This article was downloaded by: [University of Sussex Library] On: 13 January 2015, At: 14:09 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

International Journal of Clinical and Experimental Hypnosis Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/nhyp20

40-Hz Eeg Activity During Hypnotic Induction and Hypnotic Testing a

Vilfredo Depascalis & Pietronilla M. Penna

a

a

University of Rome, “La Sapienza,” , Rome, Italy Published online: 31 Jan 2008.

To cite this article: Vilfredo Depascalis & Pietronilla M. Penna (1990) 40-Hz Eeg Activity During Hypnotic Induction and Hypnotic Testing, International Journal of Clinical and Experimental Hypnosis, 38:2, 125-138, DOI: 10.1080/00207149008414507 To link to this article: http://dx.doi.org/10.1080/00207149008414507

PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions

40-HZEEG ACTIVITY DURING HYPNOTIC INDUCTION AND HYPNOTIC TESTING VILFREDO DEPASCALIS AND PIETRONILLA kl. PENNA','

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

Uniomify of Rome, 'Lo Sapienza.' Rome, Italy

Abstract: The present study evaluates changes in left and right 40-H~ EEG production for 19 high and 20 low hypnotizable female Ss during the hypnotic induction and the administration of the Stanford Hypnotic SusceptibilityScale, Form C (SHSS:C)of the Weitzenhoffer and Hilgard (1962). Scalp recorded 40-Hz EEC density was obtained &omthe middle of the 01-P3-TS and 02-P4-T6triangles. As the hypnotic induction proceeded, high hypnotizable Ss exhibited a shift to greater right-hemisphere activity as compared to a waking-state rest condition. In contrast, low hypnotizable Ss, showed a reduction in left- and right-hemisphere activity. No differences between groups for SHSS:C ideomotor items were observed. A main effect for Hypnotizability among SHSS:C imaginative items was found. A Hypnotizability x Hemisphere x Trial interaction was found fbr both sensory distortion and imaginative SHSS:C items. A comparison was made between low versus high hypnotizable Ss of 40-Hz EEG activity while they passed the same item. The results of these comparisons indicate that differences in brain activity might be partially related to the differences between experiencing a hypnotic suggestion or fiiiling to do so. Significant relationships between 4 0 - H ~ EEG production and hypnotizability and 40-Hz EEG production and level of amnesia were as0 found. In examining the literature concerning psychophysiological correlates of hypnosis (see Dumas, 1977; Engstrom, 1976; Evans, 1979 for a review), two main trends can be found. The first trend attempts to evaluate the relationship between electroencephalographic (EEG) resting levels with hypnotizability level. The second trend attempts to define the relationship between hypnotizability and individual differences in cognitive abilities and how these differences are reflected in shifts of EEG hemispheric functioning. In support of the first trend, many studies have evaluated the link between EEG alpha production and hypnotizability. A number of studies found a significant EEG alpha and hypnotizability relationship (Bakan & Svorad, 1969; DePascalis, Silveri, & Palumbo, 1988; Engstrom, London, & Hart, 1970; London, Hart, & Leibovitz, 1968; MacLeodMorgan, 1979; Morgan, Macdonald, dc Hilgard, 1974; Nowlis & Rhead, 1968). Other studies failed to find an alpha-hypnotizability relationship Manuscript submitted August 24.1988; 6 d revision received May 5,1989. 'The authors wish to thank Margberita Di Pietm and Paoh Ciaralli for their valuable contribution to acquisition and data analyses. 'Reprint requeJtr zhwld be ddressedto Dr.V i i DePpralis, Diportimentodi P s i c o h Univenita di Roma, 'La Sapienza,"V i degli Apuli 8,00185 Roma, Italia.

