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.
The first was decreased activity in a part of the brain called the dorsal anterior cingulate in those highly hypnotisable.
That part of the brain is part of what’s called the salience network and contributes to a person’s self-awareness by integrating sensory, emotional and cognitive information.
Less activity there equals less self-awareness, Spiegel says: “In hypnosis, you’re so absorbed that you’re not worrying about anything else.”
Another clear signal in the hypnotisable was boosted connectivity between two other components of the salience network: the dorsolateral prefrontal cortex and insula. The insula is responsible for processing functions such as body control, emotion, empathy and time, while the dorsolateral prefrontal cortex is – among other things – involved in cognition, memory and decision-making.
During hypnosis, boosting the link between the two may help the brain control and process what’s happening in the body.
Finally, they found less connectivity between the dorsolateral prefrontal cortex and the “default mode network” in the highly hypnotisable.
The default mode network comprises many areas throughout the brain and is active, as its name suggests, when a person’s mind is wandering – it is involved in thinking about the self, the future and remembering the past.
Uncoupling from the dorsolateral prefrontal cortex gives rise to a disconnect between a person’s actions and their awareness of those actions, Spiegel says: “When you’re really engaged in something, you don’t really think about doing it – you just do it.”
This could let a person change a behaviour, as suggested by a clinician, without being self-conscious about it.
Knowing how hypnosis changes the brain may help develop treatments for those less susceptible, Spiegel says – particularly through brain stimulation.
And while it’s still very early days, simply knowing which brain regions and connections switch on or off during hypnosis is a big step towards that goal.
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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