Feel that sight

New Scientist, 21 February 1998

FEELING a key in your pocket is almost like seeing it on a table: you can pick out its shape almost as if you can see it. But how does tactile information produce a visual mental image? Neuroscientists in Sweden say they may have found the part of the brain that allows different senses to swap information.

Nouchine Hadjikhani and Per Roland at the Karolinska Institute in Stockholm used positron emission tomography to scan the brains of a group of subjects while they decided if two similar objects were identical. In two of the tasks, they made comparisons using a single sense: touching both or seeing both. In the third task, they were asked to compare an object they touched with an object they saw.

In the third task alone, a structure in the frontal lobe called the insula-claustrum became active (The Journal of Neuroscience, vol 18, p 1072). "The claustrum has some role in binding these two separate processes together," Roland concludes.

"The findings are very interesting and very reasonable," says Eraldo Paulesu, a neuroscientist at the Scientific Institute of San Raffaele in Milan. His earlier work on synaesthesia—the mixing of the senses—supports the new findings. Synaesthetes, who often perceive sounds as colours, also have unusual activity in the insula-claustrum area, unlike normal controls.

However, Paulesu cautions that more parts of the brain are probably involved. "To circumscribe the multimodal integration to this area alone would be unwise," he says.