The MMN amplitude increases in hypnosis: a case study.

The neural mechanisms associated with hypnosis were investigated in a single highly hypnotizable subject by measuring the mismatch negativity (MMN) component of auditory ERP, reflecting the preattentive discrimination of change in stimulus flow, in normal baseline state and under hypnosis. It has been proposed that the frontal inhibition associated with hypnosis can be measured as a decrease in MMN. ERPs were elicited using the passive oddball paradigm with standard and deviant sine tone stimuli of 500 and 553Hz, respectively. The measurement was repeated in five separate sessions. In hypnosis the MMN was significantly larger compared to baseline. The results indicate that hypnosis can give rise to altered information processing in the brain even at a relatively early, i.e. preattentive level and that the larger MMN measured under hypnosis does not support frontal inhibition theory.