MONDAY, June 4, 2012 (HealthDay News) -- A human touch can feel sensual or scary or somewhere in between. Now a new study provides insight into how minds translate a sensation on the legs into a message in the brain.
A study of 18 straight men suggests the brain reacts differently to the same touch depending on the context -- in this case whether the men thought it was an attractive woman or a man caressing them.
It appears that "our sense of touch is infused with emotional aspects even at primary levels, so how we value the touch we receive affects the brain's processing of that touch in ways we didn't suspect before," said study co-author Michael Spezio, assistant professor of psychology at Scripps College in Claremont, Calif.
The researchers launched their study to gain a better understanding of how the brain processes the emotional aspects of interpersonal touch, Spezio said. They wanted to know whether it happens in the part of the brain that primarily handles touch (the primary somatosensory cortex) or in other areas.
To find out, the researchers scanned the brains of 18 men between 21 and 31 years old with functional MRI as a woman sensually touched their legs.
In some cases, they thought a man was stroking their legs. In other cases, they were led to believe it was a woman. Either way, the men were asked to imagine that the person -- male or female -- was coming on to them. To help complete the illusion, the subjects watched synchronized video clips that strongly suggested the gender of the person caressing them.
The subjects found the caress from a man less pleasant than that from a woman. Monitoring of their skin showed that the touches from the men stimulated them on an emotional level.
The researchers discovered that the primary somatosensory cortex is less objective than scientists had thought.
"The primary somatosensory cortex is sensitive to the emotional qualities of being touched in a sensual way by a woman or by a man," Spezio said. "We found that seeing the woman or man drove the sensitivity in the primary somatosensory cortex, since we held the actual physical properties of the touch -- speed, texture, pressure -- constant. So the emotional significance of a sensual caress is processed at a very primary stage in the brain."
The study was published June 4 in the journal Proceedings of the American Academy of Sciences.
Study co-author Christian Keysers, a professor who studies the brain at University Medical Center Groningen in the Netherlands, put it a different way, saying the findings make sense "if we embrace the notion that our brain is not there to objectively represent the world, but to make us thrive and reproduce."
Through that perspective, he said, caresses "that are the foreplay of a sexual encounter are what really matters, not objectivity."
Paul Zak, a brain researcher and founding director of the Center for Neuroeconomics Studies at Claremont Graduate University in California, said the differences in the brain's reactions to their perceptions of touch show that "value is likely being attached to everything we do, and not only in areas of the brain classically associated with value."
For more about the brain, check out Harvard Medical School's Whole Brain Atlas.