The human brain is naturally wired to reward itself with the “feel-good” neurotransmitter dopamine when its basic needs of food, water, and sex are met. Addiction taps into this reward system to “trick” the brain into wanting more. This is why opioids like fentanyl and carfentanil, which increase dopamine production in the brain, have taken such a strong hold of North America, with over twenty million substance abuse cases recorded by the USA’s National Survey on Drug Use and Health in 2016 alone.
But new information has recently come to light to suggest that more than just dopamine production in the brain is affected by substance abuse. After collecting more than one hundred studies and publications, doing a meta-analyses, that used Magnetic Resonance Imaging (MRI) to examine the effects of opioids on the brain’s reward network, the National Survey on Drug Use and Health found that, contrary to prior belief, neurotransmitters aren’t the only part of the brain affected by drug use, and that six separate parts of the brain—including areas that deal with reward, habit, salience, as well as executive, memory and self-directed networks—are all affected by opioids in specific ways.
“Because we showed that the effects are very distributed across the six different networks,” says Anna Zilverstand, lead study author and assistant professor of psychiatry at the Icahn School of Medicine at Mount Sinai in New York City, “We can conclude that an approach that only looks at one of these networks isn’t really justified…[and] this [finding] will hopefully lead other researchers to look beyond the reward network.”
An example of the long reach of opioids is the effect they have on memory, as some research suggests that people with substance abuse disorders shift learning from the memory network to the habit network, which then drives habitual behaviour like finding and using drugs.
Additionally, the self-directed network, which is associated with self-awareness and self-reflection, will increase cravings in people with substance addictions, while the executive network—which controls goal oriented behaviour—can be compromised to affect a decreased rate of inhibition. In regards to the salience network, it redirects the attention it pays to social and environmental clues to feeding the body’s addiction, which subsequently increases cravings.
Specific drugs are not more impactful on the brain’s networks than others. As Zilverstand said, “The most surprising [finding] was how consistent the effects were across addictions [and] the fact that the effects are quite independent of the specific drug use points to them being something general that might actually precede drug use rather than be a consequence of drug use.”
Zilverstand encourages the scientific community to further differentiate between existing abnormal brain behaviours in the six networks, and to determine whether those areas of difference are made more noticeable after drug use. This will help researchers to understand whether these abnormalities exist in some cases naturally prior to any drug use, and perhaps lead to some understanding of whether or not these traits indicate that certain people are more prone to drug addiction.
Zilverstand cites the Adolescent Brain Cognitive Development Study that is currently monitoring ten thousand youth across the USA, ages nine to twenty, for substance abuse and addiction problems. Through this study, Zilverstand believes “We’ll be able to see if the effects that we found [in the review] exist in youth who have not yet abused drugs.” Currently, it’s not known whether the brain’s networks can recover and resume their “normal” state once drug use is stopped.
“We know that four of the networks (partially — not fully) recover but not yet what happens to the other two networks,” says Zilverstand. This is due to the fact that some of the regions of the brain under study are small and don’t send out strong signals for analysis. Researchers believe that drug use can affect other parts of the brain, but we simply do not yet have the technology to identify the potential damage.