Hypnosis doesn’t work on everyone, with some people being particularly responsive to suggestion while others are more difficult to mesmerize. To try and understand why certain individuals are so easily entranced, researchers have recorded the brain activity of a group of volunteers while attempting to hypnotize them, revealing key differences between the brains of the most and least susceptible subjects.
The study – which has yet to be peer-reviewed – involved a total of 75 participants, all of whom were asked to complete an assessment designed to reveal their susceptibility to hypnosis. This pre-screening stage allowed the authors to identify 40 individuals who scored either extremely high or unusually low, meaning they were classified as very likely or unlikely to respond to being hypnotized.
The researchers then used electroencephalography (EEG) to record the neural activity of these 40 volunteers before and after “hypnotic induction”, which was achieved by one of the researchers reading a suggestive script. “By recording [EEG] before and after hypnotic induction and analyzing diverse neurophysiological features, we identify several features that differentiate between high and low hypnotic susceptible individuals for both pre- and post-induction periods, which underscores the multifaceted nature of hypnotic phenomena,” write the researchers.
“Instead of pinpointing a singular neural pattern, our results corroborate the understanding that hypnotic experiences possess a layered neural foundation,” they continue.
However, while the factors separating strong and weak responders were numerous, one element of brain activity stood out as a clear predictor of susceptibility to hypnosis. Specifically, differences in the aperiodic exponent of neural activity prior to hypnotic induction were found to correlate with a person’s predisposition to being put under.
EEG readings are made up of two parts, known as the periodic and aperiodic exponents. Periodic signals are oscillatory, meaning they repeat at regular time intervals. These neural oscillations emerge from a background of aperiodic signals, which don’t repeat.
It’s likely that these differences in baseline aperiodic signals influence a person’s “mental absorption, feelings of relaxation, and preparation for hypnotic responding.” According to the researchers, these traits are typically higher in those who are more easily beguiled, and are therefore likely to influence a person’s suitability for hypnosis.
Perhaps the most important finding here is that the patterns that determine susceptibility to hypnosis were found in the period before hypnotic induction, rather than afterwards. “Susceptibility to hypnotic suggestion therefore reflects a predisposition that is captured by neural features independent from the hypnotic procedure,” write the study authors.
“This finding resonates with the hypothesis that hypnotic susceptibility is an inherent psychological trait predisposing certain individuals to be more responsive to suggestions,” they conclude.
A preprint of the study, which is a preliminary version of a scientific paper that has not been validated by peer review, can be found on bioRxiv.