Your Brain’s Responses to Caressing

Simple acts such as the nuzzling of the neck, the stroking of the wrist, or the brushing of the knee can signify either a tender loving touch or a highly demeaning action, depending on who’s doing the touching. These seemingly innocuous actions were recently studied by neuroscientists at the California Institute of Technology to determine the connection between touch and emotion.

The scientists from Caltech have found that the association of touch and emotion starts at the primary somatosensory cortex of the brain. This is a region of the brain that was previously thought to only provide responses to the basic touch and not the emotional attachments associated with the touch. These findings were published in the Proceedings of the National Academy of Sciences.

The research team measured the brain activity through heterosexual males laying in front of an MRI scanner. Each individual’s leg was caressed under two different conditions. The first condition exhibited a video of an attractive female bending down to caress them while the second condition showed a video of a masculine man doing the very same action. The participants indicated that they felt pleasure when the touch was perceived to come from the woman while they felt averse when the touch came from the man, despite the two touches being performed identically. This sensation was backed up when the experiences was related to the measured activity of the participant’s somatosensory cortex under the MRI.

According to Michael Spezio, a visiting associate at Caltech who also is an assistant professor of psychology at Scripps College in Claremont, “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.”

He further added, “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, whatever 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.”

Unknown to the subjects, the actual caress on their leg was exactly the same in both scenarios, and came from a woman. The touch felt different, according to the participants, when they had a well-founded belief that a man did the touching and not a woman.

The research was conducted at the Caltech Brain Imaging Center, to which Bren Professor of Psychology and Director of the Center Ralph Adolphs said, “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 the part of the brain though 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.”

The study was headed by spouses Valeria Gozzola and Christian Keysers, who were visiting professors at Caltech from the University of Groningen in the Netherlands.
According to Gazzola, “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 more or less.”

She added that the experiment showed that the two-step vision is incorrect, just for separation between brain regions as many believe that touching distorts the objective representation of the kind of touch done on the skin.

Keysers added, “Nothing in our brain is truly objective. Our perception is deeply and pervasively shaped by how we feel about the things we perceive.”
The practical implication of these findings would be reshaping social responses to touch in people stricken with autism. Another avenue would be the use of film or virtual reality experience to help heal victims of sexual abuse, physical touch and torture, as gentle touch causes cringing in their victims. Other possibilities include exploration of sensory pathway development in infants or children in general.

Spezio says, “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 gently touch of their parents and siblings.”

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