And so do a number of other things.
<http://www.nytimes.com/2007/08/19/sports/playmagazine/0819play-brain.htm
l?ex=1345176000&en=70ec7d22ef2dece6&ei=5088&partner=rssnyt&emc=rss>
August 19, 2007
PHYS ED
Lobes of Steel
By GRETCHEN REYNOLDS
The Morris water maze is the rodent equivalent of an I.Q. test: mice are
placed in a tank filled with water dyed an opaque color. Beneath a small
area of the surface is a platform, which the mice can¹t see. Despite
what you¹ve heard about rodents and sinking ships, mice hate water;
those that blunder upon the platform climb onto it immediately.
Scientists have long agreed that a mouse¹s spatial memory can be
inferred by how quickly the animal finds its way in subsequent dunkings.
A ³smart² mouse remembers the platform and swims right to it.
In the late 1990s, one group of mice at the Salk Institute for
Biological Studies, near San Diego, blew away the others in the Morris
maze. The difference between the smart mice and those that floundered?
Exercise. The brainy mice had running wheels in their cages, and the
others didn¹t.
Scientists have suspected for decades that exercise, particularly
regular aerobic exercise, can affect the brain. But they could only
speculate as to how. Now an expanding body of research shows that
exercise can improve the performance of the brain by boosting memory and
cognitive processing speed. Exercise can, in fact, create a stronger,
faster brain.
This theory emerged from those mouse studies at the Salk Institute.
After conducting maze tests, the neuroscientist Fred H. Gage and his
colleagues examined brain samples from the mice. Conventional wisdom had
long held that animal (and human) brains weren¹t malleable: after a
brief window early in life, the brain could no longer grow or renew
itself. The supply of neurons ‹ the brain cells that enable us to think
‹ was believed to be fixed almost from birth. As the cells died through
aging, mental function declined. The damage couldn¹t be staved off or
repaired.
Gage¹s mice proved otherwise. Before being euthanized, the animals had
been injected with a chemical compound that incorporates itself into
actively dividing cells. During autopsy, those cells could be identified
by using a dye. Gage and his team presumed they wouldn¹t find such cells
in the mice¹s brain tissue, but to their astonishment, they did. Up
until the point of death, the mice were creating fresh neurons. Their
brains were regenerating themselves.
All of the mice showed this vivid proof of what¹s known as
³neurogenesis,² or the creation of new neurons. But the brains of the
athletic mice in particular showed many more. These mice, the ones that
scampered on running wheels, were producing two to three times as many
new neurons as the mice that didn¹t exercise.
But did neurogenesis also happen in the human brain? To find out, Gage
and his colleagues had obtained brain tissue from deceased cancer
patients who had donated their bodies to research. While still living,
these people were injected with the same type of compound used on Gage¹s
mice. (Pathologists were hoping to learn more about how quickly the
patients¹ tumor cells were growing.) When Gage dyed their brain samples,
he again saw new neurons. Like the mice, the humans showed evidence of
neurogenesis.
Gage¹s discovery hit the world of neurological research like a
thunderclap. Since then, scientists have been finding more evidence that
the human brain is not only capable of renewing itself but that exercise
speeds the process.
³We¹ve always known that our brains control our behavior,² Gage says,
³but not that our behavior could control and change the structure of our
brains.²
The human brain is extremely difficult to study, especially when a
person is still alive. Without euthanizing their subjects, the closest
that researchers can get to seeing what goes on in there is through a
functional M.R.I. machine, which measures the size and shape of the
brain and, unlike a standard M.R.I. machine, tracks blood flow and
electrical activity.
This spring, neuroscientists at Columbia University in New York City
published a study in which a group of men and women, ranging in age from
21 to 45, began working out for one hour four times a week. After 12
weeks, the test subjects, predictably, became more fit. Their VO2 max,
the standard measure of how much oxygen a person takes in while
exercising, rose significantly.
But something else happened as a result of all those workouts: blood
flowed at a much higher volume to a part of the brain responsible for
neurogenesis. Functional M.R.I.¹s showed that a portion of each person¹s
hippocampus received almost twice the blood volume as it did before.
Scientists suspect that the blood pumping into that part of the brain
was helping to produce fresh neurons.
The hippocampus plays a large role in how mammals create and process
memories; it also plays a role in cognition. If your hippocampus is
damaged, you most likely have trouble learning facts and forming new
memories. Age plays a factor, too. As you get older, your brain gets
smaller, and one of the areas most prone to this shrinkage is the
hippocampus. (This can start depressingly early, in your 30¹s.) Many
neurologists believe that the loss of neurons in the hippocampus may be
a primary cause of the cognitive decay associated with aging. A number
of studies have shown that people with Alzheimer¹s and other forms of
dementia tend to have smaller-than-normal hippocampi.
