Elderly adults who are more physically fit tend to have bigger hippocampi, a part of the brain that has a bearing on spatial memory.
Remove the hippocampus, as was done in the well-known case of surgical patient Henry Gustav Molaison, and a person's ability to store most new experiences in memory is destroyed.
The hippocampus, a curved structure deep inside the brain, also is a key player in spatial navigation and other types of relational memory.
Certain activities are believed to modify hippocampus size in humans. For example, a study of London taxi drivers found that the posterior portion of the hippocampus was larger in experienced taxi drivers than in other subjects.
Earlier studies found that exercise increases hippocampus size and spatial memory in rodents, but the new study is the first to demonstrate that exercise can affect hippocampus size and memory in humans.
The researchers, from the Universities of Illinois (U-I) and Pittsburgh, measured the cardiorespiratory fitness of 165 adults (109 of them female) between 59 and 81 years of age.
Using magnetic resonance imaging, the researchers conducted a volumetric analysis of the subjects' left and right hippocampi. They also tested the participants' spatial reasoning.
They found a significant association between an individual's fitness and his or her performance on certain spatial memory tests. There was also a strong correlation between fitness and hippocampus size, said a U-I release.
"The higher fit people have a bigger hippocampus, and the people that have more tissue in the hippocampus have a better spatial memory," said U-I psychology professor Art Kramer, who led the study with his Pittsburgh counterpart Kirk Erickson.
The study was published in Hippocampus.