40-Hz EEG asymmetry during recall of emotional events in waking and hypnosis: differences between low and high hypnotizables.

Sixteen high and thirteen low hypnotizable women, who had participated in our previous study (De Pascalis et al., 1987), were enrolled in a hypnotic session. After the hypnotic induction they were requested to recollect 2 positive and 2 negative personal life experiences. In our previous study subjects performed similar tasks in a waking-state. Hypnotizability was evaluated the first time with the Harvard Group Scale of Hypnotic Susceptibility (Form A) and, a second time, individually, with the Stanford Hypnotic Susceptibility Scale (Form C). The State Trait Anxiety Inventory, Maudsley Personality Inventory, and Tellegen Absorption Scale were administered. Upper-trapezius electromyogram (EMG) and bilateral electroencephalogram (EEG) activities within the 35-45 Hz band were recorded. Self-report rating scores for vividness of visual imagery and emotional feeling of the material recalled were evaluated. The 40-Hz EMG amplitude and the left and right hemisphere 40-Hz EEG densities were obtained. The data collected in hypnosis were compared with those in the waking-state. High hypnotizables, with respect to the lows, displayed significantly lower 40-Hz EEG density in the rest condition. High hypnotizables, while they were in hypnosis, showed an increase of 40-Hz EEG density during emotional recall compared with rest periods. In contrast, low hypnotizables, after hypnotic induction, showed no density change during tasks compared to the rest conditions. Different hemispheric trends were found between groups. Highs showed an increase of 40-Hz EEG density over both hemisphere during positive emotions and a density increase in the right and a density reduction in the left during negative ones. This hemispheric trend was found in waking and hypnotic conditions although in the hypnotic condition more pronounced hemispheric patterns were observed. The Tellegen Absorption Scale was found positively related to hypnotizability and with the level of 40-Hz density increase on the right hemisphere during emotional tasks. High hypnotizables, with respect to the lows, were able to access affects more readily. They also showed a greater hemispheric specificity in waking and hypnotic conditions.