Oohashi Et Al. Electroencephalographic Measurement of Possession Trance in the Field

Electroencephalographic measurement of possession trance in the field

Tsutomu Oohashia,b,c,*, Norie Kawaic,d, Manabu Hondae,f, Satoshi Nakamurae,g,Masako Morimotoh, Emi Nishinai, Tadao Maekawaj

aDepartment of Information and Network Science, Chiba Institute of Technology, Narashino 275-0016, JapanbDepartment of KANSEI Brain Science, ATR Human Information Processing Research Laboratories, Kyoto 619-0288, Japan

cFoundation for Advancement of International Science, Tsukuba 305-0062, JapandDoctoral Programs of Medical Sciences, The University of Tsukuba, Tsukuba 305-8577, Japan

ePRESTO, Japan Science and Technology Corporation, Kawaguchi 332-0012, JapanfLaboratory of Cerebral Integration, National Institute for Physiological Sciences, Okazaki 444-8585, Japan

gBiomedical Imaging Research Center, Fukui Medical University, Fukui 910-1193, JapanhJapan Society for the Promotion of Science, Tokyo 102-8471, Japan

iHuman Interface Research and Development Section, National Institute of Multimedia Education, Chiba 261-0014, JapanjATR Media Information Science Laboratories, Kyoto 619-0288, Japan

Accepted 17 December 2001

Abstract

Objectives: To verify the utility of a portable electroencephalogram (EEG) measurement system developed for investigating spontaneous

EEG from vigorously moving healthy subjects in a possession trance under a natural condition.

Methods: A portable multi-channel EEG telemetry system was developed to record the EEGs of 3 healthy male Balinese while they were

performing a ritual dedicatory drama in the field. After reducing extraneous artifacts using a digital filter, the EEGs and their power spectra

were analyzed in terms of evolution from one state to another.

Results: During the drama, one of the subjects became possessed while the others did not. The EEG of the possessed subject did not show

any pathological findings including epileptic discharges, but indicated enhanced power in the theta and alpha frequency bands during the

trance. This finding was not observed in the other two subjects, who did not go into trances, with no pathological EEG findings.

Conclusions: The measurement system and data analysis methods we developed have allowed us, for the first time, to obtain an EEG from

healthy subjects who are vigorously moving while in a possession trance. The present technique enables us to use a spontaneous EEG as a

marker of the underlying physiology of a state of possession trance. q 2002 Elsevier Science Ireland Ltd. All rights reserved.

Keywords: Possession trance; Spontaneous electroencephalogram; Field recording; Portable electroencephalogram recording system; Topography; Spectral

analysis

1. Introduction

In some traditional cultures, it is widely observed that

ordinary, healthy participants in a ritual ceremony enter a

state of possession, or a possession trance, without

psychoactive drugs. Based on a survey of 488 human socie-

ties worldwide, Bourguignon (1973) reported that 90% had

institutionalized some form of altered state of consciousness

and 57% associated these states with a possession trance.

Therefore, it is likely that some biological mechanisms

common to all human beings may underlie possession

phenomena. Nevertheless, since possession trance has so

rarely been investigated from a psychophysiological

perspective, such mechanisms are not clear. In the late

1960s, Prince (1968) pointed out that possession states

had not been studied physiologically although the unusual

behavior and the alterations of consciousness that are asso-

ciated with possession phenomena suggest an altered state

of cerebral physiology. He suggested that future improve-

ments in a portable electroencephalogram (EEG) recording

system, including a telemetry system, would make it possi-

ble to record physiological data from possessed individuals

in the field under natural conditions. Until now, however, no

one has yet successfully recorded an EEG under such condi-

tions.

There are at least three major problems facing researchers

who wish to make a physiological study, under natural

Clinical Neurophysiology 113 (2002) 435445

1388-2457/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved.

PII: S1388-2457(02)00002-0

www.elsevier.com/locate/clinph

* Corresponding author. Foundation for Advancement of International

Science, Tokyo project office, 1-53-11-022 Higashinakano, Nakano-ku,

Tokyo 164-0003, Japan. Tel.: 181-3-3366-8788; fax: 181-3-3366-8737.

E-mail address: [email protected] (T. Oohashi).

