Medical Research Council - London Institute of Medical Sciences

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Mental Block
23 August 2017

Mental Block

“Calm down, relax, and breathe smoothly,” says a voice in your ear. Counting shapes on a screen will be difficult, the voice continues, because there is a block of wood in front of your eyes. “Just relax. It is easy for you to ignore everything but the wooden board.” But there is no wooden board – this is a hypnotic suggestion. Electroencephalography (EEG) measures the brain waves of a hypnotised woman wearing a cap full of electrodes. In the overall study, those who believed the wooden block was real had altered brain activity and struggled to count the shapes. But scientists noticed something else – brain waves accompanying the early stages of visual perception were not affected. This hints that hypnosis works deep in the brain, and that participants can still 'see' the shapes, but are powerless to process the information until the hypnotic spell is lifted.

Written by John Ankers

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