Hypnosis and Electrical Activity In the Brain

Following my post on Meditation and the Brain a perceptive reader just asked a great question:

“Has any of the research found any difference between hypnosis and meditation as it relates to brainwaves. And do people in a state of hypnosis demonstrate these high gamma waves?”

This is so interesting that I thought it was worth a short note of its own.

On the first occasion that I was hypnotized during my training, I remember thinking that the experience was very like the first stage of meditative practice: I was primarily using Vipassana back then. Subsequent subjective experiences have all tended to confirm that view: there are some similarities between trance and early meditative experiences.

There is a good amount of empirical research that tends to confirm that. John Gruzelier’s group at Imperial College in London has published some very fine work using not just electroencephalographic (EEG) measurements, but also functional MRI (fMRI). Gamma waves are between 30 to 100 Hertz, or cycles per second, and appear to reflect the way in which cells exchange information about the environment and form mental impressions. Gamma oscillations have a role in the subjective experience of pain. Not only has Gruzelier’s group shown some of the same gamma wave coherence, but also, research published in October of last year suggests that individual differences in hypnotic susceptibility are linked with the efficiency of the frontal lobe attention system. Hypnosis appears to involve a dissociation of the prefrontal cortex from other neural functions. Both the meditation and hypnosis studies have indicated that the key regions are primarily in the left frontal lobe.

The difference is that although people can demonstrate similar gamma wave activity when hypnotized, in the experienced meditators the gamma wave activity was there all the time, but would increase dramatically when meditating. How dramatic? Thirty fold higher activity than in a non-meditator. The trained brain is physically different from the untrained one.

Bob McCarley’s group at Harvard has done some interesting work in which healthy volunteers and people with schizophrenia were asked to look at images. The people suffering from schizophrenia showed no gamma wave activity at all.

Interestingly, there is also a very recent paper out in the Journal of Psychoactive Drugs showing the same EEG gamma coherence in two experienced people using the Brazilian drug ayahuasca, which suggest further similarities between meditation and shamanic psychedelic practices.

Technorati tags: brain waves, hypnosis