Pain perception and EEG dynamics: does hypnotizability account for the efficacy of the suggestions of analgesia?

We report novel findings concerning the role of hypnotizability, suggestions of analgesia and the activity of the Behavioral Inhibition/Activation System (BIS/BAS) in the modulation of the subjective experience of pain and of the associated EEG dynamics. The EEG of high (highs) and low hypnotizable participants (lows) who completed the BIS/BAS questionnaire was recorded during basal conditions, tonic nociceptive stimulation without (PAIN) and with suggestions for analgesia (AN). Participants scored the perceived pain intensity at the end of PAIN and AN. The EEG midline dynamics was characterized by indices indicating the signal predictability (Determinism) and complexity (Entropy) obtained through the Recurrence Quantification Analysis. The reduced pain intensity reported by highs during AN was partially accounted for by the activity of the Behavioral Activation System. The decreased midline cortical Determinism observed during nociceptive stimulation in both groups independently of suggestions remained significantly reduced only in lows after controlling for the activity of the Behavioral Activation System. Finally, controlling for the activity of the Behavioral Inhibition System abolished stimulation, suggestions and hypnotizability-related differences. Results indicate that the BIS/BAS activity may be more important than hypnotizability itself in pain modulation and in the associated EEG dynamics.

Cross-evidence for hypnotic susceptibility through nonlinear measures on EEGs of non-hypnotized subjects.

Assessment of hypnotic susceptibility is usually obtained through the application of psychological instruments. A satisfying classification obtained through quantitative measures is still missing, although it would be very useful for both diagnostic and clinical purposes. Aiming at investigating the relationship between the cortical brain activity and the hypnotic susceptibility level, we propose the combined use of two methodologies - Recurrence Quantification Analysis and Detrended Fluctuation Analysis - both inherited from nonlinear dynamics. Indicators obtained through the application of these techniques to EEG signals of individuals in their ordinary state of consciousness allowed us to obtain a clear discrimination between subjects with high and low susceptibility to hypnosis. Finally a neural network approach was used to perform classification analysis.

Hypnotic assessment based on the recurrence quantification analysis of EEG recorded in the ordinary state of consciousness.

The cerebral cortical correlates of the susceptibility to hypnosis in the ordinary states of consciousness have not been clarified. Aim of the study was to characterize the EEG dynamics of subjects with high (highs) and low hypnotisability (lows) through the non-linear method of Recurrence Quantification Analysis (RQA). The EEG of 16 males--8 highs and 8 lows--was monitored for 1min without instructions other than keeping the eyes closed, being silent and avoiding movements (short resting), and during 15 min of simple relaxation, that is with the instruction to relax at their best. Highs and lows were compared on the RQA measures of Determinism (DET) and Entropy (ENT), which are related to the signal determinism and complexity. In the short resting condition discriminant analysis could classify highs and lows on the basis of DET and ENT values at temporo-parietal sites. Many differences in DET and all differences in ENT disappeared during simple relaxation, although DET still separated the two groups in the earliest 6min of relaxation at temporo-parietal sites. Our RQA based approach allows to develop computer-based methods of hypnotic assessment using short-lasting, single channel EEG recordings analyzed through standard mathematical methods.