Poster
# 37
Poster |
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6th Internet World Congress for Biomedical Sciences |
Marcelle Bartolo Abela(1)
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[Neuroscience] |
[Physiology] |
Investigators have tried defining hypnosis since the last century, resulting in the postulation of numerous theories, some aspects of which have been supported and replicated, while others have been found to be totally incorrect, if not actually outrageously far-fetched. The main difficulty in defining hypnosis has always been its intangibility as a state, the measuring of which was hampered by the very limited noninvasive techniques available at the time. However, the relatively recent advent of EEG, CT, PET, and MRI, additionally to intracranial electrophysiological studies during surgery, has permitted the undertaking of the effective but concomitantly ethical study of hypnosis. This has provided a substantial amount of physiological evidence in support of hypnosis as a distinct state in its own right, with specific and opposite neurophysiological characteristics according to high or low hypnotizability, concurrently with a greater than normal ability to access and experience affect, the degree of such ability also being variable according to hypnotizability.
Theories of hypnosis are generally divided into psychological and physiological theories, with the former being sub-divided into psychological and psychoanalytical: the psychological theories of hypnosis emphasize role definition, expectation, and subject motivation, while the psychoanalytical theories emphasize hypnosis as a regressive state. However, these will not be presented here as they are not pertinent to the subject matter under discussion. Physiological theories, meanwhile, emphasize the neural bases of hypnosis, an overview of which is provided herewith:
The first physiological theory was Mesmer´s theory of animal magnetism, which maintained that an invisible magnetic fluid resided in the therapist´s body, and was responsible for curing the afflicted parts of a patient´s body by means of hand-passes. This was followed by de Puysegur´s sleep theory, which considered hypnosis to be a "sleeping" trance (Udolf 1987), later redefined by Abbe Faria as lucid sleep, and eventually combined with Braid´s suggestibility hypothesis, to form the latter´s nervous sleep theory (Abela 1998). Sleep theories were supported by the resemblance in the appearance of subjects in the somnambulistic state to those in natural sleep, and because phenomena ordinarily taking place during the act of falling asleep constitute a large part of the usual induction suggestions (Horvai 1959). However, such theories were incorrect, because clinical and experimental evidence listed in Table 1 has demonstrated that hypnosis is distinctly different from sleep. Therefore, such theories were rejected in favor of a theory of hypnosis as a waking state (Lesser 1985) which is also incorrect, because the same data also shows distinct differences between hypnosis and the normal waking state, even though some similarities do exist, as shown in Table 2. Moreover, a review of the evidence also shows converse differences in the neurophysiological characteristics of hypnosis according to high or low hypnotizability, as listed in Table 3.
Meanwhile, Pavlov regarded hypnosis as a state of cerebral inhibition because the monotony of a low-intensity stimulus, presented to a subject whose motor functioning was inhibited, was considered to produce a radiating area of neural inhibition in the cerebral cortex, which inhibition differed from that of normal sleep in that the latter was generalized cortical inhibition (Crasilneck and Hall 1985). The localized inhibition was considered to allow the more primitive part of the brain - the part more susceptible to suggestion (Waxman 1981) - to become dominant, and this theory eventually developed into the theory of hypnosis as partial sleep in a regressed state (Kubie and Margolin 1944, Roth 1962), later redefined as a learned state of partial cortical inhibition (Das 1958) and excitation (Kraines 1969), after findings that the development of inhibition in the presence of monotonous stimuli improved with practice, and could possibly be correlated with increasing hypnotizability (Das 1958). Concurrently, others contended that the effects of suggestibility were the result of ideomotor action and inhibition (Arnold 1946, Eysenck 1947), with suggestibility being merely the experience of imagining what is actualized through ideomotor activities (Arnold 1946). However such a theory is incomplete, because it failed to explain the complex psychological reactions elicited during hypnosis (Kroger 1977).
