with a decision about whether or
not they'd want to eat the food shown after the experiment was
over. They could either give the food a "strong no," a "no," a
"yes," or a "strong yes." Once all of the images had been flipped
through, a single food image was chosen at random; if the volunteer
had said "yes" or "strong yes" to the idea of eating that food, he
or she was served that item.
"Because only one random trial was selected to 'count,'" says
Rangel, "the optimal strategy for subjects is to treat each
decision as if it were the only one."
Simple, right? But here's the catch: before every 10 food
choices, an instruction would come on the screen for five seconds
telling the subjects either to "consider the healthiness,"
"consider the tastiness," or "make decisions naturally." This meant
that of the 180 decisions, the subjects made 60 in each of the
three "instruction conditions."
What this was meant to do, Rangel explains, is shift the
subject's attention during the experiment and, potentially, shift
the way in which they made decisions.
Afterward—outside the scanner—the subjects were
asked to rate the same foods on both a tastiness scale (very
untasty, untasty, tasty, very tasty) and a healthiness scale (very
unhealthy, unhealthy, healthy, very healthy). That way, the
researchers were able to associate the choices the subjects made
during the brain scan with their stated perceptions of those foods'
attributes—showing that a subject who chose broccoli during
the "consider the healthiness" portion of the test might think of
it nonetheless as untasty.
The researchers then classified the foods for each subject based
on that subject's ratings: unhealthy-untasty, healthy-untasty,
unhealthy-tasty, and healthy-tasty. Unsurprisingly, people chose
healthy-tasty foods no matter where their attention had been
Things got interesting when the researchers looked at the other
three categories, however. Among their findings:
- When thinking about healthiness, subjects were less likely to
eat unhealthy foods, whether or not they deemed them to be tasty,
and more likely to eat healthy-untasty foods.
- Being asked to think about healthiness led subjects to say "no"
to foods more often than they did when asked to make decisions
- There were no real differences between the choices made during
the "consider the tastiness" and "make decisions naturally"
portions of the experiment.
When the researchers turned to the fMRI results, they found that
the vmPFC was, as predicted, "more responsive to the healthiness of
food in the presence of health cues," says Rangel. And, as they'd
seen previously, the robustness of that response was due to the
influence of the dlPFC—that bastion of
self-control—which was much quieter when the study's subjects
were thinking about taste or their own personal choice than when
they were asked to throw healthiness into the equation.
"This increased influence of the health signals on the vmPFC
results in an overall value for the food that is based more on its
health properties than is the case when the subject's attention is
not focused on healthiness," says Hare.
These results are most likely not limited just to choices about
food, Hare says. "Our findings are also relevant to the current
changes to cigarette warnings many governments have started to
make," he notes. "These changes include adding graphical images of
the health risks of smoking. It remains to be seen whether these
images will be more effective in drawing attention to the
unhealthiness of smoking than the text warnings. If the graphical
warnings do increase attention to health, then our results suggest
that they could decrease the desire to smoke."
Jonathan Malmaud, a former research assistant at Caltech who is
now a graduate student at MIT, was also an author on the
Journal of Neuroscience paper, "Focusing attention on the
health aspects of foods changes value signals in the vmPFC and
improves dietary choice." The scientists' work was funded by a
grant from the National Science Foundation.