The perception of pain is impacted by social, emotional, and psychological factors as well as biological ones, and these factors can all affect one another. Skin-to-skin touch—a clearly social phenomenon—is known to alleviate pain. What is not quite known is how.

A touch of pain

The Social and Affective Neuroscience Lab at the University of Haifa decided to find out. A team of researchers there designed an experiment in which 20 heterosexual romantic couples were recruited for a study on pain perception. The couples were exposed to six different conditions: holding hands when the woman was subjected to pain and when she wasn’t, just being together but not holding hands when the woman was subjected to pain and when she wasn’t, and being in separate rooms when the woman was subjected to pain and when she wasn’t.

During all conditions, the partners’ brains were simultaneously scanned so the researchers could assess the relationship between brain coupling, pain perception in the suffering partner, and empathy in the observing partner. This simultaneous scanning of individuals while they interact is a pretty new thing and a pretty big deal.

“To decrease the impact of gender differences,” the researchers note in their report of the study, “the roles assigned to the male and female partners remained constant throughout the experiment. Since women are known to benefit from social support more than men, they were selected for the role of pain target.”

(A couple gets pasted all over with electrodes and then maybe or maybe not gets to shake hands while she gets a hot poker applied to her arm? Not my idea of a great date but... whatever.)

Touch is a nonverbal way of communicating empathy. It is known to reduce stress, anxiety, blood pressure, and can mitigate the conscious perception of pain. Since touch seems to work through the emotions, the designers of this study speculated that the degree of his empathy might correlate to the degree of her pain reduction. Empathy for another’s pain and the firsthand experience of one’s own pain activate the same brain regions, so the toucher is feeling some of the same emotions as the sufferer—the idea of their bran waves synchronizing seemed plausible.

In synch

So the hypothesis was that touch would increase brain coupling between members of the couple and the extent of coupling would be associated with the degree of pain reduction. It would also be linked to the degree of empathy in the man. And this is, in fact, just what was found.

EEG recordings of alpha waves revealed an “interbrain coupling network” in the touch + pain scenario that exceeded the brain coupling seen in any of the other scenarios. The alpha-mu band of brain waves was primarily examined because it has known roles in pain perception, empathy, and interbrain synchronization; beta waves were examined as well, since interbrain coupling has been seen there, too, but none was found in this case.

The coupling was asymmetrical, linking her central-frontal regions with his right hemisphere. But EEGs are notoriously poor at defining precise brain regions; imaging must be done for that.

This study does not propose a cause-and-effect relationship between the observed brain coupling, feelings of empathy in the man, and reduced pain in the woman. But the authors suggest a couple of ways they might be linked. One idea is that touch enhances the brain coupling, which alleviates pain by making the sufferer feel understood; feeling understood activates reward mechanisms. Alternatively, the reverse could also be what’s happening: maybe touch blurs the borders between the partners, allowing him to be more empathetic to her pain, which she senses. The synchronous brain waves are then an expression of the empathy.

On the one hand, it seems really cool that scientists can find hard evidence of changes in brain activity to explain emotional phenomenon like how empathy can reduce pain. But on the other hand, of course these types of things work by changing brain activity. How else could they possibly work?

PNAS, 2018. DOI: 10.1073/pnas.1703643115 (About DOIs).