Is There One Area of the Brain at the Root of Addiction?

Addiction is an affliction that only some people develop in particular circumstances due to certain stimuli. However, the disease of addiction isn’t treated quite the same as diseases like diabetes or cancer. Rather than giving an addict a treatment or medication that essentially alleviates the effects of addiction, he or she can hope only to gain and maintain control over the powerful effects of substance abuse. With such a strong behavioral component, one might think that addiction was more a moral sickness than anything else; and yet the evidence continues to indicate that addiction is a disease.

In order to find ways of preventing the development of addiction — or even to find more effective ways of treating it when it does develop — researchers continue to try to reduce this deadly, destructive force to its most essential, underlying mechanisms. By all appearances, there seems to be something at the heart of addiction’s development that eludes the naked eye, and which distinguishes addicts from non-addicts. If that one, singular moment in which a substance abuser becomes an addict could be compared to the flipping of a switch, we must determine where or what that switch is. In other words, what is it — biological, behavioral or otherwise — that facilitates the development of an addiction?

The Lateral Habenula

The human brain has a number of different zones, delineated or distinguished based not only on where they are located, but also according to specific duties. Most people are familiar with terms like “hemisphere” and “brainstem” while terms like “lateral habenula” and “ventral tegmental area” are less known. The lateral habenula 1 is located near the inner core of the brain not far from where the spinal cord begins and is part of a structure called the epithalamus. In terms of its function, the lateral habenula has been implicated in negative reinforcement, activated by experiences that involve punishment or a lack of reward. The lateral habenula has an inverse relationship with the ventral tegmental 2 and other areas of the brain involved in releasing dopamine, serotonin and other neurochemicals. When the lateral habenula is activated, it sends signals to the nucleus accumbens and other areas in the ventral tegmental area that causes them to essentially deactivate; conversely, when the ventral tegmental area is activated, the lateral habenula is inactive.

When a person has a negative experience from some sort of behavior or decision, the lateral habenula inhibits the release dopamine as part of the cognitive processing of the experience. With the experience stored as a negative memory, the individual becomes very unlikely to make the same choice or behave in the same way in the future. In effect, the lateral habenula allows individuals to learn from their mistakes and avoid situations and behaviors that might result in a negative experience.

Learning the Negative Outcomes of Substance Abuse

Anyone who has ever consumed alcohol to excess, whether inadvertently or intentionally, will remember waking the next morning with a hangover, which is the physical sickness an individual feels once the effects of a binge-drinking episode have worn off, usually indicating dehydration, lack of quality sleep, nutritional deficiencies and so on. In a study conducted by neuroscience researchers at the University of Utah, the lateral habenula was found to play an important role 3 in the development of alcoholism and, by extension, addiction as a whole. In particular, the researchers wanted to understand why one would abuse substances after experiencing a negative outcome like a hangover.

The study involved two groups of rats. The test group of rats had their lateral habenula deactivated while the lateral habenula of the control group were left functioning. Both groups were given intermittent access to a solution containing alcohol for a period of a couple weeks. The test group continued to escalate their drinking of the alcohol solution while the control group quickly tapered off their alcohol consumption. In another part of the experiment, both groups were fed a very sweet, palatable juice, and then injected with enough alcohol to cause the rats a hangover; the control rats with functioning lateral habenula learned to associate the juice with the feeling of hangover caused by the injection of alcohol and began avoiding the juice. However, the test group of rats with the inactive lateral habenula did not learn to associate the hangover with the sweet juice and continued to drink the juice anyway.

Is Addiction the Result of a Dysfunctional Lateral Habenula?

For an individual who consumes alcohol, the rewarding effects of alcohol consumption compete with the negative effects. Although intoxication might be pleasurable to some, the resulting hangover — or any other negative outcomes that might result from an individual drinking too much alcohol — deters most individuals from drinking to excess because the lateral habenula effectively logs the experience as having been unpleasant, which is negative reinforcement. In short, the lateral habenula is instrumental in decision-making as individuals weigh the possible costs and benefits of an experience according to how the experience has been processed previously. The implication of the University of Utah study is that an ineffective lateral habenula tips the balance by making it either difficult or impossible for negative outcomes to discourage that behavior in the future.

This study suggests that one potential cause that could lead to the development of addiction is an individual having an ineffective lateral habenula. Unable to learn from the negative consequences of substance abuse, such individuals may exhibit an escalation in their consumption behavior, which is how an addiction can develop. With continued research, a more thorough understanding of addiction and its underlying mechanisms will result in improved treatments and perhaps even more effective prevention efforts. As we continue searching for the root of this deadly disease, the day when a neurological scan identifies a person as being at risk for addiction before it develops may not be very far away. In the meantime, those who currently suffer from substance abuse have a number of treatment options available that can help them to regain their health and independence.

Sources:

1. http://www.neuroscientificallychallenged.com/blog/what-is-the-habenula2. http://thebrain.mcgill.ca/flash/i/i_03/i_03_cr/i_03_cr_par/i_03_cr_par.html3. https://healthcare.utah.edu/the-scope/shows.php?shows=0_ci0cdgi5Written by Dane O’Leary

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