The loved ones of an individual addicted to a destructive substance such as methamphetamine or heroin often watch, perplexed, as the addict destroys their life for a substance that makes them miserable.
A new study may help explain why addicts keep going back to a substance that produces an unpleasant consequence. Researchers at the University of Michigan recently uncovered clues to the change in motivation that often occurs in drug users as they become addicted by testing similar behaviors in animal models.
The study found that a salt appetite can be manipulated in rats to transform something repulsive into a craving. Lead author Mike Robinson, a research fellow in the Department of Psychology, explained that the findings illustrate how activity in the brain could activate certain processes that cause a person to want something that they have previously disliked.
Robinson says that the transformation of motivation is rooted in the use of events to activate certain circuits in the brain, located in a structure known as the nucleus accumbens. It is located at the base of the front area of the brain and is affected by the use of addictive drugs.
Certain reward stimuli are triggers for motivation, such as when a smell introduces hunger in a person who wasn’t previously hungry. Similarly, drug cues create cravings in those who are trying to abstain from using the drug. In some situations, these cues can activate desire for a substance that has been regarded as unpleasant.
Rats were exposed to a metal object that either represented a pleasant sugary taste or a strong Dead Sea salt taste. The rats were conditioned to nibble the sweet object and avoid the salty object.
At one point during the study, the rats woke to the experience of a sodium appetite introduced through drugs administered the previous night. When exposed to the salty objects, the rats were immediately drawn to the salty object and nibbled at it as if it were the sweet object they had previously preferred.
Robinson said that the salt cue became the focus of the rats’ cravings, despite their experience of the salt tasting unpleasant.
The immediate changes in the brain help provide insight into how something such as taking a drug could become a desirable event, even though the person taking the drug may be familiar with the unpleasant effects of the drug.
Robinson says that the study’s findings help explain how drugs can derail a person’s natural reward system.
Identifying specific areas of the brain affected by a drug can also be helpful in developing new strategies for treatment. Certain addictions to substances like heroin and methamphetamine can be exceptionally difficult to overcome and identifying this area of the brain as immediately impacted by the drugs may help in the development of therapies for treatment.