jou rn al hom epage: www.elsev ier .com/ locate /neule t
ommentary
he role of motivational factors in the relationship betweenypnotizability and pain-inducing imagery
lexa Huber ∗
epartment of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Via Campi 287, I-41125 Modena, Italy
r t i c l e i n f o
rticle history:eceived 2 September 2013
ccepted 6 September 2013
ypnotic susceptibility, or hypnotizability, is a stable cognitiverait defined as the generalized tendency to respond to hypnoticuggestions [20,23]; it also predicts the efficacy of suggestionsdministered in the normal waking state, i.e. out of hypnosis [35].he trait is in part heritable [38] and can be reliably measured withtandardized scales [15,37]. Hypnotizability shows a normal distri-ution in the general population, including approximately 10–15%ighly hypnotizable individuals (Highs) [14].
The hypnotizability trait shows but moderate associations withther psychological constructs, including attentional absorption50], imagery vividness [17], creativity [22] and fantasy-proneness31]. The difficulty in identifying reliable psychological or neurobi-logical correlates of hypnotizability remains a major challenge forhe field [25].
Over the last decade, Enrica Santarcangelo’s group has studiedhe physiological correlates of hypnotizability, accumulating evi-ence on hypnotizability-related differences in many areas, also outf hypnosis and in the absence of specific suggestions [5]. For exam-le, hypnotizability accounts for part of the physiological variability
n posture [6,42–44,47] and locomotion [33,34], visual recognitionf haptically explored objects [9], imagery [3,4,7,42,48], writtenanguage [32], cardiovascular activity [5,26–29,39,40], and pain andain modulation [1,26,36,40,45].
One important insight obtained from this line of research is thatighs show a peculiar ability to “embody” mental images (expe-
ience them as real perception/action and show corresponding
djustments in motor activity) and can even show imagery-inducedlterations in motor reflex activity, in contrast to low hypnotiz-ble subjects (Lows) [7,42]. This impressive demonstration of the
∗ Correspondence to: Dipartimento di Scienze Biomediche, Metaboliche e Neu-oscience, Sezione Fisiologia e Neuroscienze, Università di Modena e Reggio Emilia,ia Campi, 287, I-41125 Modena, Italy. Tel.: +39 059 205 5684;
sensorimotor capabilities of Highs adds to the literature indicat-ing a higher neurocognitive flexibility in Highs [21,23], due to theirability to shift cognitive strategies and states of awareness and toundergo functional neurocognitive changes following instructionsfor hypnosis.
A second important finding by Santarcangelo’s group concernsthe autonomic domain: Higher parasympathetic tone in restingconditions [41] and more efficient endothelial function duringstress and pain [26,29] have suggested that Highs may be naturallyprotected against cardiovascular events.
However, being highly hypnotizable may also have dis-advantages. Indeed, associations between hypnotizability andpsychopathology have been proposed since the 19th century, withwarnings about precipitating psychosis in vulnerable individuals[22]. High hypnotizability has been associated with increased inci-dence of developing chronic pain [13,52] as well as phobias [12]and post-traumatic stress disorder [2].
According to the High Risk Model of Threat Perception (HRMTP),which is based on electrodermal activity studies, the developmentof chronic pain as well as reinforcement of phobia/post-traumaticstress disorder occurs more frequently in Highs because of theirhigher tendency to vividly imagine and re-experience traumaticevents, such as past pain episodes, associated with congruent auto-nomic activation [51,52]. Thus, the theory assumes that the Highs’exceptional ability to imagine pain makes them more vulnerableto a shift from acute to chronic pain.
Santarcangelo’s group confirmed in two experimental studiesthat Highs show a higher ability to imagine pain in the normalwaking state compared to Lows. Highs reported higher pain inten-sity and congruent postural adjustments during imagery of a leginjury [48], and higher pain intensity during imagery/memory ofpreviously experienced pressor pain on the thorax [36]. Most Lows
were unable to imagine pain. The finding that pain imagery trig-gered postural adjustments in Highs further strengthens the viewthat these individuals are more vulnerable to developing chronicpain, because they may assume pain-avoiding postures that can
ead to chronic pain. For example, pain avoidant behavior andisuse during and after acute low back pain episodes is thoughto increase the risk of developing chronic low back pain [30].lso, imagery/memory of pain may contribute to the persistencef abdominal muscle activation observed in patients during thesymptomatic weeks/months between two low back pain episodes24].
On the other hand, in the Paoletti et al. [36] study Highs reporteduite moderate pain intensities, and no substantial differences inutonomic activity were observed between Highs and Lows. Inddition, some studies failed to detect elevated hypnotizability lev-ls among patients with chronic pain [5], leading to doubts abouthe HRMTP theory.
