Research using animals has shown that an elevated level of brainderived neurotrophic factor (BDNF), which is a protective brain hormone increased by such activities as calorie reduction, fasting, and mental and physical exercise, imparts a high level of protection for the hippocampus, making it resistant to damage from elevated cortisol; and we now

anti-inflammatory because cortisol acts on receptors on immune cells to reduce the expression of cytokines [this is the concept of hormesis, explained here

heart rate variability (HRV). HRV had recently been discovered to be a good way to measure the integrity of one of the brain’s arousal systems, the one located in the oldest part of the brain: the brain stem.