They were cigarette smokers. Then the stroke conquered their addiction.

Scans of the affected brain often produce a map of the irreparable losses, revealing where the damage causes memory difficulties or tremors.

But in rare cases, these scans can reveal just the opposite: cutting out areas of the brain where infection miraculously relieves someone’s symptoms, providing clues about how doctors might do the same.

A team of researchers has now taken a new look at a set of these brain images, taken from nicotine-addicted cigarette smokers whose strokes or other injuries helped them quit spontaneously. The scientists said the findings demonstrated a network of interconnected brain regions that they believe underpin addiction-related disorders that may affect tens of millions of Americans.

The study, published in the scientific journal Nature Medicine on Monday, supports an idea that has recently gained traction: that addiction lives not in one region or another of the brain, but rather in a circuit of regions linked by thread-like nerve fibers.

The findings may provide a clearer set of targets for addiction treatments that deliver electrical impulses to the brain, new techniques that have shown promise in helping people quit smoking.

Dr. said. Juhu Gutsa, one of the study’s lead authors and a neurologist at the University of Turku in Finland. “Hopefully we will then have a very good idea of ​​those regions and networks.”

Research over the past two decades has reinforced the idea that addiction is a disease of the brain. But many people still think that addiction is voluntary.

Some independent experts said the latest study was an unusually powerful exposition of the brain’s role in substance use disorders. Among smokers who had had strokes or other brain injuries, those who had damage to a particular neural network experienced immediate relief from their cravings.

The researchers replicated their findings in a separate group of patients with traumatic brain injury who had completed an alcohol dependence risk assessment. The brain network associated with reduced risk of alcoholism was similar to that for reduced risk of nicotine addiction, suggesting that the circuit may underlie a broader set of dependencies.

Thomas McClellan, MD, professor emeritus of psychiatry at the University of Pennsylvania and former deputy director of the Office of National Drugs Control Policy, who was not involved in the study, said. “It relaxes a lot of the stereotypes that still circulate in the addiction field: that addiction is bad parenting, addiction is a weak personality, and addiction is a lack of morals.”

In recent years, a series of studies have identified specific areas of the brain where a lesion or injury appears to be associated with addiction relief. But the goals kept changing.

Dr. said. Hamid Ekhtiari, an expert in addiction treatment at the Laureate Brain Research Institute in Tulsa, Okla.

In the new study, Dr. Joutsa applied sophisticated statistical techniques to an old set of brain scans from Iowa smokers who had suffered neurological injuries. An earlier analysis of the same scans had suggested that patients with damage to the insula, a brain region involved in conscious urges, were more likely to quit smoking.

But Dr. Joutsa noted, referring to the same scans pixel by pixel, that many patients without insula injuries also lost the desire to smoke. “There was something about Insula’s story, but it wasn’t the whole story,” he said.

working with dr. Michael Fox, MD, assistant professor of neurology at Harvard Medical School, Dr. Joutsa examined a second set of scans of stroke smokers in Rochester, New York.

The team struggled to find individual brain regions where injuries helped patients quit smoking. Instead, the researchers turned to standard brain connectivity graphs that chart how activity in one area correlates with activity in another.

Suddenly, the researchers were able to identify networks of connected brain regions where injuries caused immediate relief from nicotine cravings and other networks where it did not.

Dr. said. Fox said. “If you take into account the way the brain communicates, you can improve treatment.”

The study didn’t take into account how patients’ home lives — how often they were exposed to cigarettes, for example — might affect their habits. Patients who are thought to have gone into addiction remission after they had stopped smoking generally reported no desire to smoke and had not started again during their follow-up.

However, the researchers looked at whether other injury-related changes — to intelligence or mood, for example — could help explain the disappearance of nicotine cravings in some patients. They didn’t seem to make a difference in the end.

Outside experts said parts of the brain network identified in the study were familiar to them from previous research. Dr. Martijn Figee, a psychiatrist at the Center for Advanced Circuit Therapies at Mount Sinai in Manhattan, is studying how electrical impulses delivered to the brain can treat obsessive-compulsive disorder, depression, and addiction. In general, he said, addiction appears to be associated with underactivity of the brain’s cognitive control circuit and overactive reward-related circuits.

By applying electrical stimulation to the surface of patients’ heads or using more invasive methods such as deep brain stimulation, doctors can suppress activity in certain areas, mimic the effect of an injury, and elicit activity in others. The study identified one area, called the medial polar frontal cortex, that seemed to be a good candidate for excitatory stimulation. That area overlapped with a treatment goal recently approved by US regulators to help smokers quit.

This treatment uses an electromagnetic coil placed on the patient’s scalp to deliver electrical impulses to the surface of the brain. Other techniques include implanting electrodes in specific areas of the brain or permanently deactivating delicate brain regions.

Dr. said. Fiji said.

While brain stimulation has become more popular for treating depression and OCD, use of those treatments for addiction has been slower. It will take years to honey these techniques, the researchers said.

Despite studies showing that electrical or magnetic stimulation can reduce craving for addictive substances, it is not clear how long these effects last. Some of the most promising targets are deep in the brain. Accessing them may require deep brain stimulation or a certain type of file that has only recently become available. Fiji said.

Knowing where to direct brain stimulation also doesn’t solve the question of how often to use, the scientists said. And the connections are different in different people’s brains, increasing the possibility that customized treatments will be needed.

The researchers said that people with addiction were slower to adopt brain stimulation than those with depression or movement disorders, partly reflecting the taboo about thinking of addiction as a brain disorder.

There may also be structural challenges. Judi Luigis, assistant professor of psychiatry at the University of Amsterdam Medical Centers, recruited among a group of thousands of patients at addiction treatment centers in the Netherlands to study deep brain stimulation. Within three years, only two patients had started the trial.

Dr. Luigis and colleagues write that substance use disorder patients may have avoided the procedure in part because their motivation to treat the illness fluctuated more than it did in patients with OCD.

And the instability that often accompanies substance use disorders can make it more difficult to invest in time-consuming treatments. Only one-third of patients who had an appointment with the research team brought a family member or friend, Dr. Luigjes found.

Some scientists are working to address these concerns. For example, the addiction team at Mount Sinai administered minimally invasive brain stimulation to patients at home or in community centers rather than a hospital, reducing barriers to treatment.

But while the brain may be an entry point for addiction treatment, Dr. It might not have been the most important thing, Luigis said. Other scientists have also argued in recent years that the focus on the addiction model of brain disease has diverted attention and money from research that addresses the social and environmental factors that contribute to addiction.

“We put a lot of our hopes, money, and energy into one side,” she said, referring to the field’s focus on brain stimulation. “I don’t know if it will pay the way we thought it would.”

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