A new study led by researchers at Columbia University provides the first evidence in humans that a structured exercise training program increases neurogenesis—the birth and development of new nerve cells—in a memory hub of the brain.
The area, a subregion of the hippocampus called the dentate gyrus, is one of only two brain regions for which the evidence for lifelong neurogenesis is incontrovertible, and it is particularly vulnerable to age-related degeneration.
Exercise-induced hippocampal neurogenesis is already well-established in rodents. Studies from various laboratories have found two- to three-fold increases in the rate of new neurons when mice or rats are allowed to freely run on an exercise wheel. (Unlike humans, rodents tend to be natural runners, and need no prodding to get on the treadmill.)
From Mouse to Human
Researchers measure neurogenesis in animals by sacrificing the critters and counting newly generated cells, which are tagged with a chemical marker to make them stand out. Until now, there has been no reliable way to measure neurogenesis in humans.
Columbia neuroscientist Scott Small and colleagues appear to have found a way around this problem. First, they put mice that had been running voluntarily for two weeks into a magnetic resonance imager to map exercise-induced changes in cerebral blood volume, a measure of increased blood vessel formation in the dentate gyrus. Then, by sacrificing the animals and counting new neurons, they were able to correlate the neuronal proliferation they observed with changes in blood volume.
The researchers then conducted magnetic resonance tests on a small group of middle-aged people who had been exercising about an hour a day, four times a week, for three months. By charting exercise-induced changes in cerebral blood volume in the human hippocampal region and applying the same algorithms used in the mice, they were able to deduce that neurogenesis was also occurring in the humans. Changes in blood volume in the dentate gyrus, they concluded, provide a correlate of neurogenesis in humans.