Previous studies have found that the region of the brain known as the hippocampus shrinks in late adulthood, leading to impaired memory and increased risk for dementia. Kirk I. Erickson, from the University of Pittsburgh (Pennsylvania, USA), and colleagues enrolled 120 sedentary older adults without dementia, in a year-long study. Each subject was assigned to one of two groups: those who began an exercise regimen of walking around a track for 40 minutes a day, three days a week; or those limited to stretching and toning exercises. The team conducted Magnetic Resonance Imaging (MRI) at the study’s start, at six months, and at the end of the year-long study term.  The aerobic exercise group demonstrated an increase in volume of the left and right hippocampus of 2.12% and 1.97%, respectively. Whereas, the same regions of the brain in those who did stretching exercises decreased in volume by 1.40 and 1.43%, respectively. In conducting spatial memory tests for all participants at the three intervals, the researchers found that those in the aerobic exercise group showed improved memory function – as compared their performance at the start of the study, an improvement associated with the increased size of the hippocampus. The team also examined several biomarkers associated with brain health, including brain-derived neurotrophic factor (BDNF), a small molecule that is involved in learning and memory, and found that the increases in hippocampal size were associated with increased amounts of BDNF. The researchers conclude that: “These theoretically important findings indicate that aerobic exercise training is effective at reversing hippocampal volume loss in late adulthood, which is accompanied by improved memory function.”