The pathological theory of hypnosis primarily promoted by Charcot, Pere, and Binet regarded hypnosis as a product of some disease process in the CNS, similarly to hysteria: this was temporarily supported by Freud, who found that hysterical patients would often improve after hypnotic trance. Later evidence, though, indicated that both hypnotic and hysterical phenomena may occur in persons whose central nervous systems are normal (Crasilneck and Hall 1985). However, from Charcot´s theory was formulated Janet´s dissociation theory, which considered hypnosis to be primarily as a defense mechanism (Waxman 1981), and this theory was to become the basis for the current theories of neo-dissociation, hypnosis as an altered state of consciousness, dissociated control, and controlled dissociation. Meanwhile, hypnosis has also been considered as an altered state of consciousness (Ludwig 1966, Tart 1969, Walrath and Hamilton 1975), while a controlled dissociation theory has also been put forward (West 1960), which regards hypnosis as a state of altered awareness maintained through parassociative mechanisms mediated by the ascending reticular activating system (Crasilneck and Hall 1985).
Other physiological theories of hypnosis are the state and informational theories, the former maintaining hypnosis to be a distinct state from either wakefulness or sleep (Orne 1972) being a state of intensified attention and receptiveness, and an increased responsiveness to an idea or sets of ideas (Erickson 1958) - a theory having the most physiological support, as demonstrated by the data listed in Tables 1, 2, and 3, while informational theory is a speculative hypothesis representing hypnosis as a regression from functioning, like a general purpose computer to that of a special purpose computer (Kroger 1977).
The two main current theories of hypnosis are those of neo-dissociation and dissociated control, the former postulated from Janet´s theory (Hilgard 1976) and maintaining that responses are due to a division and co-existence of consciousness into two or more simultaneous streams which are separated by an amnestic barrier preventing access to suggestion-related executive functions, monitoring functions, or both (Kirsch and Lynn 1998, Woody and Bowers 1994), but which maintain realistic, logical relations among themselves. The dissociated part in Hilgard´s theory is the postulated "hidden observer," i.e., that part of a person´s mind knowing about the presence of pain but which that other conscious part of him knows nothing about (Woody and Bowers 1994). From this theory arose an advanced modified version known as the dissociated control theory of hypnosis (Bowers 1992), which maintains that hypnotic inductions weaken frontal control of behavioral schemas, thereby allowing direct activation of behavior by the hypnotist´s suggestions (Kirsch and Lynn 1998).
Support for this is found in two recent dissertations by Hughes (1988) and Miller (1986) respectively, which show that hypnotic behavior can be purposeful (i.e., the suggested state of affairs is [or can be] achieved) and nonvolitional (the suggested state of affairs is not achieved by high-level executive initiative and ongoing effort), thus making it easily integrated as a concept with current views of frontal executive function (Woody and Farvolden 1998) - i.e., the representative two-tier control model of volition (Norman and Shallice 1986). Briefly, this model maintains that multiple subsystems interact to coordinate goals and actions, which are controlled by two qualitatively different mechanisms, i.e, the decentralized lower-level contention-scheduling mechanism which handles relatively routine selections and behaviors not requiring conscious or attentional control, and the higher-level supervisory attentional system (SAS) which intervenes in novel or competitive situations to govern non-routine actions in a qualitatively different, centralized manner (Woody and Farvolden 1998, Zigmond et al 1999). So the SAS, posited to involve the frontal lobes and limbic system (Posner and Peterson 1990, Shallice and Burgess 1991), influences behavior indirectly by modulating the lower-level system and by contributing extra activation and inhibition to particular schemas, consequently biasing the schema selection process of the contention-scheduling system (Woody and Farvolden 1998).
