There are four mood engines in your brain.

Scientifically speaking, these are called "neurotransmitters." The neurotransmitters specific to mood regulation are serotonin, catecholamines, GABA, and endorphins. Each neurotransmitter has a distinct role in your mood depending largely on the availability of the amino acid required to fuel it.

How do you know how you've run too low on fuel? By taking The Mood Checkup and evaluating what mood symptoms are bothering you the most.