CNRS (Délégation Paris Michel-Ange)
Until now, the reason why some people hate cheese has been a mystery. Researchers at the Centre de Recherche en Neuroscience de Lyon and the Laboratoire Neuroscience Paris Seine (CNRS/INSERM/UPMC) have just elucidated it. Their results are published online on the Frontiers in Human Neuroscience website.
It is difficult to remain lukewarm
when faced with a ripe camembert or goats cheese: people love it or hate it.
France may well be the country that has the largest number of cheese varieties
(almost 1600), yet many there are disgusted by it.
Aversion is an extremely powerful
factor in the animal world: it is a key element for survival, hence the
importance of studying the cerebral mechanisms at play.
Why cheese? Because it seemed to the
researchers that many people do not like this type of dairy product. Therefore
they studied a sample of 332 individuals to check their intuition: cheese is
indeed the food that most frequently triggers aversion.
It affects 6.0% of respondents, whereas only 2.7% of those tested have an aversion to fish and 2.4% to cured meats.
Among those with an aversion to
cheese, 18% say they are intolerant to lactose. In 47% of cases, at least one
of their family members does not like cheese either. These figures suggest that
there is a genetic origin to this aversion, which might be related to lactose
intolerance.
To find out what happens in the brain,
fifteen people who like cheese and fifteen who do not were selected and
participated in a functional magnetic resonance imaging (fMRI) study.
They were simultaneously exposed to
the image and smell of six different cheeses and six other types of control
foods. They had to state whether they liked the smell and sight of the foods or
not, and whether, at that moment, they wanted to eat them.
The researchers then observed that the
ventral pallidum, a small structure usually activated in people who are hungry,
was totally inactive while the smell and image of cheese was being presented to
individuals with an aversion to cheese, whereas it was activated for all other
food types.
Even more surprisingly, the
researchers observed that areas of the brain, the globus pallidus and the
substantia nigra, which participate in the reward circuit (activated when we
love something), were more involved in people who do not like cheese than in
those who do.
These structures, typically involved
in processing reward, may therefore also be triggered in response to an
aversive stimulus.
To explain this dual nature, the
researchers suggest that these regions include two types of neurons with
complementary activity: one related to the rewarding aspect of a food, the
other to its aversive nature.
This work provides an insight into the
areas of the brain that are activated when an individual is presented with an
aversive food and suggests that the reward circuit may also encode disgust.