ABSTRACT

Joutsa, J., Moussawi, K., Siddiqi, S.H. et al. Brain lesions disrupting addiction map to a common human brain circuit. Nat Med (2022).

https://doi.org/10.1038/s41591-022-01834-y

By studying brain scans of human patients who incurred lesions in their brains after an accident, and then spontaneously quit smoking, researchers map out the brain networks associated with addiction. The study published in Nature Medicine sheds light on areas of the brain that can be used as target for modulation and therapy for addiction to nicotine or alcohol. The authors of the paper caution that more larger studies need to be done to ascertain what side effects such modulation and therapy will produce.

The harms of substance abuse

Substance use is a term in common parlance that includes the use of a range of products, including psychoactive drugs. Psychoactive drugs are substances which when taken or administered into the system cause an alteration in mental processes, such as perception, consciousness, cognition and mood or emotions. Psychoactive drugs include alcohol and nicotine. While not all of these are addictive, substance use disorders are a major health hazard. They affect 8-10% of adult population and are a leading cause of death. Hence there is an interest in understanding how to treat addictions and substance use disorders.

Among these, tobacco alone is a major factor, and the data on tobacco use is grim. India is the second largest consumer of tobacco. According to the Global Adult Tobacco Survey (2016-17) nearly 267 million adults (15 years and above) in India, which is about 29% of India’s adult population, use tobacco in some form or the other. To add one more datapoint to this, about 8 million people annually die because of tobacco use — that is nearly half the people who use it — and of this, over 7 million are primary users and around 1.2 million are non-smokers exposed to tobacco in a passive manner.

Treatment for substance use disorders are inadequate and do not show promise in the long term. New methods of treatment try modulating specific parts of the brain which are believed to be implicated in addiction. Now, a study published in Nature Medicine tries to identify the network of regions in the brain that are involved in substance addiction. The study finds that brain lesions that lead to spontaneous remission of tobacco addiction in people affect a part of a common brain network. Further, they find evidence of commonality of this network across different substance addictions and this seems to suggest new targets for neuromodulation therapies.

Brain circuits, not regions

The researchers studied the brain scans of 129 patients addicted to smoking at the time they suffered localised brain damage. Of these, 60% were male and their average age was 56 years. Of the 129, 34 patients experienced spontaneous addiction remission following the injury. That is, they were able to quit smoking without experiencing craving or relapse. They also show that though the lesions associated with remission occurred in many different places in the brain, these can be mapped to a specific brain network. Additionally they found this network was reproducible in the case of other substances of abuse, in independent groups of people with lesions. These included people with reduced risk of alcohol addiction and case reports of lesions that disrupted addiction to substances other than nicotine.

Broadly speaking, the authors found that brain circuits rather than specific brain regions may be involved in causing addiction, and damage to these circuits — whatever the reason —may result in remission. Common areas were found for alcohol and tobacco addiction. “These results did not correlate with psychological tests which indicates that anatomical rather than behavioural factors may be involved,” says Dr. Smita Deshpande who is a professor of psychiatry at St. John’s Research Institute, St. John’s National Academy of Health Sciences, in Bengaluru.

Dr. Deshpande also points out that the authors have measured alcohol dependence by a questionnaire which did not actually mean that those people were alcohol dependent. “They also did not look at issues such as degree of recovery, ability to function in daily life, family support, occupational factors and psychological factors other than those described in the paper,” she says. It is also not specified for how long the patients studied had quit smoking (remained free of nicotine), “as relapses are common in all addictions.”