Binaural beat induced Theta EEG activity and hypnotic susceptibility: Contradictory results and technical considerations

American Journal of Clinical Hypnosis,  Apr 2003  by Stevens, Larry,  Haga, Zach,  Queen, Brandy,  Brady, Brian,  Et al

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Procedures

EEG Configuration

During all training sessions, earlobe and forehead electrode sites were prepped with Ten-20 Abrasive EEG Prep Gel to decrease skin resistance. Ten-20 EEG conductive paste was used as a conduction medium to fill silver-chloride electrode cups. One monopolar EEG derivation was used, located according to the International 10-20 system (Jasper, 1958) at FZ3, 30% of the nasion-inion distance along the longitudinal midline; the reference for this study was the left ear, with forehead (Fp) common/ground.

Double-Blind, Repeated Measures Design

Participants were identified as either Low Hypnotizable (LH) or Moderate Hypnotizable (MH) on the basis of SHSS:C scores and were scheduled individually for three training sessions over each of two consecutive weeks, for a total of six training sessions for each participant. In a repeated-measures design, each participant received 10 minutes of pre-training baseline EEG recording, followed by 40 minutes of stimulus training, followed by 10 minutes of post-training baseline in each of the training sessions. Baseline periods consisted of sitting quietly with eyes closed with no auditory stimulation. Of the original 27 participants recruited for the study, 5 (3 LH, 2 MH) were randomly selected to receive the control, pink noise only training4; the remaining 22 (10 LH, 12 MH) participants were assigned to receive Theta Binaural Beat (TBB) stimulation training. Participants and all experimenters involved in the training program and posttraining SHSS:C testing were blind as to participant hypnotizability and training status.

For each training session, the participant was seated comfortably in a recliner with back upright but slightly reclined and with feet and legs resting on the foot rest. Each electrode site was prepped, electrodes were attached, impedances were checked and held below lOK ohms, EEG recording equipment was activated and a clear EEG trace was established, participants were advised about noise artifact and requested to remain as still as possible, and headphones were secured in place. Participants were asked to remain awake, with eyes closed, and passively attentive as the 10-minute pretraining baseline phase was initiated, followed by 40 minutes of auditory stimulation training, followed by the 10-minute post-training baseline, with frontal EEG's recorded throughout. At the conclusion of each training session, electrodes were detached and cleaned, and participants were asked about their experiences during the session. Immediately (within 2 hours) following the final training session, each participant was administered the SHSS:C again.

Data Analysis

Since the primary hypothesis of this study was that 4 hours of TBB training with low and moderate hypnotizable individuals would significantly increase hypnotizability, pre- and post-training hypnotizability scores for each group were analyzed by a simple between-groups, repeated-measures 3 (LH vs MH vs Controls) x 2 (Pre-training vs Post-training) ANOVA. As a measure of the efficacy of TBB training in enhancing frontal theta, frontal EEG's within the theta frequency band were averaged across the 10-minute pre-training and post-training baselines and each 10-minute quarter of the training session for each participant. Averages were computed for LH, MH, and Control participants separately and were examined for significant changes by a 3 (groups) x 5 (training phases) between-groups, repeated-measures ANOVA. To control for baseline differences among subjects, dependent variables in EEG analyses were the differences between the respective EEG training and initial baseline measures.