Hypnosis, Memory and the Brain

October 7, 2008 | 16 comments

Hypnosis, Memory and the Brain

A new study points to specific areas of the brain affected by hypnosis. The technique could be a tool for exploring what happens in the brain when we suddenly forget.

By Amanda J. BarnierRochelle E. Cox and Greg Savage




Hypnosis has long been considered a valuable technique for recreating and then studying puzzling psychological phenomena. A classic example of this approach uses a technique known as posthypnotic amnesia (PHA) to model memory disorders such as functional amnesia, which involves a sudden memory loss typically due to some sort of psychological trauma (rather than to brain damage or disease). Hypnotists produce PHA by suggesting to a hypnotized person that after hypnosis he will forget particular things until he receives a “cancellation,” such as “Now you can remember everything.” PHA typically only happens when it is specifically suggested and it is much more likely to occur in those with high levels of hypnotic ability, or “high hypnotizable” people. Now a new study shows that this hypnotic state actually influences brain activity associated with memory.

High hypnotizable people with PHA typically show impaired explicit memory, or difficulty consciously recalling events or material targeted by the suggestion, and a dissociation between implicit and explicit memory, so that even though they can’t recall the forgotten information it continues to influence their behavior, thoughts and actions. The forgetting is reversible—when the suggestion is cancelled, their memories come flooding back. These last two features—the dissociation and reversibility—confirm that PHA is not the result of poor encoding of the memories or of normal forgetting, because the memories return as soon as PHA is cancelled. Rather, PHA reflects a temporary inability to retrieve information that is safely stored in memory. That makes it a useful tool for research.

Researchers have used PHA as a laboratory analogue of functional amnesia because these conditions share several similar features. Case reports of functional amnesia, for instance, describe men and women who, following a traumatic experience such as a violent sexual assault or the death of a loved one, are unable to remember part or all of their personal past. However, as in PHA, they might still show “implicit” evidence of the forgotten events. For instance, they might unconsciously dial the phone number of a family member whom they can’t consciously recall. (In contrast, explicit memories are those we consciously have access to, such as remembering a childhood birthday or what you had for dinner last night.)  And, as suddenly as they lost their memories, they can just as suddenly recover them.

Forgetting in the Brain But for the comparison between PHA and functional amnesia to be most meaningful, we need to know that they share underlying processes. One way to test this is to identify the brain activity patterns associated with PHA. In a groundbreaking study published in Neuron, neuroscientist Avi Mendelsohn and colleagues at the Weizmann Institute in Israel did just that using functional magnetic resonance imaging (fMRI). They carefully selected 25 people to participate in their experiment. Although all were susceptible to hypnosis, earlier testing had shown that half could respond to a PHA suggestion (labelled “the PHA group”) and half could not (the “non-PHA group”). In the Study session of their experiment, participants watched a 45-minute movie. One week later, in the Test session, participants returned to the laboratory and were hypnotized while they lay within the fMRI scanner. During hypnosis, people in both the PHA and non-PHA groups received a suggestion to forget the movie until they heard a specific cancellation cue.

After hypnosis, participants’ memories were tested twice while the fMRI scanner recorded their brain activity. For Test 1, they were asked 40 questions about the content of the movie (for example, the actress knocked on her neighbor’s door on the way home) and 20 questions about the context in which they saw the movie (for instance, during the movie, the door to the study room was closed). These questions required a “yes” or “no” response. For Test 2, participants were asked the same 60 recognition questions, but first they heard the cue to cancel PHA. So Test 1 measured memory performance and brain activity while the PHA suggestion was in effect and Test 2 measured memory performance and brain activity after it was cancelled.

In Test 1 Mendelsohn and colleagues found that people in the PHA group (who could experience PHA) forgot more details from the movie than people in the non-PHA group (who could not experience PHA). But in Test 2, after the suggestion was cancelled, this memory loss was reversed. People in the PHA group correctly recognized just as many details from the movie as people in the non-PHA group. Somewhat surprisingly, however, the suggestion to forget was selective in its impact. Although people in the PHA group had difficulty remembering the content of the movie following the forget suggestion, they had no difficulty remembering the context in which they saw the movie.

This finding—that PHA temporarily disrupted some people’s ability to recall the past—echoes decades of hypnosis research. What is entirely new in Mendelsohn et al.’s study is their demonstration that PHA was associated with a specific pattern of brain activation. Consistent with what normally occurs in remembering, when people in the non-PHA group performed the recognition task and successfully remembered what happened in the movie, fMRI showed high levels of activity in areas responsible for visualizing scenes (the occipital lobes) and for analyzing verbally presented scenarios (the left temporal lobe). In stark contrast, when people in the PHA group performed the recognition task and failed to remember the content of the movie, fMRI showed little or no activity in these areas. Also, fMRI showed enhanced activity in another area (the prefrontal cortex) responsible for regulating activity in other brain areas.

