Commentary: At least eighty percent of brain grey matter is modifiable by physical activity: a review study

Exploratory analysis of cortical thickness in low- and high-fit young adults

OBJECTIVE

Studies have shown changes in the human brain associated with physical activity and cardiorespiratory fitness (CRF). The effects of CRF on cortical thickness have been well-described in older adults, where a positive association between CRF and cortical thickness has been reported, but the impact of sustained aerobic activity in young adults remains poorly described. Here, exploratory analysis was performed on cortical thickness data that was collected in groups of fit and sedentary young adults.

METHODS

Twenty healthy sedentary individuals (<2 h/week physical activity) were compared to 20 active individuals (>6 h/week physical activity) and cortical thickness was measured in 34 cortical areas. Cortical thickness values were compared between groups, and correlations between cortical thickness and VO2 max were tested.

RESULTS

Cardiorespiratory fitness was significantly higher in active individuals compared to sedentary individuals. Cortical thickness was lower in regions of the left (lateral and medial orbitofrontal cortex, pars orbitalis, pars triangularis, rostral anterior cingulate cortex, superior temporal cortex and frontal pole) and right (lateral and medial orbitofrontal cortex and pars opercularis) hemispheres. Only the left frontal pole and right lateral orbitofrontal cortical thickness remained significant after false discovery rate correction. Negative correlations were observed between VO2 max and cortical thickness in the left (frontal pole) and right (caudal anterior cingulate and medial orbitofrontal cortex) hemispheres.

CONCLUSION

The present exploratory analysis supports previous findings suggesting that neuroplastic effects of cardiorespiratory fitness may be attenuated in young compared with older individuals, underscoring a moderating effect of age on the relationship between fitness and cortical thickness.

A Critical Systematic Review of Current Evidence on the Effects of Physical Exercise on Whole/Regional Grey Matter Brain Volume in Populations at Risk of Neurodegeneration

BACKGROUND

Despite the intriguing potential of physical exercise being able to preserve or even restore brain volume (grey matter volume in particular)-a tissue essential for both cognitive and physical function-no reviews have so far synthesized the existing knowledge from randomized controlled trials investigating exercise-induced changes of the brain's grey matter volume in populations at risk of neurodegeneration. Our objective was to critically review the existing evidence regarding this topic.

METHODS

A systematic search was carried out in MEDLINE and EMBASE databases primo April 2020, to identify randomized controlled trials evaluating the effects of aerobic training, resistance training or concurrent training on brain grey volume changes (by MRI) in adult clinical or healthy elderly populations.

RESULTS

A total of 20 articles (from 19 RCTs) evaluating 3-12 months of aerobic, resistance, or concurrent training were identified and included, involving a total of 1662 participants (populations: healthy older adults, older adults with mild cognitive impairment or Alzheimer's disease, adults with schizophrenia or multiple sclerosis or major depression). While few studies indicated a positive effect-although modest-of physical exercise on certain regions of brain grey matter volume, the majority of study findings were neutral (i.e., no effects/small effect sizes) and quite divergent across populations. Meta-analyses showed that different exercise modalities failed to elicit any substantial effects on whole brain grey volume and hippocampus volume, although with rather large confidence interval width (i.e., variability).

CONCLUSION

Altogether, the current evidence on the effects of physical exercise on whole/regional grey matter brain volume appear sparse and inconclusive, and does not support that physical exercise is as potent as previously proposed when it comes to affecting brain grey matter volume.

Effects of Exercise on Brain and Cognition Across Age Groups and Health States

Exercise has been shown to benefit brain structure and function, particularly in aging populations. However, the mechanisms by which exercise exerts its effects, especially in humans, are not fully understood. This review argues that one reason for this knowledge gap is that exercise likely operates through multiple levels of mechanisms. Furthermore, the mechanisms of exercise may vary depending on factors such as age and health state. We discuss the state of evidence at each of three levels of analysis (molecular/cellular, brain structure/function, and mental states and higher-order behaviors) and highlight consistencies across these levels, inconsistencies within them, and knowledge gaps. Lastly, based on these, we speculate about which mechanisms of exercise may be universal across age groups and populations versus those that might be distinct to specific age ranges or populations.