Sunday, June 18, 2006

Hypnosis and Consciousness

Next in a continuing series on hypnosis:

Functional neuroanatomy of the hypnotic state
In Press, Corrected Proof, Journal of Physiology (Paris).
Marie-Elisabeth Faymonville, Mélanie Boly and Steven Laureys

What is hypnosis and how to induce it

There is not a generally accepted definition of hypnosis. For many authors it is seen as a state of focused attention, concentration and inner absorption with a relative suspension of peripheral awareness (Laureys et al., in press).
And after writing that lengthy dissertation or grant proposal, it's time to enter a fugue state...

Yeah, OK, The Neurocritic is [probably] not hypnotizable (not even by Hypnotoad). I don't know anything about hypnosis, either, but let's take a look at the process:

Hypnosis has three main components: absorption, dissociation and suggestibility (Spiegel, 1991). Absorption is the tendency to become fully involved in a perceptual, imaginative or ideational experience. Subjects prone to this type of cognition are more highly hypnotizable than others who never fully engage in such experience (Hilgard et al., 1963). Dissociation is the mental separation of components of behavior that would ordinarily be processed together (e.g., the dream-like state of being both actor and observer when re-experiencing autobiographical memories). This may also involve a sense of involuntariness in motor functions or discontinuities in the sensations of one part of the body compared with another. Suggestibility leads to an enhanced tendency to comply with hypnotic instructions. This represents not a loss of will butrather a suspension of critical judgment because of the intense absorption of the hypnotic state.
Hmmm, "suspension of critical judgment" -- that's not gonna happen here. But what are the "neural correlates" of a hypnotic state?

The Precuneus and Conscious Experience

First off, Faymonville et al. review their PET studies comparing hypnosis to a control state. Since their hypnotic induction procedure involves asking the subjects to vividly reimagine pleasant autobiographical memories, the control state was "recalling pleasant autobiographical memories while NOT under hypnosis." Which brain areas showed greater blood flow (and presumably greater neural activity) under hypnosis than in the control state? A huge chunk of the brain: "occipital, parietal, precentral, prefrontal, and cingulate cortices." Which area showed less activity under hypnosis than alertness: the medial parietal cortex (i.e., precuneus).

This area is hypothesized to be involved in the representation (monitoring) of the world around us (Gusnard and Raichle, 2001).
Raichle and colleagues have argued for a "default mode" or "resting state" of brain function that engages a certain network of brain regions (posterior cingulate and precuneus and medial prefrontal cortex) during "rest." These regions become DEactivated when people are engaged in the typical types of cognitive tasks they're asked to do in a scanner. So it's really only a "resting state" when compared to doing, say, the Stroop task. When asked to rest and stare at a plus sign, you may engage in idle daydreaming or think about what you'll have for dinner or remember your hot date from last night or silently sing.

Anyway, Faymonville et al. mention that the precuneus is "one of the most dysfunctional brain regions in states of unconsciousness or altered consciousness such as coma, vegetative state, general anesthesia, slow wave and rapid eye movement sleep, amnesia and dementia [referernces available upon request], suggesting that it is part of the critical neural network subserving conscious experience."

References

Gusnard, D.A., Raichle, M.E., 2001. Searching for a baseline: functional imaging and the resting human brain. Nat. Rev. Neurosci. 2: 685-694.

Hilgard, E.R., Lauer, L.W., Morgan, A.H., 1963. Manual for Standard Profile Scales of Hypnotic Susceptibility, Forms I and II. Palo Alto, Consulting Psychologists Press.

Laureys, S., Maquet, P., Faymonville, M. E. Brain function in hypnosis (in press) In: Audenaert, K., Otte, A., Dierckx, R. A, van Heeringen, K. (Eds.), Nuclear Medicine in Psychiatry. Springer-Verlag, Berlin.

Spiegel, D., 1991. Neurophysiological correlates of hypnosis and dissociation. J. Neuropsychiat. Clin. Neurosci. 3: 440-445.


Next up: Hypnosis and Pain Control.

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1 Comments:

At February 06, 2007 6:45 AM, Blogger Sekhar said...

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