How do you feel?” You have asked, and been asked, this question many times. How does your brain answer this question? How you feel is determined by far more factors than your level of happiness or depression. Maybe you feel thirsty or hungry or cold; all of these would affect your answer to the question. Your answer to the question of how you feel is intimately connected with your survival.

The purpose of your emotions is to control evolutionarily conserved behaviors that are critical to your survival. If you are cold or hungry, you need to act upon this information in order to increase your likelihood of survival. For this reason, your brain has evolved a series of interwoven systems that work together with sensory inputs from inside your body to answer the question of how you feel; this brain network is called the limbic system. The limbic system controls many aspects of...