Changes In Brain Viscolasticity In Subjects With And Without A History Of Exercise

INTRODUCTION: It is well established that exercise has a positive effect on brain health. Specifically, exercise has been noted to increase perfusion of the motor cortex of humans1 as well as rats2. However, it is not known how physiological adaptations to exercise may alter brain tissue mechanical properties, which may have implications for brain injury risk. PURPOSE: To examine the investigate the effect of exercise on brain mechanical properties. METHODS: Ten subjects (age: 28 years ±7.9, height: 171.5 ± 6.7 cm, mass: 74.4 ± 20.8 kg, 50% female) were recruited from the general population to participate in the study. Half of the subjects participated in regular exercise (3 male, 2 female) as defined by150 minutes of moderate intensity exercise and two days of strength training weekly3. Subjects underwent a single magnetic resonance elastography (MRE) session to noninvasively assess viscoelastic tissue properties4. Image data was acquired with the following parameters: 27 slices, matrix 128x128, FA = 25 deg, TR/TE 375/9.84 ms. Output variables include lambda which is a measure of brain tissue stiffness. This study was approved by the institution’s IRB. RESULTS: Modulus maps, which represent brain stiffness, were recovered for each subject and overlayed with anatomical images. Comparison between the two regions showed that while the exercise group had a higher stiffness (mean = 18.412 mm ± 2.512 mm) compared to the non-exercise group (mean = 15.732 mm ± 2.88 mm), the groups were not significantly different (t = 1.57, df = 8, p = 0.08). CONCLUSION: While the results were not significant these preliminary data showed that brain stiffness tended to be higher in those who exercised. If differences are seen in a larger population, a possible hypothesis for this difference is that the vascular smooth muscle responses increases with exercise training5. By extension, changes in the smooth muscle cause an increase in stiffness in the brain6. Changes in stiffness could affect brain health and/or modulate the brain’s response to head impacts, and by extension the risk of traumatic brain injury. These results suggest the MRE is a promising path to understanding the interaction between exercise and brain health and could ultimately lead to effective therapeutics to supplement the positive effects of exercise. Brigham and Women's Hospital, Department of Radiology, Pilot Grant