CLINPH 2001113

conditions, of a person in a state of possession. First, as

Bourguignon and Peitay (1965) have pointed out, the sacred

context of most possession phenomena make it extremely

difficult to record physiological data in the field. Second, the

standard telemetry system does not work in the field because

there is no electric power supply and the system lacks port-

ability. In addition, since the equipment is not shockproof,

any vigorous movement that a possessed subject makes

would easily cause malfunctions during the recording.

Third, even if an EEG could be recorded, it would be

seriously contaminated by various kinds of artifacts, espe-

cially those caused by physical vibratory shocks continu-

ously applied to the electronic circuits of the transmitter

during the recording. We have been trying to overcome

these difficulties for a long time.

In the present study, we have two aims. The first is to

verify the practical utility of the EEG portable recording

system that we developed for field use and the reliability

of the analysis procedure for a spontaneous EEG excluding

the artifacts from body movement. The second is to report

the first EEG findings on the subject of possession trances as

a pilot study.

We selected Bali Island, Indonesia, as the site for our

study based on cultural anthropological studies. Bali is

well known as a traditional society where possession trances

frequently occur in ordinary healthy people in a ritual cere-

mony (Covarrubias, 1937; Mead, 1942; Belo, 1960). There

are several festal dramas and ritual ceremonies in which

participants go into possession trances, but they are

performed in a garden deep inside a temple, on grounds

that are open only to villagers. Foreigners are rarely allowed

in. It is impossible for foreigners to even obtain information

about the time and place of such a performance beforehand.

We visited Bali several times since 1973 to find a ritual

drama or ceremony suitable for our study as well as to

establish a relationship of mutual trust with the Balinese

people. Due to the sanctity of the rituals and the inviolability

of the performance space, it was difficult to persuade perfor-

mers to put an electric device on their body during a perfor-

mance, nor could we bring a recording system into the

performance space. It took us 11 years to establish mutual

trust with the local community and to obtain the consent for

our research from executive officers of the temple and reli-

gious administrators. We finally received permission to

enter a performance space for EEG recordings in 1984.

We had begun the development of a portable multi-chan-

nel EEG telemetry system that could be used in the field in

the mid-1980s, and continued to test and improve it in the

1990s. With this system, we have been able to identify the

temporal and spectral characteristics of extraneous artifacts

in the data obtained from vigorously moving subjects, and

have developed analysis methods to effectively reduce

them.

In this way, we have finally succeeded in recording a

multi-channel EEG from a possessed subject in a Balinese

ritual ceremony.

2. Methods

2.1. Subjects

In Bali, Indonesia, the participants and/or spectators of

ritual ceremonies and dramas are known to go into a posses-

sion trance without any psychoactive drugs. This phenom-

enon is called Kerauhan. One of the prominent

characteristics of Kerauhan is the fact that it usually occurs

not in a professional shaman but in ordinary healthy people

en masse during ritual ceremonies. In this study, we focused

on a Kerauhan that occurred during a dedicatory ritual

drama called Calonarang. In this drama, several partici-

pants usually show a similar pattern of possession trance.

Therefore, the homogeneity of this drama is potentially

suitable for a physiological study. Two healthy right-handed

male volunteers (aged 28 and 32) were studied (Subjects 1

and 2). Prior to the experiments, we carefully explained the

experimental procedure to them and the subjects gave their

informed consent. Basic personal data of each subject, such

as family history, past medical history and possession

experiences, were obtained through interviews. On a sepa-

rate occasion, we recorded the EEG of another male subject

(Subject 3, aged 31). This subject behaved as though

possessed but was thought not to have gone into a posses-

sion trance during the drama according to his appearance

(e.g. eyes, face) and behavior (e.g. muscle stiffness and

tremor, recovery from the episode) during the drama and

the lack of anterograde amnesia during the episode (see

Section 3).

