This article is supported by the NSW Government, who want to help empower you to quit smoking. In this article, we look at how addiction affects your brain.
Even when we know that something—drugs, alcohol, smoking, checking our Instagram for the thirtieth time that day—might be bad for us, the pull can be too strong to resist. While addiction is often described as the compulsive seeking of, and partaking in, behaviours despite negative consequences, addiction can also be seen as a disorder of the brain’s reward system. To best understand how addiction works, we need to understand a bit about this system.
The brain’s reward system
The brain’s reward system is a group of structures that are activated by rewarding substances, such as drugs and alcohol. A key component of this system is the Ventral Tegmental Area (or VTA), a group of neurons located in the midbrain. The VTA produces the neurotransmitter dopamine (known for its role in reward and pleasure), and it’s the release of dopamine that enables the VTA to communicate with other parts of the reward system. The connection between the VTA and the nucleus accumbens (a reward and motivation centre located towards the front of the brain) is known as the mesolimbic pathway, and is the most important reward pathway in the brain. Other forebrain regions linked to the VTA via dopamine include the amygdala (the emotional centre of the brain), the prefrontal cortex (needed for planning and decision-making), and the hippocampus (the area responsible for memory formation).
When these regions of the brain are activated, we feel pleasure, as well as the desire to repeat the activity. We also make memories about the rewarding substance, so that in the future we can try to emulate the experience.
When addiction kicks in
We’ve established that when we first use an addictive substance, the release of dopamine and subsequent reward system activation causes feelings of anticipation, pleasure, and desire. But as we continue to use the substance, the reward system function begins to change. This is why we might lose control over the use of the substance, may need more of it to have the desired effect (tolerance), or may experience withdrawal symptoms.
“Drug use can impair the functioning of brain regions implicated in decision-making, hence asking an addict to “make a good” can be futile, just like asking someone with depression to “cheer up” can be futile,” says Professor Andrew Lawrence, Head of Behavioural Neuroscience at the Florey Institute of Neuroscience and Mental Health. “As use progresses it can become habitual in nature rather than goal-oriented. In this case the behaviour is more “automatic”. In many respects drug addiction could be described as a pathological habit,” he tells VICE.
How addiction reprograms both the reward system and the brain depends on different factors, including the type of addictive substance. For example, dopamine transporters are reduced in the striatum (another part of the reward system) with repeated meth exposure, and cannabinoid receptors are reduced in this area when cannabis is used. The speed at which these changes occur relies on lots of other factors, for example, it may be faster if there are genetic vulnerabilities, chronic stressors, psychiatric conditions, or early drug abuse.
One of the many biochemical changes that occurs in nearly all forms of addiction is the increased activity of the protein ΔFosB in the nucleus accumbens. ΔFosB is a transcription factor—a protein that controls gene expression—which when present leads to the expression and suppression of a number of genes involved in addiction.
The amount of ΔFosB present in neurons is proportional to the amount of drug used: if you use drugs chronically, ΔFosB will accumulate at higher levels and cause stronger addictive symptoms, including increased drive and motivation for drugs. Additionally, as ΔFosB is a very stable and long-lasting protein, even if you stop using the drug it can exert its effects for weeks after.
There are three main addiction management strategies being used today.
Withdrawal (otherwise known as ‘detox’ or ‘going cold turkey’) is where a person abstains from taking a drug so it’s cleared out of their body. This process is accompanied by withdrawal symptoms, the nature of which depends on the drug being stopped. Some drugs like alcohol have potentially life-threatening withdrawal effects, so it’s important that preventative medications (such as benzos to prevent alcohol withdrawal seizures and delirium tremens) are prescribed.
Drug replacement therapy involves switching a harmful addictive drug for a legal drug in order to control withdrawal symptoms, reduce cravings, or alter the effects of the addictive drug. Over time, the amount of substitution therapy can be reduced until no withdrawal symptoms or cravings are present. A well-known example of this is using nicotine replacement therapy for people addicted to smoking. By using patches, gum or inhalers, a person gets their daily dose of nicotine while avoiding the myriad of toxic chemicals present in cigarette smoke. Another example is where controlled amounts of methadone or buprenorphine are given to people addicted to opioids such as heroin. While methadone and buprenorphine are also opioids, they have a reduced risk of overdose and are not associated with IV use (a very risky behaviour).
Evidence-based psychosocial treatments such as cognitive behavioural therapy, motivational interviewing, and relapse prevention, can play an important role in curbing addiction. They can allow a person to develop skills, receive necessary information, challenge and explore their attitudes and values, and develop sustainable behaviours and motivations that allow them to stay addiction-free. Interestingly, it has been shown that psychosocial treatments are more effective when used in conjunction with medicine-based therapies (such as drug replacement therapy) than when medication or psychosocial treatments are used alone.
The future of addiction
Addiction is highly complex and we’re far from understanding all of the changes that occur in the brain. It’s important that research into addiction continues so that new treatments and preventative strategies can be identified.
An exciting area of research, some of which is being done at the University of Adelaide, is looking at how the immune system affects addiction. More specifically, cocaine and opioids can bind to Toll-like receptor 4 (TLR4—a protein that plays a key role in the immune system) on certain cells in the brain. When these drugs bind to TLR4 their addictiveness is amplified, making this receptor a potential target for opioid and cocaine addiction treatments. Studies have already shown that a particular configuration of the drug naloxone can block TLR4 and stop the immune system’s response to opioids.
Other Australian addiction research, this time at UNSW, has focused on the ventral pallidum (VP), a part of the brain known for its role in promoting relapse. It turns out that silencing specific communication pathways between the VP and the VTA and the VP and the subthalamic nucleus (yet another brain region in this hugely complicated reward system) reduces alcohol-seeking behaviour and motivation in rats. This opens up the potential for using deep brain stimulation, a treatment currently used for Parkinson’s disease, in addiction management.
This article is supported by the NSW Government, who want to help empower you to quit smoking. You can take the first step to quitting smoking here.