A dive into the neural predictors of deep hypnosis

A study published this month (cited below) aims to understand how hypnosis affects the brain. Despite many studies, we still don't fully grasp how hypnosis works in our brains and the neural aspects of hypnotic depth. The researchers acknowledge the complexity of hypnosis, which seems to describe both a process and a mental condition. The process involves techniques aimed at altering suggestibility and inducing imaginative experiences.

According to the sociocognitive model of hypnosis, any induction is hypnosis if the participant accepts it as such. This is irrespective of its outward characteristics, provided it meets certain expectations and is presented in the appropriate context. Conversely, heightened focused attention, diminished peripheral awareness, and increased suggestibility often characterise the hypnotic state. However, limited empirical evidence supports this.

The researchers explored this further. Using EEG samples that measured brain activity during hypnosis, they analysed this brain data to see any correlations in deep hypnosis. They found that brain patterns, like fast gamma waves and connections between different brain areas, link to the depth of hypnosis. To make things easier to understand, they used this brain data to create computer models that predict the depth of hypnosis.

The experience of hypnosis varies from person to person and is subjective. However, some common descriptions include decreased peripheral attention, deep relaxation, and vivid mental imagery. The term "hypnotic depth" refers to how deeply a person feels immersed in this experience. Although the idea of consciousness having different depths is metaphorical, research suggests a correlation between deeper levels and subjective/objective measurements.

There is no universally accepted way to measure hypnotic experiences, but simple self-reported scales show reliability. These scales reflect hypnotic depth and correlate strongly with standard measures and comprehensive assessments. In neuroscience and clinical settings, these scores are crucial for treatment success.

Self-reported scales offer an alternative to traditional tests, being less influenced by suggestibility and applicable in various settings. Given that hypnosis-like experiences can occur without formal induction, the study explored the neural correlates of deep hypnosis after different induction methods, including unconventional approaches. This was to expand the understanding of hypnosis beyond traditional methods.

52 participants from Eötvös Loránd University, School of Psychology, participated in the study. Participants had to be over 18 years old, in good health, and medically fit. Exclusion criteria included a history of epilepsy, schizophrenia, or other mental illnesses with symptoms of delusions or paranoia. The study excluded participants with prior experience in hypnosis. Before the experiment, participants provided informed consent and received vouchers valued at approximately 25 USD as a token of appreciation.

As a traditional hypnosis induction, the researchers used two commonly used methods: relaxation induction and confusion induction. For unconventional hypnosis, they introduced two distinct approaches: "white noise hypnosis" and "embedded hypnosis".

The "white noise hypnosis" used white noise, previously used in studies as a form of hypnosis induction. The researchers told participants that subtle alterations in the frequencies of the white noise would induce a specific brain pattern associated with a hypnotic state.

Embedded hypnosis was a novel technique devised for this study. Participants listened to a narrative about the human body and muscles. When the researchers presented this technique as hypnosis, participants were told the audio included embedded subliminal suggestions, designed to remain unnoticed and only affect the unconscious mind at various volumes and frequencies.

In alignment with the sociocognitive model of hypnosis (any procedure accepted by participants as hypnosis, regardless of its outward appearance, is hypnosis, providing it meets their expectations), the researchers treated all conditions as hypnosis scenarios when described as such to the participants. To ensure consistency in the analysis, they used hypnosis depth expectancy ratings, confirming the anticipated level of hypnosis was similar across conditions described as hypnosis, regardless of the specific induction method used.

Participants listened to a 6-minute induction recording. After the induction, participants rested with their eyes closed for 5 minutes. A brief alerting signal marked the end of the resting phase. Participants rated how deeply they felt hypnotised during the rest period on an 11-point scale, ranging from 0 (not hypnotised) to 10 (extremely hypnotised).

The results of the study suggest faster brain waves may hinder the hypnotic experience. The subjective perception of hypnotic depth correlates with diminished gamma power in the midline frontal area and heightened connections between the left and right dorsal attention networks (DANs). These brain regions and networks play essential roles in integrating information from different sources, exerting cognitive control, and shifting attention between stimuli.

The findings include the four distinct induction methods used in the study and, interestingly, how individuals perceive the depth of their hypnosis experience. Still, we are not much closer to finding out exactly what hypnosis is and how it works. This is why hypnotherapists must always consider the wider picture and take a holistic approach that encompasses all aspects of life.

References:

Farahzadi, Y., Alldredge, C. & Kekecs, Z. Gamma power and beta envelope correlation are potential neural predictors of deep hypnosis. Sci Rep 14, 6329 (2024). https://doi.org/10.1038/s41598-024-56633-x