E E G A N D A U T O N O M I C R E S P O N D I N G TO V E R B A L , S P A T I A L A N D
E M O T I O N A L L Y A R O U S I N G TASKS: D I F F E R E N C E S A M O N G A D U L T S ,
A D O L E S C E N T S A N D I N H A L A N T A B U S E R S *
D A N B. SMITH, R O B E R T J. G A T C H E L , M A U R I C E K O R M A N and
S H E L L E Y S A F F E R
University of Texas Health Science Center at Dallas, Dallas, Texas, U.S.A.
Accepted for publication 18 October 1979
The present study investigated the physiological responses of an adolescent inhalant abuse group, an adolescent non-abuse group, and an adult non-abuse group elicited by three types of tasks: verbal, spatial, and emotionally arousing. Each group consisted of 10 male Mexican- American subjects. Bilateral EEG and electrodermal activity, as well as heart rate, were moni- tored. While exploring for possible heart rate and hemispheric alpha wave differences in response to predominantly verbal and spatial tasks, an attempt was also made to discover if electrodermal responses could be bilaterally differentiated. Another purpose of the study was to explore possible psychophysiological differences between a younger and older group, and between an inhalant abusing group and a non-abuse group, in response to the three types of tasks. Results indicated that attempts to produce task-related EEG hemispheric asymmetry were largely nonsueeessful. Bilateral electrodermal responses were also not greatly differenti- ated. It was suggested that stronger task manipulations were needed. Significant group differ- ences were found for initial physiological response levels (adults demonstrated higher levels than the two adolescent groups) and for heart rate response to the emotionally arousing task (non-abusing subjects demonstrated greater heart rate acceleration than inhalant abusing sub- jects). It was suggested that group differences in initial levels occurred due to the adult groups's greater involvement in the experimental situation. Heart rate differences to the emotionally arousing situation were discussed in terms of Zuckerman's sensation seeking hypothesis.
I. Introduction
Few s tudies in the pas t have sys temat ica l ly e x a m i n e d t he a u t o n o m i c and cor t ical
d i f fe rences b e t w e e n drug-abus ing individuals and non-abusers . Wi th respect to one
* This article is based on the thesis submitted by the first author to the Department of Psychology of the University of Texas at Arlington in partial fulfillment of the requirements for the M.A. degree. This research was ssupported in part by Grant #DA01300 from the National Institute of Drug Abuse. Requests for reprints should be addressed to Robert J. Gatchel, Uniformed Services University of the Health Sciences, School of Medicine, 4301 Jones Bridge Road, Bethesda, Maryland 20014, U.S.A.
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type of drug abuse - the abuse of inhalants - there have been some attempts made at exploring its long terms effects on cortical activity. For instance, Anderson and Kaada (1953) and Dodds and Santostefano (1964) found no long lasting effects of inhalant abuse on EEG or central nervous system functions. Other studies, however, have indicated abnormal EEG slow wave activity (4 -6 Hz), suggesting diffuse cortical damage after intense gasoline inhalation (Carroll and Abel, 1973; Faucett and Jensen, 1952). Prockop and Tison (1974) also noted that abuse of some organic solvents can cause neuropathy, or a decrease in nerve conduction rates. As can be seen, these cortical studies have tended to be rather inconclusive and narrow in scope. There has also been very little examination of autonomic differ- ences which may be present in inhalant abusers relative to non-abusers.
The tack of central and autonomic nervous system response data comparing abusers and non-abusers is unfortunate in view of some of the behavioral differ- ances found between these two groups of individuals which might suggest con- comitant physiological differences. For instance, Friedman and Friedman (1973) found that inhalant abusers reported the greatest amount of violence and aggres- sion when compared to other-drug and non-drug users. It is also possible that the inhalant-abuse population may show some differences in response to emotionally stressful situations, which may be cause or effect of the drug abuse syndrome itself. In addition, Berry, Heaton and Kirby (1976) note that heavy use of inhalants may cause cognitive and affective changes in the abusers. Their preliminary reports show ability deficits of several types, such as poor learning and memory skills, and poor ability to respond adaptively to stressors. These studies suggest that psycho- physiological differences may be found in certain cognitive tasks or situations between this population and a non-abuse population. Exactly what these differ- ences might be, and to what extent they may occur, it not known at present. This study attempted to determine whether or not any actual differences occur between abusers and non-abusers during verbal, spatial, and emotionally arousing tasks.
