No longer a mere vaudeville routine, hypnosis is being used in labs to cast light on the innermost workings of the brain.

Hypnotism has moved off the stage and into the laboratory. Whenever AR sees a face, her thoughts are bathed in colour and each identity triggers its own rich hue that shines across her mind's eye. This experience is a type of synaesthesia which, for about one in every 100 people, automatically blends the senses. Some people taste words, others see sounds, but AR experiences colour with every face she sees. But on this occasion, perhaps for the first time in her life, a face is just a face. No colours, no rich hues, no internal lights.

If the experience is novel for AR, it is equally new to science because no one had suspected that synaesthesia could be reversed. Despite the originality of the discovery, the technique responsible for the switch is neither the hi-tech of brain stimulation nor the cutting-edge of neurosurgery, but the long-standing practice of hypnosis.

The surprising reversal of AR's synaesthesia was reported in a recent study by psychologist Devine Terhune and his colleagues at Lund University in Sweden. The researchers showed photos of colour-tinted faces to AR and asked her to identify the onscreen hue while electrical activity was measured from her brain using scalp electrodes.

When the colour of the onscreen face clashed with the colour that appeared in her mind's eye, she reacted slowly, as if trying to read traffic lights through tinted glasses. Meanwhile, the electrical measurements showed her brain struggling to resolve the conflict.

But after hypnotic reversal, she glided through the colour naming, reacting as quickly as people without synaesthesia, and showing none of the tell-tale neurological signs of trying to resolve competing mental demands. Hypnosis had not only altered her experience but had modified the workings of specific brain pathways in ways that we cannot usually manage through conscious will alone.

In a growing number of labs around the world, hypnosis is being used as an experimental tool to allow researchers to temporarily unpick our normally integrated psychological responses to better understand the mind and brain.

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