125

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

126

DEPASCALIS AND PENNA

(Edmonston & Grotevant, 1975; Evans, 1979; Travis, Kondo, & Khott, 1973). In addition, there are also studies in which the theta-hypnotizability relationship was found to be significant (Akpinar, Ulett, Q Itil, 1971; Galbraith, London, Leibovitz, Cooper,6r Hart, 1970; Sabourin, 1982; Sabourin, Cutcomb, Q Pribram. 1986; Ulett, Apkinar, & Itil, 1972). A second line of research has attempted to evaluate the diEerence between high and low hypnotizable Ss in hemispheric engagementduring task performances purported to activate the hemispheres differentially. An EEG alpha asymmetry ratio has been used as an indicator of the hemispheric balance and a relative decrease in alpha activity has been assumed to indicate the activated hemisphere. A greater task-related hemisphericengagement (hemispheric specificity)has been found for high hypnotizable Ss when compared to low hypnotizables (Karlin, Goldstein, Cohen, Q Morgan, 198@; MacLeod-Morgan, 1979; klacleod-Morgan & Lack, 1982; Meszaros, Banyai, Q Greguss, 1986). There are also studies in which no differences in hemispheric shift between high and low hypnotizable Ss have found (DePascalis et al., 1988; Morgan et al., 1974). Since there are discrepant results among EEG alpha studies, it remains unclear whether these discrepancies may be attributed to variations in methodological procedures (e.g., EEG recording in an eyes-open or an eyes-ciosed condition) and/or in EEG alpha measures (e.g., alpha density or alpha amplitude). Apart from differences in the methodology used, it appears that incongruities could be produced by the underlying theoretical assumptions about the meaning of alpha abundance in the arousal theory. The common assumption has been that the level of alpha production has an inverse relationship to the arousal level involved in mental processes. Moreover, it has also been assumed that alpha and beta activities are inversely related. There are experimental data which support the view that the relaxation condition does not produce increases in alpha activity (Paskewitz Q M. T. Ome, 1973) and that a reduction of alpha activity is not a necessary consequence of apprehension or heightened arousal (M.T. Orne Q Paskewitz, 1974). Moreover, alpha activity and beta activity are not always found to be inversely related (Daniel, 1965). Ceneral theories of attention (Posner, 1975; Pribram & McGuinness, 1975)have suggested an information processing approach which Merentiates arousal, activation, and degree of conscious effort. In particular, Sheer (1976)has developed a psychophysiologid construct of "focused arousal" in considerable detail as a fun0 tional component of multidimensional attentional processes. Focused arousal, its brain circuitry, and its physiological representation in the 40Hz EEG activity (36-44 Hz) has been described by Sheer (1970, 1976, 'Karlin, R. A., Coldstein, L., Cohen, A.. & Morgm. D.Hypnotizability, attention, and hemispheric EEG activity during verbal and nonverbal tasks. Unpublished manuscript,

1980.

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

EEG ACTIVITY DURING HYPNOTIC INDUCTION AND TESTING

127

1984). Taskdependent lateralizations of 40-Hz EEG rhythm and the independence of 4O-Hz EMG activity from 40-Hz EEG have been found in a variety of cognitive performances (Spydell, Ford, & Sheer, 1979; Spydell & Sheer, 1982). Assuming that hypnosis is characterized by a state of focused attention (Hilgard, 1965)and that the level of 4O-Hz EEG activity reflects the level of focused attention, it is possible to hypothesize that this EEG activity may reflect Merences in attentional patterns between high and low hypnotizable Ss. In particular, on the basis of previous findings (&Pascalis, Marucci, Penna, & Pessa, 1987) it was expected that in an eyes-closed condition high hypnotizable Ss could produce less 40-Hz EEG activity compared to the low hypnotizables. Moreover, this study was to evaluate, according to the model proposed by Gruzelier and his colleagues (Gruzelier Q Brow, 1985; Gruzelier, Brow, Perry, Rhonder, Q Thomas, 1984), the possibility that the hypnotic condition requires the inhibition of the left hemisphere which thus permits an increase of right-hemisphere processes. Finally, one of the main aims of the present study was to evaluate the 4 0 - H ~EEG hemispheric differences between high and low hypnotizable Ss during the hypnotic induction and the administration of the Stanford Hypnotic Susceptibility Scale, Form C (SHSS:C) of Weitzenhoffer and Hilgard (1962). METHOD Subjects and Hypnotic Tests The Harvard Croup Scale of Hypnotic Susceptibility, Form A (HGSHS:A) of Shor and E.C. Orne (1962)was administered to an original pool of 108 women HGSHS:A score = 6.7, S.D.= 2.8, N = 108;age 19-26 years). The Ss who exhibited HGSHS:A scores within the 9-12 range were considered high hypnotizable, and a 0-4 range designated the low hypnotizable Ss. Forty-two Ss h m the low and high hypnotizable groups responded to an invitation to participate in a session in which physiologicalrecordings were to be obtained during the administration of SHSS:C. One S was not able to be available for the physiological recording session. Two Ss were excluded from the original grouping because they scored a medium level of hypnotizability on SHSS:C (High hypnotizable Ss: SHSS:C m r e = 10.3, S.D.= .8, N = 19; Low hypnotizable Ss: SHSS:C score = 3.5, S.D.= .7,N = 20). All Ss were right-handed. The handedness was evaluated with the Italian version of the Edinburgh Inventory Questionnaire (see Salmaso & Longoni, 1985).The hypnotist was female.

(x

x

x

Apparatus

Silver-silver chloride cup electrodes were &ed on the left side of the scalp approximately in the middle of the 01-P3-T5 triangle and in the corresponding location on the right side of the scalp of the International

