Caught on the hop by phantom rabbit


28 February 2006

The difference between real and illusory touch is revealed today in the journal ‘PLoS Biology’ by Dr Felix Blankenburg [UCL Institute of Neurology], Professor Jon Driver [UCL Institute of Cognitive Neuroscience] and their colleagues.

They used a classic illusion called the ‘cutaneous rabbit’, first reported in 1972, when a rapid succession of taps to the wrist is quickly followed by taps to the elbow.
Rather than ‘feeling’ each of the taps where they occurred, subjects report an equidistant series ‘hopping’ up their arm in regular sequence, like a tiny rabbit bounding gleefully upon their nervous system towards the armpit.
This effect troubles neuroscientists because the brain seems to warp time to create the illusion: how can the brain feel the taps on the forearm before those on the elbow? How did the brain know where the next tap was going to fall? …

Using a brain scanner, and electrical stimulation of the arms of the subjects, Dr Blankenburg’s team revealed the illusion feels like the real thing in that the same brain sector is activated whether the tactile sensation is due to touch or the ‘cutaneous rabbit’. In both cases, a part of the brain lights up called the postcentral gyrus, a key area used to represent touch. …

This connection between conscious perception and events in the brain may shed light on conditions such as phantom limb pain, he said.

Phantom pains occur in around 80 per cent of amputees, when the missing limb causes discomfort.

Roger Highfield, ‘Daily Telegraph’, 28 February 2006