2.2. EEG recordings

Many telemetry EEG recording systems are commer-

cially available, however, most of them are designed to

record EEGs in the laboratory. When we began our study,

none of them could record EEGs from vigorously moving

subjects in the field with no electric power supply, although

some commercial products are now available. In addition, it

was very important that the EEG recording system not

disturb the visual and auditory information of the sacred

ceremonial space, and not distract the subjects participating

in the drama. Therefore, we developed a multi-channel

portable EEG recording system based on a WEE-6124 tele-

metric system (Nihon-Kohden, Tokyo, Japan) (Fig. 1). We

made a stable, long-life battery-based, portable power

supply to use the receiver system in the field. We also rede-

signed the electrode cap (Electro-cap, Ohio, USA). Each

electrode was tightly affixed to an elastic cap. The cap

was fixed to the subjects head by means of a strap that

went under the chin in order to reduce constraints on the

subject and simultaneously to keep it tightly in contact with

the scalp. These modifications prevented a major dislodg-

ment of the electrodes. In addition, an electroconducting gel

was put on the scalp to maintain the electrical contact

between the electrodes and the scalp and to compensate

T. Oohashi et al. / Clinical Neurophysiology 113 (2002) 435445436

for slight dislodgments of the electrodes. The electrode cap

had holes for the subjects ears so that the earlobes were

exposed and the subject could easily listen to the music with

no undue unpleasantness. The length of the cable connect-

ing the electrode cap and the head amplifier was shortened

to less than 10 cm. The head amplifier was tightly affixed to

the electrode cap. These modifications significantly reduced

extraneous artifacts caused by electromagnetic induction

and body movements. The transmitter was attached to a

flexible cloth belt, which was fastened tightly around the

subjects waist. Receiving antennas with high-performance

boosters, which improved sensitivity and expanded the area

of reception, were installed at multiple locations around the

performance field. As a result of these modifications, the

EEG data were clearly received from subjects moving

around in an area more than a 100 m2.

The EEG was recorded from 12 scalp sites (Fp1, Fp2, F7,

Fz, F8, C3, C4, T5, Pz, T6, O1 and O2 according to the

International 1020 System) using linked earlobe electrodes

as a reference with a filter setting of 160 Hz (23 dB). Fp1and Fp2 were linked and used as Fp for analysis. Data

recorded from the two subjects were stored on an analog

magnetic tape with a 28-channel data recorder (XR-9000,

TEAC, Tokyo, Japan). Thirty minutes before the drama

started, the electrodes were quickly attached to the subjects.

It was confirmed that the subjects did not feel unpleasant-

ness or constraint. The electrode cap and the transmitter

were hidden under the costumes so that the subjects did

not look different from the other performers. Before the

performance began, a 3 min resting EEG was recorded

with the subjects eyes closed. The EEGs were continuously

recorded during the drama, which lasted approximately

70 min. When the performance was over, another 3 min

resting EEG was recorded with eyes closed. Before the

EEG recordings, the subjects were interviewed regarding

personal facts and past history. Episodic recall and subjec-

tive impressions before, during and after the trance were

obtained from each subject after the ritual drama ended,

through a standard clinical interview by a Balinese medical

doctor. The behavior of each subject during the drama was

also recorded on a videotape.

2.3. Data analysis

The entire observation period of Subject 1, who became

possessed, was categorized into two states: normal state

(NS) and trance state (TS). The NS was further subdivided

into 3 phases: the resting phase with eyes closed before the

drama (PRE), the music-playing phase (MUSIC) and the

resting phase with eyes closed after the drama (POST).

The TS was subdivided into 5 phases: the first moving

phase with eyes opened (MOVE-I), the first falling-down

phase with eyes closed (FALL-I), the second moving phase

with eyes opened (MOVE-II), the second falling-down

phase with eyes closed (FALL-II) and the final phase

(FINAL). The EEG data for Subject 2 (whose EEG was

recorded simultaneously with that of Subject 1 but who

did not become possessed) was compared phase by phase

with that of Subject 1 in real-time. The data for Subject 3,

whose EEG was recorded on a separate occasion, was also

analyzed. He behaved as though possessed but did not go

into a possession trance (see Section 3). Since the behavior

of Subject 3 was similar to that of Subject 1, although he did

not play a musical instrument, we used the phases of Subject

T. Oohashi et al. / Clinical Neurophysiology 113 (2002) 435445 437

Fig. 1. The multi-channel portable EEG recording system and analysis system developed for field use.

1, except for MUSIC, for the analysis of Subject 3. WAIT

was used in place of MUSIC for Subject 3 when he was

waiting to come on the scene before his possession-like

behavior. Note that all of the phases for Subject 3 are NS.

