Brain activity in hypnosis has been detectably different using EEG studies. The general trend for hypnostised subjects when compared to control is more low frequency activity. Some studies suggest that this is an absolute higher value to well versed hypnotised subjects and is a practice effect of doing hypnosis regularly. Other studies imply that the relative ratio of high frequency activity over low frequency activity changes; with the relative increase in low frequency activity.
Either way, there is research that distinctively assigns detectable brain activity differences in hypnotised subjects when compared to non-hypnotised subjects. These differences are more evident in EEG studies than they are in MRI studies.
