The Guardian
30-09-2010
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Hypnosis reaches the parts brain scans and neurosurgery cannot
No longer a mere vaudeville routine, hypnosis is being used in labs to cast light on the innermost workings of the brain
Vaughan Bell blogs at Mind Hacks
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.
Synaesthesia is an automatic psychological association that occurs only in a very few people, but we are blessed (and, indeed, cursed) with minds that mostly operate on autopilot. Take words, for example. As you read the words in this text, you are not consciously identifying each letter, joining them together in your head, and matching the collection to a memory of what it means, it just seems to happen automatically when you see each one.
In an analogy to AR’s colour-clash face task, if I ask you to name the colour that the word green is highlighted in, I hope you would say red. It turns out that you are slightly slower at naming the highlight colour when it clashes with the word (like in red, green and blue) than when the colours and the words match (as in red, green and blue) because we can’t decide not to read the words when we see them – it happens automatically – and this interferes with trying to name the ink colour.
This interference is known as the Stroop effect and, along with the normal brain responses that accompany it, have also been reversed with hypnosis by “switching off” automatic word reading.
If you’re not familiar with hypnosis, I suspect you might be entertaining visions of a Victorian gentleman in a three-piece suit swinging a pocket watch in a brain scanner, but there is no magic to the procedure – it simply requires that someone concentrates on your voice. Even the relaxation part has been found to be optional after an innovative study managed to hypnotise people while on exercise bikes.
Perhaps the most important thing to know about hypnosis is that not everyone is hypnotisable to the same extent: countless research studies have shown that we each differ in our susceptibility. Most people can experience their arm feeling light or heavy at someone else’s suggestion, a few less can feel as if movement is being prevented on command, and only a minority – about 10% of the population – experience changes in the workings of perception, memory and thought.
For those who are “low hypnotisable”, being hypnotised is often like listening to one of those slightly dull relaxation tapes that go on for too long, but for high hypnotisables, known as “virtuosos” in the scientific literature, the effects are compelling.
We don’t know why we have this tendency, but we do know it is partly genetic, that it’s influenced by specific genes, and has been linked to differences in the structure of the brain.
The trait seems to be normally distributed throughout the population and no reliable methods have been found to alter how hypnotisable we are. Most likely, some people have it, while others do not. This trait is usually described as “suggestibility” but it is nothing to do with gullibility or being easily led. People susceptible to hypnosis are not more naive, trusting or credulous than anyone else, but they do have the capacity to allow seemingly involuntary changes to their mind and body.
The key phrase here is that they “have the capacity to allow” because hypnosis cannot be used to force someone against their will. It’s a bit like watching an emotional movie. If you want, you can turn away, ignore what’s going on, or play sudoku in your head, but if you engage with the story you don’t consciously decide to feel joy or sadness as the story progresses, you just react. Hypnosis works in a similar way – some people just seem to have the capacity to get more “caught up in the story”.
When a suggestion is successful, the experience of it seeming to “happen on its own” is key and this is exactly what neuroscientists have been working with – by suggesting temporary changes to the mind that we wouldn’t necessarily be able to trigger on our own. In the case of the two experiments that managed to temporarily “switch off” the Stroop effect in highly hypnotisable people, the suggestion was that the words appeared as “meaningless symbols”. This avoided a clash between the colour and the word because the text suddenly appeared to be gibberish.
These studies have been useful because they have found that the brain’s system for resolving conflicting demands, part of our system for managing attention, seemed to go offline. Hypnotic virtuosos apparently have the capacity to put this system on standby when they need to, something that low hypnotisables lack. Neuroscientists Amir Raz and Jason Buhle suggest hypnosis is really when we allow suggestions to take over from our normally self-directed control of attention that deals with mental self-management, allowing science an exciting tool to “get under the hood” of the conscious mind.
As well as allowing us to better explore the nuts and bolts of the mind and brain, hypnosis is also being used to simulate experiences that normally cause people problems, such as hallucinations or loss of control over the body. Because the effects of suggestions are only temporary, hypnosis can be used to trigger these experiences without distress and for only a few minutes at a time. “Virtuosos” are now highly sought after for brain scanning experiments where researchers look at patterns of brain activity when, for example, they are asked to hear illusory music or feel as if they can’t move their hand.
Several research groups have shown that hypnosis seems to emulate these experiences very closely and that the effects on the brain are different from when participants are asked to fake or imagine the same thing – both important comparisons because we can’t tell just from what someone says that they are genuinely experiencing the effects (as parents of school-shy youngsters with mysteriously timed stomach aches could attest).
Our own research group is using hypnosis to simulate changes in control of the body, in part to examine whether similar brain processes are involved both in hypnosis and a condition called conversion disorder – where what seem to be neurological symptoms appear, like paralysis or blindness, despite there being no damage to the nervous system that could explain them.
So far, there seems to be similarity between the disorder and the effects of hypnosis in that the frontal lobe attention systems seem to be taking other brain areas offline. What we’re not sure of, is why this is only temporary in hypnosis but long-term in conversion disorder.
But perhaps even more mysterious is why we have the capacity to be hypnotised at all. As a species, about 10% of the population can have their reality profoundly altered simply by tuning in to suggestions made by someone else – something that is deeply weird when you think about it.
Virtuoso hypnotisability has never been reliably linked to any problems or difficulties and it has been suggested that, on the contrary, it actually reflects a more efficient control of the brain’s attention systems. It could be a side-effect of other benefits, but we still don’t have any good theories. If you have any suggestions, do let me know.