We first visually inspected the original raw EEG for

epileptic discharges. Then, we digitalized the data with a

sampling frequency of 256 Hz and filtered it with an equi-

ripple FIR digital bandpass filter (pass-band cutoff frequen-

cies, 4 and 30 Hz; stop-band cutoff frequencies, 3.5 and

30.5 Hz; stop-band attenuation, 20 dB; pass-band ripple,

0.1 dB; filter order, 768) to extract the frequency bands of

interest: theta (48 Hz), alpha 1 (810 Hz), alpha 2 (10

13 Hz) and beta (1330 Hz). Artifacts caused by body

movements, wire vibration and mechanical shocks were

thus effectively reduced (see Fig. 2) without affecting the

frequency band we were interested in. After this filtering

procedure, epochs containing other artifacts with an extre-

mely large amplitude including those arising from the

subjects eye movement were carefully excluded from

further analysis through visual inspection of both the raw

and filtered EEGs. We then subjected the EEG data to power

spectrum analysis. The power spectrum of the EEG at each

electrode was calculated by fast fourier transform (FFT)

analysis for every 2 s epoch with an overlap of 1 s, at the

frequency resolution of 0.5 Hz with a sampling frequency of

256 Hz. Then the averaged power spectrum within each

phase was calculated. The square root of the averaged

power level in the theta, alpha 1, alpha 2 and beta bands

at each electrode position was calculated to get the equiva-

lent potential of the EEGs. Based on these values, colored

contour line maps with 2565 scalp grid points were

constructed by linear interpolation and extrapolation. This

map is called a brain electrical activity map (BEAM), which

describes the scalp distribution of the equivalent EEG

potentials (Ueno and Matsuoka, 1976; Duffy et al., 1979;

Oohashi et al., 2000).

3. Results

3.1. Appearance of the subjects

3.1.1. Subjects 1 and 2

Approximately 50 persons participated in the drama. At

the beginning, 3040 players, including Subjects 1 and 2,

entered the performance space and started vigorously beat-

ing a bamboo musical instrument with a stick. During the

drama, they sat at the side of the performance space,

continuously playing their instruments. At the climax,

about 60 min into the drama, Subject 1 along with a few

participants suddenly became possessed. He left his musical

instrument and jumped into the center of the performance

space. He then attacked the person playing a witch with a

sword. He dashed himself against the witch, glowered at

her, then staggered around for a while and dashed again

(Fig. 2A). He repeated these automatism-like actions

several times (MOVE-I and MOVE-II). During this time,

he fell down on the ground twice and closed his eyes

(FALL-I and FALL-II) (Fig. 2B). He stiffened and showed

tremors in FALL-II. After FALL-II, he wiggled on the

ground with eyes closed (FINAL). When a priest sprinkled

a few drops of sacred water on him and patted him, he was

barely able to stand up with assistance and gradually

returned to NS. The TS lasted 7 min and 50 s. While Subject

1 was in TS, the drama came to a climax at which time the

music was being played very loudly. A questionnaire

completed after the drama revealed that Subject 1 had ante-

rograde amnesia during TS, namely he did not remember his

own behavior during that time. By contrast, Subject 2 sat

and played his instrument with concentration and strength

throughout the drama with his eyes open. Note that although

Subject 2 had experienced TS many times before, he did not

go into a trance during this particular performance. Table 1

shows the time of each phase of the trances.

3.1.2. Subject 3

Subject 3 was recorded at another performance of the

drama Calonarang in a similar setting. He attacked the

witch with a sword several times and fell down on the

ground twice with his eyes closed. His behavior was similar

to that of Subject 1. However, he did not stiffen and did not

have any tremors during FALL-I and FALL-II. After the

drama, he suddenly and easily stood up without assistance

and behaved as usual. He did not show anterograde amnesia

at any point during the drama.

3.2. Achievement of the EEG recording system and digital

bandpass filter

It was difficult to keep a good contact between the elec-

trodes and the scalp in the possessed subjects, who vigor-

ously moved and sometimes fell down, especially when the

subject tried to remove the electrodes from his body. Due to

mechanical shocks caused by the subjects movement, the

transmitter temporarily became inoperative. In addition, the

signal was sometimes intercepted by an obstacle. Neverthe-

less, the multi-channel EEG data were successfully trans-

mitted for approximately 90% of the time of the experiment.

