If a zebra is attacked by a lion and survives, its cortisol levels will normalize in forty-five minutes. By contrast, humans can retain elevated cortisol levels for days, weeks, or even months at a time. That can be a problem, in part, because chronically elevated levels of cortisol will impair and eventually kill cells in the hippocampus, the place where memories are created and stored. This is why students have trouble learning when they are under acute stress.
