Brain Circuits and Addiction

Human brain lesions provide lead to brain circuit that could be targeted to treat addiction

MRI-type image of brain scan, profile view
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Using a new technique known as lesion network mapping, Harvard Medical School researchers at Brigham and Women’s Hospital have mapped addiction remission to entire brain circuits rather than specific brain regions, pointing to new targets for treatment. Their results are published June 13 in Nature Medicine.

In the United States, substance use disorders are a leading cause of death among young people. Treatments such as deep brain stimulation hold promise for helping people overcome addiction, but many questions remain about which brain areas should be targeted.

The new work contributes to growing knowledge gained from patients who are no longer addicted to nicotine after experiencing a brain lesion, such as a stroke. 

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“By looking beyond individual brain regions and, instead, at the brain circuit, we have found targets for addiction remission and are eager to rigorously test them through clinical trials,” said Michael D. Fox, HMS associate professor of neurology at Brigham and Women's.

“Ultimately, our goal is to take larger steps towards improving existing therapies for addiction and open the door for remission,” he said.

Neuromodulation therapies, such as deep brain stimulation, transcranial magnetic stimulation, and MRI-guided focused ultrasound, allow clinicians to directly target brain circuits and improve symptoms in ways that may not be possible through treatment with medication. But knowing the location to target is critical.

In a previous study, researchers used lesion network mapping to examine patients whose essential tremors resolved, confirming targets used in treatment with deep brain stimulation. The study authors set out to apply the same approach to addiction remission.

“Although we know a great deal about the neurobiological mechanisms in addiction, treatment options are still very limited. Our findings with essential tremor made us realize the potential of this approach to localize key brain circuits mediating symptom improvement,” said Juho Joutsa of the Turku Brain and Mind Center and Clinical Neurosciences at the University of Turku.

Fox and colleagues used data from two independent cohorts of patients with an addiction to nicotine who then suffered a brain lesion, usually from a stroke.

Comparing lesions

Fox’s team compared lesions in patients who were unable to quit smoking to lesions resulting in remission of smoking addiction. They then used a database known as the human connectome to map each lesion to the larger brain circuit.

They found that the two smoking lesion datasets that led to remission of smoking addiction mapped to a specific brain circuit.

To their surprise, they also discovered in a third alcoholism lesion dataset that a reduced risk of alcoholism mapped to a similar brain circuit, suggesting a potentially therapeutic, targetable neural pathway for addiction in general, rather than addiction to a specific substance. 

“Although neuromodulation treatments using electricity or even brain lesions have shown promise in relieving substance addiction, the therapeutic target has been unclear,” said Fox.

“Now that our study has identified a target—a specific human brain circuit—we hope to test whether targeted neuromodulation to this brain circuit provides sustainable symptom relief to our patients,” he said.

The authors acknowledge two primary study limitations. First, the results are solely based on retrospective analysis of existing datasets and, second, the datasets examined covered only specific substances of abuse.

The researchers therefore advocate for prospective validation of their findings through clinical trials testing and an examination of additional substances of addiction to determine whether their findings can be applied widely.

“We were excited to discover that our mapped lesions associated with addiction remission led back to a common brain circuit. While our findings point towards therapeutic targets for addiction, we need to test these targets in randomized clinical trials,” said Fox.

“We study brain lesions in the context of the brain circuit because it provides a powerful way to understand the causal links between addiction and our neuroanatomy. We have hope that we can make significant strides towards helping patients with substance use disorders,” he added.

This work was supported by the Academy of Finland (#295580), Finnish Medical Foundation, Finnish Foundation for Alcohol Studies, U.S. National Institute on Drug Abuse (NIDA DA 048085), Brain & Behavior Research Foundation, Intramural Research Program of the NIDA/NIH, Sidney R. Baer, Jr. Foundation, NIH (R01MH113929, R21MH126271, R56AG069086, R21NS123813), Nancy Lurie Marks Foundation, Kaye Family Research Fund, Ellison/Baszucki Foundation, and the Mathers Foundation.

Disclosures: Fox and Shan H. Siddiqi own patents on using brain connectivity to guide brain stimulation. Fox and Siddiqi have received investigator-initiated research funding from Neuronetics Inc., and are both consultants to Magnus Medical, all unrelated to the present work. 

Adapted from a Brigham and Women's news release.