Fig. 2 shows an example of the raw and filtered EEG

recorded from Subject 1 during the possession trance. The

digital bandpass filter effectively removed low-frequency

noises below 4 Hz caused by mechanical shock to the trans-

mitter as well as high-frequency noises above 30 Hz. This

filtering procedure enabled us to easily avoid the contami-

nation of extraneous artifacts and to obtain an overview of

the data.

3.3. EEG findings

3.3.1. Visual inspection of the raw EEG of the possessed

subject

The raw EEG waveforms indicated that during the PRE

and POST phases, Subject 1 showed a symmetrical domi-


nant rhythm in the occipital regions with normal waxing and

waning. Peak frequencies were 11 and 10.5 Hz for PRE and

POST, respectively. No apparent spikes or sharp waves

were observed during the 3 min PRE and POST recordings.

Considering the filter setting, we cannot definitively state

that slow waves did not exist. However, no localized contin-

uous or intermittent rhythmic slow waves have been

observed so far. Even just before TS, Subject 1 did not

show any obvious rhythmic paroxysmal discharges or an

electrical decremental pattern suggesting an ictal EEG. In

MOVE-I and MOVE-II, it was difficult to evaluate the exis-

tence of spikes and sharp waves by a visual inspection of the

raw EEG because of the extraneous artifacts. On the other

hand, in FALL-I and FALL-II an occipital dominant rhythm


Fig. 2. A subject in TS and corresponding EEGs. (A, upper) Subject in an eyes-open moving phase of TS. The subject in TS (left) attacks the witchs (center)

abdomen with a short sword. (A, lower) Subject 1s raw EEG, filtered EEG (430 Hz) and power spectra of filtered EEG at each electrode. The peak frequency

of power was observed at 9 Hz. (B, upper) Subject in an eyes-closed falling phase of TS. (B, lower) Subject 1s raw EEG, filtered EEG (430 Hz) and power

spectra of filtered EEG at each electrode. Prominent alpha 2 rhythm is observed predominantly in the occipital region. The peak frequency of the power was

observed at 10.5 Hz.

peaking at 10.5 Hz was clearly observed without spikes,

sharp waves or generalized slow waves.

3.3.2. Power spectrum analysis of the EEG

In Subject 1, a remarkable difference between NS and TS

was seen in the power spectra of the spontaneous EEG as

well as between the different phases within TS. Fig. 3A

compares the BEAMs of Subjects 1 and 2 chronologically.

Subject 2 (Fig. 3A, lower panel) showed little change in

EEG power throughout the drama except for a slight

enhancement of the beta and theta bands in the frontal

region at the climax of the drama. Subject 1 (Fig. 3A,

upper panel) showed BEAMs similar to those of Subject 2

during the PRE and MUSIC phases in NS. During TS, by

contrast, Subject 1 showed a distinctive increase in the

power of the theta, alpha 1 and alpha 2 bands. The power

of the alpha 1 band was relatively predominant during

MOVE-I and MOVE-II, whereas that of the alpha 2 band

was more prominent during FALL-I and FALL-II. The

enhancement of the power in these frequency ranges

became more prominent as time went on. This tendency is

also recognizable in Fig. 3B, which shows the temporal

evolution of the averaged EEG potential for each band

across all the electrodes in Subjects 1 (upper panel) and 2

(lower panel). In addition, Subject 1 showed a greater

enhancement of the theta, alpha 1 and alpha 2 bands during

POST than during PRE, whereas Subject 2 did not show

such an enhancement at all.

Fig. 4 shows the time course of the BEAMs and the

averaged power of each band across all the electrodes

recorded from Subject 3, who did not become possessed

but showed behavior, including vigorous body movement,

similar to that of Subject 1. Subject 3 did not play a musical

instrument but just waited for the scene with his eyes open

during the WAIT phase. During the PRE and POST phases,

an occipital dominant rhythm was clearly observed with a

peak frequency at 10 Hz. During the MOVE and FALL

phases, when he mimicked a possessed person and behaved

as Subject 1 did but without actual possession, the BEAM

did not show any remarkable changes, except for a slight

enhancement of the alpha 1 and alpha 2 bands during FALL-

I and FALL-II (Fig. 4A). The time course of the power

spectra of Subject 3 shown in Fig. 4B resembles that of

Subject 2 (Fig. 3B, lower graph) who was not possessed

and who continuously played his instrument throughout

the drama without making any vigorous movement. A

lack of prominent change in the power spectra of Subject

3 is in marked contrast to those of Subject 1, who showed

similar body movement during TS.