In their study appearing in this volume of Neuroscience Let-ers, Santarcangelo et al. [46] (2013) report results that furtherhallenge the HRMTP theory and propose a possible explanationor the inconsistent findings of previous research. The idea ishat, in spite of their exceptional ability to imagine pain, Highs
ay not always be willing to exert that ability depending onmotional-motivational factors, given that successful pain imagerys unpleasant.
To explore this possibility, Santarcangelo et al. [46] (2013)ssessed pain imagery as a function of the so-called Behavioralnhibition/Activation Systems (BIS/BAS). According to a theory pro-osed by Gray [8,18], two general motivational systems underlieehavior and affect – one of these systems regulates aversive moti-ation, the other regulates appetitive motivation. The aversiveotivational system, called the Behavioral Inhibition System (BIS),
s sensitive to signals of punishment, non reward and novelty ands involved in the negative feelings induced by these cues [18,19].ubjects with high BIS sensitivity may consequently learn how tovoid aversive/punishing situations [16], such as pain. In contrast,he appetitive motivational system, called the Behavioral Activa-ion System (BAS), is associated with high levels of dopamine and isensitive to potential rewards, thus to motivation to seek out pos-tive experiences [19]. Greater BIS sensitivity should be reflectedn greater proneness to anxiety, greater BAS sensitivity in greatermpulsivity, i.e. a proneness to engage in goal-directed efforts ando experience positive feelings when the person is exposed to cuesf impending reward.
Santarcangelo et al. [46] (2013) assessed the subjective efficacyf pain imagery in the normal waking state as a function of hyp-otizability and of BIS/BAS sensitivity, compared to a control taskf neutral tactile imagery. Questionnaires on BIS/BAS sensitivity,magery ability and various other traits were administered to aroup of Highs and to a group of Lows. Subjects rated the inten-ity of the perceived pain or tactile sensation, respectively, duringmagery of cold pressor pain – the increasingly painful sensation ofaving a hand immersed in ice water – as compared to imagery of
neutral tactile sensation.This study obtained several results with important implications
or the relationship between hypnotizability and pain imagery:irst, Highs displayed greater imagery abilities than Lows both inhe questionnaire results and in the neutral tactile task, but not inhe pain imagery task. Indeed, Highs reported significantly highercores for tactile perception than for pain, while Lows gave sim-lar, moderate, ratings in both tasks. This result contradicts thessumptions of the HRMTP theory.
Second, questionnaire results yielded higher BIS scores (aver-ive motivation) in Highs compared to Lows, while BAS scoresappetitive motivation) were similar in both groups. The authorsoncluded that the Highs’ lower efficacy of pain imagery may be
elated to their high sensitivity to aversive/painful outcomes (BIS),eading to a tendency to avoid/inhibit situations possibly leading toain experience, for example by not performing the pain imageryask at their best. This is an intriguing hypothesis, which prompts
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further research on the role of emotional-motivational factors inthe relationship between hypnotizability and pain. Future studiesusing larger samples should try to directly confirm this hypothe-sis by assessing correlations between BIS and subjective efficacy ofpain imagery in Highs and Lows. Following Santarcangelo et al.’shypothesis we would predict that BIS scores should be negativelycorrelated with efficacy of pain imagery in Highs, especially fortypes of pain known to the subject. On the other hand, the relation-ship may be more complex than that: While making the subjectunwilling to imagine pain, a highly sensitive Behavioral InhibitionSystem may also render pain imagery more effective by facilitatingthe activation of anxiety and autonomic correlates during imagery.Finally, BIS and pain imagery may be less or not at all related inLows, given that these individuals may be unable to imagine painin any case.
Third, Santarcangelo et al. (2013) also found that pain imagerybecame more effective in Highs compared to Lows when the activ-ity of the Behavioral Activation System (BAS) was controlled for,even though Highs and Lows had similar BAS scores. This result isdifficult to interpret, but it indicates that the subject’s motivationto seek out positive experiences is relevant for pain imagery, pos-sibly hampering it. Interestingly, it has been shown that rewardresponsiveness, which is a facet of BAS sensitivity [8], is also pos-itively correlated with the response to placebo analgesia [49], aform of cognitive pain modulation mediated by expectancy and/orconditioning [10]. Future studies should explore possible associa-tions between pain imagery and dopamine-related characteristicssuch as the responsiveness to reward and to some types of placeboanalgesia.
The study by Santarcangelo et al. [46] (2013) highlights theimportance of considering emotional-motivational factors whenstudying the relationship between hypnotizability and pain. Anintegration of the HRMTP theory with Grey’s theory on the role ofaversive/appetitive motivational systems or later revisions thereof[11] may move forward the scientific knowledge about the transi-tion from acute to chronic pain.
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