Empedocles also noted that there were corrective factors that would restore balance. Our bodies produce stress hormones such as cortisol, epinephrine, and norepinephrine that affect us by breaking down certain tissues to mobilize fuel, increasing our heart rate, preparing our muscles to move us. All these responses are necessary when we are in danger, but they can have long-term medical consequences if stress becomes our chronic state. Cortisol enhances fear-related behavior. If you are a rat being chased by a cat, you cannot afford to stop and smell the roses.
Fear is essential to a rat's survival.
If you are a rat being chased by a cat, you should not stop to sleep or eat, even if you have missed a meal and it is past your bedtime. Internal programs for sexual behavior and metabolic programs for growth and reproduction are turned off. The amygdala, as we have seen, encodes the memories of fear. The hypothalamus controls many of the vegetative functions and the secretion of stress hormones, and sexual behavior. Now let us consider how stress relates to depression.