4. Discussion

We successfully recorded EEGs during possession

trances under natural conditions for the first time. This

was achieved by establishing a stable relationship of mutual

trust with the Balinese people and by developing the neces-

sary recording and analysis systems. The recorded EEG in

this study showed an enhancement of the theta and alpha

bands of spontaneous EEG activity, and differed from

epileptic disorders and mental disorders.

4.1. Utility of the portable EEG telemetry system and

analysis method

The multi-channel portable EEG telemetry system that

we developed for use in the field enabled us to record the

EEG data from the subjects under a possession trance.

Major points that enabled us to do this are as follows: (1)

improvements in the manner of affixing the electrode cap

allowed a tight connection of the cap with less constraint;

(2) strengthening and shortening the wire connections

between the electrodes and the head amplifier decreased

artifacts caused by vibration and increased the resonance

frequency of the input circuit and (3) application of a digital

bandpass filter with a sharp frequency characteristic effec-

tively reduced low-frequency artifacts, especially the drift

of the baseline caused by mechanical vibration of the elec-

tric circuit.

4.2. Validation of the power spectrum analysis

We hypothesized that the stationary aspect of the

frequency structure of a spontaneous EEG, which can be

elaborated by FFT and averaging multiple epochs, might

reflect a physiological change of neuronal activity specific

to each phase of the possession trance because a sponta-

neous EEG is a good index of the global state of the

brain. From this viewpoint, it is ideal for all of the EEG

data recorded from each phase to be analyzed. In this case,

however, we could not avoid deterioration of the quality of

the data due to contamination by artifacts. Therefore, multi-

ple epochs free from artifacts were carefully sampled from


Table 1

Time of each phase of EEG recordingsa

Phase 1 2 3 4 5 6 7 8

PRE MUSIC MOVE-I FALL-I MOVE-II FALL-II FINAL POST

Subjects 1 and 2 120 3564 188 29 229 21 113 172

Subject 3 180 2350 208 32 220 25 105 180

a Numbers represent time in seconds of various phases of EEG recordings. Note that the EEG data from both Subject 1 and Subject 2 are categorized based on

Subject 1s behavior.

the data, and consequently, the time of the selected epochs

in each phase might not be enough to manifest the general

state of phase. To verify whether the findings based on the

sampled data represented each phase, we examined the

power spectra of all data from each phase without excluding

the epochs contaminated by artifacts. Then to evaluate the

overall similarity between the data from all epochs and

those from the sampled epochs in terms of spatial distribu-

tion and spectral proportion of BEAMs, Pearsons correla-

tion coefficients were calculated in each phase using the

values at all electrodes in all frequency bands. In all of

the phases except for MOVE-I and MOVE-II for Subjects

1 and 3, which contained excessive artifacts because of the

subjects intense movement, the power spectra of the entire

period compared quite well with those obtained from the

sampled data. Correlation coefficients ranged from 0.61 to

0.89 and the significance was always less than 0.01. There-

fore, it is likely that the sampled data represented the entire

period of each phase in a possession trance. Regarding the

MOVE-I and MOVE-II, the excessive noise introduced by

the subjects intensive movements disabled us from evalu-

ating similarity between the entire data and the sampled

data. Therefore, we calculated correlation coefficients

across the multiple sampled epochs in these phases to test

their mutual similarity. Correlation coefficients calculated

between two different sampled epochs were ranged from

0.31 to 0.91 and the probability was always less than 0.05,

which means that the sampled epochs in the present study

resembled each other in terms of the spatial distribution and

spectral proportion of BEAMs. Thus, it is reasonable to

consider that the sampled data reflected a common character

through the entire period even in these phases. These find-

ings suggest that the data obtained from our measurement

and analysis methods reflect the physiological states specific

to each phase of a possession trance.

