Stress causes the release of a hormone called cortisol. This stress hormone has been shown to damage and kill cells in the hippocampus (the brain area responsible for your episodic memory) and even cause premature brain ageing. Without cortisol you would die – but too much of it makes your brain vulnerable to damage. The cortisol released in stress travels into the brain and binds to the receptors inside many neurons (in the cytoplasm). Through a cascade of reactions, this causes neurons to admit more calcium through channels in their membrane. In the short-term cortisol presumably helps the brain to cope with the life-threatening situation. However, if neurons become over-loaded with calcium they fire too frequently and die – they are literally excited to death.