Our brain thrives on novelty and dopamine helps us store information about novel situations. We know that dopamine is released when we receive a reward, but it is also involved in noting unexpected rewards. If you get more juice than you anticipated, your brain releases dopamine and sends it to the anterior cingulate in your frontal cortex, a brain region responsible for anticipating rewards and making decisions. Get less juice than you anticipated and, again, your brain will encode the information, but this time, by sending less dopamine to the anterior cingulate. If you get the same amount of juice you expected, no dopamine is released. This mechanism enables us to recognize patterns and learn which behaviors lead to risk versus reward.
How does this translate into drug and behavioral tolerance? When you use cocaine for the first time, your brain registers it as a pleasurable experience. After using it a few more times, you might notice that you don’t experience the same level of euphoria as before. That’s because the experience has lost novelty and your brain has learned to recognize the pattern. In other words, dopamine isn’t released since there isn’t anything novel about the experience. Tolerance is born. In order to achieve euphoria from cocaine, you must now use more.
The same process occurs with compulsive behaviors. The first few times you shoplift (and don’t get caught) you experience relief and pleasure, but with subsequent trials you notice a decrease in the euphoria you experience. So, you start shoplifting more frequently.
Note: There are many neurobiological mechanisms at play in addiction and compulsive behaviors and the role of dopamine in addiction and tolerance is just one facet of a complex biopsychosocial phenomenon.