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Chronic pain signals have been identified in the brain

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Activity in an emotion-regulating region of the brain appears to be linked to episodes of chronic pain – a finding that will hopefully aid in therapies.

For the first time it has been possible to record live what happens in the brain when a person experiences chronic pain, a type of pain that persists for at least three months regardless of the medical and pharmacological treatments addressed to counter it. The results of a small scientific study published on Nature Neuroscience could help to study future therapies to alleviate this condition, still poorly understood and difficult to cure.

Endless malaise. Chronic pain can be considered a disease that affects over 30% of the world‘s population and which embraces not only sensations of physical pain, but also the emotional sphere and memory. Its causes can be many, from arthritis to cancer, from diabetes to endometriosis and up to neurological trauma. The point is, treating chronic pain as a protracted form of acute pain often has no effect, and the new study provides some clues as to why.

Press record. Prasad Shirvalkar, a neurologist at the University of California, San Francisco, surgically implanted electrodes in the brains of four patients suffering from chronic pain, as a result of stroke or amputation (phantom limb pain). The pacemaker-like devices recorded the electrical activity of two brain regions, the anterior cingulate cortex and the orbitofrontal cortex, whenever the patient pressed a button on a remote control.

A more reliable measure. Over the next three to six months, the volunteers had to complete a questionnaire about the intensity of the pain they felt several times a day, and then press the button to allow the implant to record the electrical activity in the two regions. brain for 30 seconds.

The scientists then used a machine learning system to connect the recorded electrical signals to the severity of the pain perceived by the patients: this operation made it possible to understand what happened in the two areas in question when the patient felt intense or, on the contrary, mild pain. In other words, for the first time it was possible to have a trace of the electrical activity of the brain and use it as a parameter to evaluate the patient’s discomfort, rather than relying only on self-evaluation.

An important turning point. As designed, the experiment allowed to follow the patient in real life and in all daily activities. Previous pain neuroscience studies instead involved calling volunteers into the laboratory to undergo brain imaging tests in a context very different from that of everyday existence.

One area in particular. The scientists had hypothesized that the two brain areas where the electrodes were placed were more likely to be involved in the perception of chronic pain than other brain regions, which fire in response to immediate and resolvable pain stimuli. But the study determined that it is above all activity in the orbitofrontal cortex to be associated with chronic pain. This part of the cerebral cortex is involved in emotion regulation, self-evaluation and decision making.

Quite another thing. In a second part of the study, in which the volunteers were momentarily “tortured” with acute pain stimuli produced with a hot object in contact with the skin, it was seen that the brain activity associated with this type of “temporary” pain was completely different and more dependent on the anterior cingulate cortex. “Chronic pain is not just a prolonged version of acute pain, but a fundamentally different thing in the brain,” Shirvalkar says. This would explain why common painkillers are often ineffective in treating those who experience it.

Practical implications. The finding could help study more effective drug therapies for regulating chronic pain, but also have a more immediate impact in clinical trials of deep brain stimulation for protracted pain control. This procedure, invasive and used as a last resort treatment, makes use of surgically implanted electrodes to administer electrical impulses to the brain and regulate its abnormal activity: at the moment it is mainly used in some cases of Parkinson’s disease or major depression, but for it to be effective, you need to understand exactly which signals to interfere with.

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