Tuesday, February 23,
1999
Active
Mind, Body Linked to Brain Growth
By
ROBERT LEE HOTZ, Times
Science Writer
Regular running and intensive
mental exercise may revitalize the mind by spurring the growth of new brain
cells responsible for learning and memory, new animal experiments suggest.
The research, made public Monday, sheds light on
how the effects of daily experience can foster new brain cells in adult mammals
from mice to human beings. In essence, the research suggests that an active
life--whether the activity be physical or mental--can have a positive impact on
the brain.
In separate studies published in Nature
Neuroscience, scientists at the Salk Institute for Biological Studies in La
Jolla and at Princeton University discovered that some kinds of physical and
mental exercise promoted the growth of new neurons, while also measurably
prolonging the survival of existing brain cells. The changes took place in a
part of the brain called the hippocampus, which is crucial to the formation of
new memories.
"That is terribly exciting, given that we
know the hippocampus plays a role in the memory of new facts and new
events," said Neal J. Cohen, a cognitive neuroscientist at the University
of Illinois. "It is clear the adult brain continues to be modified
structurally and functionally by experience."
The Salk researchers, to their surprise, found
that adult mice exercising on a running wheel regularly developed twice as many
new brain cells in the hippocampus as mice housed in standard cages.
The scientists had designed their experiment to
test the effects of learning and had only included the running wheels as one of
several different variables. The mice ran at their own pace, as often and for
as long as they liked.
"The difference was so striking," said
neurobiologist Fred H. Gage, senior author of the Salk study. "And because
we know now that human brains also make new cells, it just might be that
running or other vigorous exercise stimulates brain cell production in people
as well."
Until recently, the idea that the human brain can
produce new neurons well into old age was a scientific heresy. Most experts
were convinced the human brain had done almost all its growing by the time a
child was born.
But several animal studies have shown that,
contrary to expectations, the hippocampus of the adult brain can produce
thousands of new neurons every day. Recently, Gage and his colleagues
demonstrated that the human brain is no exception, producing new neurons even
in the elderly.
The Salk researchers do not know why running
should have such an enhancing effect on neural development. Running might
increase the flow of oxygen and nutrients to brain tissues or release special
growth factors that promote new neurons, Gage said.
It may well be that the primordial biology of
running prompts the nervous system to prepare for an onslaught of new
information as an animal navigates unfamiliar terrain in the pursuit of prey or
in flight from an enemy. In those situations, the brain may respond reflexively
to running by expanding its store of neurons in anticipation of new learning,
several experts said.
"Exercise itself over the eons may have
become associated with a bunch of effects that help the brain prepare itself
for new information, new learning, new brain work," Cohen at Illinois
said.
In their experiments, the Princeton team found
that purely mental tasks could double the number of new neurons in the adult
hippocampus and help existing neurons live longer.
Mental challenges that required the animals to
master information involving spatial relationships and timing, which placed
special demands on the hippocampus, had the greatest effect. The lab mice, for
example, had to learn how to locate platforms in a water maze, which tested
their ability to put together spatial relationships. Learning tasks that did
not place demands on the hippocampus had no effect.
"It is a classic case of 'use it or lose
it,' " said Princeton psychologist Elizabeth Gould, who conducted the
research. "Certain types of learning that require this brain region--the
hippocampus--were very good at rescuing new neurons from death. It was not just
learning in general. It was not experience in general."
Although the Princeton research was not intended
to address human well-being directly, the animal experiments underscore the
importance of an active life of the mind, Gould said.
"It is very likely if you lead a very
mentally active life you are engaging the hippocampus," Gould said.
If the right kind of mental exercise promotes a
healthy mind, the absence of mental stimulation may have an equally harmful effect
on the brain, by allowing neurons to atrophy and die. "A lack of learning
opportunities may have a negative structural impact on the brain," Gould
said.
Together, the findings hint at the physical
mechanisms underlying the human brain's unexpected "flexibility," its
ability to change in response to experience.
Previous studies have shown that animals,
including primates, created more new cells in the hippocampus if they lived in
a more stimulating, enriched environment rather than in a standard cage. In the
new research, the two teams of scientists were trying to pinpoint the tasks
most likely to spur new brain cells.
"I think it is a pretty big deal," said
neuroscientist Janice Juraska at the University of Illinois, who studies brain development.
"It helps explain why we are as flexible as we are."
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