Aerobic exercise has been well-documented to increase neurogenesis in animals. The brain was originally thought to have a fixed number of neurons by adulthood. Neuroscience underwent a paradigm shift when it was discovered that new neurons are born (and functionally integrated into neural circuitry) well into adulthood.
Neurogenesis has since been implicated in depression and a number of other disorders. Hundreds of publications have been published in the last two decades about the role of neurogenesis in the mechanism of action of antidepressants.
Researchers wondered whether exercise-induced neurogenesis is affected by ambient temperature. Specifically, they hypothesized that aerobic activity in cold conditions, but not normal or hot conditions, would further increase neurogenesis.
The rational underlying this hypothesis is that heat dissipation is challenging to the brain because it produces heat but does not rise in temperature during exercise in the cold.
To the authors surprise, aerobic exercise at both low and high-temperatures increased neurogenesis compared with aerobic exercise at normal temperatures.
Though the underlying mechanism remains unknown, it may be that temperature extremes plus exercise are mild stressors that result in beneficial adaptations in the brain. This view is inline with the observation that mild stressors improve performance (e.g., being moderately nervous before an exam), but chronic unpredictable stress impairs performance.
Moderate oxidative stress has been known to result in improved antioxidant defense, whereas severe oxidative stress overwhelms protective mechanisms, resulting in oxidative damage.
Maynard ME, Chung C, Comer A, et al. Ambient Temperature Influences the Neural Benefits of Exercise. Behav Brain Res. 2015;