International Handbook of Clinical Hypnosis - E-Lib FK UWKS

NEUROPSYCHOPHYSIOLOGY OF HYPNOSIS 65
EEG hemispheric differences in both hypnotic and nonhypnotic conditions.Highs
were signi®cantly faster than lows in recognizing angry and happy affect in the
discrimination of faces presented to the left or right visual ®eld Crawford, Kapelis
& Harrison, 1995).For highs only, angry faces were identi®ed faster when presented
to the right left visual ®eld) than left right visual ®eld) hemispheres, while lows
showed no signi®cant asymmetries.During self-generated happy and sad emotions
in hypnosis and nonhypnosis conditions, in comparison to lows, highs showed
signi®cantly greater hemispheric asymmetries greater right than left) in the parietal
region, in high theta, high alpha and beta activity between 16 and 25 Hz, all
frequency bands that are associated with sustained attentional processing Crawford,
Clarke & Kitner-Triolo, 1996).Taken together, these two studies suggest that highs
have more focused and sustained attention.Greater right parietal activity, as
indicated by faster reaction times and more EEG activity, is suggestive of greater
emotional arousal e.g., Heller, 1993) and/or sustained attention among the highs.
FRONTAL LOBE ACTIVITY AND HYPNOTIZABILITY
Our work suggests that highly hypnotizable persons have more effective and ¯exible
frontal attentional and inhibitory systems Crawford 1994a,b; Crawford, Brown &
Moon, 1993; Crawford & Gruzelier, 1992; Gruzelier & Warren, 1993).Consistent
with the above discussed research showing a relationship between hypnotizability
and sustained attentional processing, an intriguing neurochemical study by Spiegel
and King 1992) suggests that frontal lobe activation is related to hypnotizability.In
26 male psychiatric inpatients and 7 normal male controls, levels of the dopamine
metabolite homovanillic acid were assessed in the cerebrospinal ¯uid.While
preliminary in nature, the results suggested that dopamine activity, possibly involving
the frontal lobes, was necessary for hypnotic concentration.
Gruzelier and Brow 1985) found highs showed fewer orienting responses and
increased habituation to relevant auditory clicks during hypnosis, suggesting increased
activity in frontal inhibitory action Gruzelier, 1990).Gruzelier and his
colleagues Gruzelier, 1990; Gruzelier, 1999; Gruzelier & Warren, 1993; for
review, see Crawford & Gruzelier, 1992) proposed that during the hypnotic
induction there is an engagement of the left frontal attentional system and then a
signi®cant decrease of left frontal involvement with a shift to other regions of the
brain, dependent upon the hypnotic task involved.Our hypnotic analgesia work
reviewed below also strongly implicates the active involvement of the frontal
inhibitory processing system.
CEREBRAL METABOLISM DIFFERENCES BETWEEN LOW AND
HIGHLY HYPNOTIZABLE PERSONS
Only recently have we been able to begin to explore cortical and subcortical
processes during hypnosis with neuroimaging techniques such as regional cerebral