There are several points we have to be cautious about

when interpreting the results. In terms of BEAMs, it is

necessary to consider the effect of activation of the linked-

earlobe reference electrodes. Activation of the earlobe elec-

trode by the occipital alpha rhythm could distort the scalp

distribution and falsely localize the frontal activity of the

alpha band shown in the frontal region in Subject 1. In

addition, part of the slow activity induced by the noise of

the earlobe electrode might have been contaminated in the

BEAM of the theta range, although the digital bandpass

filter followed by a careful visual inspection significantly

reduced such artifacts (Fig. 2). Spectral analysis with a

better temporal resolution, such as the maximum entropy

method, may provide useful information in this regard

(Morimoto et al., 1998).

It is unlikely that the enhancement of the theta, alpha 1

and alpha 2 bands observed in Subject 1 resulted from non-

specific effects associated with physical exercise. The data

obtained from Subject 3 is useful in this regard because he

performed similar physical exercise but did not show clear

evidence of a possession trance, such as anterograde amne-

sia, during his possession-like behavior. As shown in Fig. 4,

the EEG of Subject 3 lacked enhancement of the power

spectra. His EEG resembles that of Subject 2, who did not

become possessed. It is in sharp contrast to the EEG of

Subject 1. These findings suggest that the enhancement of

the EEG power spectra observed in Subject 1 is specific to

his possession trance.

There is a possibility that a physiological difference

between an NS and a possession trance can be detected in

a spontaneous EEG as a difference in the stationary aspect

of the frequency structure described by our analysis. On the

other hand, transitional characteristics in microtime

domains and relationships across different EEG bands

cannot be assessed by the present method using the FFT.

Other techniques of spectral analysis, such as the maximum

entropy method, may be useful for this purpose (Morimoto

et al., 1998).

4.3. EEG findings and comparison with neurological and

mental disorders

Since this is a single case study, it is necessary to employ

considerable caution in interpreting the present EEG find-

ings. Nevertheless, it may be instructive to compare the

present findings with those of some typical neurological or

psychological disorders.

4.3.1. Epileptic disorders

It is important to distinguish a Kerauhan from an epileptic

disorder (Daly, 1990; Schaul, 1998). According to inter-

views with the subjects in the present study, none of them

or anyone in their family had a history of epilepsy. The EEG

waveform of Subject 1, who experienced a possession

trance, did not show obvious paroxysmal discharges before,

during or after TS. Moreover, the EEG during the FALL-I

and FALL-II phases in TS showed a prominent occipital

dominant rhythm, which is unlikely to be observed in an

ictal EEG.

4.3.2. Mental disorders

The possession trance observed in the present study must

also be differentiated from schizophrenia or dissociative

disorders that may show some state of possession. Miyauchi

et al. (1996) reported that the various kinds of change in a

spontaneous EEG, including enhancement of slow waves,

decrease in alpha rhythm and increment or decrement of fast

waves, can be observed in schizophrenia. EEG findings in

patients with dissociative disorders, such as multiple

personality disorders in a possessed state, are accumulating

but remain diverse (Coons et al., 1982; Cocores et al., 1984;

Putnam, 1984; Hughes et al., 1990). These findings are

considered rather specific to the symptoms but not to the

diseases themselves. It is difficult to formally make a diag-

nosis from the resting EEG in the present study because it

was recorded outside for only 3 min. Nevertheless, since

dissociative episodes or unusual behavior have never been


seen in the daily life of the subjects, and the possession

trance was only observed in the highly organized ritual

drama, it is unlikely that the possession trance observed in

this study is due to a mental disorder.

4.3.3. Hyperventilation

During TS of Subject 1, the power in the theta, alpha 1 and

alpha 2 frequency bands was greatly enhanced. This

enhancement continued after Subject 1 returned to NS. To

account for these changes, we should consider the possible

effect of hyperventilation associated with the exercise done

during the possession trance because hyperventilation causes

a shift to a lower frequency of alpha or theta in a spontaneous

EEG. Since Subject 3, who seemed to be doing almost the

same amount of exercise, did not show this kind of hyper-

ventilation-induced phenomenon, we do not think that hyper-

ventilation is the sole reason for the spectral changes in the

EEG of Subject 1. The concentration of expiratory carbon

dioxide must be measured to prove this point.

