Walking cane reveals dramatic sensory re-mapping by the brain

There is a force-field like zone around our bodies, known as peripersonal space, in which our brains integrate information across the senses. For example, we have individual neurons that respond when we sense touch and sound occurring in the same place, such as at or near our hand, at the same time. If you could record the activity of all the relevant individual neurons, you could plot an imaginary border around our bodies within which this sound-touch integration occurs.

Now Andrea Serino and colleagues have shown there is dramatic flexibility in where this sensory integration zone begins and ends. Recording single neurons in healthy participants would be a little intrusive, so the researchers instead took advantage of the fact that where tactile and auditory information is integrated, participants will be quicker to respond to a tactile stimulus when it is accompanied by a sound.

Sixteen sighted participants were blindfolded and held a cane. At first, as expected, they were quicker to respond to a mild electric shock on their hand when that shock was accompanied by a sound located at their hand rather than by a sound at the end of the cane (or no sound at all).

But then they trained for ten minutes with the cane, practising locating objects blindfolded. After the training, the participants were just as quick to respond to a shock on their hand whether it was accompanied by a sound located at their hand, or at the end of the cane - in both cases the accompanying sound speeded their reaction compared with when there was no sound.

This shows there had a been a dramatic remapping of the sound-integration boundary – participants were now integrating sound information at the end of the cane with touch information at their hand. However, by the next day, without any further practice, the boundary had returned to near space and the reaction time advantage was once again only conferred by sounds near their hand.

More extreme, longer-term re-mapping can also occur. The researchers also tested eight blind participants who routinely used a cane. Remarkably, among these participants, touch stimulation at the hand was actually integrated more with sound at the end of the cane than with sound located near the hand.
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Serino, A., Bassolino, M., Farne, A. & Ladavas, E. (2007). Extended multisensory space in blind cane users. Psychological Science, 18, 642-648.

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