Hypnotic Analgesia

The Experience of Being Hypnotized

conducted an experiential–phenomenological study of the common elements that make up the experience of a hypnotic state. In this study the common elements that were found to be necessary or sufficient for a hypnotic state to be experienced included the following:

• 1.

  A feeling of mental relaxation (letting go of tensions or becoming at ease, not necessarily physical relaxation)

• 2.

  Absorbed and sustained focus of attention on one or a few targets

• 3.

  Relative absence of judging, monitoring, and censoring

• 4.

  Suspension of the usual orientation toward time, location, and/or sense of self

• 5.

  An experience of one’s own responses as automatic (i.e., without deliberation and/or effort)

It was also evident from descriptions of the observers’ direct experiences of the hypnotic state that interrelationships existed among these elements. Thus, element 1 (“relaxation, becoming at ease”) and element 2 (“absorbed and sustained focus”) appeared to provide a supportive general background for elements 3 (“absence of judging, monitoring, censoring”) and 4 (“suspension of usual orientation toward time and location”). The latter two elements, in turn, appeared to maintain element 5 (“automaticity”). Finally, it was determined that elements 4 (“suspension”) and 5 (“automaticity”) directly contribute to perceived hypnotic depth. In a separate study ( ), subjects then rated these factors during conditions of normal waking baseline and the hypnotic state, and path analysis of these ratings provided a preliminary confirmation of these interactions, as illustrated in Figure 25-1 . The experiential and conceptual basis for these common experiential dimensions is generally supported by the work of others ( ) and is illustrated in the following description.

A hypnotic state typically begins with a relaxed condition of mental (and often physical) ease in conjunction with an absorbed and sustained focus on an object or objects of attention ( ). Thus, initial suggestions for induction of this state are almost always directed toward these two dimensions. However, it can occur naturally during fascination, while watching an absorbing movie, or while watching ripples in a stream. It captures us. This is consistent with the notion that hypnosis can be experienced spontaneously in various contexts. At first it can be effortful, but with time one proceeds from an active form of concentration to a relaxed passive form. Initially, there may be a reduction in the peripheral range of one’s experience (active focused attention), which may reverse and lead to a gradual broadening of one’s experience (passive distributed attention). At the same time, this broadening of attention supports a lack of monitoring and censoring of what is allowed into experience. Hence, inconsistencies are now more tolerable. Contradictory statements, which once arrested attention and caused confusion or disturbance, now no longer do so. The uncensored acceptance of what is being said by the hypnotist is not checked against one’s own associations. Consequently, one no longer chooses or validates the correctness of incoming statements. This allows thinking and meaning in itself that is disconnected from active reflection. From this way of experiencing there emerges a sense of automaticity wherein thinking does not precede an action but action precedes thought.

This description is consistent with the extended notion of mental absorption and “experiential set” (as opposed to “instrumental set”) developed by to describe “a state of receptivity or openness to experiencing in the sense of readiness to undergo whatever experiential events, sensory or imaginal, that may occur, with a tendency to dwell on, rather than go beyond, the experiences themselves and the objects they represent. In this set, experiences have a quality of effortlessness, as if they happened by themselves, and in that sense, of involuntariness.” Notably, mental absorption goes well beyond the simple notion of focused attention, but cognitive neuroscience does not yet provide satisfactory concepts to describe such a state (see further discussion of the distinction between attention and mental absorption in ). The experiential description of hypnosis and the extended notion of mental absorption are also consistent with the dissociated-control model of hypnosis in which self-monitoring processes are functionally disconnected from the executive processes that exert the top-down regulatory control necessary for actualization of the suggested changes in experience ( ). Thus, when suggestions are proposed for bodily action, sensation, or lack of sensation (e.g., pain), the subject simply and automatically identifies with the proposed experiences, and although executive processes are engaged to produce these effects, this is achieved with little or no experience of deliberation of effort on the part of the subject. In this way, hypnotic states have been proposed to facilitate the substitution, modification, or incorporation of alternative or new experiences implied by suggestions.