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

128

DEPASCALISAND PENNA

10-20 system. These electrode sites were chosen because they lie over the parietal-occipital-temporal junction, an area known to be involved in cognitive processes. Electrodes were referenced to vertex (Cz). To detect the 4 0 - H ~EEG asymmetry fiom the EEC activity, a two-channel40-Hz EEC detector was built' according to the Spydell and Sheer (1982) method. Since 40-HzEEC activity may be contaminated by the low fkquency muscle activity, electromyographic (EMG)activity was recorded as a controL One EMG recording was obtained from bipoIar leads, with both electrodes on the upper right and left-trapezius of the neck, approximately 7 cm below the inion and 3 cm lateral to midline. All recordings were bipolar and impedance was below 7 k ohms for all Ss. A ground electrode was placed on the forehead. The EEG and EMG signals were amplified (gain = 200.000, bandwidth .16-200 Hz) using a low-noise differential amplifier (.85pV R M S of equivalent-input-noise-voltage in the bandwidth . l a 1 6 Hz, considering both inputs connected in common via 10 k ohms). High-pass filters were set at 10 Hz and low-pass filters at 90 Hz for both EEC and EMG amplifiers. A neumpolygraph (OTE Biom e d i a Italiana) and an oscilloscope with long persistence of the traces were used to d o w for v i s d inspection of high frequency, low amplitude activity in the record. To control for muscle artifacts in the 40-HzEEG, amplified EEG and EMC signals were sent to the three control devices. Each control device amplified, filtered, rectified, and integrated 40-Hz (35-45 Hz bandwidth) and 7 0 - H ~activity (64-76 Hz bandwidth) from the raw signal. Two control devices served for left and right EEG activity, one device served for analysesof EMC activity. The 40-Hz EEG detection device contained a comparator circuit which allowed 40-Hz activity to trigger a monostable controlled digital clock which measured the production time in .01 seconds within a &-secondepoch. Epochs were separated by 1.5-second intervals during which the time data were dqlayed and tabulated. In the presence of 7 0 - H ~activity in either an EEG or in the EMG channel, any #Hz activity in that channel within 200 ms was inhibited (see Sheer, 1976). A second control f i x muscle activity artifacts consisted of a detector which also inhibited, within 20 ms, the 40-Hz EEG activity in the EEC channel when this activity was concomitant with 40.- EMC. Time constant and minimum amplitude criterion for detecting an occurrence of a burst of 40-HzEEC and EMC response was set at 75 ms and 2.2 pV, respectively; the same criterion was used for 70Hz EMG signal. The amplitude criterion was set at the mean d u e of the amplitude variation within the 1-minuterest preceding tasks (2.2 to 10 pV range). The time period in which the two EEG signals exceeded these criteria resulted in a WtaI time display. The mean amplitude of &Hz EMC in pV within the 2-second epoch was obtained. The EEG was Clhe 40-Hz EEG system was designed and built by Din0 Montti and F'ietro Fermani. electronic technicians at the Department of Psychology.Rome University 'La Sapienza."

EEG ACTIVITY DURING HYPNCYI'IC INDUCnON AND TESTING

129

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

continuously monitored on paper and on the screen of a switchable twochannel oscilloscope to control for the elimination of artifacts from bodily movements. Procedure The monitoring equipment was shown to S and she was told that the aim of the experiment was to obtain EEG and EMG recordings during the hypnotic induction and the administration of the 12-item SHSS:C. The Ss were not, however, informed about specific experimental hypotheses, nor about their individual level of hypnotizability as previously measured by HGSHS:A. The experimental session was carried out between 3 and 7 P.M. After the electrodes were attached, each S sat in a comfortable armchair, in a sound attenuated dimly-lit chamber. During the experimental session, the hypnotist and S were in touch with the other E by means of an intercom system. Before the administration of SHSS:C, a 2-minute relaxation period was given to S during which she was invited to relax, emphasizing muscle relaxation and slow breathing. Two 1-minute rest periods (1 minute with eyes-open and 1 minute with eyes-closed) were given before beginning the hypnotic induction. The hypnotic induction was divided into two parts, the early hypnotic induction (eyes-open)and the late induction (eyes-closed). Forty Hz EEG density was obtained during the hypnotic induction in order to test whether the relaxation suggestions might differentiallyaffect those who were more or less hypnotizable. The 12 standard items of SHSS:C were then administered. The testing session lasted about 1.30 hours. Each of the 12 SHSS:C suggestions was divided into two periods: (a) the instruction period during which S received the instructions from the hypnotist to perform the suggested behavior and (b) the response period during which S did or did not perform the suggested behavior. The hypnotist indicated the beginning of the instruction period and the response period by pressing a microswitch button that produced a .5second acoustic signal outside the box. &SULTS

Statistical Analyses and Preparation of EEG Data

The time periods in which the 40-Hz EEG activity was present over 2-second epochs were collected during each experimental period and then expressed in seconddminute. The difference scores for EEG values were computed for each test item by subtracting the values obtained during the instruction period from the 40-Hz values collected during the response period. The scores for each S collected during the administration of hypnotic induction and SHSS:C items formed the bases for subsequent data analyses. The SHSS:C items were labeled as: Ideomotor-right hand

DLPASCALIS AND PENNA

130

lowering, moving hands apart, right arm immobilization, left arm rigidity; Sensory Distortion mosquito hallucination. taste hallucination, anosmia, hallucinated voice, negative hallucination; and Imaginative-dream and age regression. Separate ANOVAs across ideomotor, sensory distortion, and imaginative items for #Hz EEG difference scores, using a Hypnotizability X Hemisphere x Trial experimental design, were performed’. A two-tailed rejection region with a value of at least p < .05 was used throughout. Duncan’s multiple range test was used for post-hoc multiple comparisons. Downloaded by [University of Sussex Library] at 14:09 13 January 2015

