It is widely accepted that our perception of medicine influences the influence a treatment has on our health. A new study reveals that our brain’s reaction to a medication differs depending on whether the drug is injected or taken orally.
The study, led by a team at the US National Institutes of Health (NIH), was conducted to investigate another interesting phenomenon: drugs that reach the brain more quickly are more addictive.
The addictive quality has to do in part with the release of dopamine, but here the researchers found that a region of the brain known as the salience network is activated when drugs are taken intravenously, but not when they are taken orally.
“We’ve known for a long time that the faster a drug enters the brain, the more addictive it is, but we don’t know exactly why,” says NIH psychiatrist Nora Volkow.
“Now, using one of the newest and most sophisticated imaging technologies, we have an idea.”
The prescription stimulant methylphenidate was used for the study. Typically used for conditions such as ADHD, the 20 participants involved in the study did not have a relevant diagnosis. In addition to administering the medication intravenously and orally, they were also asked how they felt after taking it.
In addition to self-reported observations, the researchers also used PET scans to monitor dopamine levels in the brain and fMRI scans to monitor overall brain activity. As expected, dopamine levels spiked faster when injections were used.
It was in fMRI scans that differences appeared in two main regions of the salience network, the dorsal anterior cingulate cortex and the insular cortex. These areas were only activated after injections, the most addictive method of drug administration.
Salience network activity was consistent with greater feelings of euphoria felt by participants. This part of the brain has previously been linked to drug addiction, although solid and substantial evidence was lacking until now.
This is all invaluable information when it comes to figuring out how treatments should be administered to patients and how addictions can be addressed. The salience network is known to be important for interpreting internal sensations and for assigning value externally.
One of the next steps could be to conduct experiments in which activity in the salience network is deliberately blocked and then see if study volunteers have the same feeling of being high.
“Understanding the brain mechanisms underlying addiction is crucial for informing prevention interventions, developing new therapies for substance use disorders, and addressing the overdose crisis,” says Volkow.
The research has been published in Nature Communications.