The Columbia study suggests that shrinkage to parts of the hippocampus
can be slowed via exercise. The subjects showed significant improvements
in memory, as measured by a word-recall test. Those with the biggest
increases in VO2 max had the best scores of all.
³It¹s reasonable to infer, though we¹re not yet certain, that
neurogenesis was happening in the people¹s hippocampi,² says Scott A.
Small, an associate professor of neurology at Columbia and the senior
author of the study, ³and that working out was driving the neurogenesis.²
Other recent studies support this theory. At the University of Illinois
at Urbana- Champaign, a group of elderly sedentary people were assigned
to either an aerobic exercise program or a regimen of stretching. (The
aerobic group walked for at least one hour three times a week.) After
six months, their brains were scanned using an M.R.I. Those who had been
doing aerobic exercise showed significant growth in several areas of the
brain. These results raise the hope that the human brain has the
capacity not only to produce new cells but also to add new blood vessels
and strengthen neural connections, allowing young neurons to integrate
themselves into the wider neural network. ³The current findings are the
first, to our knowledge, to confirm the benefits of exercise training on
brain volume in aging humans,² the authors concluded.
And the benefits aren¹t limited to adults. Other University of Illinois
scientists have studied school-age children and found that those who
have a higher level of aerobic fitness processed information more
efficiently; they were quicker on a battery of computerized flashcard
tests. The researchers also found that higher levels of aerobic fitness
corresponded to better standardized test scores among a set of Illinois
public school students. The scientists next plan to study how students¹
scores change as their fitness improves.
What is it about exercise that prompts the brain to remake itself?
Different scientists have pet theories. One popular hypothesis credits
insulin-like growth factor 1, a protein that circulates in the blood and
is produced in greater amounts in response to exercise. IGF-1 has
trouble entering the brain ‹ it stops at what¹s called the ³blood-brain
barrier² ‹ but exercise is thought to help it to do so, possibly
sparking neurogenesis.
Other researchers are looking at the role of serotonin, a hormone that
influences mood. Exercise speeds the brain¹s production of serotonin,
which could, in turn, prompt new neurons to grow. Abnormally low levels
of serotonin have been associated with clinical depression, as has a
strikingly shrunken hippocampus. Many antidepressant medications, like
Prozac, increase the effectiveness of serotonin. Interestingly, these
drugs take three to four weeks to begin working ‹ about the same time
required for new neurons to form and mature. Part of the reason these
drugs are effective, then, could be that they¹re increasing
neurogenesis. ³Just as exercise does,²Gage says.
Gage, by the way, exercises just about every day, as do most colleagues
in his field. Scott Small at Columbia, for instance , likes nothing
better than a strenuous game of tennis. ³As a neurologist,² he explains,
³I constantly get asked at cocktail parties what someone can do to
protect their mental functioning. I tell them, ŒPut down that glass and
go for a run.¹ ² .
This Is Your Brain on Something Other Than Exercise
The human brain undergoes neurogenesis ‹ the creation of new cells ‹
throughout a person¹s life, although the amount depends on a variety of
factors, not just exercise.
MARIJUANA: We just report the data; we don¹t endorse it. A 2005 study on
rats found that stimulation of the brain¹s receptors for marijuana
increased neurogenesis.
ALCOHOL: A 2005 study found that mice that swallowed a moderate amount
of ethanol showed more neurogenesis than teetotalers. Other studies on
mice have suggested that heavier drinking can be damaging to the brain.
SOCIABILITY: One study suggests that rats that live alone and have
access to a run ning wheel experience less neurogenesis than those that
have access to a running wheel and live in group housing. So go ahead
and join that singles running club you¹ve been avoiding.
DIET: A diet high in saturated fat and sugar sharply diminishes the
brain¹s production of the proteins and nerve-growth factors necessary
for neurogenesis. Exercise may mitigate that effect somewhat.
STRESS: Mice that are subjected to uncontrollable stress (like electric
shock) suffer substantial deterioration in their ability to produce new
neurons.
CHOCOLATE: In a study published this year, an ingredient in cocoa,
epicatechin, was shown to improve spatial memory in mice, especially
among those that exercised. Epicatechin can also be found in grapes,
blueberries and black tea. ³I plan to start ingesting more epicatechin,²
says Henriette van Praag, a neuroscientist at the Salk Institute, ³as
soon as I can¹t find my car keys anymore.² G.R.
--
Crossing the starting line is 90%.
Crossing the finish line is the other 90%.