Sight. Sound. Touch. These are just a few of the senses that the body has. This theme of senses was the subject of a recent study by neuroscientists from the California Institute of Technology (Caltech
) who reported a relationship between touch and emotion via the brain's primary somatosensory cortex.
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."