International Handbook of Clinical Hypnosis - E-Lib FK UWKS

NEUROPSYCHOPHYSIOLOGY OF HYPNOSIS 63
Crawford, 1990; Galbraith, London, Leibovitz, Cooper & Hart, 1970; Graf®n, Ray
& Lundy, 1995; Sabourin, Cutcomb, Crawford & Pribram, 1990; Tebecis, Provins,
Farnbach & Pentony, 1975; Ulett, Akpinar & Itil, 1972a,b; for review, see Crawford
& Gruzelier, 1992).In a nonhypnotic state, highly hypnotizable persons referred
to as `highs') are likely to generate more theta power than the low hypnotizable
persons `lows').This is supportive of behavioral research that ®nds highs have
greater extremely focused and sustained attentional abilities, as measured by the
Tellegen Absorption Scale e.g., Crawford, Brown & Moon, 1993; Tellegen &
Atkinson 1974; for review, see Roche & McConkey 1990) or the Differential
Attentional Processes Inventory Crawford, Brown & Moon, 1993), and by performance
measures involving attentional processing.Highs have shown superior
performance on attentional tasks such as visual search Wallace & Patterson,
1984), gestalt closure Crawford, 1981; Wallace, 1990), reversible ®gures and
visual illusions e.g., Crawford, Brown & Moon, 1993, Wallace, 1986, 1988) and
other attentional tasks for review, see Crawford, 1994b).
As individuals enter into hypnosis, EEG theta power often increases, sometimes
in both lows and highs.Highs continue to generate more theta than lows in various
brain regions e.g., Crawford, 1990; Graf®n, Ray & Lundy, 1995; Sabourin et al.,
1990).Sabourin et al.1990) noted theta power increases in both hemispheres of
frontal, central and occipital regions during hypnotic induction and a subsequent
series of standardized hypnotic suggestions provided by the Stanford Hypnotic
Susceptibility Scale, Form C Weitzenhoffer & Hilgard, 1962).Graf®n, Ray and
Lundy 1995) reported that during an induction theta power increased in the
posterior areas, while during a subsequent passive hypnotic condition theta decreased
for highs.Within hypnosis, Crawford 1990) found highly hypnotizable
persons generated signi®cantly more high theta 5.5±7.5 Hz) than did lows at
frontal, temporal, parietal and occipital regions.Highs showed asymmetrical EEG
high theta power shifts, particularly in the temporal region, during cold pressor pain
when focusing on pain left hemisphere dominant) or experiencing hypnotic
analgesia right hemisphere dominant), suggesting differential involvement of
possibly the hippocampal system from which theta may be generated, particularly
during vigilant conditions e.g., Crowne, Konow, Drake & Pribram, 1972; Michel,
Lehmann, Henggeler & Brandeis, 1992).
The so-called `40-Hz band' is a high frequency, low amplitude EEG rhythm
centered around 40 Hz that has been found to be a covariate of focused arousal
e.g., Sheer, 1976). It appears to be from localized cortical neurons that receive
thalamic afferents Steriade, Gloor, Llonas, Lopes da Silva & Mesulam, 1990) and
has `been taken to be indicative of a mechanism linking or temporally coordinating
the distributed cortical representation of stimuli' Barlow, 1993, p.165).Akpiner,
Ulett and Ital 1971) reported more 40±50 Hz-activity during nonhypnotic rest and
reaction time tasks in highs than lows.De Pascalis and Penna 1990) found highs
showed greater right-hemispheric 40-Hz production during hypnosis, while lows
showed reduced activity in both hemispheres.In line with the hypothesis that highs