The role of the infralimbic cortex
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-seeking behavior. 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.
Muting the infralimbic cortex
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.”
The limbic system is the seat of emotional activity. This makes it a great area to study for addiction/impulse control/reward centered activities.
If we can come with ways to enhance infra-limbic activity that may provide another way to treat addiction. I don’t think most recovering addicts/alcoholics will be to receptive to the idea of brain surgery to implant some leads. Other ideas such as transcranial stimulation and perhaps EEG neurofeedback may be helpful in this area however. This type of basic science is good to know as we delve into the inner workings of addiction!