Just one year of moderate physical exercise in late adulthood can reverse shrinkage of the brain’s hippocampus and improve spatial memory, said US researchers in a new study, funded through the National Institute on Aging.

Researchers at the University of Pittsburgh, University of Illinois, Rice University, and Ohio State University, wrote about their project, considered to be the first of its kind, in a Proceedings of the National Academy of Sciences, PNAS paper that was published ahead of print on 31 January.

The hippocampus is a significant part of the brain in humans and other mammals. It belongs to the limbic system and sits deep inside brain tissue in the medial temporal lobe where it plays an important role in long term and other types of memory formation and spatial navigation.

As we enter late adulthood, this part of the brain starts to shrink, leading to loss of memory and increased risk of dementia.

Studies have shown that adults who are fitter tend to have larger medial temporal lobes, and that physical activity increases nutritive blood supply to the hippocampus, but this is the first study to look at the effect of aerobic exercise on the size of the hippocampus in later life.

For the randomized controlled trial, lead author Dr Kirk Erickson, professor of psychology at the University of Pittsburgh, and colleagues, recruited 120 sedentary older adults without dementia and randomized them to one of two groups.

The first group walked around a track for 40 minutes a day for three days a week, and the second group just did stretching and toning exercises.

They did this for a year, during which they also underwent MRI brain scans, spatial memory tests, and gave blood samples, at the beginning, middle and end of the period.

The researchers found that “aerobic exercise training increases the size of the anterior hippocampus, leading to improvements in spatial memory”.

More specifically, the results showed that:

  • Exercise training increased the volume of the hippocampus by 2.12 per cent on the left side and 1.97 per cent on the right side.
  • This compared to a 1.40 and 1.43 per cent reduction in those same brain regions respectively in the stretching and toning only group (the controls).
  • Increased hippocampal volume was linked to greater blood levels of brain-derived neurotrophic factor (BDNF), a biomarker for brain health that is involved in learning and memory.
  • Although hippocampal volume declined in the control group, the decline was less marked among those members whose fitness levels were higher at the start of the study, suggesting that fitness protects against volume loss.
  • However, the size of the caudate nucleus (also important for memory) and thalamus (important for processing sensory and spatial information) appeared unaffected by the intervention.

The researchers concluded 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.”

Erickson said we tend to accept it as inevitable that our hippocampus will shrink later in life:

“But we’ve shown that even moderate exercise for one year can increase the size of that structure. The brain at that stage remains modifiable,” he said in a statement.

Senior author Dr Art Kramer, director of the Beckman Institute at the University of Illinois, said the findings were particularly interesting because they show even modest exercise can make a substantial difference to memory and brain health in sedentary older people:

“Such improvements have important implications for the health of our citizens and the expanding population of older adults worldwide,” said Kramer.

“Exercise training increases size of hippocampus and improves memory.”
Kirk I. Erickson, Michelle W. Voss, Ruchika Shaurya Prakash, Chandramallika Basak, Amanda Szabo, Laura Chaddock, Jennifer S. Kim, Susie Heo, Heloisa Alves, Siobhan M. White, Thomas R. Wojcicki, Emily Mailey, Victoria J. Vieira, Stephen A. Martin, Brandt D. Pence, Jeffrey A. Woods, Edward McAuley, and Arthur F. Kramer.
PNAS, published ahead of print 31 January 2011.

Additional sources: University of Illinois at Urbana-Champaign (31 Jan 2011 press release), Wikipedia.

Written by: Catharine Paddock, PhD