杏吧原创

A good pair of dentures may fend off dementia. That鈥檚 the message from
Japanese researchers, who say that chewing helps prevent memory loss as we grow
old.

New memories are briefly stored in the hippocampus, a brain area critical for
learning. But as we age, hippocampal cells start to deteriorate and our
short-term memory gets worse. Elderly people with missing teeth often chew less,
too, and some studies have suggested that bad memory and tooth loss might be
linked.

To put this idea to the test, Minoru Onozuka of the Gifu University School of
Medicine in Japan and his colleagues looked at mice that have been genetically
altered so they rapidly develop signs of human ageing, such as hair loss,
cataracts and failing memory. Onozuka extracted the molar teeth of some mice, so
they could still eat, but couldn鈥檛 chew.

The memories of the mice were then tested in a water maze. Young mice quickly
learned to find a hidden platform, regardless of whether they had molars missing
or not, and old mice with a full set of teeth performed only slightly worse. But
the old molarless mice couldn鈥檛 remember how to find the platform, consistently
heading out into the pool in the wrong direction. Looking at their hippocampi
suggested why: essential cells called glia had deteriorated far more than
usual.

The findings suggest that chewing is essential to preserve our ability to
form memories in old age. To pursue this, Onozuka used magnetic resonance
imaging (MRI) to study brain activity while people were chewing. 鈥淭he task
causes an increase in hippocampal signals,鈥� he says.

But how exactly chewing stimulates the mind remains a mystery. 鈥淲e don鈥檛
touch the mechanism,鈥漚dmits Onozuko. 鈥淲e need more experiments.鈥�

Joyce Wau, a specialist in ageing at the Molecular Medicine Centre at
Edinburgh University, finds the work fascinating. She thinks that chewing
improves our memories by reducing stress. 鈥淎fter all, humans often chew gum to
help with stress relief.鈥�

The hippocampus helps control levels of stress hormones in the blood, she
says. So if older people chew less, their stress levels might rise enough to
cause a decline in short-term memory.