Great (Taste) Expectations: Study Shows Brain Anticipates Taste, Shifts Gears
by
Terry Devitt
Wisconsin Week
University Communications
Posted:
February 21, 2006
As the prism of our senses, the human brain has ways of refracting sensory
input in defiance of reality.
This is seen, for example, in the placebo effect, when simple sugar pills or
inert salves taken by unwitting subjects are seen to ease pain or have some
other beneficial physiological effect. How the brain processes this faked input
and prompts the body to respond is largely a mystery of neuroscience.
Now, however, scientists have begun to peel back some of the neurological
secrets of this remarkable phenomenon and show how the brain can be rewired in
anticipation of sensory input to respond in prescribed ways. Writing in the
current issue (March 1, 2006) of the journal Brain, Behavior, and Immunity, a
team of Wisconsin scientists reports the results of experiments that portray the
brain in action as it is duped.
 The new
work, conducted by a team led by University of Wisconsin-Madison Assistant
Professor of psychology and psychiatry Jack
B. Nitschke, tested the ability of the human brain to mitigate foul taste
through a ruse of anticipation. The work, conducted at the UW-Madison
Waisman Center using state-of-the-art
brain imaging techniques and
distasteful concoctions of quinine on a cohort of college students, reveals in
detail how the brain responds to a manipulation intended to mitigate an
unpleasant experience.
"There is a potent impact to expectancy," says Nitschke who, with his
colleagues, exposed 43 undergraduate subjects to potions of quinine, sugar water
or distilled water while undergoing magnetic resonance imaging (MRI).
The subjects, Nitschke explains, were asked beforehand to associate a prescribed
set of cues with a taste. A "minus sign" flashed through fiber optic goggles to
subjects undergoing MRI, for instance, was to be an anticipatory signal that a
liquid subsequently dripped into the mouth would have a very bitter taste. A
"zero "cue corresponded with a neutral taste, and a "plus sign" with a pleasant,
sugary taste.
The cues, according to Nitschke, were flashed to subjects just prior to the
administration of a few drops of liquid. But in the study, the cues would not
always match the taste they were said to presage.
What his group observed, was that when subjects were given a cue that suggested
the taste they were about to experience would be less bitter, the taste was
perceived as such, and the regions of the brain that code tastes were activated
less.
"When the subject sees the warning signal, portions of the brain activated by
the misleading cue predict the decreased brain response to the awful taste,"
Nitschke says. What's more, "the (brain's) response to the misleading cue will
predict the subject's perception of what the taste is going to be. The subject
anticipates that the taste won't be that bad, and indeed that's what they
report."
In short, the new study shows how expectancy affects how humans perceive sensory
input, and how events in the brain are directly related to those perceptions.
Importantly, by mapping how the brain anticipates an event and kicks in a
placebo effect, Nitschke argues, scientists can begin to think about ways that
knowledge could be used in clinical settings.
For Nitschke, who also practices as a clinical psychologist specializing in the
treatment of depression and anxiety disorders, the new detailed insights into
the power of anticipation could lead to better treatments for such conditions.
"The placebo operates through expectancy. In this study, we've taken the pill
out of the picture. We're just manipulating expectancies," he says. "The results
beg the question of what can we do to target anticipatory processes in our
patients that might lead to better outcomes?"
The new Wisconsin study was supported by grants from the National Institutes of
Health, the John D. and Catherine T. MacArthur Foundation, the Rockefeller
Family and Associates, and the Kohlberg Foundation.
In addition to Nitschke, authors of the study include Issidoros Sarinopoulos,
Gregory E. Dixon, Sarah J. Short and Richard J. Davidson.
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