People who use cocaine or methamphetamine on a regular basis may have differences in those brain regions that are involved in choosing between right and wrong, compared to people who don't use these drugs, according to a new study of prison inmates.

Researchers found that, during a task that tested prison inmates' moral decision making, inmates who had regularly used cocaine or methamphetamine showed less activity in the amygdala, a region in the brain that helps a person to regulate and understand emotions, compared to inmates who had never regularly used either of the two drugs.

Moreover, the longer that a person used either of the two stimulant drugs, the less activity they had in the anterior cingulate cortex, a region of the brain that coordinates mental skills involved in decision making that involved moral issues. [10 Things You Didn't Know About You]

"This is the first study to suggest impairments in the neural systems of moral processing in both cocaine and methamphetamine users," lead study author Samantha Fede, a graduate student in the department of psychology at the University of New Mexico, said in a statement.

However, while the study showed an association between drug use and differences in the brain regions involved in moral cognition, it does not prove that drug use causes these changes, the researchers noted. It is possible, for example, that people whose brains already have differences in these regions are prone to start using these drugs.

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And so although more research on this topic is needed, the study provides a better understanding of brain differences in stimulant users, she said.

In the study, the researchers asked more than 200 men incarcerated in New Mexico and Wisconsin prisons whether they had ever used cocaine or methamphetamine on a regular basis, which the researchers defined as at least three times a week. The study group contained 131 stimulant drug users and 80 nonusers, the researchers said. The users in the study had regularly used cocaine or methamphetamine for about nine years, on average.

The researchers then scanned the brains of all the inmates while they completed a task in which they evaluated whether or not certain phrases were morally objectionable.

The researchers did not find significant differences in the responses of the drug users and nonusers when they performed this task – the members of both groups were equally likely to say a certain phrase was indeed objectionable.

However, the researchers discovered differences between the groups when it came to the amount of activity in certain brain regions that are related to moral processing. [10 Things You Didn't Know About the Brain]

The new findings are in line with previous research, which has suggested that the volumes of these same brain regions may be decreased in stimulant drug users, compared with nonusers, the researchers said.

The men in the new study were in minimum- to medium-security prisons, which means that many of them had been imprisoned for drug crimes, as opposed to violent crimes, Fede told Live Science. This means that the drug users in the study can be expected to share more similarities with drug users in general, including those who are not incarcerated, than they might share with violent offenders.

However, more research is needed to confirm that the results of the new study would hold true in drug users who are not in prison, she said.

The new study was published July 12 in the journal Psychopharmacology.

Originally published on Live Science.

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