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 yesterday, sheds light on how the effects of daily experience can foster new brain cells in adult mammals from mice to humans. The research suggests that an active life -- 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 San Diego 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.
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 included the running wheels as only one of several 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 the hippocampus of the adult brain can produce thousands of neurons every day.
Recently, Gage and his colleagues demonstrated that the human brain is no exception, producing new neurons even among 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 flight from an enemy. 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 said.
In their experiments, the Princeton team found that purely mental tasks could double the number of new neurons in the adult hippocampus and also 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.
Learning tasks that did not place demands on the hippocampus had no effect.
Pub Date: 2/23/99