Researchers Identify Brain Network that is Uniquely Activated Through Injection vs. Oral Drug Use

Results from a new clinical trial suggest that a group of brain regions known as the “salience network” is activated after a drug is taken intravenously, but not when that same drug is taken orally. When drugs enter the brain quickly, such as through injection or smoking, they are more addictive than when they enter the brain more slowly, such as when they are taken orally.

Although the brain circuits underlying these differences are not well understood, this study offers new information that helps explain what may be causing this difference. The study was published in Nature Communications and led by researchers at the National Institute on Drug Abuse (NIDA) and the National Institute on Alcohol Abuse and Alcoholism (NIAAA), parts of the National Institutes of Health (NIH), at the NIH Clinical Center.

It has been commonly accepted that the faster a drug enters the brain, the more addictive it is; but researchers have struggled to understand exactly why. Now, using one of the newest and most sophisticated imaging technologies, when study participants received intravenous administration of substances, researchers were able to observe increased activity in two regions of the brain, the dorsal anterior cingulate cortex and the insula, which are part of the brain’s salience network. These same areas of the brain were not activated after taking substances orally. Study findings were consistent across all twenty research participants. Such clear and consistent fMRI results across 100% of participants is rare in imaging research.

The salience network attributes value to things in our environment and is important for recognizing and translating internal sensations—including the subjective effects of drugs. This research adds to a growing body of evidence documenting the important role that the salience network appears to play in substance use and addiction. For instance, studies have shown that people who experience damage to the insula, part of the brain’s salience network, can have a complete remission of their addiction.

The results add to the growing evidence that the brain’s salience network is a target worthy of investigation for potential new therapies for addiction.