The three tasks employed in this study were: a verbal task which consisted of reading written material aloud, a spatial task which required visuaUy examining some spatial designs, and an emotionally arousing situation which involved watching a brief traffic safety film containing some rather explicitly violent auto- mobile accident scenes. Heart rate activity was recorded during all tasks. In addi- tion, bilateral EEG was recorded in order to determine possible group differences in hemispheric alpha asymmetry during the verbal, spatial, and emotionally arousing tasks. Bilateral electrodermal responses were also recorded to assess whether they paralleled the bilateral EEG activity. Both phasic (number of spontaneous fluctu- ations) and tonic levels of electrodermal measures were recorded because Kilpatrick (1972) suggests that phasic and tonic measures of electrodermal responding may differentiate between cognitive-perceptual tasks and emotionally-arousing tasks. Specifically, he found that tonic level of skin conductance increased during cogni- tive activity, but showed little change during a psychologically stressful situation; conversely, for phasic skin conductance activity, large changes were observed
D.B. Smith et al. / EEG and autonomic responding 191
during a stressful situation, but not during the cognitive situation. This suggests that differential electrodermal results might be found depending on the particular characteristics of a task.
Another objective of this investigation was to detect any age-related physiologi- cal response differences. The non-abuse group of adolescents was compared to an older (college age) group of non-abuse individuals. This comparison was of special interest in regard to the bilateral cortical and electrodermal measures. A recent study by Waber (1976) suggests that lateralization of the speech and spatial modes may occur at different maturational levels. She found that early-maturing adoles- cents performed better on tests of verbal than of spatial abilities, whereas later- maturing adolescents demonstrated the opposite pattern. In addition, a study of task-related alpha asymmetry by McLeod and Peacock (1977) revealed greater asymmetry with increasing age (ages 17-35) regardless of the spatial ability shown by the participant. These studies suggest that age of maturation differences may be important when assessing the degree of bilateral asymmetry.
2. Method
2.1. Subjects
The 30 right-handed (as determined by self-report and writing preference) Mexican-American male subjects participating in the study were divided into three groups. One group consisted of 10 volunteers, ages 12-16, with a history of inhalant abuse (paint, glue and gasoline). Drug histories of these subjects ranged from a minimum of approximately 20 occasions of sniffing over a period of 12 months to a maximum of approximately 600 inhalant episodes lasting over a period of 6 years. The amount of time which the individuals had abstained from any sniff- ing activities ranged from about 1 week to 14 months. A second group consisted of 10 non-abusing volunteers of the same age range and socioeconomic background. None of these participants had sniffed paints, glue, or gasoline more than three times, and only two had any experience with inhalant abuse at all. These two were not considered abusers since they had not shown continued interest in sniffing. Volunteers in these two groups were individuals who were currently participating in an inhalant abuse study being carried out at the University of Texas Health Science Center at Dallas. Drug histories were derived from interviews with the subjects and their parents on several occasions, and were felt to be fairly accurate and honest histories. They received their choice of either a ticket to a local entertainment center or gift certificates to a local fast food chain for participation. Transportation to and from the laboratorY was provided by the experimenter.
The third group consisted of college-aged volunteers (ages 18-30) from similar socioeconomic neightborhoods. They were recruited from area colleges, church organizations, and through sources working with the inhalant abuse program.
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Participating volunteers in this group were paid $10.00 each for their time and to help defray transportation costs to and from the laboratory.
2.2. Apparatus
Bilateral skin conductance and temporal EEG, as well as heart rate, were con- tinuously recorded throughout the experimental session on a Beckman Type R611 Polygraph. Heart rate was monitored over the antero-lateral lower ribs and recorded through silver-silver chloride electrodes. Bilateral skin conductance was monitored from the palm and ventral side of the wrist of each hand by silver-silver chloride electrodes (17 mm diameter), Idled with Beckman electrode cream, and coupled through two Beckman Type 9844 constant-voltage skin conductance couplers. Electrode sites were cleaned with deionized water before electrode attachment. Right and left temporal EEG was monitored from the T3 and T4 placement posi- tions both referred to Cz. Recording from each side was through Grass silver cup electrodes (10 mm diameter) coupled to Beckman Type 9608A A-C couplers, with a time constant of 0.3, the high frequency filter set at midrange, and the low fre- quency filter set at 30 Hz. Attachment sites were thoroughly cleaned and scrubbed with Redux paste, and the electrodes were attached with Grass EEG electrode paste. In addition, both the left and right EEG signals were recorded on separate channels of a Hewlett Packard 3960 series instrumentation tape recorder for sub- sequent playback and computer analysis.
