Reaction to pain stimulus before and during hypnosis measured by pupillary reaction

The aim of this study was to investigate the analgesic effects of hypnotic pain control on experimental pain by measuring pupil reactions as an objective psycho-physiologic parameter. Twenty-two healthy volunteers (11 female and 11 male) aged between 22 and 35 years participated in the study. Pupil diameter was measured as baseline measurement (i.e., static measurement) in the non-hypnotic and in the hypnotic state. Pupil diameter changes to a standardized pain stimulus were measured in the non-hypnotic and hypnotic state and compared. Additionally, a Fourier analysis of pupil oscillations reflecting central nervous activation during the static measurement (25.6 sec) was calculated. During the hypnotic state the pain related pupil dilation was significantly smaller than during the non-hypnotic state. Pupil oscillations were significantly reduced during hypnosis.