New findings about the role that the brain chemical dopamine plays in reward-based learning may be helping researchers come to a better understanding of why some people are prone to opiate addiction and other forms of chemical dependency while others are not.

A team of investigators from the University of Michigan and University of Washington found that individuals’ brains respond differently in different situation, and that this plays an important role in the likelihood that they will experience addiction.

The findings contradict earlier understanding of the function of dopamine in the brain. Scientists have thought that stimuli would always result in roughly the same release of dopamine, and that other factors dictated how an individual handles this.

However, after studying the circumstances under which dopamine is released by brains of rats, the researchers found wide variation. After conditioning the mice to press a lever to receive food, the researchers found that the brains of some released dopamine as they were pressing the lever, while others showed no dopamine response until the food appeared.

The researchers believe that their findings have major implications for the treatment of addicts who have come to associate certain people, places or situations with drug use.