What's the science?
Skin-to-skin touch has been shown to reduce pain - for example, in a baby undergoing a medical procedure or in a person experiencing experimental pain. How this pain relief happens is unclear. When a person experiences pain, some of the same brain regions that activate are also active when expressing empathy for another person in pain. This week in PNAS, Goldstein and colleagues explored brain-to-brain synchrony during social touch to understand how it is related to pain perception.
How did they do it?
They measured brain activity using electroencephalography (EEG) in two individuals (one man and one woman) simultaneously, 1) while the individuals were sitting together - not touching 2) sitting together - holding hands and 3) sitting in separate rooms. Then they repeated these scenarios as the woman was subjected to mild heat pain on her arm. The aim was to understand whether brain-to-brain synchrony was enhanced while one experiences pain and touch, and whether this was related to pain relief and their partner’s empathy. Neural activity in frontal and central brain regions was measured at the ‘alpha-mu’ frequency (8-12Hz). This frequency band has been shown to be involved in inter-brain interaction (when brain activity synchronizes in social interaction).
What did they find?
When partners held hands, the male partner was more empathetic, meaning he was more likely to accurately guess what level of pain his partner reported experiencing. Women reported lower pain overall when holding hands, indicating that touch reduced pain. While experiencing both pain and touch, there was a greater degree of inter-brain synchrony between partners than during any other experimental condition - predominantly between sensory brain regions in women and the right hemisphere of the brain in their male partners. In the touch + pain condition, pain reduction in women during touch was correlated with strong synchrony between the sensory brain regions and frontal brain regions in their partner.
What's the impact?
This is the first study to assess brain communication between different individuals during pain to understand the brain mechanisms underlying touch-related pain relief during social interaction. These findings suggest that certain patterns of inter-brain communication are related to pain relief by social touch.
Reach out to study authors Dr. Pavel Goldstein and Dr. Guillaume Dumas on Twitter: @pavelgoldstein and @introspection
P. Goldstein et al., Brain-to-brain coupling during handholding is associated with pain reduction. PNAS (2018). Access the original scientific publication here.