We conducted an MEG study aimed at understanding the neural mechanisms underlying hypnosis and our main finding is a significant reduction in occipital gamma power during hypnosis. We are a bit puzzled by this finding and would appreciate any possible explanation.
Very interesting! I will just add that a 2017 fMRI ALE metanalysis (Landry et al) concluded that the only region consistently activated during hypnosis induction is in the occiptal cortex (Lingual gyrus). The authors suggest that higher-order theories of hypnotic induction may be incomplete...
I would need to know more about the study to suggest anything conclusive, eg is it a reduction in occipital gamma power during hypnosis compared to their personal baseline, compared to controls, or is it reduction of relative gamma power in relation to the other frequency bands? Were any other bands different?
Hypnosis is supposed to be associated with sleep like frequencies so perhaps there is a reduction in gamma in order to shift the frequency spectrum toward the lower bands as a mechanism of hypnosis.
Thank you so much for your answer.
It was a within subject comparison between a baseline condition (resting state at the beginning of the experiment), under hypnosis condition (after hypnosis induction), and post hypnosis condition. Participants' eyes were closed the entire time. We found a reduction in beta (on the left side) and gamma (occipital) bands during hypnosis. See figures attached. We did not find any other differences (i.e., no differences in delta, theta, or alpha).
If it were only that easy to determine what a decrease in neural activity within a brain region ultimately means! Unfortunately, I have more questions than answers.
Going along with what Derrick mentioned, when individuals are falling asleep, do they show similar patterns as your subjects "under hypnosis"? Or are they more similar to them at "post hypnosis"?
It would be interesting to compare the results of your study with one that engages the subjects in various visual discrimination tasks. That may help sort out what is it that left hemisphere is doing during an attention and discrimination task.
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