So far, so good. For people in the PHA group, brain activation measured by fMRI correlated with the failure to remember. But what if reduced activation is always found in such people regardless of whether they are remembering or forgetting? We can rule this possibility out because people in the PHA group showed reduced activation only when they (unsuccessfully) answered questions about the content of the movie, not when they (successfully) answered questions about the context of the movie. Indeed, for the context questions, they showed the same activation as people in the non-PHA group. Perhaps then, the reduced activation reflects complete forgetting of the information, not just temporary suppression? We can rule this possibility out also because, in a neat reversal, people in the PHA group showed normal activation—just as those in the non-PHA group did—as soon as the suggestion was cancelled.

Hypnosis Is Real Mendelsohn et al.’s study is important because it demonstrates that hypnotic suggestions influence brain activity, not just behavior and experience. Hypnotic effects are real! This fact has been demonstrated clearly in earlier work, for instance, by psychologist David Oakley (University College London) and colleagues, who compared brain activation of genuinely hypnotized people given suggestions for leg paralysis with brain activation of people simply asked to fake hypnosis and paralysis.

This latest study is also important because it starts to specify the underlying brain processes, which we assume are shared by PHA and functional amnesia. Mendelsohn et al. argued that the brain activation seen in PHA reflects a dampening—some form of rapid, early inhibition of memory material—due to heightened activity in the prefrontal cortex.

But how does the suppression mechanism decide what to suppress? In this study, movie content but not movie context was influenced by PHA. Memories involve the “what,” “how,” “when” and “where” of an event interwoven together, such that distinctions between content and context may be blurred (for example, “Was the movie shot with a hand-held camera?”). To make such fine discriminations, the brain’s suppressor module presumably needs to process information at a sufficiently high level. Yet this module needs to act quickly, preconsciously suppressing activation of the information before it even enters awareness. Brain imaging technologies with superior temporal resolution to fMRI, such as magnetoencephalography (MEG), might help to resolve this seeming paradox of sophisticated, yet rapid, operations.

We also wonder how the suppression mechanism in PHA relates to the vast array of forgetting in the laboratory and in the world? Whereas some forgetting is seen as strategic, effortful and conscious (say, suppression), other forgetting is seen as automatic, effortless and unconscious (say, repression). Having mapped the common features of PHA and functional amnesia, we now need to explore and compare in greater detail their common processes (such as strategy use, motivation, level of awareness).

Finally, the neural underpinnings of PHA will be even clearer when we incorporate its most important aspect in imaging studies—the dissociation between implicit and explicit memory. In PHA (and in functional amnesia) the person is unable to explicitly recall certain information, yet we see evidence of this material on implicit measures. For instance, a participant given PHA may fail to recall the word “doctor,” learned earlier, but will have no trouble completing the word fragment “d _ _ t _ r”. Mendelsohn et al. did not assess implicit memory. Rather, they tested recognition, which in a sense confounds explicit and implicit memory. We’d like to compare brain scans of a PHA group trying to explicitly recall the movie (they should show reduced activation, as above) with brain scans of the same group completing an implicit memory measure of the movie (they should show normal activation). This would be tricky to do—implicit measures of complex material such as movies and autobiographical memories are hard to find or construct. But it would contribute to a more complete neural picture of the processes involved in these fascinating forms of forgetting.
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  • So, what this actually boils down to is highly hypnotizable people have a kind of brain 'defect' that can be made to act like psychological trauma or actual physiological damage.   High hyptotizability is very often associated with extreme gullibility to all kinds of woo woo.  What we're staying here is that 'true believers' are so susceptible to belief in all the nonsense because their brains are wired goofy.    That would explain a LOT.  Heh.
    Makes me even happier to be among the non hypnotizable!

  • The following is a direct response to this comment.

    Yeah, well maybe you were just hypnotized to think that.

  • Oh crap... I didn't think of that... maybe I was hypnotized into thinking that and to then hypnotized into not considering that maybe I had been hypnotized to think that?!  Or ... oh man... maybe I was hypnotized into thinking that and then hypnotized into thinking that I was hypnotized into thinking that and then hypnotized into not considering that maybe I had been hypnotized into not considering that I might have been hypnotized in to thinking that I had been hypnotized to think that...  OR!??  ....Oh GOD!!

  • This illuminating article demonstrates that Israeli scientists are making a major contriubtion to knowledge.  Well done, Avi Mendelsohn and colleagues, and congratulations to Weizmann Institute.

