Neural Bases of Hypnosis

Erik Woody
ewoody@watarts.uwaterloo.ca

     Beginning with the infancy of both psychology and neurology, and continuing to the present day, hypnosis has been the object of intensive scientific research (Dixon & Laurence, 1992). Nonetheless, it is a topic about which there is sometimes notable skepticism in academic circles. Fortunately, much of this skepticism is based on misunderstandings. Hence, the objective of the first part of this presentation is to provide some basic information about what hypnosis is and isn't. In addition, this information presents an essential framework for appreciating the contribution of the research reported in the various reports in this symposium.

     A common idea is that hypnosis may be defined as a more or less unique, altered state of consciousness. Nonetheless, many hypnosis researchers have become uncomfortable with such a definition, because clear, specific signs of such a hypnotic state seem to be lacking (Kirsch & Lynn, 1995). Instead, hypnosis may be defined as a social interaction in which one person, the hypnotist, gives suggestions to another person, the subject. These suggestions invite the subject to experience various sensations, perceptions, and so forth.

     Hypnosis typically begins with a hypnotic induction. Inductions commonly involve instructions for focussed attention (e.g., to stare at a spot on one's hand) and for relaxation of the body, and suggestions of becoming ever more "deeply hypnotized." Nonetheless, there do not seem to be any particularly essential properties of such an induction, aside from the subject's belief that it is plausible. Hence, although many inductions involve instructions for muscle relaxation and slow, deep breathing, subjects can become hypnotized via strong physical exertion as well, such as riding a stationary bicycle (Banyai & Hilgard, 1976).

     The induction makes subjects somewhat more responsive to suggestions. Many hypnosis experts, especially practitioners, like to think the induction produces an altered state of consciousness. However, others, including many hypnosis researchers, think the induction is simply part of the "ritual" of hypnosis, and mainly encourages positive expectancies for what is to come (Kirsch & Lynn, 1995).

     If we think of hypnosis as a certain kind of social interaction, we are naturally interested in how the individual characteristics of both parties, the hypnotist and the subject, affect the interaction. Hypnotists tend to take considerable pride in developing an arsenal of many techniques--for example, knowing many different types of induction procedure. Indeed, a common idea is that the success of hypnosis is largely a reflection of the skill and power of the hypnotist (who may look very active and mysterious), rather than the properties of the subject (who perhaps looks rather passive and merely reactive). Nonetheless, a great deal of research contradicts this view. By far, the most important determinant of the success of hypnosis tends to be the individual characteristics of the subject (Hilgard, 1965; Bowers, 1983). People vary greatly from one another in how susceptible they are to hypnosis--in how responsive they are to the suggestions. A small proportion of people are so susceptible to hypnosis that they can hallucinate a "double" of a person so vividly that as they look at the person and the hallucinated double before them, they cannot tell which is the real one. Or they can sniff a bottle of ammonia and smile at the pleasant, suggested smell of a rose. In contrast, most people are responsive to some suggestions, but not to other, more difficult ones. And finally, a remaining small proportion of people tend not to respond much to any hypnotic suggestions at all, even ones most people are responsive to.

     Hypnotic susceptibility is quite an interesting individual-difference variable, and it figures prominently in all the presentations in this symposium. It can be assessed with standardized tests, in which an induction is given and followed by various suggestions, the subject's score typically being the total number of suggestions enacted, or "passed" (Perry, Nadon, & Button, 1992). One very intriguing fact about such hypnotic susceptibility is that it is very stable over time--if subjects' hypnotic responsiveness is retested, even 25 years later, it tends to stay at approximately the same level. Another intriguing fact about hypnotic susceptibility is that it is not associated at all with most other traits in people--for example, it is not correlated with intelligence or gullibility. One of the very few other traits it is consistently related to is fantasy proneness or imaginative involvement, but the magnitude of the relationship is quite small (a correlation of approximately .30 or less) (Kirsch & Council, 1992). Hence, at least with regard to other traits and abilities, hypnotic responsiveness seems to be rather unique.

     Because of the joint importance of a hypnotic induction and hypnotic susceptibility, hypnosis researchers are typically interested in varying both factors in a crossed design. The usual prediction is of an interaction, in which high hypnotizable subjects given an induction show distinctive behavior, compared to high hypnotizables without an induction, and to low hypnotizables with and without an induction. However, main effects of each factor are sometimes of considerable interest, as well.

