Introduction to the Special Issue on Contemporary Research From the Guest Editor

Over the last few decades, hypnosis has matured as both a fascinating topic for scientific research and an effective technique for clinical application. As an area of scientific inquiry and clinical practice, hypnosis dates back over 240 years. Although interest in hypnosis has waxed and waned over centuries, today, in the second decade of the 21st century, it remains fairly strong. The aim of scientific hypnosis is to go beyond popular perceptions and misperceptions to reveal the true nature of hypnosis and the value of its applications.

Researchers and clinicians have strived to understand the essence of hypnosis from the vantage point of theory and method. Although numerous hypnosis studies appear in journals, this research has not yet had a sufficiently strong impact in the domains of psychology, psychiatry and neuroscience. The essential nature of hypnosis still fascinates and eludes, and many of the basic questions regarding hypnosis still remain unanswered.

The 21st International Congress on Hypnosis held in Montreal 2018 not only put a special emphasis on the practical role of hypnosis in medical and psychological care but also was committed to building bridges of knowledge and understanding between basic research and clinical practice in the field of hypnosis.

This special issue reviews the challenges we face as a field of scientific and clinical endeavor and offers six papers from leading hypnosis theorists and researchers from all over the world. Their articles comprehensively cover definitions, theory, research, and practice. What do we know, what can we do? What do we still not know, what are we still learning or trying to do?

Current hypnosis research focuses on two major areas (De Benedittis, 2015): (a) intrinsic research, i.e., the research line concerned with the functional anatomy of hypnosis per se, in the absence of specific suggestions, so-called neutral hypnosis or default hypnosis, and the neurophysiological mechanisms underlying the hypnotic experience in dynamic conditions and (b) instrumental research (or extrinsic studies), the use of hypnosis and suggestion for studying a wide range of cognitive and emotional processes as well as for creating “virtual analogs” of neurological and psychopathological conditions in order to elucidate their underpinnings and eventually positively change the way we treat them.

In taking stock, Santarcangelo and Scattina (this issue, p. 394, 2019) postulate an evolutionary perspective of hypnotizability, arguing that it seems quite unlikely that Mother Nature had selected 15% of individuals just because of their high proneness to respond to suggestions, but that hypnotizability might be associated with other physiological differences that could have sustained the natural selection of highly hypnotizable subjects and can induce their responsiveness to suggestions as a side effect. Indeed, highs seem to be less vulnerable to cardiovascular events than lows and the general population, since low vascular response to stress (i.e., reduced flow-mediated artery dilation (FMD) during stress) and high parasympathetic tone are factors predicting better cardiovascular prognosis (Amiya, Watanabe, & Komuro, 2014). Blood flow stimulates the artery endothelial cells to release nitric oxide (NO), which is responsible for the increase in the artery diameter (Van Hove, Van der Donckt, Herman, Bult, & Fransen, 2009). They hypothesize that highs should be less vulnerable than lows and the general population to cardiovascular events. In human evolution they may have survived owing to this cardiovascular advantage.

Another important aspect related to hypnotizability is the volume of cerebellar gray matter, which is involved in sensorimotor and cognitive-emotional control. Reduced cerebellar gray matter is found in high hypnotizables, as compared to lows. Highs’ lower cerebellar gray matter (likely due to noncontrolled release of endothelial NO) may reduce inhibition of the cerebral cortex by the cerebellum, thus leading to greater functional equivalence between imagery and perception and, finally, to consequent greater responsiveness to sensorimotor suggestions.

The hypothesized physiological basis of the responsiveness to sensorimotor suggestions has two main elements: (a) nitric oxide (NO) is a gaseous signaling molecule that is involved in the regulation of the cardiovascular, immune, and nervous systems. In the CNS, physiological amounts of NO are neuroprotective, while excessive release of NO becomes noxious and can cause cell damage (Calabrese et al., 2007). Physiological NO might be the “molecule of hypnotizability” owing to its effects on neurons’ maturation; (b) stronger functional equivalence between imagery and perception can account for highs’ greater proneness to respond to sensorimotor suggestions and their experience of effortless nonvolition.

Several studies reported that hypnosis can modulate pain perception and tolerance by affecting cortical and subcortical activity in brain regions involved in these processes (e.g., De Benedittis, 2003; Faymonville, Boly, & Laureys, 2006; Faymonville et al., 2003). Paqueron, Musellec, Virot, & Boselli (this issue, p. 408, 2019) assessed whether a focal glove hypnotic hand anesthesia induced thermal changes within the area of hypnotic protection. Their main finding was that unilateral hypnotic glove analgesia was associated with the occurrence of ipsilateral thermal alterations that were restricted to the side of hypnotic analgesia, compared with proximal forearm and control side.

Surprisingly, differential patterns of cutaneous thermal alterations were observed, with subjects showing most often an increase of temperature and less frequently a temperature decrease, probably reflecting either a vasodilation or vasoconstriction induced by hypnosis. Reasons for these different thermal profiles remain unclear, but idiosyncratic responses to hypnotic suggestions while visualizing their own glove hand could account for different psychophysiological effects.

Palsson, Twist, S., and Walker (this issue, p. 428, 2019) provided the first ever nationally representative survey about the views and experiences of the American public regarding therapeutic hypnosis. Key findings were that most people have either a positive or neutral overall view of clinical hypnosis, with very few people viewing it negatively. Most people (about 80%) believe hypnosis can be of substantial therapeutic value, deemed to be moderately or very useful by about half the population in major areas of therapeutic application like treating psychological problems; extinguishing negative habits, such as smoking; or improving physical health problems. Though only an estimated 7% of respondents had used hypnosis at some point in the past, about half of them would consider undergoing hypnotherapy if they needed it. Finally, highly hypnotizable self-estimated subjects (around 10%) had significantly more positive attitudes toward hypnosis, confirming what was previously reported in the literature (Lynn et al., this issue, p. 475, 2019; Spanos, Brett, Menary, & Cross, 1987).