4.4. Enhancement of the EEG in the alpha rhythm

The alpha rhythm of an EEG is considered to occur in

relaxed yet alert subjects and to be sensitive to the subjects

emotional as well as arousal state (Drennen and Oreilly,

1986; Iwaki et al., 1997). Although there is considerable

intersubject variability in the amount of alpha rhythm, a

normal alpha rhythm can be treated as an intraindividually

stable trait in terms of its testretest reliability (Gasser et al.,

1985; Kohrman et al., 1989; Fernandez et al., 1993). There

is a considerable amount of literature reporting the enhance-

ment of alpha-EEG during meditation or Zen (Kasamatsu

and Hirai, 1966; Banquet, 1973; Banquet and Sailhan, 1977;

Dillbeck and Bronson, 1981; Khare and Nigam, 2000).

Although the mechanisms underlying the generation of the


Fig. 3. Change of EEG power associated with the transition to and from TS. (A) Time course of BEAMs. In Subject 1 (upper), who went into TS, the power of

the theta, alpha 1 and alpha 2 frequency bands is markedly enhanced during TS. Such enhancement is also recognizable in the POST phase of NS. By contrast,

Subject 2 (lower) did not show any change in EEG power during MUSIC. (B) Time course of the mean of the EEG power across all electrodes in each

frequency band. Subject 1 (upper) shows increased power in the theta, alpha 1 and alpha 2 frequency bands in TS. The power of alpha 2 is more prominent in

FALL-I, FALL-II than in MOVE-I, MOVE-II, while the opposite is seen in the alpha 1 band. By contrast, Subject 2 (lower) shows stable EEG power

throughout the recording period.

Fig. 4. Change of EEG power in Subject 3, who did a similar amount of exercise without going into a possession trance. (A) Time course of BEAMs. (B) Time

course of the mean of EEG power across all electrodes in each frequency band. Subject 3 shows stable EEG power during the exercise.

alpha rhythm have yet to be fully clarified, an animal model

suggests the involvement of at least the thalamocortical and

intracortical networks (Steriade et al., 1990). A focal

decrease of the background EEG in the alpha band occurs

in association with corresponding cortical activation. It is

known that an occipital alpha-EEG closely reflects the acti-

vation of the visual cortex; a significant negative correlation

between the occipital alpha rhythm and activity in the visual

cortex has been reported (Sadato et al., 1998). The remark-

able enhancement of the occipital alpha-EEG during eye-

closed phases (e.g. PRE, FALL-I and II, FINAL and POST)

in the present study is in parallel with this evidence. More

importantly, when the eye-closed phases and eye-open

phases are compared within each category, the enhancement

of the alpha-EEG is more evident in the later part of the

trance (Fig. 3B). Although there is marked variability in

alpha power in normal individuals from one period of

time to another, depending on their level of mental activity,

this finding may suggest some linkage between the depth of

trance and alpha-EEG. A positive correlation has been

shown between the occipital alpha-EEG and the regional

cerebral blood flow in the deep brain structure (Sadato et

al., 1998), including the thalamus (Oohashi et al., 2000).

Therefore, we need to consider the possibility that a posses-

sion trance may be associated with a change of activity in

deep-lying structures, including the thalamus. However, we

lack a sufficient number of subjects in a possession trance; it

is necessary to collect more data in the field to determine

whether the observed findings reflect a physiological

phenomenon specific to possession trances, or alternatively,

if they are simply associated with that particular subject.

In conclusion, we consider that we have verified the abil-

ity of the developed portable EEG recording system and the

utility of the EEG analysis method for subjects with move-

ment in the field. Namely, this methodology was recognized

as being useful to some extent for EEG recording under

severe conditions and for investigating the features of spon-

taneous EEGs. We also succeeded in our second goal of

measuring the EEG of a possessed subject under natural

settings for the first time. This EEG lacked apparent patho-

logical findings and showed an enhancement of EEG power

in the theta and alpha frequency ranges. This is still only a

single case study on the EEG findings of a possession trance.

In the near future, we plan to increase the number of cases

using the present system to examine general physiological

findings of possession trance.

Acknowledgements

We express our special thanks to the Balinese people who

accepted us and allowed us to carry out our experiment

during their ritual ceremony. We also sincerely thank Ms

Sari Sudo and Mr Ida Bagus Sunarta for their continuous

support for 20 years in Bali, and the members of the Yama-

shiro Institute of Science and Culture for their technical

support.

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Oohashi Et Al. Electroencephalographic Measurement of Possession Trance in the Field