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."
     
                                                * * *

     Exercising the Brain's Gray Matter
     New research with laboratory animals suggests that running
regularly might build up the number of neurons in an area of the brain
called the hippocampus, while other new research shows that learning
can help brain cells there live longer.
     Hippocampus
     Prefrontal cortax
     Olfactory bulb
     Temporal lobe
     Motor cortex
     Primary visual cortex
     Cerebellum

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