-

40-Hz EEG Density IIhree separate ANOVAs for left- and right-40-Hz EEG difFerence scores each for ideomotor, sensory distortion, and imaginative items were carried out. The ANOVA for ideomotor items found a main effect for Trial (F = 3.45,df = 3,111;p < .02).This effect indicated a significantly smaller 40Hz EEG difference score in response to the moving-hands item and a significantly greater difference score in response to the left-arm rigidity item, as compared with the other ideomotor items (3.3,.9,2.7,and 6.5 for diEerence scores obtained in the right-hand lowering, moving hands, right-arm immobilization, and left-arm rigidity items, respectively; see Table 1). Analysis across sensory distortion items found a main effect for Trial (F = 3.93, df = 4,148; p < .005) and for Hemisphere (F = 21.64,df = 1,37; p < .ooOl).Trial effect evidenced a greater increase of 4 0 - H ~EEG density during mosquito hallucination, anosmia, and negative hallucination as compared to the increase of activity obtained during taste and voice hallucinations (8.4, 9.5,10.5,5.6,and 4.8 for mosquito, anosmia, negative, taste, and voice hallucinations, respectively). The Hemisphere effect showed a greater increase of activity in the left hemisphere as compared to the right (9.5versus 6.0,respectively). Moreover, a significant Hypnotizability x Hemisphere X Trial effect (F = 5.21,df = 4,148; p < .0006) was bund, indicating a Merential hemispheric pattern between groups among sensory distortion items. In particular, high hypnotizable Ss showed a left-hemisphere prevalence during mosquito, anosmia, and voice hallucinations, while they showed a hemisphere balancing during taste and negative hallucinations (highhypnotizable Ss: 14.2 versus 7.2,10.5 versus 6.3,7.7 versus 3.9,4.9 versus 5.4, 10.8 versus 12.1, for left versus right hemisphere during mosquito, ?be urigmal m data and ANOVA tables h v e been depositea with the N a t i d A d h r y Publicntions Service (NAPS). For 52 pages order h a t No. 047159 fhn ASIS-NAPS, do hfkdchc Publiatkms. P.0.Box 3513, G d Ceobd Station. Ness Yo&, NY 101633513. Remit in advance m U.S. fundc only, $14.35 for photocopy w $4.00 for microfiche and make checks payable to Miaofi& Publications NAPS. Outside the United Stat- and Canada, add postage of $8.50 for a photocopy and $1.50 for a fiche. Then is a $15.00

-

invoicing fee for orders not prepaid.

EEC ACI'IVITY DURING HYPNOllC INDUCTION AND TESTING

131

TABLE 1 Lem AND RIGHT 40-HzEEG DIFFERENCE SCOW AND THE D I F F E R U V ~ , ~ RATIO SCORESFOR HIGHAND LOWHYPNOTXUBLESs DCTRINCH m m c I N D U ~ O N AND THE SHSS:C ITEMS (STANDARDERRORS ARE REPORTED IN PMUNTWISES) Hi& Hypnotb.bb

cmditlan

EECM

EylyindIJction

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

Late induction

-0.7 (0.5)

-0.4 (0.4)

-0.04 (0.15)

-0.1 (0.4)

1.9 (0.9 20 (1.7)

0.84 (0.06) 0.32 (0.11)

-1.1 (0.4)

-1.9 (0.4)

3.9 (1.1)

26 (1.3)

-0.23 (0.12) 0.a (0.12)

(2.3)

0.3 (24)

0.16 (0.13)

2 MovingHands

5. Mosquito

Hallucination 6. Tste HdUCin?tion

7. Anosmh

8. Hdlsinated voice

9. Negative HducinatiOll 10. Dream

11. Age Regression 12. Amnesia

Ratio

0.08 (0.12)

40

4. Arm Rigidity (left)

L-HrpaotlnMn E E G M EEGIU&

1.5 (0.5)

(25) 26 (21)

3. Arm Immobitization

R*b

0.6 (0.6)

1. H a n d h M g

w

EEG-Ribt

5.6

23 0.26 (22) (0.W

- 1.0

21 (28)

0.28 (0.10)

0.9 (24)

0.5 (21)

-0.11 (0.13)

7.3 (24)

0.46 (0.10)

6.4

(23)

(28)

5.1 (25)

-0.04 (0.14)

14.2 (22)

7.2

(25)

0.15 (0.12)

6.1 (22)

0.22 (0.15)

4.9 (1.3)

5.4 (1.9)

0.36 (0.10)

6.3 (27) 8.6

3.3

(Z3)

(27)

0.00 (0.16)

10.5 (21) 7.7 (1.9)

6.3 (26) 3.9 (1.8)

0.09 (0.09)

13.7 (1.9)

7.5 (20)

-0.12 (0.16)

0.14 (0.13)

38

40

(21)

(20)

-0.02 (0.14)

10.8 (1.6)

121 (1.5)

0.32 (0.10)

14.9

4.2 -0.24 (25) (0.13

-4.7 (1.1)

5.4 (0.8)

0.60 (0.10)

8.9 (1.0)

6.6 (0.8)

(27) 7.2

0.5

(0.3

-1.7

(as)

(25)

-1.2 (0.5)

-0.4 (0.6)

0.10 (0.14)

0.37 (0.11)

