This theory of emotion may help to explain the habituation of emotional responses. The onset of a stimulus (i.e. drug) elicits an emotional reaction (euphoria) which quickly reaches a peak in intensity and then gradually declines to a plateau. This initial emotional response is called the primary emotional response. With the offset of the stimulus (drug is eliminated from the system), there is a sudden switch to an emotional after-reaction that is in the opposite direction as the initial emotion (dysphoria). This emotional response is called the emotional after-reaction.
Solomon and Corbit theorized that there are 2 intervening variables, internal processes, that produce this pattern of responding.
The a-process, which is largely responsible for the initial emotional reaction and
the b-process, which is responsible for the after-reaction.
The a-process is initiated by the presentation of the stimulus. It is a fast-acting response that decays quickly when the stimulus is taken away.
The b-process is initiated by the a-process, but it is more sluggish in its rise and decay.
What happens with repeated presentations of the stimulus?
With repeated presentations of the stimulus, we see a decrease in the primary emotional response (habituation) and an increase in the after-reaction. So, after repeated drug use, the drug is no longer so effective in producing euphoria (tolerance) and leads to a greater withdrawal reaction.
Why does this happen?
According to their theory, the a-process does not change, but with repeated presentations of the stimulus, the b-process becomes stronger and longer-lasting.
This theory has been used to explain changes in a diverse range of human behaviors, including skydiving and exercise. For example, the first time a person jumps from a plane, they have intense fear. When they land, they feel euphoric. With repeated jumps, the fear is less, but the subsequent euphoria is much greater. Same with exercise. Initially, it is painful, but may lead to longer-lasting euphoria after exercise.
Koob adds two elements to this model. He first adds a sensitization, increasing the initial emotional response to the drug. He also adds a change in set-point, so that the neutral hedonic state is no longer achieved in the absence of the drug.