Additional apparatus consisted of a Realistic cassette tape player and micro- phone which were used to monitor all sound in the experimental chamber. The experimental chamber was sound deadened and copper screened to reduce all out- side noise and electrical interference. Lights in the room were bright enough for the participant to easily see all stimuli. The room was equipped with a confortable reclining chair which was fixed in the upright position for the participants. Directly in front of the chair was a Sony Trinitron color television monitor positioned about 18 in. from the ground and 5 ft from the viewer's head. This was cabled to a Sony AV-50OOA videotape recorder which was in the experimenter's room. Additional furniture consisted of a chair for the experimenter and a board which was laid across the arms of the recliner and used for a working surface during the experi- mental tasks.
2.3. Procedure
Participants were first introduced to an assistant (a female) who would later be directing them in the tasks while the experimenter was supervising recording of the physiological data. They were then seated in the experimental room, and the experimenter (a male) briefly described the procedure for the experiment. All participants were then given a short drug questionnaire to determine any recent drug intake. After electrode attachment was completed, the participant was
D.B. Smith et al. / EEG and autonomic responding 193
instructed to sit quietly for about 15 min while machine calibration occurred. After baseline, the assistant entered the participant's room and read some general task instructions.
The spatial, verbal and emotionally arousing task situations were then presented in sequence. The spatial and verbal tasks used were similar to those suggested by Galin and his colleagues (personal communication) to be effective in producing bilateral EEG differences. For half of the participants in each of the three groups, the procedure was as follows: the assistant first presented instructions for the spatial task and briefly demonstrated the procedure. Then, two practice trials were administered to insure understanding of the task. After the practice trials, the participant was given the three test trials. This task consisted of a block design procedure similar to that used in the Wechsler Adult Intelligence Scale. On each of the three different trials, the participant was presented with an example design card placed directly in front of him to minimize visual activity predominantly to either side. He was then asked to look at, and memorize, the design for 60 sec during which time physiological recordings were monitored. At the end of that time the example card was withdrawn and four blocks were placed in front of the subject with which to reconstruct the design. Sufficient time was given for the participant to complete reconstruction of the design. Successful completion never took longer than 30 sec for any subject. At the end of the third trial, the assistant left the room, and the participant was given a 3 min rest period to allow physiological responding to return to a steady pre-stimulus level. After this rest period, the assistant returned to the room and presented instructions for the verbal task. The participant was then given a practice trial to insure understanding of the task, followed by the three test trials. Only one practice trial was given since the reading task was a more familiar task than the prior block design task, and no subjects demonstrated problems in completing the practice trial. This verbal task consisted of three written paragraphs presenting a variety of both word and number information on weather and climate, inflation and the value of the dollar in recent years, and populations of major cities of the world. Each paragraph was long enough to avoid allowing the participant to complete the material in the allotted time. For each of the paragraphs, the subject was given 60 sec to read aloud and memorize the information during which time the physiological recordings were again monitored. The paragraph was then with- drawn, and the participants were briefly questioned concerning the material they had read. This was followed by a second 3 min rest period alone, after which the assistant returned to the room and presented instructions for the final task. This emotionally arousing task situation consisted of viewing a 6 min videotaped film which contaihed scenes depicting the results of some violent traffic accidents. The film was presented on a monitor placed directly in front of the subject. The subject was again reminded to sit quietly and remain attentive throughout the film. Physiological recordings were again monitored during three 60 sec periods while the participant was viewing the film.
The procedure for the remaining half of the participants in each of the three
194 D.B. Smith et al. / EEG and autonomic responding
groups was identical to the above except that the sequence of presentation of the spatial and verbal tasks was reversed. The subjects were run in random order during a similar time each day to preclude any time-related physiological differences.