Based on the results of these experiential studies, hypnosis can be defined as changes in subjective experience characterized by mental ease, absorption, reduction in self-orientation, and an altered sense of agency. The suggestions included in standardized procedures used to establish a hypnotic state and the associated behavior target these four dimensions directly or indirectly. Typically, suggestions for mental ease and absorption are given explicitly, and suggestions for reduced self-orientation and automaticity are given more or less implicitly (e.g., suggestions expressed in the passive form). The altered sense of agency corresponds to the feeling of automaticity and effortlessness associated with changes in experience (e.g., analgesia) and/or their behavioral consequences. Behavioral responses to standardized suggestions are often used to infer that the procedure induced a hypnotic state and to evaluate subjects’ level of hypnotic susceptibility (hypnotic susceptibility scales). However, self-report measures of subjective dimensions may more directly assess whether subjects experienced a hypnotic state.

Changes in Brain Activity Associated with Hypnosis

There have been a number of attempts to establish the neural correlates of hypnosis via electroencephalographic (EEG) methods. In some studies, hypnosis has been associated with alpha activity (e.g., ), with left hemisphere beta activity (e.g., ), or with 40-Hz activity ( ). However, the most consistent finding has been activity in the theta (4- to 8-Hz) range (reviewed in ). For example, found that subjects with very high hypnotic susceptibility displayed more theta activity, both in a baseline normal waking state and during hypnosis. Furthermore, both high and low hypnotic-susceptible subjects showed increases in theta activity during hypnosis as compared with a baseline state. This finding has generally been interpreted as engagement of attention and imaginative processes. This is consistent with the experiential data described previously that demonstrate an increase in mental absorption during hypnosis and with the modest but significant and frequently reported association between hypnotic susceptibility and the ability to experience deep mental absorption (e.g., ). However, this association between theta activity and hypnosis has not been replicated systematically (e.g., ), thus leaving open the question of the EEG signature of hypnosis. Thus, EEG studies have been equivocal and difficult to interpret, in part because of methodological problems such as the use of different induction procedures in different studies and contrast of the hypnotic states with different control conditions. Furthermore, in many studies it is impossible to distinguish between the effects of inducing a hypnotic state and those associated with additional suggestions to alter specific aspects of experience (e.g. hypnotic analgesia). As will be seen later, hypnotic states and responses to specific hypnotic suggestions are associated with considerably different patterns of brain activity.

The advent of modern functional brain-imaging techniques with relatively good spatial resolution in comparison to the traditional EEG methods has allowed better specification of the brain structures involved in the production of hypnotic states. used positron emission tomography (PET) to show differences in brain activity between normal waking and hypnotic states. When compared with normal baseline status, hypnotic states displayed higher neural activity (measured by regional cerebral blood flow) in the occipital cortical areas, as well as in the anterior cingulate regions (also see ). In a subsequent study, showed significant associations between the subject’s self-ratings of mental relaxation and absorption and activity in brain areas critically involved in the regulation of consciousness, as illustrated in Figure 25-2 (also see ). These areas included the pontomesencephalic brain stem, medial thalamus, and rostral anterior cingulate cortex (ACC).

These areas are part of distributed brain networks involved in the regulation of vigilance and attention. In the case of mental relaxation, decreases in brain stem tegmental activity and increases in occipital cortical activity were very similar to those observed by in states of decreased vigilance. The additional changes in the right and left parietal cortices observed in these studies may further relate to the alteration of self-orientation in space and time, consistent with the function of these areas ( ). Interestingly, both studies of Rainville were conducted on the same subjects who exhibited decreased pain responses as a result of hypnotic suggestions. Thus, taken together, both self-ratings and changes in the activity of brain structures involved in the regulation of consciousness provide evidence that subjects of hypnotic analgesia studies do indeed enter a hypnotic state. This interpretation is further supported by the finding that self-ratings of absorption, relaxation, and brain activity, as well as the degree of analgesia, were significantly correlated with hypnotic susceptibility scores.