According to this model, the experience of volition (i.e., will) is associated with SAS involvement in the initiation and control of behavior, and if the SAS is actively modulating the selection of schemas (what can be interpreted as conscious filtering), the individual has the phenomenal experience of will, or deliberate volitional control. Alternatively, if the SAS neither modulates nor monitors the contention-scheduling system, then the person experiences the action as automatic (ibid.), i.e., as immediately following the idea of it in the mind - a circumstance termed an ideo-motor act (Norman and Shallice 1986). However, such a model is only partially in keeping with findings from experimental intracranial electrophysiological studies, because these have shown that deliberate volitional control - the phenomenal experience of will - is not as free as traditionally defined (i.e., taken to include a conscious intention to act, and a conscious ability to control such an act), because results of investigations (Libet et al 1982, 1983a, b, Libet 1985) of cerebral "time-on" theory (this states that the transition from an unconscious mental event to one that reaches awareness and is consciously experienced, can be a function of a sufficient increase in the duration or "time-on" of appropriate neural activities [Libet 1989]) have demonstrated that the performance of even a freely voluntary act is initiated unconsciously, some 350 msec before the individual becomes consciously aware of wanting to move, and that it is the conscious control of whether to carry out the act, which will actually still be performed during the remaining 150 to 200 msec before activating the muscles (ibid.). This theory is also indirectly supported by the presence of an error detection system operating at an early, i.e., possibly pre-conscious stage during Stroop-like tasks with hypnosis, and which was not found to be compromised by the latter (Gruzelier 1998).
So since conscious (volitional) control appears only after awareness of the wish to move has developed - the control process depending upon prior awareness of the volitional direction, but not being an awareness in itself (ibid.) - in the case of the SAS its activation is also unconsciously-initiated, because volitional process starts with unconscious cerebral activity (Libet et al. 1991): the transition between psychological detection of a sensory signal without awareness, and detection with awareness, has been found to be controlled simply by differences in duration of repetitive ascending activations of the sensory cortex, with a minimum duration of up to approximately 500 msec being necessary to elicit a conscious experience of an event, while appropriate neural activity having a duration briefer than that required for awareness mediates unconscious mental functions, but without any subjective awareness of them (Libet 1993, Taylor and McCloskey 1990). Therefore, although the role of free will is not excluded, Freud´s deterministic stance is somewhat supported, as free will is changed from being an initiator of the voluntary act as commonly believed to one of only controlling the outcome of the volitional process, after the individual becomes aware of an intention or wish to act (Libet 1991). This also provides indirect support for the dissociated control theory of hypnosis, physiological support for which has been even more forthcoming from the rCBF increases in the caudal part of the right anterior cingulate gyrus (i.e., Brodmann´s area 32 - a powerful behavioral part of the limbic system), and the fact that hallucination of auditory stimuli also activates this area similarly to the actual hearing of such stimuli, but not similarly to what happens in imagined hearing (Szechtman et al 1998) - in fact, there is activation of the temporal areas, which is considered to reflect acoustical attention (Meyer et al 1989).
The anterior cingulate gyrus, found to be engaged in the processing of pain (Casey et al 1994, Davis et al 1995, Talbot et al 1991), is a portion of the limbic system that communicates between the prefrontal cerebral cortex and subcortical limbic structures - the limbic system being the entire neuronal circuitry controlling emotional behavior and motivational drives (Guyton 1992), and performs executive functions which are subdivided into affective and cognitive components - the former being involved in the regulation of autonomic and endocrine functions, assessment of motivational context, and the significance of sensory stimuli and emotional valence, while the latter are involved in response selection processing such as Stroop interference (Devinsky, Morrell, and Vogt 1995). Metabolic activity in this gyrus has been found to increase when people generate semantic associates to words, and when a situation requiring divided attention is present, as evidenced by divided-attention versus selective-attention tasks (Gazzaniga, Ivry, and Mangun 1998). Therefore, since divided-attention conditions require a higher-level attentional system which simultaneously monitors information across the specialized modules, this function conforms to the attributes of an SAS, causing the anterior cingulate to be implicated during planning or decision-making, error correction, novel and not-well-learned responses, situations regarded as difficult or dangerous, and the overcoming of habitual responses (Posner 1994) - during a PET study of language where activation in a repeat condition was subtracted from the generate condition, greater blood flow was found to consistently occur in the dorsolateral prefrontal cortex and anterior cingulate (Peterson et al 1988), a result similar to the rCBF increases found during hypnosis.
