In the study, researchers found that moderate walking three times per week for a year increased brain connectivity and brain function in older adults.
The study followed 65 adults, aged 59 to 80, who joined a walking group or stretching and toning group for a year.
All of the participants were sedentary before the study, reporting less than two episodes of physical activity lasting 30 minutes or more in the previous six months. The researchers also measured brain activity in 32 younger (18- to 35-year-old) adults.
Rather than focusing on specific brain structures, the study looked at activity in brain regions that function together as networks.
"Almost nothing in the brain gets done by one area - it's more of a circuit," said University of Illinois psychology professor and Beckman Institute Director Art Kramer, who led the study with kinesiology and community health professor Edward McAuley and doctoral student Michelle Voss.
"These networks can become more or less connected. In general, as we get older, they become less connected, so we were interested in the effects of fitness on connectivity of brain networks that show the most dysfunction with age."
Neuroscientists have identified several distinct brain circuits. Perhaps the most intriguing is the default mode network (DMN), which dominates brain activity when a person is least engaged with the outside world - either passively observing something or simply daydreaming.
The new study used functional magnetic resonance imaging (fMRI) to determine whether aerobic activity increased connectivity in the DMN or other brain networks.
The researchers measured participants' brain connectivity and performance on cognitive tasks at the beginning of the study, at six months and after a year of either walking or toning and stretching.
At the end of the year, DMN connectivity was significantly improved in the brains of the older walkers, but not in the stretching and toning group, the researchers report.
The walkers also had increased connectivity in parts of another brain circuit (the fronto-executive network, which aids in the performance of complex tasks) and they did significantly better on cognitive tests than their toning and stretching peers.
The study appears in Frontiers in Aging Neuroscience.