Caressing someone, like touching a shoulder, stroking someone’s cheek, brushing over someone’s head, etc. often indicates a loving touch, although these signals can also be perceived as highly aversive depending on who is doing it and who is the recipient.

Neuroscientists from California’s Institute of Technology (Caltech) in collaboration with Valeria Gazzola and Christian Keysers from the University of Groningen in the Netherlands decided to investigate they brain’s dynamics of making connections between touch and emotion.

Their findings, published in the Proceedings of the National Academy of Sciences (PNAS) reveal that the association starts in the brain’s primary somatosensory cortex, the region of the brain that was believed until now to only respond to basic touch but not to its emotional quality.

During a functional MRI scan, the researchers measured the brain activity of self-identified heterosexual male study participants who were being caressed on the leg watching a video with two scenarios. In the first video, an attractive female bent down to caress them, whilst the second scenario consisted of the same caressing touch, but by a man. The participants reported a pleasurable experience when they thought the woman had touched them, but an aversive reaction in response to the man they believed touched them. Their reports were confirmed by the MRI scans, which reflected the different experiences in the activity measured in each man’s primary somatosensory cortex.

Michael Spezio, a visiting associate at Caltech who is also an assistant professor of psychology at California’s Scripps College in Claremont, explained:

“We demonstrated for the first time that the primary somatosensory cortex – the brain region encoding basic touch properties such as how rough or smooth an object is – also is sensitive to the social meaning of a touch. It was generally thought that there are separate brain pathways for how we process the physical aspects of touch on the skin and for how we interpret that touch emotionally – that is, whether we feel it as pleasant, unpleasant, desired, or repulsive. Our study shows that, to the contrary, emotion is involved at the primary stages of social touch.”

The participants were unaware that on both occasions it was a woman caressing their leg like in the video. They perceived the touch differently when they believed the man touched them instead of the woman.

Ralph Adolphs, Bren Professor of Psychology and Neuroscience at Caltech and director of the Caltech Brain Imaging Center, explained:

“The primary somatosensory cortex responded more to the ‘female’ touch than to the ‘male’ touch condition, even while subjects were only viewing a video showing a person approach their leg. We see responses in a part of the brain thought to process only basic touch that were elicited entirely by the emotional significance of social touch prior to the touch itself, simply in anticipation of the caress that our participants would receive.”

Gazzola commented: “Intuitively, we all believe that when we are touched by someone, we first objectively perceive the physical properties of the touch – its speed, its gentleness, the roughness of the skin. Only thereafter, in a separable second step based on who touched us, do we believe we value this touch more or less.”

She continued stating that the experiment proves this two-step vision is incorrect, at least with regard to the brain regions being separate from each other. She adds that the person we believe is touching us distorts even the supposedly objective representation of what the touch felt like on the skin.

Keysers said: “Nothing in our brain is truly objective. Our perception is deeply and pervasively shaped by how we feel about the things we perceive.”

The findings may shed new light on helping to reshape social responses to touch in people with autism.

Spezio comments: “Now that we have clear evidence that primary somatosensory cortex encodes emotional significance of touch, it may be possible to work with early sensory pathways to help children with autism respond more positively to the gentle touch of their parents and siblings.”
br> The findings also indicate the potential of using film clips or virtual reality to re-program positive responses to gentle touch in victims who experienced torture as well as sexual and physical abuse.

In future experiments, the researchers hope to evaluate whether the effect is as robust in women as in men, as well as in men and women of all sexual orientations in addition to investigating the potential development of these sensory pathways in infants or children.

Written By Petra Rattue