So activation of the anterior cingulate gyrus during hypnosis is related to the cingulate´s establishing a node in the working-memory system of the lateral prefrontal cortex to hold representations retrieved from longer-term semantic representations of word meanings in the posterior cortex (presumably Wernicke´s area), and as processing spreads among the latter´s semantic network, the working-memory system inhibits representations of irrelevant associates, allowing task-relevant associates to be sufficiently activated. This permits the SAS to allow the task´s goal to influence interactions between working and long-term memory (Gazzaniga, Ivry, and Mangun 1998) and is in keeping with the neuropsychological translation of hypnotic induction where hypnosis is initiated by engaging anterior executive control systems which orchestrate top down changes influencing thalamic and brainstem mechanisms (Gruzelier 1998). The anterior cingulate gyrus and the dorsolateral prefrontal cortex are also implicated in the volitional system - a totally different system from stimulus-driven action (Frith 1992, 1995), so under hypnosis it is considered that anterior, frontal lobe functions become engaged through instructions of focusing attention (left hemispheric frontotemporal processing [Gruzelier 1998]) and once engaged become inhibited, with such inhibition underpinning the suspension of reality testing, abdication of planning functions, and reduced attentional monitoring of external cues (Gruzelier and Warren 1993).
Even more support for the dissociated control theory is provided by the hypnotic responsiveness of high hypnotizables, who respond non-volitionally when compared to lows who seem to respond more intentionally (King and Council 1998), making the former group´s responsiveness more likely to result from dissociated control. In this case, hypnotic suggestions more often directly activate subsystems of cognitive control (ibid., Bowers 1992) in keeping with Norman and Shallice´s model, while compliance and social influence is more apt to account for the low hypnotizables´ responsiveness (Bowers 1992). Such agrees with evidence of dissociations between explicit and implicit memory and perception in hypnosis (Kilhstrom 1998) and is confirmed by the deterioration in performance by low hypnotizables when the structure of hypnotic suggestions precludes the use of absorption rather than dissociation (Bartis and Zamansky 1990). This implies that lows respond to suggestions only by assimilating them and not by dissociation, a finding supported by evidence showing that highs use imagery to dissociate effectively, while lows perceive and assimilate suggestions by means of mental math (Ray 1997), which can also be considered to account for the greater levels of emotional experiences of highs in comparison to lows, the former group´s increased ability to access affect (De Pascalis et al 1987, 1989, 1998, 1999), as well as their ability to reduce both the sensory and motivational components of pain (Price and Barber 1987) achieving better pain control (Crawford et al 1998), conversely to lows who are less able, or unable, to reduce the sensory-discriminative component of pain (Price and Barber 1987).
So even though theories of hypnosis are numerous and quite diverse in nature, the somewhat conflicting but co-existing data presented tends to support the dissociated control theory of hypnosis, as well as supporting rather strongly the theory of hypnosis as a state in its own right, because the evidence demonstrates that hypnosis is distinctly different from either normal waking or sleep, and is not on a continuum between the latter two states: occipital increases in theta-1 amplitude (De Pascalis et al 1998), rCBF, and delta activity reflect the alteration of consciousness associated with decreased arousal and possible facilitation of visual imagery (Rainville et al 1999), increased mean theta power also suggesting the intensification of attentional processes (Crawford 1989, 1990, 1994, Crawford and Allen 1983, Crawford, Clarke, Kitner-Triolo 1996, De Pascalis 1998, Gruzelier 1998, Sabourin et al 1990) and imagery enhancement (Sabourin et al 1990), which visual processes have been shown to depend on occipital activity (D’Esposito et al 1997, Kosslyn et al 1995). The critical properties of the hypnotic image have been proposed not as stimulus components, or propositions giving rise to the experience of the image, but as response propositions associated with overt behavior, processing of the latter being conceptualized as a negative feedback system between the brain and the effector site (Heynemann 1990).