2.4. Data reduction and analysis
Computer analyzed Fast Fourier Transforms (FFT) were performed on EEG signals collected at time periods during baseline and tasks, which coresponded to times at which electrodermal measures were assessed. Thus, samples were taken 15 and 45 sec into each 60 see trial period, and at about 15 and 45 sec into each of the three baseline 1 min periods. Each sample was screened to eliminate periods of significant muscle artifact and noise. Only samples which were free of visible artifacts were analyzed. The Fourier Transformwas calculated using 256 points sampled via an A/D converter with a PDP-11/45 computer system. The sampling rate was one point samples every 5 msee. Thus, the 256 points represent a maxi- mum cycle every 1.28 seconds. This gives a value of 0.7813 for every harmonic increment. The fundamental freqnecy is thus 0.7813 Hz, with the first harmonic at 1.5625. The alpha band was defined as 8 - 1 2 Hz. To determine if the frequency was present, peak measurements were used.
Analyses of variance for group differences in initial baseline levels "were con- ducted for heart rate, EEG, and both tonic and spontaneous electrodermal mea- sures. Planned contrasts of group means were also performed for each set of data to reveal possible differences between the two juvenile groups (inhalants versus non- inhalants) and between the adult group versus the two juvenile groups. These analyses yielded significant baseline differences between the adult and juvenile groups for the EEG and electrodermal measures. Due to these baseline differences, analyses of covariance with baseline measures as a covariate were applied to the paragraph, block and emotionally arousing task data. A one-way analysis of covariance was used for all emotionally arousing task comparisons, whereas a one- beween (groups) and one-within (tasks) analysis of covariance was used for the paragraph and block task comparisons. Planned contrasts were also applied to these data.
3. Resul t s *
3.1. Electroencephalographic measures
Analysis of variance of baseline levels of alpha activity (8 -12 Hz) revealed a significant group difference [F(2,27) = 3.68, MSe = 23.90]. Non-abusing adoles- cents were found to have the greatest alpha concentrations, followed by inhalant
* The 0.05 confidence level was adopted in all statistical analyses.
D.B. Smith et al. / EEG and autonomic responding 195
abusing adolescents; adults had the lowest concentration of alpha frequencies. Analyses of the alpha data were also conducted using ratios of the power values
T3/T4 (left/iight) so that laterality differences could be taken into account. Analyses of covariance, using baseline resting ratios as the covariate, revealed no group, tasks, or interaction effects in EEG laterality for the paragraph, block, or emotionally arousing tasks.
3.2. Electrodermal measures
3.2.1. Tonic skin conductance Tonic skin conductance was determined by sampling skin conductance levels 15
and 45 sec into each of the 1 min task periods, and then deriving a mean score for each subject on each task. Baseline level was divided into three 1 min periods and similarly sampled. Analysis of variance of left tonic electrodermal levels failed to reveal group differences, although the adult group demonstrated the highest base level, followed by the inhalant group and then the non-inhalant group. Planned contrasts, though, revealed that the adults had significantly higher initial levels when compared to the juveniles [F(1,27) = 5.30, MSe = 2620.35]. Right tonic electrodermal measures revealed similar results. Initial baseline differences were found, with adults having the highest tonic levels, followed by the inhalant, and finally the non-inhalant groups [F(2,27) = 4.89, MSe = 1854.38]. As with the left tonic measure, the two younger groups did not significantly differ from each other; combined, they showed significantly lower tonic levels than did the adult group [F(1,27) =9.48, MSe= 1854.38]. Analyses of covariance, using baseline resting levels as the covariate, yielded no group, trial, or interaction effects for the emo- tionally arousing, paragraph, or block tasks for either left or right tonic activity.
3.2.2. Spontaneous skin conductance fluctuations Spontaneous measures for each task period and baseline were derived by count-
ing the number of spontaneously occurring fluctuations in skin conductance during each 1 rain period and obtaining a mean. The planned contrasts for right-hand spontaneous activity showed a significant difference for juveniles versus adults [F(1,27) = 4.68, MS¢ = 2.39], with adults demonstrating greatest activity. For left- hand measures, the planned contrast failed to reveal statistically significant baseline differences between juveniles and adults. Analyses of covariance yielded no left or right differences between groups during the emotionally arousing task, nor were any group differences found for paragraph or block tasks. However, for the right- hand spontaneous measure, a significant task effect was found, with the right spontaneous' response greater during paragraph trials than for block trials for all groups [F(2,27) = 8.58, MSe = 0.17].
