Meaning of brain scans for 'pain' called into question

brain
White matter fiber architecture of the brain. Credit: Human Connectome Project.

Patterns of brain activity thought to show pain responses have been called into question after researchers from UCL and the University of Reading saw such patterns in rare patients born without a sense of pain.

The study, published in JAMA Neurology and funded by the Medical Research Council and European Commission, was designed to test the 'pain matrix'. This is a pattern of brain activity that has been so consistently observed in almost every neuroimaging study of pain in humans that it is often considered a marker for pain. The association is so pervasive that the 'pain matrix' has been used in research to suggest that social rejection or mental effort can cause 'pain'.

To test whether this pattern actually represents the sense of pain, researchers used imaging (fMRI) to measure brain activity in two rare individuals born without the ability to feel pain and four age-matched healthy volunteers. They were exposed to painful 'pinprick' stimuli while their brain activity was measured.

The people with no sense of pain showed the same pattern of brain activity as the , casting doubt on the theory that this pattern represents pain.

"Our results suggest that these patterns are not in fact 'pain responses' but responses to attention-grabbing sensory stimuli regardless of whether a person feels pain," explains lead author Dr Tim Salomons (University of Reading). "By testing people with no sense of pain, we can categorically rule out that these are pain-specific responses. These people still retain all other senses including non-painful touch, so the brain activity that has been dubbed the 'pain matrix' is likely to represent these senses rather than actual pain."

The findings highlight the need to be cautious when interpreting observed associations between brain activity and human experiences.

"Every science student knows that correlation does not imply causation, and we should not forget this when interpreting ," says senior author Professor John Wood (UCL Medicine). "Although correlations between pain and have repeatedly been made, a causal relationship between neuronal activity and pain sensation has yet to be established. Just like a sense of beauty or happiness, the precise location of in the brain remains elusive for now. It would be therefore misguided to use brain scans to inform diagnosis or drug discovery relating to pain management. In order to understand how our brains give rise to the of , human brain imaging will need to be supplemented by research in animals where individual cells can be modified and measured."


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More information: JAMA Neurology , DOI: 10.1001/jamaneurol.2016.0653
Journal information: Archives of Neurology

Provided by University College London
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Apr 26, 2016
A person with a functioning eye and optic nerve can still be blind. Indeed, a person with perfectly functioning visual cortex can still be blind of the ventral and dorsal path between the visual cortex and the rest of the brain is damaged.

No subjective experience of pain can be caused by a deficit at any point on the pathway of pain. Clearly in the case studied the deficit occurs after the 'pain matrix'.

On the other hand 'pain' may be an interpretation of activity of the 'pain matrix'. Either way, a deficit after this area would cause the observed effect. Stimulating this area directly would be instructive.

If this area is associated only with attention grabbing in response to a particular stimuli then non-pain inducing touch should stimulate the same area in the same way.

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