The study of a hundred people affected by stroke reveals how the brain is unhooked from addictions
The brain circuitry for nicotine addiction is not the same as quitting tobacco.
The brain circuitry for nicotine addiction is not the same as quitting tobacco.Europe Press

They smoked an average of 23.1 cigarettes a day and after suffering a stroke they quit, as if they had never lit a cigarette. This phenomenon of spontaneous remission of a hundred people has served a group of scientists to study the brain circuit involved in tobacco addiction and, in particular, how to quit. The work, recently published in Natural Medicine, suggests that other addictions such as alcohol would share the same map of brain connections. The finding will allow sharpening the aim in treatments against addictive substances and behaviors.

Sometimes brain damage can have an unexpected positive effect. This is the case of smokers who quit after suffering a stroke. A group of scientists from the United States and Finland collected information and studied in detail 129 people affected by a stroke and who smoked a lot. Of these, a quarter stopped smoking already from the first day after the injury, had not done so since then and did not feel the need to light a cigarette. The researchers were convinced that behind this spontaneous remission was a specific brain area or circuit.

The study with imaging techniques of the brain of these ex-smokers dismantled a first idea. The lack of blood supply (the stroke) that leads to smoking cessation does not always occur in the same region of the brain. This is highlighted by Juho Joutsa, professor at the University of Turku (Finland) and co-author of the study: “The heterogeneity of the affected brain areas in these cases was one of the main motivations for our approach. We compared the connections of the injured areas of patients who remitted with patients who continued to smoke to determine those that mediate addiction remission.” The damaged areas do not overlap, but the affected circuits do. “Here, the circuit refers to these functional connections rather than a single integrated circuit in the brain,” adds the director of the Brain Stimulation and Neuroimaging Laboratory at Turku University Hospital.

“We compared the connections of the injured areas of patients who remitted with patients who continued to smoke to determine those that mediate addiction remission”

Juho Joutsa, professor at the University of Turku (Finland)

For decades, neuroscientists believed that each brain area had a specific function. For example, for speech and language comprehension, Broca’s and Wernicke’s areas are key. This connection between anatomy and function was one of the great contributions to science by Wilder Penfield, who used epilepsy as a window from which to peer into the functioning of the brain. But since the end of the last century, with discoveries such as mirror neurons or the complexity of the interconnections between the two cerebral hemispheres, things have become more complicated. Now the idea has prevailed that each function is supported by a more or less complex circuit of connections between certain neuronal areas.

In this case, what they have observed is that lesions in certain areas of the brain (such as the insular cortex, deep in the brain, and the cingulate gyrus, in the middle zone) alter the circuit that intervenes in the remission of the nicotine addiction. In contrast, damage to the connection profile observed in other patients did not make them stop smoking.

They also noted that the circuitry for tobacco addiction could be the same as for other addictions. They had the opportunity to compare the profiles of post-stroke quitters with those of nearly 200 brain-injured Vietnam War veterans. They found that ex-soldiers (who have been followed for decades) with a lower risk of falling into alcohol had damage to the same circuits as ex-smokers. The study authors would have liked to extend this observation to other addictions, but they did not find reliable databases for cases such as cocaine, heroin or gambling.

The director of the Brain Circuit Therapeutics Center at Brigham and Women’s Hospital (Harvard University, USA) and senior author of the research, Michael Fox, highlights the finding in a note: “We were excited to discover that our map of lesions associated with addiction remission led to a common brain circuit.” Fox has patented several of his findings on brain connectivity to guide brain stimulation.

In the United States, but not yet in Europe, health authorities have approved the use of transcranial magnetic stimulation (TMS) to interfere with certain brain circuits as a therapeutic measure. For now, this neuromodulation technique (essentially electromagnetic pulses sent inward by a device attached to the skull) is being used to treat depression and eating disorders. But it could be very useful to treat addictions. Hence the interest in locating the target at which the magnet should point.

“Although neuromodulation treatments using electricity or even brain injury have shown promise for treating substance addiction, the therapeutic target was unclear,” says Fox. “Now that our study has identified a target, a specific human brain circuit , we hope to see if the neuromodulation directed to this circuit provides a sustained recovery of the symptoms of our patients”, he adds.

“Taken to the extreme, could they change the circuit of religiosity or being left or right?”

Tomás Segura, member of the Spanish Society of Neurology

The knowledge of the brain thanks to the bad luck of some, due more to injuries than to the normal performance of its functions, is not something new. Dr. Tomás Segura is a member of the cerebrovascular disease study group of the Spanish Society of Neurology (SEN) recalls the case of the tremor. “In people with a disabling tremor, a thalamic cerebral infarction takes away the tremor. Observed by hundreds of neurologists over many years, it has resulted in us now curing tremor by causing controlled injury to the thalamus through deep cranial stimulation. We do the same with Parkinson’s. We cured tremor and parkinsonism because before there were harmful models. In this study, what is interesting is that they do not make a lesion model of a specific area in the style of Penfield. There are a lot of different areas, they say, we’re going to see if they’re all on the same circuitry and find out they are,” he explains.

However, Segura has his doubts about the application of these findings. “Tracing the map of addictions is one thing, but what about the ability to concentrate? It’s sure to be bigger.” A second question: “Does an injury have the same impact at any point in the circuit of this map of connections that explains addictions? Is it just as therapeutic or is it more important to interrupt it in the cingulate or striatum, for example?” He also raises a concern: if they can make you stop smoking, “taken to the extreme, could they change the circuit of religiosity or being left or right?” And he concludes: “Penfield did his homework very well in the 20th century, discovering specific areas linked to simple phenomena, such as moving the hand or feeling the abdomen. He now he is not up to us to discover if all the complex functions of the brain can be integrated into neural circuits ”.

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