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The findings, described in a recent issue of the Proceedings of the National Academy of Sciences (PNAS), were discovered by researchers Valeria Gazzola and Christian Keysers, who were visiting Caltech from the University of Groningen in the Netherlands.
"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," noted researcher Gazzola in the statement. "Only thereafter, in a separable second step based on who touched us, do we believe we value this touch more or less."
The experiment involved measuring the brain activity of heterosexual males with an MRI scanner in relation to caresses during two different conditions. In the first condition, the participants saw a video of a female bending down to caress their leg. In the second condition, the participants were shown a clip of a male completing the same action. When the men reported their experiences, they expressed positive reactions when they thought that they were caressed by the female and commented on having negative feelings when they thought that they were being caressed by a male. Their brain activity also demonstrated this difference, which was shown in the primary somatosensory cortex.
"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," remarked Michael Spezio, a visiting associate at Caltech who is also an assistant professor of psychology at Scripps College, in a prepared statement. "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 caresses in the study were always the same and always done by a female, but the participants believed otherwise when they saw a different visual representation via the video clips.
"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," explained Ralph Adolphs, the Bren Professor of Psychology and Neuroscience at Caltech and director of the Caltech Brain Imaging Center, in the statement. "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."
The experiment showed how two-step vision can be incorrect, in regards to the separation of parts of the brain, and the perception of the person behind the touch can lead to a distortion of the objective qualities of the touch.
"Nothing in our brain is truly objective," stated researcher Keysers. "Our perception is deeply and pervasively shaped by how we feel about the things we perceive."
The researchers hope that the results of the project can help reconfigure social responses to touch for people diagnosed with autism. The findings also show that film clips or virtual reality can be developed to assist victims of physical and sexual abuse or torture to have a more positive reception to gentle touch. The team is looking to continue to research by looking at how females respond to the experiment and will work to understand how sensory pathways are developed in infants and children.
"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," commented Spezio in the statement.
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