Neurophysiology and neuropsychology of hypnosis: Recent advances and future perspectives: Part 2

In recent years, hypnosis has become increasingly popular in health care and education (De Benedittis, 2020; Hauser, Hagl, Schmierer, & Hansen, 2016). However, the role of hypnosis has not been fully explored, and the mechanisms of action are not well understood. This Special Issue represents Part 2 of an outstanding effort of the American Journal of Clinical Hypnosis to explore and elucidate the neurophysiological and neuropsychological underpinnings of hypnotic processes and responses, in order to improve understanding of hypnotic practices.

For Part 2 we invited six additional leading researchers and clinicians from all over the world to contribute their perspectives, research, and recommendations for future work. The articles in this special issue address some crucial questions, such as: the role of hypnotizability and, particularly, of medium-responders, which represent the majority of the general population; clinical pain and neural correlates in patients suffering from Temporo-Mandibular Disorder (TMD); the real essence of hypnosis and its axiological uncertainty; the effects of hypnotic relaxation response on psychophysical indices of ANS activity; the role of the anterior cingulate cortex in mediating neurocognitive and somatosensory aspects of the hypnotic experience; and the effects of hypnotic suggestions in modulating the pain matrix activity in chronic pain patients. These peer-reviewed articles provide fascinating insights into hypnosis processes and responses. Critical analysis, cutting-edge research, emerging perspectives, and future directions for research and practice are presented, filling the gap between basic research and clinical practice.

In taking stock of the papers in this issue, Perri critically addresses one of the major methodological issues of hypnosis research which is that clinical and experimental investigations on hypnosis utilize dichotomous comparison between highs and lows while neglecting the medium responders who represent the majority of the general population. The main risk of this medium-neglecting bias is to overshadow the most common hypnotic effects. In addition, methodological reasons suggest that the within-subjects design should be preferred over the between-subjects research design.

Abrahmsen and Naish comparatively evaluate experimentally induced pain, clinical pain, and neural correlates (i.e., blink reflex) in patients suffering from Temporo-Mandibular Disorder (TMD). Patients were able to reduce their chronic self-reported pain, reduce self-reported experimental pain, produce changes in brain responses, and demonstrate hardly any involvement of brainstem reflex pathways, suggesting a top-down rather than a bottom-up mechanism. Hypnotic analgesia effects in both conditions showed little, or even no correlation, with the measured hypnotic susceptibility, possibly due to limitations of the standard susceptibility scales, that contain items with sensory-motor behavioral responses, but not experiential, subjective items (Acunzo & Terhune, 2021). The authors argue that right cerebral hemisphere and anxiety might have a significant role in differentially modulating the pain experience.

A comprehensive overview of the main issues related to the real essence of hypnosis and its axiological uncertainty has been provided by Facco. The epistemological reflection covers the fundamental components of hypnotic construct (i.e., suggestibility, absorption, dissociation, hallucination, free will, and agency). The author emphasizes the apparent paradox between the prejudicial negative perception of established hypnosis effectiveness and the dominant paradigm of the current positivistic perspective of medicine. This paper offers an intriguing and questioning insight into the major controversies of hypnosis such as current mind/body dichotomy. This ruling paradigm dating back to the Cartesian structural dualism has turned science into ideological dogmatism and is unable to explain the complex interface between mind and subjective experience, brain and its neural correlates, and consciousness (including hypnosis). The ontological approach offers a better perspective encompassing both the physical and the mental world and merges them in a whole, and an essential aspect in the understanding of hypnosis, as well. The author advocates a critical reappraisal of all the major components of the hypnotic construct (i.e., suggestibility, agency, absorption and dissociation, and some kind of hallucinations).

In addition to central effects, hypnosis is thought to induce a relaxation response associated with concomitant changes in the autonomic nervous system (ANS) activity. Fernandez, Urwicz, Vuilleumier, and Berna reviewed the relevant literature and elucidated the effects of hypnosis on psychophysical indices of ANS activity and more specifically of the stress/relaxation response such as heart rate variability and electrodermal activity. Overall converging results demonstrated reductions in sympathetic responses concomitant with increases in parasympathetic activity under hypnosis despite significant limitations (e.g., small sample sizes and low quality of the studies). The authors provide suggestions for guiding and optimizing future work in the field.

Del Casale, Ferracuti, Adriani, Novelli, Zoppi, Bargagna, and Pompili investigated the attentional determinants of hypnotic suggestions mediated by the activation of the anterior cingulate cortex and other brain areas thus modifying the conflict monitoring and cognitive control.

The anterior cingulate cortex is also involved in modulating the activity of pain circuits under hypnosis in the affective, sensory-cognitive, and behavioral components. The role of the cingulate cortices, mainly the anterior and medial portions, appears to be crucial for better understanding the hypnotic phenomena related to both the neurocognitive and somatosensory aspects.

Finally, Bicego, Rousseaux, Faymonville, Nyssen, and Vanhaudenhuyse explored the effects of hypnotic suggestions in modulating the pain matrix activity in chronic pain patients. Hypnosis seems to act mainly upon regions underlying emotion and cognition (e.g., the anterior cingulate cortex) with an influence on pain perception and emotional regulation. The authors emphasize that a better knowledge of the neurophysiological mechanisms underlying hypnotic analgesia should enable a more systematic and fruitful use of hypnosis in the management of this complex problem. Summing up, the pattern of activation in chronic pain is related to activation of the cortico-limbic system involving brain areas that contribute to the affective and cognitive aspects of chronic pain (e.g., medial PFC (mPFC), amygdala, nucleus accumbens, hippocampus, ACC, and insula) rather than the sensory ones. Consciousness is composed of two types of consciousness: the internal/self and the external/environment. During hypnosis, significantly less (or no) external awareness, and significantly higher internal awareness have been reported. This occurs concomitantly with decreased functional connectivity of the external-control network and changes in connectivity of the internal-control network. During deep hypnosis, the functional connectivity in regions responsible for spontaneous thought and environmental processing is lower, whereas increased connectivity in the ACC might account for increases in attentional and executive processes leading to higher absorption.

Differences in functional connectivity are also related to the level of hypnotizability. Highly hypnotizables seem to have greater functional connectivity between the left dorsolateral prefrontal cortex and the salience network, while studies relying on EEG and structural brain differences yielded different results, according to the authors, and remain controversial. Hypnosis is more effective than other complementary techniques in modulating chronic pain. The transition from acute to chronic pain is characterized by a shift in pain representations from sensory/nociceptive perceptions to emotionally driven cognitions. Neuroimaging studies in hypnosis have shown that these changes are associated with a concomitant positive emotional modulation of the pain matrix and a reduced negative-emotional processing of pain.

This special issue is a review of the challenges we face as a field of scientific and clinical endeavor, offering significant contributions 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?

This Guest Editor wants to thank all the authors for contributing to this special issue and the excellent reviewers for their feedback and great help that made this special issue possible. Their research and insights can contribute to a greater understanding of the range of hypnosis, further innovative areas of research, and more fully explore the potential for integration and use within hypnosis interventions.