Another key aspect of hypnotic phenomenology is the sense of agency. Self-agency is a feeling that oneself is the agent of self-generated actions or mental processes. Although the hypnotized subject is the critical player in the actualization of hypnotic suggestions, the experiences suggested during hypnosis are typically felt by the subject as happening by themselves, without active engagement of the subject’s intention or effort. An active movement (e.g., lowering the arm) may be felt as happening by itself or under the influence of an external cause (e.g., a heavy weight on the hand). Similarly, changes in sensory experiences (e.g., analgesia or visual hallucination) may be felt as simply happening by themselves or as real properties of external objects rather than being caused by self-generated imaginative and top-down cognitive processes. Functional brain imaging studies have explored the neural correlates of agency and are suggesting that the anterior insula and the posterior parietal cortex may be critical for the attribution of agency to the self or to an external source ( ). One study further specifically examined the cerebral correlates of the altered sense of agency associated with the production of movement in response to hypnotic suggestions ( ). In this study the experimenter gave hypnotic suggestions to six highly susceptible subjects that their left hand and forearm would be moved rhythmically by a pulley (deluded passive movement) while their brain was being scanned by PET. This condition was contrasted to active movement and “real” passive movement performed at the same rate to examine the brain correlates of the altered sense of agency experienced during the deluded passive movement. The results suggested stronger activity in the parietal operculum and cerebellum associated with the self-produced movement under the passive suggestions. Based on a neural model of intentional action developed in animal electrophysiological studies ( ), concluded that self-generated actions normally involve efferent signals both to the output motor system and to the sensory systems of the parietal cortex. The latter predictive corollary signal would allow the parietal sensory systems to anticipate the sensory changes produced by the motor command generated intentionally. The altered sense of agency experienced by volunteers undergoing hypnotic procedures may reflect a failure to update information about the upcoming movement in the posterior parietal system or an alteration in communication between the anterior control system and the parietal systems.

Using a more complex study design, examined brain activity with functional magnetic resonance imaging (fMRI) during hypnotically induced paralysis of one hand while subjects performed a task involving voluntary action and inhibition of action of either hand to a sensory cue (go/no-go task). In addition to a normal control condition with no hypnosis, this study also included a control in which participants were instructed to simulate paralysis of one of the hands that was cued to respond. Contralateral motor activation was found across conditions in the movement preparatory phase, and this response was not affected by hypnosis-induced paralysis, consistent with preservation of an “intention to move.” The prefrontal cortex was further activated in the no-go trials in the normal state (as usually observed) and in both go and no-go trials during the simulation paralysis, consistent with a role in activation of the executive processes involved in the voluntary inhibition of movement. However, during hypnosis, prefrontal activation was found to be independent of the go/no-go condition and of the hand cued (normal or hypnosis paralysis). Furthermore, the precuneus, a medial parietal area involved in imagery and self-representation, was activated and showed stronger functional connectivity with the motor areas during hypnosis paralysis. Consistent with the authors’ interpretation, this pattern of response observed during hypnosis paralysis cannot be explained by voluntary simulation and suggests the activation of top-down processes (prefrontal) leading to modification of the self-representation of the paralyzed hand (possibly reflected by precuneus activation) and secondarily leading to a lack of motor response to “go” cues to the paralyzed hand and experienced as involuntary inhibition of movement. This contrasts with the more direct inhibition of motor output induced by the no-go signal in the normal state and by the go signal in the simulated paralysis condition, which probably reflects more direct interactions between the prefrontal and motor cortices.

Another study has further examined the effect of hypnosis on executive control and the prefrontal systems during the Stroop task. Performance of this task involves the production of motor or verbal responses in the presence of conflicting information and constitutes a classic executive task. Brain activity was measured with EEG and fMRI studies during the task performed before and after basic hypnotic induction in high and low hypnosis-susceptible participants ( ). Interestingly, brain activity associated with monitoring of conflict in the ACC was stronger during hypnosis in highly hypnotizable individuals. In contrast, lateral prefrontal activity associated with executive control did not vary between groups or conditions. However, highly hypnotizable subjects also displayed hypnosis-induced decreases in EEG coherence between the midline frontal and lateral areas in the gamma band. This was interpreted as dissociation between cognitive control and monitoring processes, consistent with the dissociated-control theory of hypnosis.

Taken together, these studies demonstrate how the different dimensions of the hypnotic experience are associated with changes in distinct brain networks underlying vigilance/arousal, attention, executive processes, and self-agency. When suggestions of altered sensation or emotion are given during hypnosis, similar mechanisms may be involved whereby the brain systems underlying the monitoring of top-down mental actions (e.g., mental imagery and reinterpretation of sensory signals) are no longer updated to represent the internal generator of experiential changes. The consequence of this is a modification of the experiential landscape with reduced awareness that the self is the mediator or the agent of these changes.