Solomon discovered two components in every reaction to an emotional situation. The first component he called the A reaction. It is short-lived and intense. For example, while receiving an award, you may feel great joy at the moment when you are handed your medal or certificate. This response probably correlates with neural activity in the brain; it is quick and almost simultaneous with experience of the emotion-causing stimulus.
The B reaction is opposite from the A component in hedonic value. In other words, if the A reaction is a happy emotion, the B reaction is sad, and vice versa. The B response is slower to build and slower to decay. An hour after getting an award, you may feel a bit let down, but the feeling gradually disappears toward the end of the day.
Sometimes a B reaction can be rapid. Solomon points out that a small child who is in a good mood can be put into a bad mood by giving the child a lollipop then taking it away. Instead of returning to a neutral emotional state, the child reacts to sudden reinforcement, by crying. That reaction is immediate.
However, most of the time, a B reaction is slower. The slower B reaction is probably hormonal, involving chemical messengers that move in the bloodstream. An hour after a moment of great excitement, the body's response might be, "You've been under a lot of stress; time to get away from it all, rest, and recuperate."
The B response occurs with both pleasure and pain. Both lead to rebound reactions which Solomon called hedonic contrast. Feelings of joy are often followed by a let-down or irritability, a few hours later. Feelings of tension and anger may be followed by a more happy or mellow period.
Drug addiction phenomena can be explained with the opponent process theory. First an addictive event causes a large A reaction, for example, great feelings of joy, with possibly a mild depression as an aftereffect. This is sometimes called the honeymoon period or the first time...