8.2 (1.3)

3.0 (1.4)

-0.15 (0.17

0.06 (0.17)

22 (0.7)

-0.4 (0.4)

-0.24 (0.19)

anosmia, voice, taste, and negative hallucinations, respectively). Low hypnotizable Ss exhibited a greater density increase on the left hemisphere during taste, anosmia, and negative hallucinations, while they exhibited a hemispheric balancing during mosquito and voice hallucinations (lows hypnotizable Ss: 8.6 versus 3.3,13.7 versus 7.5, 14.9 versus 4.2,6.3versus 6.1,3.8versus 4.0,for left versus right hemisphere during taste, anosmia, negative, mosquito,and voice hallucinations, respectively). The ANOVA for imaginative responses evidenced a main effect for Hypnotizability (F = 3.99, df = 1,37;p < .05), indicating a greater density increase for high hypnotizable Ss compared to low hypnotizables (4.0versus 2.4, respectively). Furthermore, the following effects were significant: ((I) Trial (F = 72.16,df = 1,37;p < .OOO1; (b) Hemisphere X

DEPASCALIS AND PENNA

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

132

Hypnotizability (F = 31.5, df = 1,37; p < .OOOl; (c) Hemisphere x Trial x Hypnotizability (F = 6.51, df = 1,37; p < .02).Multiple comparisons of the means indicated that high hypnotizable Ss tended to show a balanced increase in left- and right-hemisphere activity during age regression and a reduction in left-hemisphere activity, and an increase in righthemisphere activity during the dream item. Low hypnotizable Ss showed a greater increase in left-hemisphere activity, as compared with the right, in response to age regression and a reduction of activity in both hemispheres in response to the dream item (see Table 1). An ANOVA across the early and late hypnotic induction periods for 40-Hz EEG difference scores (found by subtracting the averaged rest scores from those obtained in the early and late induction) was carried out. The followingeffects were found to be significant: (a) Hypnotizability (F = 8.62, df = 1,37; p < .(Mi); (b) Hemisphere (F = 14.77, df = 1,37; p < .oooS);(c) Hemisphere x Hypnotizability (F = 24.56, df = 1,37; p < .OOO1); (d)for Trial (F = 19.31, df = 1,37; p < .OO01); (e) for Hemisphere x Trial (F = 5.35, df = 1,37; p < .Q3); and v) for Hemisphere x Trial x Hypnotizability (F = 47.19, df = 1,37; p < .OO01). The main results indicated by these interactions can be summarized as follows. High hypnotizable Ss, compared to the low hypnotizables, showed a significantly greater increase of 40-Hz EEG density during the hypnotic induction compared to the rest condition. High hypnotizable Ss in the early hypnotic induction showed an increase of 40-Hz EEG activity in both hemispheres, but as the induction proceeded, they tended to show a progressive inhibition of activity in the left hemisphere and an increase of activity in the right (late induction). Low hypnotizable Ss, in contrast, showed a reduction of activity in the left and right hemispheres during both the early and late hypnotic induction (see Table 1). Analyses computed for 40-Hz EEG raw scores found similar results as those obtained for the difference scores. Moreover, an ANOVA across the two waking rest conditions (eyes-open, eyesclosed) for left and right 40Hz EEG raw scores, evidenced a main effect for Hypnotizability (F = 17.38, df = 1,37; p < .0002), indicating a greater production of 4 0 - H ~ activity for low hypnotizable Ss compared to the high hypnotizables (7.0 versus 5.0, for low versus high hypnotizable Ss, respectively). 40-HZ EEC Ratio

In order to verify the possibility that the effect of the hypnotic condition is similar to that of a right-hemisphere task (Crawford, 1985; MacLeodMorgan, 1982), a hemispheric asymmetry ratio was used in which the evaluation of task-induced asymmetry is measured as the change of 40-

Hz EEG hemispheric activity with respect to the corresponding rest period in waking state. To satisfy this assumption, a differential ratio m r e was calculated with the formula: (A Right density - A Left density)/l(A