Frontal rCBF increases (Crawford et al 1993, Rainville et al 1999) are associated with suggestions for altered perception, possibly reflecting the verbal mediation of said suggestions, working memory, and top-down processes involved in the re-interpretation of the perceptual experience (Gruzelier 1998, Rainville et al 1999), and evaluation of cortical activity has shown that frontal areas of the left hemisphere control the degree of inclusion of foci of increased activity, specific and non-specific for each type of activity, and possibly even regulate the way of information transformation (Sviderskaia, Korol’kova, and Selitskii 1990). Bilateral increases in the inferior frontal gyri (Rainville et al 1999) indicate increased activity in the prefrontal association cortex and Broca’s area - i.e., the areas where the elaboration of thoughts and word formation occur respectively (Guyton 1992), while decreases in rCBF in the right inferior parietal lobule, left precuneus, and posterior cingulate gyrus (Rainville et al 1999) indicate decreased activity in areas having to do with spatial and object recognition (Romanes 1993), thus agreeing with current neuroscientific views that deeper encoding leads to greater blood flow in the left inferior prefrontal cortex (Brodmann’s areas 45, 46, 47) and the inferior and middle frontal gyri (Brodmann’s area 10) (Gazzaniga, Ivry, and Mangun 1998).
Concurrently electro-dermal responding, visual ERP’s, and the Stroop interference test involve the left hemisphere in some hypnotic phenomena such as the concentrated attentional focus, and the role of language in the establishment of hypnotic reality (Jasiukaitis et al 1997), in keeping with recent findings and theories about a left-basis for synthetic or generational capabilities (Corballis 1991), and a neuro-evolutionary model of a left-hemisphere dopaminergic activation system for the implementation of predetermined motor programs (Tucker and Williamson 1984). Such a system - i.e., the mesolimbic dopaminergic system - in fact, feeds mainly into the nucleus accumbens, amygdala, anterior caudate nucleus, and anterior cingulate gyrus (all powerful behavioral control centers) and dopamine is a neurotransmitter which, in excess, causes dissociation of an individual’s drives and thought patterns (Guyton 1992): such a pathway is seen as part of a gating mechanism governing the translation of motive states into overt motor responses (Mogenson, Jones, and Yim 1980). So this is in keeping with more recent models of hypnosis, which is considered to involve largely the left hemisphere (Rainville 1998).
Meanwhile, neurophysiological evidence also demonstrates the activation of the right hemisphere and subcortical mechanisms during hypnosis (Cikurel and Gruzelier 1989, Gruzelier and Brow 1985, McCormack and Gruzelier 1993, Torta and Zanalda 1990), which is postulated to occur during stage III of Gruzelier’s 3-stage model of hypnotic induction (De Pascalis and Penna 1990, Gruzelier 1998) and during emotional processing (Crawford, Clarke, and Kitner-Triolo 1996), with possibly direct action on the mesolimbic structures and hypothalamus, following reduced cortical activity (Torta and Zanalda 1990). This implies direct activation of the encoding and retrieval mechanisms of the brain, and the major output pathway of the limbic system respectively among others: the hippocampus, whose inhibitory action facilitates the habituation of the orienting response with stimulus repetition (Gruzelier 1998, Pribram and McGuinness 1975) and recordings of which by intracranial electrodes has been shown to be activated by hypnosis (De Benedittis and Sironi 1988), primarily encodes and consolidates knowledge in long-term memory (Gazzaniga, Ivry, and Mangun 1998). Additionally, the hippocampus seems to be involved in the explicit retrieval of significant experiences and not merely attempts to retrieve information (Schacter et al. 1996), since PET studies have shown that implicit and explicit retrieval of information is subserved by separate brain systems (Gazzaniga, Ivry, and Mangun 1998). In fact, the left hippocampus is activated for the encoding of verbal tasks, while the right is activated for the encoding of perceptual tasks, which in turn activates the left dorsolateral prefrontal cortex - i.e., part of the SAS and also the predominant site for information encoding and retrieval (ibid.), since storage occurs in a variety of cerebral cortical areas. Activation of various hippocampal parts occurs by almost any type of sensory experience, and stimulation of such parts results in hallucinations that cannot be suppressed, although the person knows such to be unreal. Meanwhile, the amygdala has been shown to be functionally inhibited by hypnosis (De Benedittis and Sironi 1988), in keeping with its mainly excitatory exertive influences on electrodermal orienting activity (Gruzelier 1998, Pribram and McGuinness 1975). Meanwhile, the hypothalamus is the major output pathway to the brain stem, diencephalon, cerebrum, and infundibulum, thus controlling most of the vegetative and endocrine body functions additionally to having control centers, the stimulation of which gives rise to profound effects on emotional behavior (Guyton 1992).
