Interbrain Coupling During Handholding Associated With Analgesia, Empathy

Interbrain coupling of areas implicated in pain processing may be enhanced when romantic partners hold hands while 1 of the 2 is subjected to pain, according to a first-of-its-kind study published in the Proceedings of the National Academies of Sciences.¹

Few studies to date have examined analgesic benefits associated with nonmassage touch in people. In a 2015 article published in Pain, high-powered laser pulses were used to selectively activate dermal Aδ and C nociceptors on the hand of participants, thus producing pricking and burning pain, respectively and sequentially.²

Touch, a tactile stimulus delivered using 0.4 mm von Frey hairs along an axis intersecting with the laser stimulus, was found to reduce the amplitude of both Aδ- and C-laser-evoked potentials, indicating inhibition of the initial ascending nociceptive input. ²

In addition, coupling laser with touch vs laser alone led to a reduction of the magnitude of the “laser blink reflex,” a marker of subcortical nociceptive processing, indicating touch-induced inhibition of nociceptive input. ²

In another study using laser-evoked noxious stimuli coupled or not with pleasant touch administered to skin devoid of C nociceptive fibers (palm of the hand), individuals with high vs low attachment anxiety reported higher laser-evoked pain levels.³ The opposite was observed when the noxious stimulus was delivered to a dermal region containing unmyelinated C fibers.³ “[C fiber tactile]-based affective touch can modulate pain in early and late processing stages…with the direction of effects depending on attachment style,” concluded the authors of this study. ³

“Considering that emotional factors may affect touch-induced analgesia, it is possible that the toucher’s empathy may contribute to pain reduction,” hypothesized the researchers in the current study. Empathy was shown to provide analgesia, and alpha waves in the frontocentral brain have been associated with both pain perceived by the individual and pain observed in others.^4,5 “These studies imply that shared neural networks are activated in the target and the observer, suggesting that brain-to-brain coupling should occur during empathy for pain,” postulated the authors of the current article.

In this study, 22 heterosexual couples (ages 23-32 years, in long-term relationships [ie, 3.46±2.25 years], with no chronic pain) had their neural activity simultaneously recorded using dual electroencephalography. For each couple, the woman received a painful stimulus (heat delivered to the forearm and eliciting a numeric rating scale score of 60) and was asked to rate her pain levels with the numeric rating scale, 2 seconds before the end of each condition (of a 120-second duration each). For each dyad, men were asked to rate their partner’s pain levels while either holding her dominant hand or not. The test for each couple consisted of 6 successive phases, each interspaced by a 10-minute break: no pain alone, pain alone, no pain plus partner touch, no pain/no partner touch, pain plus partner touch, and pain/no partner touch. Men and women were facing each other during each condition, with the exception of the no pain condition.

The absolute difference between the male and the female’s pain ratings was used to evaluate empathic accuracy, and the reduction in pain ratings by female participants between the final condition (no touch/pain and touch/pain) and the initial pain-alone condition was used to estimate levels of analgesia.

Couples holding hands during the noxious stimulus (pain plus partner touch) displayed higher empathic accuracy (P =.003) and lower pain levels (P =.021) compared with couples not holding hands (pain/no partner touch). These results indicate that touch may improve empathy and is associated with an analgesic effect.

Interbrain coupling was visible in the no touch/no pain (between the man’s right parieto-occipito-temporal areas and the woman’s right parietal regions), the touch/no pain (between the man’s fronto-central regions and the woman’s central regions), and the no touch/pain (between the man’s left central-frontal regions and the woman’s right frontal regions and between the man’s left central-frontal areas and the woman’s left central-frontal areas) conditions. Couples holding hands while the woman was receiving a noxious stimulus had greater brain-to-brain coupling than couples in the other 4 conditions examined, with a total of 22 “links,” the majority of which were between the right frontal-parietal-occipital regions of men and the left and right central-frontal regions of their partner.

Identified interpartner networks in the pain/touch and no pain/touch conditions were categorized into 3 clusters using nonnegative matrix factorization. In the pain/touch condition, 1 of the 3 brain-to-brain coupling clusters, but not the other 2, correlated with touch-associated analgesia in women (r, −0.56; 95% CI, −0.14 to −0.81; P =.012), and another cluster correlated with empathic accuracy in the male partner (r, −0.66; 95% CI, −0.28 to −0.86; P =.002).

“[W]e found that the power of partner touch–pain coupling is related to the degree of pain analgesia in the target and to the partner’s empathic accuracy…. Thus, a touch-related brain-to-brain coupling network during pain may reflect expressions of empathy in the observer and pain analgesia in the target,” concluded the researchers.

“Our findings support the theoretical framework of a biopsychosocial model of pain that suggests a dynamic interaction between biological, psychological, and social factors affecting pain perception. Partner touch (social factor) may help in empathy sharing (psychological factor) with the target of the pain, resulting in analgesia and accompanied by interpersonal central neurophysiological coupling (biological factor),” they added.

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References

1. Goldstein P, Weissman-fogel I, Dumas G, Shamay-tsoory SG. Brain-to-brain coupling during handholding is associated with pain reduction. Proc Natl Acad Sci USA. 2018;115(11):E2528-E2537.
2. Mancini F, Beaumont AL, Hu L, Haggard P, Iannetti GD, Iannetti GD. Touch inhibits subcortical and cortical nociceptive responses. Pain. 2015;156(10):1936-1944.
3. Krahé C, Drabek MM, Paloyelis Y, Fotopoulou A. Affective touch and attachment style modulate pain: a laser-evoked potentials study. Philos Trans R Soc Lond, B, Biol Sci. 2016;371(1708):20160009.
4. Tait RC. Empathy: necessary for effective pain management? Curr Pain Headache Rep. 2008;12(2):108-112.
5. Perry A, Bentin S, Bartal IB, Lamm C, Decety J. “Feeling” the pain of those who are different from us: Modulation of EEG in the mu/alpha range. Cogn Affect Behav Neurosci. 2010;10(4):493-504.