Drug abuse and addiction is a big problem in the United States and much of the industrialized world. In 2014, 21.5 million U.S. adults battled a substance use disorder.
In 2007, drug abuse cost the country’s society almost $200 billion in legal, criminal justice, healthcare, and workplace costs.
Drug addiction has the potential to ruin friendships, careers, and lives. It is a topic of much debate among scientists, and there is still a lot of ground to cover before we can understand exactly how addictive substances are able to exert their control.
Over recent years, the ways in which the brain reacts to addiction have come under close scrutiny. The pathways and chemicals involved are steadily being unpicked, and one area of particular interest is the infralimbic cortex (IL).
The IL is part of the ventromedial prefrontal cortex, positioned toward the front of our heads. One of the ventromedial prefrontal cortex’s roles is inhibiting emotional responses; it plays a role in self-control.
The IL has been found to play a substantial part in the initiation of cocaine-seekingbehavior. Specifically, activation of the IL appears to help suppress learned addictive behaviors.
Recently, researchers from the University of Iowa (UI) in Iowa City set out to investigate this relationship in more detail – more specifically, they wanted to understand more about how the IL controls cravings and other habit-forming behaviors, and whether or not it could be manipulated to moderate impulsive behavior.
Andrea Gutman, a postdoctoral researcher in the UI Department of Psychological and Brain Sciences, led the team of researchers.
Rats were provided with a lever that, when pressed, administered cocaine. They had access to the lever for 2 hours per day for 2 weeks. For the following 2 weeks, the rats did not receive cocaine when they pressed the lever.
As the rats cottoned-on to the fact that the drug supply had dried up, they pressed the lever less and less, until, by the close of the second 2-week period, they did not press it at all. The rats had learned to curb their cravings.
A second group of rats was given the same regimen as the control rats: using cocaine for 2 weeks and then going without it for the second 2 weeks. For the first 5 days of the cocaine-less third week, the researchers turned off activity in the rats’ IL for 20 seconds every time they pressed the lever.
By silencing the neurons within the IL with each lever press, the rats did not learn to curb their appetite. Instead, their cravings remained intense throughout the entire study, even when no drug was being administered.
Interestingly, the second group of rats was also more likely to relapse into addiction than those that underwent normal withdrawal.
The findings confirm earlier work that demonstrated a link between the IL and addiction, as well as also giving insight into the importance of timing. Their study hints that activity in the IL immediately after an unreinforced level press is important for reducing cocaine-seeking behavior.
“No study has looked intensively at exactly how the infralimbic cortex functions, nor the importance of the first 5 days of treatment when it comes to curtailing drug-seeking behavior,” says the paper’s co-author Ryan LaLumiere, an assistant professor in UI’s Department of Psychological and Brain Sciences.
“And, while our experiments involved cocaine, we think the results could hold true for the infralimbic cortex’s role in conditioning withdrawal and relapse from other addictive substances, including opioids.”
Prof. Ryan LaLumiere
Further research is likely to be hot on this study’s heels, and, although using this knowledge to treat drug addicts is a long way off, it does offer fresh hope. Tailoring drugs to work at the IL, at the right point in time, could be highly effective in curbing addictive behavior.