As your breathing slows, your arms go limp and you feel weightless under the gentle lull of a hypnotic trance, your brain activity shifts too – and now, scientists uncovered three hallmarks of a hypnotised brain.
Researchers in the US scanned brains of 57 people during guided hypnosis and showed specific changes in activity and connectivity of just a few areas, such as those involved with brain-body connection.
The results, published in Cerebral Cortex, could let clinicians better administer hypnosis for problems such as pain control, says senior author and Stanford University psychiatrist David Spiegel.
Far from the realm of swinging pocket watches and clucking like a chicken on cue, hypnosis is a growing clinical treatment for a host of disorders such as phobias, post-traumatic stress disorder and pain in childbirth.
A typical hypnosis session starts with the patient and therapist discussing goals.
The patient is then placed in a state of relaxed focus. The therapist retells the goals to the patient, who might imagine and visualise them.
In patients easily hypnotised, such sessions are effective in reducing chronic pain and quitting smoking, for instance. But exactly what goes on in the brain during hypnosis isn’t clear.
To further muddy the waters, while some people are highly hypnotisable, others are almost impossible to put under.
So Spiegel, study lead author Heidi Jiang and colleagues wanted to find out what went on in the brain during hypnosis. They started by screening 545 healthy people for hypnotisability and picked the 36 who consistently scored highly and 21 who scored at the extreme low end.
The subjects’ brain activity was measured using functional magnetic resonance imaging, a scanning technique that measures changes in blood flow to the brain. If a subject is listening to music, for instance, the fMRI will pick up blood rushing to the parts of the brain responsible for hearing and analysing sound.
These subjects didn’t listen to music, though – they were instructed to run through four exercises: let their mind rest and wander (called the resting-state scan), think about their day in great detail (memory control scan), or enter two different hypnotic states.
In the hypnosis exercises, subjects were told to look up, close their eyes, inhale deeply, exhale deeply and let their body “float”, as if in a lake or in space.
For one exercise, they were told to imagine a time when they felt happiness, while in the other, imagine or remember a vacation or holiday.
Each subject did the four exercises once in random order, each of which was followed by an eight-minute fMRI scan.
‘When you’re really engaged in something, you don’t really think about doing it – you just do it.’
When they compared the hypnotisable group with the less susceptible, they found three main differences.
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