Fitness, Hippocampus and Forgetting

Hippocampus in Green from 3D Brain iPad App

Cardiorespiratory fitness appears to be associated with a variety of benefits in cognitive functioning.  The mechanisms for this benefit are unclear.  Association studies do not provide evidence for the pathways between related variables.  For understanding pathways, clinical trials, longitudinal studies and multivariate approaches are more powerful approaches.

Amanda Szabo and colleagues at the University of Illinois at Urbana-Champaign recently published a multivariate study looking at fitness, hippocampus and forgetting in a group of elderly adults in the journal Neuropsychology.  The hippocampus is a brain region known to crucial to working memory.  Changes in hippocampal volume have been linked to age-related cognitive decline and the development of Alzheimer's disease.

The key elements of design in this study included:
Subjects: 158 older adults with a mean age of 66.5 years
Variables: Fitness level as measured by VO2 estimate from a graded exercise test, brain hippocampal volume from a brain 3T MRI scan, spatial working memory task, subjective rating of forgetfulness (Frequency of Forgetting Questionnaire)
Statistics: Path analysis examining direct and indirect effects of fitness on hippocampal volume, working memory test performance and subject rating of forgetfulness using the comparative fit index (CFI)

The authors started with a presumed pathway model for the mechanism of the relationship between fitness and forgetfulness in the following pathway:

• fitness levels predict hippocampal volume
• hippocampal volumes predicts working memory function performance
• working memory performance predicts subjective forgetfulness

Fitness levels were associated with a variety of sociodemographic and medical variables at baseline including: self-reported physical activity, presence of hypertension, cardiovascular disease, body mass index, education level, gender and age.  These baseline variables were evaluated and controlled in the final pathway analysis.

The authors found their predicted model held up in the analysis: "cardiorespiratory fitness is associated with the frequency of forgetting indirectly through its influence on hippocampal volume and, in turn, spatial working memory".

The study noted fitness level is not the sole determinant of hippocampal atrophy.  Age alone is an independent contributor of hippocampal atrophy.  Fitness may reduce the effects of age-related hippocampal atrophy and forgetfulness but it is unable to reverse the effect.

So fitness is not a panacea but it appears to be an important factor in maintaining cognitive function in later life.  Now, I just wonder if my wife can help me find my running shoes?

3D Brain image of the hippocampus in green screen shot from the author's collection.

Szabo, A., McAuley, E., Erickson, K., Voss, M., Prakash, R., Mailey, E., Wójcicki, T., White, S., Gothe, N., Olson, E., & Kramer, A. (2011). Cardiorespiratory fitness, hippocampal volume, and frequency of forgetting in older adults. Neuropsychology, 25 (5), 545-553 DOI: 10.1037/a0022733