  • Of course hypnosis is real.  It's been around for over 2,000 years and have helped millions of people with everything from memory recollection, to addictions to public speaking.  It's guided meditation with specific goals. There's nothing "woo woo" or  "goofy" about it.  The brain is changed to influence the mind and actions redirected into doing what the intelligent and mindful subject wishes to do differently, better, or more of.

  • "The brain is changed to influence the mind and actions redirected into doing what the intelligent and mindful subject wishes to do differently, better, or more of."
    Uh... what?  The brain is changed?!  Not!  This just doesn't even make sense.  "...redirected into doing what the intelligent and mindful subject wishes to do..."  What exactly is getting "redirected" if the "subject wishes" to do something in the first place?  If a person wants something to happen, some change in his or her life, he or she is going to take the actions, whether consciously or unconsciously, to get there.  The act of hypnotism only serves as a focusing piece for the otherwise unfocused.
      I'm sorry, but a genuinely intelligent and mindful person usually doesn't need some kind of woo woo, yes, it actually is rather woo woo, hokum in order to make changes to his or her actions or attitudes.  At best you are talking about placebo affect.   Intelligent and mindful people evaluate the benefits of making changes and simply, or with much work, as the case may be, take action to bring them about.
    2000 years.  Wow thats a long time.  Hey, acupuncture has been around for about 4000 years, and it is hokum too.  Astrology has been around since we could look up.  2000 years of gullible subjects doesnt lend legitimacy to a process.  If hypnotism works it is only because the "subject" is impressionable, probably gullible, and possibly not completely rational of mind.
    The only thing this "research" really demonstrates is that impressionable people can, as we already well know, be woo-wooed into believing pretty much anything.  It also provides some confirmation of the correlation between high hypnotizability and tendency toward gullibility.
    No hypnotism has been proven to be pretty much bunk and no one TRULY legitimate uses it for anything butn entertainment purposes.

  • The following is a direct response to this comment.

    I think if you look at the research literature you will find that it can be used for far more than entertainment purposes. Reduction of pain, reductions in medication, increases in activities of daily living with people living with dementia...
    Welden S,Yesavage J A. Behavioural improvement
    with relocation training in senile dementia. Clin
    Gerontol. 1982;1:4549.
    Dyas R.Augmenting intravenous sedation with hypnosis,
    a controlled retrospective study. Contemp
    Hypn. 2001;18:128134.
    Witz M, Kahn S. Hypnosis and the treatment of
    Huntingtons disease. Am J Clin Hypn. 1991;34:
    Liossa C, Hatira P. Clinical hypnosis in the alleviation
    of procedure-related pain in pediatric oncology
    patients. Int J Clin Exp Hypn. 2003;51:428.
    Duff, S. & Nightingale, D. (2007) Alternative Approaches to Supporting Individuals With Dementia: Enhancing Quality of Life Through Hypnosis. Alzheimer's Care Today, vol 8 issue 4,  321-331.
    We also have a long history of rubbishing good ideas.

  • It "can" be used for these things, but is anything but reliable.  It is placebo effect, nothing more.  There is plenty to indicate that relaxation and meditation can ease some kinds of pain.  It is plainly amazing what meditation can do with a stress related headache.   Test with dementia patients is suppose to distinguish between genuine physiological effect and placebo?  Pain is almost impossibly subjective under the best circumstances.
    "Research" doesn't automatically imply GOOD research.  There is all manner of "research" supporting everything from homeopathy to shark fins.  There are WAY too many people out there with PhDs and MDs that I wouldn't trust with a finger bandage.  Anyone touting hypnosis is already working behind the legitimacy curve.  It will take a LOT more than a few small studies.
    Our history of venerating awful ideas is much more pervasive and dangerous.
    Over time, the ones that are genuinely rubbish GET "rubbished."  But, we still have to fight against dangerous, harmful junk medicine like homeopathy, chiropractic, acupuncture, theraputic touch, kinesiology, reflexology.. and on and on.  They are all crap and they all have many, many seemingly legitimate people touting their virtues, and, of course, much "research."
    Hypnosis's 2000 year history has revealed little of any real value.  In the more than 2000 years of, say, surgery, we have acquired huge amounts of knowledge and insight.  Hypnosis is still the medical version of the parlour trick.
    The hypnosis needs to be left in Vegas.

  • The following is a direct response to this comment.

    This illuminating article demonstrates that Israeli scientists are making a major contriubtion to knowledge.  Well done, Avi Mendelsohn and colleagues, and congratulations to Weizmann Institute.
    A major contribution yes, but scary also. Concerning hypnosis, the potential for abuse is obvious, people should remain in the dark about this.

  • The potential for abuse is everywhere, especially in the sciences.   Perhaps we should have kept lobotomies as a scientifically proven method in helping those with "brains wired goofey"?
    That's what I call dangerous!