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

EEG ACTIVITY DURING HYPNOTIC INDUCIlON AND TESTING

133

Right density + A Left density)[;where A represents the density change from the waking state rest period, and the denominator scores are considered as absolute values. A positive differential ratio indicates a righthemisphere prevalence and a negative ratio shows a left-hemisphere prevalence. Differential ratio scores are reported in Table 1. An ANOVA across averaged ratios, for ideomotor, sensory distortion, and imaginative items, found a main effect for Hypnotizability (F = 6.61, df = 1,37; p C .02); a main effect for Trial (F = 3.36, df = 1,37; p < .a); and an interactional effect for Hypnotizability x Trial (F = 3.25, df = 1,37; p C .a). The first effect indicated that high hypnotizable Ss, compared to the low hypnotizables, exhibited a more pronounced bias towards the right-hemisphere activity (i.e., greater and positive differential ratio scores). The second and third effects indicated a differential hemispheric trend between groups: High hypnotizable Ss showed an increasing right-hemisphere activation &om sensory distortion to ideomotor and even more right-hemisphere activation to imaginative items ( 2 1 , .33, and .49 for sensory distortion, ideomotor, and imaginative items, respectively). Low hypnotizable Ss, in contrast, tended to show a hemispheric balancing in the sensory distortion, imaginative, and ideomotor items (- .O3, - .O3,and .01 for sensory distortion, imaginative, and ideomotor items, respectively). 40-Hz EEG Differences between Groups for Passed and Failed ltems Some of the 4 0 - k EEG differences obtained in the above described analyses may reflect the difference between Ss who successhlly respond to an item, as opposed to those Ss who have Ear more failure experiences as is inevitable with low hypnotizables. Because of this, items that were passed by more than three low hypnotizable Ss and by more than three high hypnotizables and items that were &led by at least three high hypnotizables and three low hypnotizable Ss were selected. The passed items were: left-arm rigidity (4 low and 18 high), mosquito hallucination (5 low and 13 high), and moving hands apart (8 low and 17 high). The failed items were: hallucinated voice (20 low and 13 high) and mosquito hallucination (15 low and 6 high). Separate ANOVAs were performed between groups for left and right 40-Hz EEG and 4 0 - H ~EEG ratio scores. High hypnotizable Ss compared to the low hypnotizables tended to show a greater amount of 40-Hz EEG (1.1 versus -.3; F = 3.81, df = 1,20; p = .W) while they passed the left-arm rigidity item. No sigxllficant differences between high and low hypnotizable Ss were found while these Ss passed the mosquito hallucination and moving hands apart items. Analyses across failed items indicated that high hypnotizable Ss, compared to the low hypnotizables, produced a greater amount of 4O-Hz EEC during the mosquito hallucination item (1.6 versus .5; F = 6.96, df = 1,19; p < .02). No other differences for these two items were found.

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

1%

DEPASCALIS AND PENNA

Amnesia, Hypnotizability. and 40 Hz-EEC Actiuity High hypnotizable Ss, who experienced amnesia, showed a mean recall score of 1.8 (S.D. = 1.5 items) and low hypnotizable Ss, had a mean recall = 1.3 items) during amnesia. The rank correlation score of 4.9 (S.D. coefficient between SHSS:C scores and recall scores during amnesia was - .76. Assuming that 40-Hz EEG density within amnesia is a function of how hypnotized S is, a positive correlation was expected between the amount of 40-Hz EEG density and the number of items recalled. This hypothesis was confirmed: the rho coefficients between the number of items recalled and the left and right 40-Hz EEC densities during amnesia were .44and .52 (N = 39,p < .005), respectively.

DISCUSSION The present study examined changes in 40-Hz EEG production in high and low hypnotizable Ss during hypnotic induction and during the administration of SHSS:C items. High hypnotizable Ss tended to show an increase of 40-Hz EEG density (with respect to the rest periods) over both hemispheres in the early hypnotic induction, and they showed a decrease of activity over the left and an increase over the right hemisphere in the late hypnotic induction. A reduction of 40-Hz EEG activity in both hemispheres characterized the low hypnotizable Ss.This result appears in agreement with Cruzelier’s (1986, 1988) and Meszaros et d.’s(1986) neuropsychologid models of the hypnotic condition, where the inhibition of the initially dominant lefthemisphere activity and the release of right-hemisphere processes characterize the hypnotic condition. Based on the 40-Hz EEG patterns obtained across SHSS:C items, it cannot be unequivocally stated that group Merences may be due to the EEG characteristics of hypnosis. The EEC differences between groups during SHSS:C items may result from Merences in task pe&rmance which are independent of hypnosis. This statement appears to be in agreement with the fact that for ideomotor SHSS:C items, which were most likely to be passed by high and low hypnotizable Ss, Merences were not found in 40-Hz EEG responses between groups. Moreover, lbr sensory distortion and imaginative SHSS:C items, which were mainly passed by high hypnotizable Ss, significant interactional effects with hypnotizability were found. Because it has been shown that nonspecific or placebo effand the hypnotic effect itself are components involved in hypnosis (McClashan, Evans, & M. T. h e , 1969). it was attempted ‘ by comparing passed and Wed post-hoc to evaluate the hypnotic & items for high and low hypnotizable Ss. It was found that high hypnotizable Ss,compared to the lows, may show a greater amount of40-Hz EEG activity either when an item is passed (i.e., left arm rigidity) or when an item is failed (i.e., mosquito hallucination). These results support the view

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

EEG ACTIVITY DURING HYPNOTIC INDUCTION AND TESTING

135

that differences in 4 0 - H ~EEG activity between groups may only be partially related to the differences in experiencing or failing a hypnotic suggestion. The fact that high hypnotizable Ss, compared to the low hypnotizables, showed significantly lower 4 0 - H ~EEG activity in waking rest condition is in agreement with the present authors' previous waking state finding (DePascalis et al., 1987,and it can be explained by the assumption that in the waking state high hypnotizable Ss are more able to shut off external or internal distracting stimuli which are competing with task requirements. In the present study it has been shown that the level of amnesia is related to hypnotic depth and to the level of 40-Hz EEG production (i.e., 4@Hz EEG activity increased with the number of items recalled). This result may be interpreted as indicating a chapcteristic mode of cognitive work for high hypnotizable Ss compared with the low hypnotizables. Finally, using the differential asymmetry ratio, it has been also demonstrated that hypnosis could be considered as a right-hemisphere task.

