How Hypnosis Induced Paralysis Can Teach Us How the Brain Works


FRIDAY JUL 31, 2009

The June 2009 issue of the Journal Neuron just published a fascinating study that could be the next step towards figuring out how hypnosis actually works in the brain.

As you probably know, I am big into brain science – and especially studies employing functional magnetic resonance imaging (fMRI). What I like about fMRI is that it provides a window into the brain; allowing scientists to find out what is really going on as opposed to solely relying on reporting or behavioral assessments.

I wish they had this technology when I was in graduate school in the mid 90’s – I never would have left.

Anyway, let’s take you through the experiment. I think you will find this interesting and maybe even helpful in some strange way.

The Study

Researchers recruited 18 healthy volunteers, and asked them to perform a “go-no go” task while their brains were being watched via fMRI.

The participants were first required to fixate on a cross which was shown for half a second. This was followed by a grayscale picture of either a left or a right hand; this was a cue shown to indicate which hand was at play.

After an interval of 1-5 seconds, the hand changed color.

If it turned green, they had to respond, as quickly as possible, by pressing a button with the corresponding hand.

If it turned red, they were to withhold the prepared movement and do nothing.

Here is the Fun Part!

Twelve of the participants played the game both under hypnosis (and told that their left hand was paralyzed), or in a normal state.

6 of the participants performed the task while feigning paralysis (acting “as if” they were unable to move the fingers of the left hand).

Both the control group (the group that feigned paralysis and the hypnosis group were able to resist pushing the button with the left hand – but the brain scans showed that the mechanisms involved were completely different!

This alone blows away the hypothesis that there is no difference between hypnosis and just acting. The evidence against this theory is more than compelling, but it is nice to see this happening in the brain itself.

More about The Test (and why science is so cool)

There were two tests going on here.

First, they were testing how the hypnosis paralysis group suppressed the movement:

It either suppressed the movement in the preparatory level (by not “gearing up” the left hand when the grey left was displayed).


It suppressed the movement after the preparatory level (meaning the brain recognized the left hand and it geared up, but just didn’t allow the left hand to move.

Second (and what is really interesting to me)

By comparing the brain activity measured during hypnosis and in the feigned paralysis group, they could see whether the mechanisms in the brain were similar.

Test One Results – It is Not about the Planning

The results of the first test were pretty interesting. It turns out that when the hypnosis group was shown the grey left hand, that there was in fact brain activity in the right motor cortex which is associated with planning to execute a necessary command on the left side of your body.

In fact in both the hypnosis group and the feigned paralysis group, both group’s brains planned and/or “got ready” to move the left hand. This was true of all the subjects regardless of whether they were not hypnotized or just pretending.

So the answer to the first test is that the preparatory part of the brain is NOT blocked, it happens after preparation.

Test Two Results: Why Hypnosis is not like Pretending

The next step was examining the activity of the motor cortex at the time of actual hand movement execution.

At the time when the movement should be executed, the normal group again showed activity in the right motor cortex, but the hypnotized group did not (kind of expected since they did not move their left paralyzed hand).

However, the hypnotized group did show increased activity in the prefrontal and parietal cortexes (these are involved in executive control and attention). More relevant, there was also increased activity in a part of the brain called the precuneus.

The precuneus is involved in mental imagery and especially in making representations of self (it is heavily involved in creating your self-image).

In the feigning or “pretending” group, these areas of the brain did not experience more activity. Instead, there was increased activity in the right inferior frontal gyrus, which is involved in motor inhibition. (The hypnosis group did NOT experience increased activity in this area).

So What Does this Mean?

Sorry for all the brain talk (don’t worry; I have to refer to charts as well). And of course it is not wise to jump to conclusions. But, this not only shows a difference between pretending and hypnosis – it indicates that hypnosis uses internal representations and self imagery to take control of your behaviors – while “pretending” relies on will power.

Instructions given under hypnosis seem have the ability to override habitual action, without conscious awareness. And it seems to do so by working at the level of self image. This is why it is such a powerful tool for self-change.

The author of the study, Dr. Yann Cojan, said it differently, “These results suggest that hypnosis may enhance self-monitoring processes to allow internal representations generated by the suggestion to guide behavior but does not act through direct motor inhibition,” says Dr. Cojan.

Here is my two cents. Having been “hypnotized” more times than I can count, and talking to our customer base (full disclosure - my company sells hypnosis CDs), the results make sense.

When folks use hypnosis for weight loss, for example, they report that when they go to the fridge to get a snack – it is almost as if something pulls them away from this action. It seems like as the self image is built, it gets in the way of behaviors that were causing you trouble. And this is without a person having to think about it, or use will power.

Anyway, there is still a lot to learn!

I am very interested in what you think about this article, and would love to start a good conversation about brain science and behavior in general.

Please comment and sign up for Intense Debates. I promise to answer any questions on the blog.  My answers are usually replies to specific posts.

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*Source: The Brain under Self-Control: Modulation of Inhibitory and Monitoring Cortical Networks during Hypnotic Paralysis Neuron, Volume 62, Issue 6, 25 June 2009, Pages 862-875 Yann Cojan, Lakshmi Waber, Sophie Schwartz, Laurent Rossier, Alain Forster and Patrik Vuilleumier