Chronic pain linked to distinctive patterns of brain activity

Signatures of electrical activity have been identified in the brains of people with chronic pain. Although a small study, the discovery could one day lead to more effective treatments.

Chronic pain, which lasts longer than 3 months, affects more than 30 per cent of the world’s population, with existing therapies often having limited effectiveness. To help in the development of new treatments, Prasad Shirvalkar at the University of California, San Francisco, and his colleagues set out to better understand how the brain regulates pain.

The team implanted electrodes and stimulators into the brains of four people with chronic pain as a result of a stroke or amputation. These recorded electrical activity in the brain regions that have been associated with the potentially long-term emotional and cognitive aspects of pain – the orbitofrontal cortex (OFC) and the anterior cingulate cortex (ACC) – which the researchers anticipated are more involved in chronic discomfort than some other brain regions that have been linked to short-lived pain.

Over the next three to six months, the participants answered surveys on the severity of their pain multiple times a day. After reporting this, they pressed a button that took a 30-second recording of the activity in their OFC and ACC.

Machine learning then linked these electrical signals to the participants’ self-reported pain severity. From this, the researchers identified neural patterns that indicated whether the individual was experiencing a high or low pain state, acting as a biomarker for different levels of discomfort.

To assess how these neural patterns differ between chronic and acute pain, which is of a short duration and normally resolves, the researchers then recorded the brain activity of the same four participants while heat was applied to areas of their bodies.

They found that the OFC is more linked to chronic pain, while activity in the ACC is associated with acute discomfort. Marco Loggia at the Center for Integrative Pain Neuroimaging at Harvard University hopes that this will motivate other researchers to study the OFC for chronic pain relief. Researchers could test whether non-invasive stimulation to the OFC, for example via transcranial direct current stimulation or transcranial magnetic stimulation, helps to ease ongoing discomfort, he says.

The results are an early step towards uncovering the brain patterns that are linked to pain, which could help with the development of more effective treatments, say the researchers.

People with particularly severe chronic pain could even have the electrodes and stimulators implanted in their own brains, to show how their unique neural signatures link to their discomfort. “The hope is that, as we understand this better, we can actually use this information to develop personalised brain stimulation therapies for the most severe forms of pain,” says Shirvalkar.