REFERENCES AKPINAR, S.,U L ~C., A., & ITIL, T.M. Hypnotizability predicted by digital computeranalyzed EEG pattern. B w l . Psychiat.. 1971. 3.387-392. E m . P.,& SVORM,D. Resting EEG alpha and asymmetry of reflective lateral eye movements. Nature, 1969,223,975-976. CMWFORD,H. J. Cognitive flexibility. dissociation. and hypnosis. Paper presented at 93rd Annual Convention of the American Psychologid Association, Los Angeles. California. August 1985. DANIEL,R. S. Electroencephdographicpattern quantificationand arousal continuum. Psyc h u p h y s i o f o ~1965,2,146-160. DEPASCALIS.V., MARUC~I,F. S., PENNA.M. P.,h MSA, E. Hemispheric activity of 40Hz EEG during r e d l of emotional events: Differences between low and high hypnotizables. Znt. 1.Psychophysiol., 1987.5, 167-180. DEPASCALIS, V., S I L ~ RA, ~ . C P A L U M G. ~ , EEG asymmetry during covert mental activity and its relationship with hypnotizability. I n t . J . din. esp. H y p M s i s . 1988.36, 3852. DUMAS,R. A. EEC alpha-hypnotizability correlations: A review. Pqchophydobgy. 1977, 14.4314.

EDMONSTON, W. E., JR., & C

~ M W. , R. Hypnosis and alpha density. A m r . J . din. 1975,17,221-232. E ~ c s r r rD ~.~R. Hrplotic nuceptibility, E E G d p b . and self-regulatfon. In C. E. Schwartz & D. Shapiro (Eds.). Conrciaunrss Md srlf-ngdatiun:Advances in nuarch. (Vol. 1.) New York: Plenum, 1976. Pp. 173-221. ENCSTROM. D. R., LONDON,P.. & m.J. T. Hypnotic susceptibility increased by EEC alpha training. Natun, 1970,227,1%1-1!262. EVANS.F. J. Hypnosh and deep: Techniques Tor upbring cognitive activity during sleep. In E. Fromm & R E. Shor (Eds.), Hypnarir: D e o e in~m a r c h and new pcrrpcetioca.(Rev2nd ed.) New York: Aidine, 197X F'p. 13Q-183. GALBRAITH,G . C., LONDON, P., Lumvm, M. P., C o o p ~ qL. M..t HART, J. T. EEC and hypnotic susceptibility. 1.cum. physiol. Pqchol.. 1970, 72, 1S131. Htppnatir,

DEPASCALIS AND PENNA

136

CRUZELIER, J. Left and right hemsphere dynamics in the induction of hypnosis. Paper presented at the Third International Conference of the International Organization of Psychophysiology. Vienna. Austria, July 1986. GRUZELIER,J . H. E.~$mtng mind-body nlotionrhipr through ncuropsychophysiobgid inocsrigoriorrt of hypmais. Paper pmented at the 11th International Coagress of Hypnosis and Psychosomatic Medicine. The Hague,The Netherlands, August 1988. GRUZLLIER.J. H., h BROW, J. D. Psychophysiobgd evidence for a state theory of hypnosis and susceptibility. J . ptychaurm. Rw..1985,29.287302 CRUZELIER. J., BROW,J., PERRY, A., RtiomE~, J.. &THOMK%. hi. Hypnoticsuxeptibility: A lateral predisposition and altered cerebral asymmetry under hypnosis. Znt. J . Pq-

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

~ h o p h ~ ~1 dW .. . 2. 131-139. HILCARD,E. R. Hypnotic swceptibility. New York: Harcourt, Brace & World, 1965. LONDON. P.. HART, J. T., & LEIBOVITZ.M. P. EEG alpha rhythms and susceptibility to hypnosis. Nature, 1968, 219. 71-72. MACLEODMORCAN,C. Hypnotic susceptibility, E E C theta and alpha waves, and hemispheric specificity. In C. D. Burrows, D. R. Collinson. & L. Dennentein (Eds.), H y p m J i r 1979. Amsterdam: Ehviier/North-Holknd, 1879. Pp. 181-188. MACLEODMORCAN, C. Hypnosis is a right-hemisphere task: A model bored on arguments from the Laboratory and the literature. Paper presented at the 34th A n n d Meeting of the Society br Clinical and Experimental Hypnosis, Indianapolis. October 1982. MACLEODMORCAN, C.. h LACK,L. Hemispheric specificity: A physiological concomitant of hypnotizability. Pqchophysidogy, 1982, 19. 687-690. MCCLASHAN, T. H., EVANS,F. J., & ORNE, M. T. The nature of hypnotic analgesia and placebo response to experimental pain. P s y c h . Med.. 1969. 31,227-246. MESZAROS. I., BANYAI,E.. & GREGUS.A. C. E b d right hemisphere xtivation during hypnosis: EEC and behaviounl task performance evidence. Paper presented at the Third International Conference of the International Organization of Psychophysiology, Vienna, Austria, July 1986. MORGAN. A. H.. MACWNALD. H..& HILGARD.E. R EEG alpha Lateral asymmetry related to task and hypnotizability. Psychuphysldogy. 1974, 1l.Z7%282 NOWLIS, D. P.. & RHW, J. C. Relation of eyes-closed resting EEG alpha activity to hypnotic susceptibility. Percept. mot. Skills, 1968.27, 1047-1050. ORNE.M .T., & PASKEWITZ, D. A. Aversive situational effects on alpha feedback training. Science, 1971, 1 8 6 , 6 f M 6 0 . PASKEWITZ.D. A., & OWE, h.1. T. Visual effects on alpha feedback training. Science, 1973, 181,360363.