Even more specifically it is the thalamus, posterior commissure, pretectal zone, and Cajal and Darschewitsch nuclei which are neuroanatomically correlated with the upward gaze, “eye rolling”, and trance type changes of consciousness (Orengo-Garcia 1998), the thalamus acting as the main relay station via which cortical and sub-cortical structures communicate, due to its innumerable two-way connections with all cortical areas (Guyton 1992). So the neuro-anatomical and -physiological substrates of hypnosis definitely implicate the thalamus as a general relay station, for directing sensory and other signals to appropriate cortical and cerebellar regions; the hypothalamus as the controller of secondary behavior in conjunction with the entire limbic system, which regulates behavior, emotions, and motivation (ibid.); and the hippocampus for the evaluation of whether inputs should access long-term memory stores or otherwise, and whether such incoming information should consolidate events in long-term memory or otherwise. This has obvious implications for confabulation, with such being demonstrated to happen more in high hypnotizables (Laurence, Slako, and LeBeau 1998), because the Papez circuit connected to the diffuse thalamic system permits the selective inhibition of cortical areas, which inhibition prevents the checking of the accuracy of incoming information against that stored in the neocortical areas, the thalamic network in turn mediating the reduction or intensification of neural conduction to the limbic system and hippocampus, thus being instrumental in excluding sensory impressions (Kroger 1977). Moreover, results from previously mentioned intracranial electrophysiological studies also show that the content of an introspectively reportable experience of an event may be modified considerably, in relation to the actual content of the originating mental events (Libet 1993), because such content is in itself formed by neuronal activities in which there is some delay between the initial cerebral event (i.e., the neuronal priming by the gist of an occurrence), and the development and actual appearance of the conscious experience of it, during which delay the conscious function can evaluate its options (ibid.). So not only can there be (and generally is) a difference between what is actually registered unconsciously and what is reported verbally (especially initially) by the subject, but there may also be an instantaneous difference between what is actually registered unconsciously at the instance something happens and the immediate awareness of it milliseconds later, before being removed from awareness and stored unconsciously.
Also implicated during hypnosis is presumably Wernicke’s area, since it is here that the interpretation of the ultimate meanings of almost all types of sensory information occurs (Guyton 1992), and the temporal lobes for the activation of experiential and interpretive memory sequences (Kroger 1977), because electrical stimulation of certain areas of these lobes was found to result in flashbacks to seemingly random events in the subject’s past (Penfield 1959). Meanwhile, a substantial amount of evidence demonstrating distinct differences in the neurophysiological substrate of hypnosis in high versus low hypnotizables argues in favour of the adminstration of reliable hypnotizability tests such as the HIP or the TAS during clinical situations, to determine the best induction and treatment strategies. Highs show:
- Greater sustained and automatic attentional abilities (Crawford 1989, 1994, Crawford and Allen 1983, Crawford, Clarke, and Kitner-Triolo 1996, Crawford et al 1998, De Pascalis 1998, Gruzelier 1998, Laurence, Slako, and Le Beau 1998, Nadon, Laurence, and Perry 1987) as well as greater automatic information processing (Laurence, Slako, and Le Beau 1998) and faster habituation and reaction times (Crawford, Horton, and Lamas 1998, Gruzelier 1998), probably due to more frontal to posterior connections, greater coherence between anterior brain regions, shorter propagation times (Ray, Blai, Aikins, Coyle, and Bjick 1998), and anterior disconnection (Kaiser et al 1997).
