Monday, 1 December 2008

A touch emotional

Researchers have documented a new form of synaesthesia - the brain condition that leads people to experience a crossing over of the senses.

While synaesthesia often involves letters or sounds triggering the perception of specific colours, celebrated brain scientist V.S. Ramachandran and his colleague David Brang have identified two young women who experience strong emotions when they feel the touch of certain fabrics or textures.

For 22-year-old AW, for example, the feel of denim provokes a powerful sensation of disgust. The researchers say their discovery provides further support for the idea that synaesthesia is caused by abnormal connections in the brain, rather than being a simple case of associative learning, as others have suggested.

As well as denim triggering disgust, AW also experiences perfect contentment and happiness at the feel of silk, guilt in response to sand paper, embarrassment for wax, and humour at the feel of ridged plastic, to name but a few of her touch-emotion combinations. Meanwhile, 22-year-old HS feels creeped out by contact with a textured glove, disgust at wax and fleece, disappointed by corduroy but calmed by ridged plastic. "Both individuals enjoy the freedom and ease of simply touching a 'positive' texture after experiencing a negative emotion" caused by a bad day or a fight, the researchers said.

Curiously, AW experiences different emotions depending on whether she touches a texture with her hands or feet (contact with other body areas triggers little or no emotion). The researchers said this shows that the phenomenon isn't simply a case of AW having come to associate certain materials with specific emotional experiences earlier in life. HS only experiences her touch-based emotions via her hands.

Filming of AW and HS by hidden video camera as they touched various textures showed that their facial expressions consistently matched their emotional reports. Recording of the sweatiness of their fingertips (a physiological indicator of emotional reactivity) also supported their claims. The same wasn't true for 18 normal control participants. Moreover, AW and HS's emotional reports stayed consistent when tested again up to 8 months later, even if the specific language they used changed.

Ramachandran and Brang believe the tactile-emotional synaesthesia they've documented is caused by heightened connectivity between the parts of the brain responsible for our sense of touch (the somatosensory cortex) and for emotion (the insula). The more subtle categories of emotion, such as jealousy and guilt, might be related to enhanced connectivity with the front of the brain.

ResearchBlogging.orgV. S. Ramachandran, David Brang (2008). Tactile-emotion synesthesia Neurocase, 14 (5), 390-399 DOI: 10.1080/13554790802363746

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

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