How do different types of touch affect our emotions?
An international team of scientists from the Netherlands, Italy and the United States has discovered that when the brain makes the connection between touch and emotion, the association begins in the brain's primary somatosensory cortex. Until now, neuroscientists were under the impression that this region only responded to the actual touch and not to its emotional quality.
Writing in the journal PNAS, the team explains how they measured brain activation. Self-identified heterosexual male subjects were placed in a functional magnetic resonance imaging (MRI) scanner and were each caressed on the leg under two different conditions.
The first condition involved them watching a video of an attractive female bending down to caress them, and the second involved a video of a man doing the same thing. The male test subjects reported the experience as pleasurable when they thought the touch came from the woman, and aversive when they thought it came from the man; their assertions were backed up by the activity measured in each man's primary somatosensory cortex.
However, unbeknownst to the subjects, it was consistently a woman administering the touches. But it felt different to them when they believed the agent was a man rather than a woman. The primary somatosensory cortex responded more to the 'female' touch than it did to the 'male' touch condition, even while subjects viewed a video showing a person merely approaching their legs.
The study was carried out by researchers at the Caltech Brain Imaging Center in the United States, in collaboration with husband-and-wife team Christian Keysers and Valeria Gazzola, visiting neurologists from the University of Groningen in the Netherlands.
Professor Keysers was awarded a EUR 1.34 million Marie Curie Excellence Grant (EXT) to help him set up his own research team: the Social Brain Lab at the Netherlands Institute for Neuroscience at the Royal Netherlands Academy of Arts and Sciences (NIN-KNAW).
Professor Keysers says: 'Nothing in our brain is truly objective. Our perception is deeply and pervasively shaped by how we feel about the things we perceive.'
Valeria Gazzola adds: '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.'
Valeria Gazzola concludes that their research findings show that this two-step vision is incorrect in terms of separation between brain regions. The study shows that who we believe is touching us distorts even the supposedly objective representation of what the touch was like on the skin.
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Document Reference: Gazzola, V. et al., 'Primary somatosensory cortex discriminates affective significance in social touch', PNAS, 2012. doi:10.1073/pnas.1113211109
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