- Better ignoring of irrelevant environmental stimuli than do lows, such attentional differences being reflected in underlying neurophysiological differences in the far fronto-limbic attentional system (Crawford 1994, Gruzelier 1998) implicating the anterior cingulate gyrus, limbic system, and SAS as previously discussed.
- Greater evidence of central inhibitory processes (Gruzelier 1998), particularly the left hemisphere, in response to hypnotic suggestions (Gruzelier and Warren 1993).
- Greater hemispheric asymmetries (Crawford, Clarke, and Kitner-Triolo 1996, De Pascalis and Penna 1990, De Pascalis and Perrone 1996, De Pascalis et al 1998, Gruzelier and Brow 1985, Sabourin et al 1990) with greater right hemispheric activity.
- Greater vagal efferent activity (De Benedittis et al 1994).
- Increased attenuation of evoked P1 and N1 ERP’s (De Pascalis 1994, Zachariae and Bjerring 1994).
- Greater skin conductance levels (Wickramasekera, Pope, and Kolm 1996).
- Greater rCBF and bilateral CBF increases (Crawford et al 1993).
- Greater increases in the right temporal lobe during auditory stimulation (Jutai et al 1993).
- Greater levels of emotional experiences, especially negative, and a greater ability to access affect (Crawford 1989, Crawford and Allen 1983, De Pascalis et al 1987, 1989, 1998), implying greater use of the imagination (Ray 1997, Ray, Blai, Aikins, Coyle, and Bjick 1998) as demonstrated by a consistent pattern of chaos dimensionality (Ray, Blai, Aikins, Coyle, and Bjick 1998).
- The use of both dissociation and absorption (Bartis and Zamansky 1990, Ray 1997) to achieve the hypnotic state and its phenomena.
- The ability to reduce both the sensory-discriminative - i.e., tissue (Cheek 1994)and motivational-affective components of pain (Price and Barber 1987), resulting in significantly greater pain intensity reduction (De Pascalis et al 1998).
- More effective attention-processing systems in normal everyday experiences, hypnosis often involving an amplification of such underlying abilities (Crawford et al 1998).
Therefore it is evident that highs utilize a greater amount of imagery and also employ both absorption and dissociation rather than absorption only, to enter and maintain the hypnotic state as opposed to lows, who use more cognitive activity and absorption only, to enter and maintain hypnosis. Absorption is defined by Tellegen and Atkinson as the individual’s disposition to experience episodes of total attention on a certain type of event which becomes particularly relevant (De Pascalis 1998).
