PIONEERING research in the US suggests that new nerve cells may be generated
in the memory centres of adult humans鈥� brains. The findings overturn the
long-standing notion that nerve cells in areas of the brain associated with
learning do not divide after birth. They also hint that memories could be
recorded not only when nerve cells form new connections, but also when new
neurons appear.
Studies in the 1970s showed that in rat brains, new nerve cells can grow in
the hippocampus, which has a role in laying down new memories. But the failure
of scientists to repeat the results in monkeys at that time led neurologists to
believe that this was unique to rodents.
In this month鈥檚 Journal of Neuroscience, Elizabeth Gould of
Princeton University in New Jersey and her colleagues report that adult tree
shrews can also grow new hippocampus neurons. Because these shrews are closely
related to primates, this suggests that the same may happen in humans.
Advertisement
Gould鈥檚 team injected six shrews with a labelling chemical called
bromodeoxyuridine, which mimics one of the building blocks of DNA. This chemical
can be stained to make it visible. The team found that the label became
incorporated into newly synthesised DNA in the hippocampus, suggesting that
neurons had divided there. The team has since found the same result in macaque
monkeys.
鈥淭his suggests that neuron production in the hippocampus in adulthood is a
general phenomenon that may occur in humans,鈥� says Gould. It is already known
that human brains make new neurons in a primitive part of the brain called the
olfactory bulb, which is responsible for our sense of smell. But this is the
first evidence of new nerve cells being produced in a part of the brain
associated with memory and learning.
Gould鈥檚 team also showed that under the stress of being confined with others,
male shrews stop producing new hippocampus neurons. Stress is known to alter the
brain鈥檚 structure by raising levels of hormones that shrink the hippocampus.
Now it seems that stress also blocks the production of new nerve cells.
Roger Keynes, a neurobiologist at the University of Cambridge in Britain,
agrees with Gould鈥檚 interpretation of the results. 鈥淚鈥檇 like to see this
confirmed with larger numbers of animals,鈥� he adds. 鈥淚t鈥檚 a far-out idea but we
may in the future have a method of brain repair by making cells divide,鈥� says
Bruce McEwan, one of Gould鈥檚 colleagues. 鈥淚 would have totally disregarded that
before these results.鈥