Halsband and Wolf (this issue, p. 449, 2019) investigated brain plasticity changes in hypnosis using PET. Encoding and retrieval of high-imagery words in high hypnotizables under hypnosis produced pronounced occipital activation and increased prefrontal activity as compared with waking state, possibly improving working memory.

Another study explored the neural mechanisms of hypnotic visual illusions. Perceptual changes were associated with increased activity in the fusiform gyrus, possibly involved in visual processing (Hubbard & Ramachandran, 2005) and in the intraparietal cortex.

In a second series of experiments, the authors investigated functional changes in brain activity in dental-phobic patients by using fMRI. During brief hypnosis, patients showed significantly reduced activation in the left amygdala, bilateral ACC, insula, and hippocampus, as compared with waking state. These findings demonstrate that hypnosis can be an effective method to modulate brain structures involved in fear circuitry responses to aversive stimulation.

Lynn et al. (this issue, p. 475, 2019) present a perspective on 40 years of hypnosis research and its implications in psychotherapy. A growing body of evidence supports the notion that hypnosis is effective in treating a wide variety of psychological and medical conditions as a stand-alone intervention but also as a viable adjuvant to other treatments, such as mindfulness or CBT. The authors challenge the supposed superiority of indirect suggestions compared to direct ones, implying that clinicians can and should modify suggestion wording according to participant preferences.

The search for a discrete neurophysiological signature of hypnosis has been inconclusive so far with “few reliable brain patterns emerging across studies and inconsistency among findings” (Landry, Lifshitz, & Raz, 2017). This may contradict the state-dependent theory of hypnosis but does not invalidate the hypothesis of trance as a dynamic process that produces neurophenomenological changes (De Benedittis, 2015).

In this perspective, we need to explain individual differences in responsiveness to hypnotic suggestions. The search for individual differences on trait-like measures (including dissociation-based theories) has proved to be less than satisfying. Hypnosis can be experienced in very different ways by different participants and the clinicians should be aware of these individual differences in order to optimize participants’ skills. Furthermore, hypnotic responsiveness can be enhanced by fostering positive attitudes, beliefs, and expectancies about hypnosis and encouraging an active rather than a passive set to respond to suggestions. The Carleton Skills Training Program (CSTP; Gorassini & Spanos, 1986) was developed to modify and maximize hypnotic responsiveness. Several studies have shown that 40 to 65% of initially low hypnotizable subjects who participated in the CSTP scored as high hypnotizables after the training, with gains persisting for as long as 2.5 years (Gorassini & Spanos, 1999). Also, a positive rapport between participant and hypnotist appears to be particularly important for enhancing hypnotic responsiveness in low hypnotizable participants. However, the increased hypnotizability does not automatically mean a better clinical response to treatment (De Benedittis, Mammini, Rago, & Loriedo, 2019).

Self-agency is the sense that some actions are self-generated. The feeling of involuntariness is intrinsic to the hypnotic experience. Rainville et al. (this issue, p. 512, 2019) investigated changes in brain activity measured using arterial spin labelling (ASL), a functional magnetic resonance imaging method that enables comparison of regional cerebral blood flow (rCBF) between states and between individuals. Based on previous literature suggesting a key role of the parietal operculum (PO) in an altered sense of self-agency observed during hypnosis, Blakemore and Frith (2003) reported an increase in perceived automaticity in neutral hypnosis (i.e., without any stimulus or behavioral task) positively correlated with rCBF changes in the PO, with additional associations in the anterior of the supracallosal cingulate cortex (aMCC). These areas are part of the executive network of the brain, underlying the experience of volition (Darby, Joutsa, Burke, & Fox, 2018). This suggests that both executive and monitoring processes are active in individuals reporting high levels of hypnotic automaticity but that their representation may be modified such that executive engagement is experienced with an altered sense of agency.

Increases in perceived automaticity during hypnosis at rest were significantly related to increases reported in hypnotic depth, which in turn correlated with individual hypnotic susceptibility.

Since training can enhance the feeling of automaticity and clinical suggestion of self-agency may in turn improve the therapeutic effect of hypnosis (Lynn et al., 2019, this issue, p. 475), this might help improve the clinical impact of hypnosis.

Hypnosis is increasingly being recognized by the international scientific community as a valid and flexible physiological tool to explore the central and peripheral nervous system. This seems to be a real Copernican revolution in the field (De Benedittis, 2012, 2015).

This special issue stands as a provisional summary of where hypnosis had been, where it stands today, and where it is heading tomorrow. It is devoted mainly to experimental research but also addresses itself to clinicians. In fact, good clinicians should keep abreast of research developments and modify their techniques accordingly. I hope that these papers on current research efforts will stimulate clinical researchers to search out and examine facts about hypnosis thus far ignored, ask questions not yet posed, and test ideas as yet untested. And I hope that these papers raise more questions than answers, pushing critical thinking and research at the leading edge of the fascinating and intriguing domain of hypnosis.

The future of hypnosis research depends greatly on its researchers’ capacity to integrate hypnosis research into broader areas by building bridges of understanding. This can be achieved by capitalizing on hypnosis’ potential to extend the boundaries of knowledge in socio-cognitive psychology, the neural basis of consciousness, as well as applications in other psychology areas, medicine, and psychiatry.

Disclosure statement

No potential conflict of interest was reported by the author.