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So called "state theorists" argue that subjects which respond to hypnosis are able to enter a special state of focused concentration- a trance in which people can use their brains in unusual ways, hallucinating at will and becoming insensitive to painful sensations. Others disagree and have the view that hypnosis involves nothing more than everyday levels of suggestibility and imagination spiced up with a little pretence. Who is right? Can we believe someone who claims under hypnosis that they have forgotten their own name, become colour blind or regressed to childhood?
Recent controlled experiments involve subjects following the direction of a hypnotist while lying in a brain scanner, or sitting beneath an electrode array as data is transferred to a computer. One example of this is experiments which use PET scans to measure blood flow changes related to hypnosis. At Harvard, a group of imaging experts have asked subjects to manipulate in their minds eye pieces of artwork shown to them on a computer screen while being monitored by a scanner. These subjects were instructed to "colour in" grey images, or become "colour blind". Among people who claimed they had become colour blind there was a change in blood flow to an area of the cortex believed to be the brain's main colour centre.
Other work has examined pain control. In a recent study published in Science [Rainville et al., (1997) Vol.277 p968-971], a team of researchers in Montreal hypnotised eight volunteers who were all chosen because of their susceptibility to hypnosis. They had each subject place their hand in a tub of painfully hot water. In the suggestive patter that followed, subjects were instructed that the water was either more or less painful. Researchers saw significant changes in the brain's anterior cingulate. This is a brain area traditionally thought to be involved in setting the volume and tone of the emotion that the brain attaches to perceptions.
This evidence and others have made many people accept that at least some hypnosis subjects are not faking. Is this necessarily the same as believing that hypnotic subjects enter a trance state? Must "real" hypnotic experiences be coupled with subjects entering a special brain state?
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