      Now let's turn to what can be done via hypnosis. Common misconceptions are that hypnosis can be used to enable people to demonstrate abilities they would not otherwise possess, and to make people engage in behavior they would otherwise avoid because of ethical or moral restraints. Neither of these is true (Kirsch & Lynn, 1995; Orne & Evans, 1965).

     If hypnosis does not unleash new ability levels or forbidden behavior, what does it do? As it turns out, the most striking effect of hypnosis is not simply on behavior, but on consciousness: Hypnosis can profoundly alter people's subjective experience. In this way, the study of hypnosis provides a window on the processes underlying consciousness.

     The essential characteristic of hypnotic responding is what is called the "classic suggestion effect" (Weitzenhoffer, 1980): As the hypnotic subject carries out a suggestion from the hypnotist, the subjective experience is that the behavior is just happening of itself, extra-volitionally. For example, if the suggestion is that the subject's arm is rigid like a bar of iron, the classic hypnotic experience is that one's arm has really become rigid, on its own; it is not that one is holding one's arm stiffly. This phenomenon is also referred to as "hypnotic involuntariness"--that is, the lack of an experience of one's own will in producing the behavior.

     Hypnosis can be used to alter other aspects of consciousness, as well. For highly hypnotizable subjects, suggestions for analgesia are quite effective in warding off the experience of pain. Hypnosis also seems to change certain "reality monitoring" functions. Highly hypnotizable subjects tend to experience suggested perceptions, such as music playing (when there is, in fact, no music playing), not as imagined events, but as real ones with an external origin--that is, as hallucinations. Likewise, for highly hypnotizable subjects, hypnosis alters memory in a number of ways--for example, it can increase the tendency toward confabulation, or the mistaking of non-memories as genuine memories. Explaining the mechanisms underlying such suggested effects has been a major area of research, and is very well represented in the presentations in this symposium.

     Investigating the neural correlates of hypnotic phenomena offers much promise in each of two directions. First, the use of hypnosis offers to brain research a powerful method for modifying conscious experience in intriguing ways, and thereby tracking the neural underpinnings of these experiences. For example, in our own PET research on the neural bases of hallucinations, we have used hypnosis to elicit hallucinations on command (Szechtman, Woody, Bowers, & Nahmias, 1998). More specifically, we preselected highly hypnotizable subjects who could produce hallucinations readily and highly hypnotizable counterparts who could not. This approach circumvents the considerable problems inherent in trying to investigate hallucinating patients.

     Second, neurophysiological investigation offers hypnosis researchers a relatively new window from which to examine enduring questions, such as the following: What is the underlying nature of individual differences in hypnotic suggestibility? What state effects does a hypnotic induction have? What are the mechanisms by which various kinds of hypnotic suggestions work? As an example of the latter, in our own work we contrasted baseline, hearing, imagining, and hallucination conditions to examine the mechanisms underlying hypnotic hallucinations (Szechtman et al., 1998). We showed that a region in the right anterior cingulate was activated in the hallucinators when they heard a message and hallucinated hearing it, but not when they simply imagined it. This pattern differentiated them from the non-hallucinators. It is of considerable interest that other presentations in this symposium also implicate the anterior cingulate as an important site in hypnotic phenomena.

     The presentations in this symposium use a diversity of neurophysiological methods to investigate hypnosis. EEG studies of hypnosis have a long, but somewhat disappointing history (see Dixon & Laurence, 1992, for a review). This tradition is carried forward, with much greater methodological sophistication, in the EEG and ERP studies reported here by Ray; by Dywan; by Laurence, Slako, and LeBeau; by Gruzelier; by Crawford, Horton, McClain-Furmanski, and Vendemia; by De Pascalis; and by Cardena. In the presentations by Rainville and also Crawford et al., hypnosis is investigated with the newer brain imaging techniques (such as PET), which we have also employed in our own work (Szechtman et al. 1998). This methodological diversity, with its many different measures of underlying brain function, holds rich potential for advancing our understanding of hypnosis.

     The major aims of the presentations can be organized in terms of the three questions about hypnosis raised earlier:

1. What is the underlying nature of individual differences in hypnotic suggestibility? This is the main concern of the presentations by Laurence et al., and by Ray. It is also addressed to some extent by Crawford et al. Cardena deals with the related problem of the relationship of hypnotizability to psychopathlogy.

