For most of its history, hypnosis had a credibility problem. Nobody could see inside a hypnotized person’s head, so there was no way to tell a real change in experience from someone playing along. Brain imaging changed that. Since the late 1990s, a series of studies has shown that hypnotic suggestions are accompanied by changes in brain activity that match what people report.
Here are the studies that matter most.
Pain: intensity and unpleasantness
Pain has two aspects. One is sensory: where it is and how strong. The other is emotional: how much it bothers you.
In 1997, Pierre Rainville and colleagues in Montreal used this distinction in a study published in Science. Volunteers had a hand placed in painfully hot water while their brains were scanned. Under hypnosis, they were given suggestions that the pain would be more or less unpleasant, without any change in its intensity.
Activity changed in the anterior cingulate cortex, a region involved in the emotional side of pain, in step with how unpleasant the pain was rated. Activity in the primary somatosensory cortex, which registers the sensation itself, did not change.
Later work showed the reverse: suggestions aimed at intensity changed activity in sensory areas.
This was powerful evidence. The wording of a suggestion determined which part of the pain system changed.
Colour: seeing what is not there
In 2000, Stephen Kosslyn and colleagues at Harvard scanned eight highly hypnotizable people while they looked at patterns that were either in colour or in shades of grey.
Under hypnosis, when asked to see colour, colour-processing areas of the brain became more active, whether the pattern in front of them was actually coloured or grey. When asked to see grey, those areas became less active, even when the pattern was in colour.
The authors concluded that hypnosis is a psychological state with distinct neural correlates, and not just the result of adopting a role. People were not merely saying they saw colour. Their brains were responding as if they did.
Reading: switching off the automatic
Reading is so automatic in fluent readers that it interferes when you try to name the ink colour of a colour word, the Stroop effect. In 2002, Amir Raz and colleagues gave highly suggestible people a post-hypnotic suggestion that words would look like meaningless symbols. The interference was eliminated.
Brain imaging by the same group later showed reduced activity in areas involved in detecting conflict, and in visual areas.
Attention: what hypnosis itself looks like
In 2016, David Spiegel’s group at Stanford scanned highly hypnotizable people during hypnosis and found three changes:
- Less activity in the dorsal anterior cingulate, part of a network that monitors what is important in the surroundings. This fits the absorption and reduced worry people report.
- Stronger connection between the dorsolateral prefrontal cortex, involved in planning and control, and the insula, which tracks the state of the body. This may underlie the ability to influence bodily processes.
- Weaker connection between the prefrontal cortex and the default mode network, which is active during self-reflection. This may explain the reduced self-consciousness of hypnosis.
Low-hypnotizable people did not show these changes.
Differences between people
Imaging has also found differences at rest. Highly hypnotizable people show stronger connections between control and attention networks even when not hypnotized, which may be part of why the trait is so stable.
What the scans prove
- Hypnotic experiences are real. Reported changes are matched by brain changes.
- People are not simply faking. Comparison studies of people asked to pretend show different patterns.
- Suggestions are specific. Different suggestions change different regions.
- Hypnotizability has a basis in the brain.
What they do not prove
- They do not settle the “special state” debate. Any change in experience shows up in the brain. That hypnosis changes brain activity does not show it is a unique state.
- There is no single signature. No scan can tell you whether someone is hypnotized. The pattern depends on the suggestion.
- Most studies are small, often eight to thirty people, and use only highly hypnotizable volunteers. Results may not apply to everyone.
- Not every finding has been replicated. Brain imaging research in general has had problems with small samples.
- A brain change does not prove therapeutic benefit. That needs clinical trials.
Be cautious about practitioners who say “science has proved hypnosis works” and point to a brain scan. The scans show that something real is happening. The clinical trials show what it is useful for.
Why this matters to you
- You can stop wondering whether it is “all in your imagination.” Imagination is a brain process with real effects.
- The wording of a suggestion matters. “Less bothersome” and “less intense” do different things.
- How much you respond is partly down to your brain, not your effort or character.
The bottom line
Brain imaging has shown that hypnosis is more than play-acting. Suggestions for pain, colour and reading change activity in exactly the regions you would expect. That makes hypnosis a serious subject for neuroscience, while leaving plenty still to be worked out.
Next in the series: Mindful Hypnotherapy: Combining Mindfulness and Hypnosis
This article is for general information and is not medical advice.