Another finding is that it is hypnotizability, defined as susceptibility - accurately classifiable by neural networks in terms of EEG (Ray, Blai, Aikins, Coyle, and Bjick 1998) and which is an enduring trait (Piccione, Hilgard, and Zimbardo 1989) reflective of underlying individual differences in information processing (Crawford et al 1998) - plus motivational factors, and not suggestibility that moderates emotional processing (De Pascalis et al 1998), and opposite 40-Hz hemispheric activity is involved in patient use of imagery and dissociation: a significant relationship exists between 40-Hz EEG activity production and hypnotizability (De Pascalis and Penna 1990, De Pascalis et al 1987, 1989, 1998) with the 40-Hz EEG spectral amplitude increasing as a function of hypnotizability (De Pascalis 1998) or focused arousal (Sheer 1989), and highs display opposite 40-Hz hemispheric asymmetries during the processing of emotional material, with positive emotions such as happiness resulting in increased production of 40-Hz activity in the left frontal and central scalp regions, and negative emotions such as sadness, anger, or fear increasing activity in the right central and posterior regions and decreasing activity in the left hemisphere (De Pascalis et al 1987, 1989, 1998). This is wholly in keeping with data showing that negative suggestions stimulate greater use of the imagination than positive suggestions, consequently leaving a greater imprint on the mind than positive occurrences, negative-sentence suggestions having been shown to have affirmative affects, regardless of activity level (Miyashita and Monzen 1998). This effect of negative suggestions has also been confirmed by cortical ERP’s of hypnotic suggestions, which show that the structure of the latter is crucial (Barabasz et al 1999), since greater affect is experienced by highs rather than lows as previously indicated. Meanwhile, the more susceptible the individual to hypnosis, the greater the shift found towards the left ear (Levine, Kurtz, and Lauter 1984) or contralateral hemisphere (De Pascalis and Perrone 1996, Gruzelier and Brow 1985), in turn greater use of the imagination which seems more active in highs: such activation is also supported by EEG’s showing a switch of electrical activities from the left to the right hemisphere in right-handed persons during hypnosis (Bick 1989).
So differences in brain activity might be partially related to differences between experiencing a hypnotic suggestion or otherwise (De Pascalis and Penna 1990), again implying the dissociation and absorption versus absorption only factor, and other variables such as patient individuality. However, although hypnotizability is considered inheritable, because twin studies have shown the percent of hypnotizability of twins with common living to be higher than that of an appropriate value of twins with separate living (Bauman and Bul’ 1981), such inheritability is definitely not sex controlled by an autosomal gene with incomplete penetrance as claimed, because there is no concordance between the two groups and such also have a common environment.
To conclude, it can therefore be seen that hypnosis is an individual differences phenomenon, i.e., a state of enhanced attention, activating an interplay between cortical and subcortical brain dynamics such as both attentional and disattentional processes (Crawford 1994), together with a variable, but greater than normal, ability to access affect, with both dissociated control and absorption accounting for hypnotic responding, the main ingredients being imagery or imagination, absorption, dissociation, and automaticity (Perry 1992).
Clinically, the evidence indicates that hypnotizability tests such as Spiegel´s Hypnotic Induction Profile (HIP) or Tellegen´s Absorption Scale (TAS) should regularly be used before commencement of therapy to determine hypnotizability, as such would influence treatment strategies as follows: high hypnotizables can achieve successful termination of therapy in a shorter time period than lows, who may require additional sessions due to their lack of sufficient dissociation during treatment. The evidence also suggests that greater use of imagery should be employed with highs, since this effectively increases their degree of dissociation as opposed to lows. Meanwhile in the latter case, ideomotor responses should be employed more than verbal responses (if required) during treatment for the latter to be effective, because of this group´s lack of sufficient dissociation. However, it follows that IMR is equally as effective in highs as in lows, because the former are capable of both absorption and dissociation.
Finally, additional clinical extrapolation of the differences between highs and lows theoretically implicates a greater use of suggestive therapy for the latter group instead of analytical hypnotherapy, because since such therapy normally incorporates more permissive suggestions than in hypnoanalysis, lows would be better able to absorb such suggestions, terminating therapy much faster and more successfully.
The author wishes to thank her colleague Theodore A. Benton, staff clinical hypnotherapist at Winchester Hospital, USA, for his encouragement, and her assistant Silvana Camilleri for reviewing the paper. This paper would not have been presented without their constant encouragement and valuable assistance.
Gruzelier, JH (1998) A working model of the neurophysiology of hypnotic relaxation. Presented at INABIS ’98 - 5th Internet World Congress on Biomedical Sciences at McMaster University, Canada, December 7-16th. Invited Symposium. Accessed on 26 October 1999. Available at (http://www.mcmaster.ca/inabis98/woody/gruzelier0814/index.html).
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[Physiology] |