2. What state effects does a hypnotic induction have? This issue is addressed most intensively in the presentations by Rainville and by Gruzelier. De Pascalis also contributes some discussion of state effects.

3. What are the mechanisms by which various kinds of hypnotic suggestions work? The presentations by Rainville, Crawford et al., and De Pascalis thoroughly explore the neural underpinnings of hypnotic analgesia. The presentation by Dywan addresses the neural mechanisms underlying important hypnotic distortions of memory.

     The symposium attendee will see from these studies that hypnosis produces a wealth of intriguing neurophysiological phenomena. These findings will surely help anchor hypnosis in the larger landscape of brain sciences. Nonetheless, the diverse results will eventually need to be integrated into some overarching theoretical framework. Intriguing broader theoretical models are advanced particularly in the presentations by Gruzelier, Crawford et al., and Laurence. Likewise, Dywan argues for a model akin to one we have advanced (Woody & Bowers, 1994; Woody & Farvolden, 1998; Woody & Sadler, 1998). These various models have some clear commonalities, but they seem to have some sharp divergences as well. In addition, they remain to be contrasted with the predictions of other longstanding models, such as the sociocognitive theory of hypnosis (Wagstaff, 1998). Hopefully, the discussion will offer the opportunity to sharpen our thoughts on alternative underlying theoretical models.

     Without further ado, I welcome you to sample these cutting-edge presentations on the neural bases of hypnosis. You will find out for yourself what an exciting area of research this has become.

Banyai, E. I., & Hilgard, E. R (1976). A comparison of active-alert hypnotic induction with traditional relaxation induction. Journal of Abnormal Psychology, 85, 218-224.

Bowers, K. S. (1983). Hypnosis for the seriously curious. New York: Norton. (Original work published 19756)

Dixon, M., & Laurence, J. R. (1992). Two hundred years of hypnosis research: Questions resolved? Questions unanswered! In E. Fromm & M. R. Nash (Eds.), Contemporary hypnosis research (pp. 34-66). New York: Guilford.

Hilgard, E. R. (1965). Hypnotic susceptibility. New York: Harcourt, Brace & World.

Kirsch, I., & Council, J. R. (1992). Situational and personality correlates of hypnotic responsiveness. In E. Fromm & M. R. Nash (Eds.), Contemporary hypnosis research (pp. 267-291). New York: Guilford.

Kirsch, I., & Lynn, S. J. (1995). The altered state of hypnosis: Changes in the theoretical landscape. American Psychologist, 50, 846-858.

Orne, M. T., & Evans, F. (1965). Social control in the psychological experiment: Antisocial behavior and hypnosis. Journal of Personality and Social Psychology, 1, 189-200.

Perry, C., Nadon, R., & Button, J. (1992). The measurement of hypnotic ability. In E. Fromm & M. R. Nash (Eds.), Contemporary hypnosis research (pp. 459-490). New York: Guilford.

Szechtman, H., Woody, E., Bowers, K. S., & Nahmias, C. (1998). Where the imaginal appears real: A positron emission tomography study of auditory hallucinations. Proceedings of the National Academy of Sciences, 95, 1956-1960.

Wagstaff, G. (1998). The semantics and physiology of hypnosis as an altered state: Towards a definition of hypnosis. Contemporary Hypnosis, 15, 149-165.

Weitzenhoffer, A. M.(1980). Hypnotic susceptibility revisited. American Journal of Clinical Hypnosis, 22, 130-146.

Woody, E. Z., & Bowers, K. S. (1994). A frontal assault on dissociated control. In S. J. Lynn & J. W. Rhue (Eds.), Dissociation: Clinical and theoretical perspectives (pp. 52-79). New York: Guilford.

Woody, E., & Farvolden, P. (1998). Dissociation in hypnosis and frontal executive function. American Journal of Clinical Hypnosis, 40, 206-216.

Woody, E., & Sadler, P. (1998). On reintegrating dissociated theories: Comment on Kirsch and Lynn (1998). Psychological Bulletin, 123, 192-197.

Acknowledgement: I would like to acknowledge the support of the Social Sciences and Humanities Research Council.