Research shows that exercise bolsters
both the structure and function of the brain. Just a few months of moderate
exercise can create new neurons, lift mood and hone memory and thinking. But what if someone begins exercising and
then stops? How does the brain react?
the University of Sao Paulo in Brazil looked at what happens to the brain’s
hippocampus –the memory centre of the brain – when exercise is stopped. Half of a group of healthy, adult rats
injected with a substance that marks newborn neurons in the hippocampus to run at will on running wheels. Exercise is known
to spark the creation of two or three times as many new hippocampal neurons
compared to rest.
The scientists were able to track how
many cells had been created. Meanwhile, a separate control group was housed in
cages with locked wheels, thus remaining sedentary. They were also monitored
for new brain cell growth. Seven days later, the runners’ wheels
were locked so that they, too, would become inactive.
After a further week, some of the
exercised and control rats completed memory testing. Those with better memories
completed the test more quickly. The remaining animals completed the same
memory test after either three weeks or six weeks of inactivity.
The researchers then compared the
animals’ performance and the number of new brain cells in the hippocampus of
each group of rats. And guess what? After only a week of inactivity, the rats
that had run were much faster on the test than the control animals and also had
at least twice as many newborn neurons in the hippocampus.
However, the advantages faded after
several more weeks of not running. The brains of the animals that had been
inactive for three weeks contained far fewer newborn neurons than the brains of
the animals that had rested for only one week. The brains of the animals that
had been inactive for six weeks had fewer still.
The animals inactive for three or six
weeks also performed far less well in the memory test than the animals that
had been inactive for only a single week. In fact, their memories were about as
porous of those of the control animals, “indicating,” the authors write, “that
the exercise-induced benefits may be transient.”
Another new study of exercise-induced
brain changes in rats comes from McMaster University in Hamilton, Ontario. This
study explored the impacts of exercise on mood. Researchers reported that after
10 weeks of running, followed by three weeks of inactivity, the running rats’
brains were almost indistinguishable from those of animals that had never
exercised. They had almost comparable levels of an enzyme in the brain that
affects the synthesis and uptake of serotonin. It was as if they had never run.
In other words, the brain benefits wear off
quickly. Professor of psychology at the University of Sao Paulo Gilberto
Xavier, senior author of the study of hippocampal neurons, agrees. “Brain
changes are not maintained when regular physical exercise is interrupted,” he
said, “although our observations are restricted to rats, indirect evidence
suggests that the same phenomenon occurs in human beings.” So perhaps it might be wise to stick
to those New Year’s exercise resolutions...