Tastebuds alone do not determine what something tastes like.
Researchers have demonstrated that expectation, too, plays a role.
Previous research in primates had suggested that expectation had
little effect on how taste registers in the brain. Neuroscientist Jack
Nitschke and his colleagues at the University of Wisconsin lined up 30
college-age volunteers to see whether the same holds true for humans.
The neuroscience team prepared five drinks
containing water mixed with varying amounts of quinine or sugar and
paired them with five symbols: water with a strong concentration of
quinine was linked to a minus sign; water with a milder concentration
got a crossed-out minus sign; simple distilled water received a zero;
and water with either a mild or strong concentration of sugar got the
plus sign equivalents of their negative counterparts. After three trial
runs, the students had learned the associations.
The researchers then loaded the subjects into an fMRI machine for
the next round of tastings. This time, however, they mixed the signs
and drinks. For example, the crossed-out minus sign–initially paired
with the milder quinine mixture–sometimes preceded the bitterest drink
during the eight tastings in the machine.
When the participants were shown a sign indicating
that the bitter drink was going to be less bitter, the same regions of
the brain that fired when the subjects believed they were going to
taste the bitterest drink still fired, but they did so less strongly.
The subjects also reported that the drink tasted less bitter to them.
The same influence of expectation on taste perception was evident when
the subjects received the sugared water.
"These data show that neural responses to taste in the primary
taste cortex are modulated by expectations and not solely by the
objective quality of taste," the researchers write in a paper published
online today by Nature Neuroscience. In other words, taste is partly in your mind.
By David Biello