POSNER,M . 1. Psychobiology of attention. In M. S. Gazz;miga b C. Blakemore (Eds.), Handbook of psychohidogy. New York: Academic Press, 1975. F'p. 441-480. PRIBRAM,K. H . . & %iCGUtNNESS, D. Arousal, activation, and effort in the control of attention. Psychol. Rev., 1975 82. 116149. SABOURIN,M. E. Hypnosis and brain function: EEG correlates of state trait differences. Res. Comm. Psychol. Psychiat. Behuv., 1982. 7, 149-168. SABOURIN,M. E., CUTCOMB,S. D.. h PRIBRAM,K. H. E E C correlates of hypnotic susceptibility and hypnotic trance: Spectral analysis. Paper presented at the Third International Conference of the International Organization of Psychophysiology, Vienna, Austria July 1986. SALWASO. D., h LDNGONI, A. M . Problems in the assessment of hand preference. Cortex,

1985,21.533449. SHEER. D. E. Electrophysiological carrelates in memory consolidation. In C. Ungar (Ed.), Molenrlormechanh in mcmoryand learning. New York: Plenum. 1970. Pp. 177-211. SHEER,D. E. Focused arousal and 40Hz EEC. In R. hl. Knight & D. J. Bakker (Eds.). The mtmpn/choo~jof learning disorden. Baltimore: University P u k , 1976. Pp. 71-87. SHEER.D. E. Focused arousal. W-Hz EEG. and dysfunction. In T. Elbert. B. Rochstroh. W.Lutzenberger. & N. Birhaumer (Eds.). Self-reyitlution of the bruin and l e h w i o r . Berlin. Springer-Verlag, 1%. Pp. 69-34,

EEG ACTIVITY DURING HYPNOTIC INDUCTION AND TESTING

137

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

SHOR,R. E.,& ORNE.E. C. Harwrd Croup Scab of Hypnotic Surccptibilia Form A . Pal0 Alto, CA: Consulting Psychologists Press, 1962. SPYDEU, J. D., FORD,M. R., & SHEER, D. E. Task dependent nrebnl Literalization of the 40-Hz EEG rhythm. P s y c h o p h y d ~ g y1979,16,347350. , SPYDELL.J. D.,& SHEER, D. E. Effect of problem solvingon right and left hemisphere 40 Hertz EEG activity. Psychophysiobgy, 1982,19,420-425. TRAVIS,T. A.. KONW, C. Y.. & K N m , J. R. Interaction of hypnotic suggestion and alpha enhancement. 1.Psychiut., 1973,130,138B.1391. U L ~G., A., AKPINAR,S.. & ITIL,T. M. Hypnosis: Physiological, pharmacological reality. Amer. /. Psychiaf., 1972, 128,799805. WEITZENHOFFER, A. M., & HILGARD.E. R. Stanford Hypnotic Susceptibility Scale, Form C. Palo Alto, CA: Consulting Psychologists Press, 1962.

Aaivit6 EEG de 40 Hz durant I'imductioo hypmtique et la proctdure d'cv.luation de I'hypnotiddit6 vilfredo DePucpLir et PiehpdL M. Pennn R h 6 : Cette rschercho aadyse l a chpngements de productioa du rythw de 40 Hz sur l a knispkru gauche et dmit, chez 19 sujets fortemat hypwtirpbla et e0 autres fiiblement h y p o t h b k r lm da l'indwth hypnotiqua et lorn de l'dmhistm tion de l'cchelle d'hypnotisabilit6 de Stanford, Forme C (SHSS:C) de Weitzenhoffer et Hilgard ( 1 s ~ ) . &mitt du rythme de 40 Hz enregistmi mar le d p a t obtenu pprtir du centre du triangle dbtermin6 par l a dbrivatioas 01-P3-TS et Oe-P4-T6. A mesure que la procedure &induction progreupit, Ies sujets fortement hypnotisables pr6sentnicnt une 6l6vatian de l'oetivit6 de I'h6misph&redroit, comparativement P nlle pr6sentb duraut la

Downloaded by [University of Sussex Library] at 14:09 13 January 2015

138

DEPASCALIS AND PENNA

40-Hz EEG activity during hypnotic induction and hypnotic testing.

The present study evaluates changes in left and right 40-Hz EEG production for 19 high and 20 low hypnotizable female Ss during the hypnotic induction...
891KB Sizes 0 Downloads 0 Views