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3.3. Hear t rate measures
Fig. 1 presents the heart rate levels of the three groups during the various periods of the experimental session. Analysis of variance of the baseline heart rate measures revealed no significant differences among the groups. Analysis of covariance for the emotionally arousing task revealed a significant group effect [F(2,27) = 4.08, MSe = 20.42]. The inhalant abuse group was associated with the greatest amount of heart rate deceleration from baseline. The multiple contrast confirmed this, yielding a significant difference between the inhalant abuse versus the non-inhalant abuse juveniles [F(1,27)= 5.87, MSe = 20.42]. There was no significant difference found for the adult versus combined adolescence groups which further verifies the fact that inhalant abusers tended to have greater heart rate deceleration than did non- abusers during the emotionally arousing stimuli.
The analysis for the paragraph and block tasks revealed a significant task differ- ence, as would be expected, with heart rate during the reading task greatly accele- rated relative to that associated with the block task IF(1,27) = 42.42, MSe = 8.75]. There was also a significant heart rate difference between the adult group and the
" - ADULT NONABUSERS 15,,,,,,,.,,,,-,,,,11 ADOLESCENT INHALANT ABUSERS I l a ~ w . i - . i r ~ r l l ADOLESCENT NONABUSERS
85
83
81
79
~Tr
6 7
65 "*" '1
I I I I BASELINE PARAGRAPH B L O C K EMOTIONALLY
TASK TASK AROUSING TASK
Fig. l. Average heart rate levels of the three groups during baseline and the three task periods of the experimental session.
D.B. Smith et al. / EEG and autonomic responding 197
younger participants [F(1,27) = 4.27, MSe = 56.06], with the adults having higher heart rates. Unlike the emotionally arousing task analysis, however, no significant differences occurred between the non-inhalant and the inhalant groups during paragraph/block tasks.
4. Discussion
The present results revealed a significant group difference in alpha wave concen- trations during the baseline measures, with adults having the lowest amount of the slow wave activity and juveniles the highest concentration. This is in accordance with earlier research indicating greater amounts of general slow Wave activity found in children and in older adults (Shagass, 1972).
Results also indicated that the verbal (paragraph) and spatial (block design) tasks did not elicit differences in hemispheric utilization as had been predicted. There are a number of possible explanations for this lack of task laterality differences. The block task was one in which every subject may have tended to use at least some verbal self-instruction, such that any possible cortical asymmetry was reduced. Donchin, Kutas and McCarthy (1977) suggest that the physical parameters of the task-related stimuli may be critical in determining cortical asymmetry. In the present study, non-motor tasks were used. The earlier studies by Doyle, Ornstein and Galin (1974) and Galin and Ornstein (1972) produced much greater laterality differences when motor tasks, such as writing a letter or constructing a block design, were used. Perhaps the motor movement involved in those types of tasks introduce other factors into hemispheric utilization which were not involved in the present experiment. Future research will need to carefully evaluate the importance of the physical parameters of stimuli and the tasks utilized in the production of laterality differences.
Lack of demonstrable asymmetry may also have been due to use of the Cz reference placement of the EEG electrode. This placement may have obscured alpha differences by masking some of the activity in the temporal regions of the brain. As a consequence, more centrally located alpha rhythm may have appeared on both channels of the recorder.
Finally, it is possible that the method for determination of handedness was not sufficient. Use of a handedness questionnaire may have revealed subjects who were mixed dominant and who, therefore, should have been excluded from the results.
As with the EEG data, the most obvious differences found for electrodermal measures were seen between groups for the baseline period. Specifically, for both left and fight'tonic electrodermal activity, and for right-hand spontaneous fluctua- tions, the adult group showed significantly greater baseline activity levels than did the younger participants. These results, coupled with the baseline differences found for EEG, indicate that the older participants tended to have greater physiological activation relative to the two juvenile groups at the beginning of the experiment,
198 D.B. Smith et al. /EEG and autonomic responding
One reason for this higher activation level might be that the adults were more interested in the procedures of the experiment due to their advanced age, educa- tion, and greater ability to comprehend the significance of the experiment. It was generally found that the adults as a group tended to be more interested in the entire experimental procedure and purpose.
Despite the differences between groups during baseline, analyses of covariance revealed no group differences in electrodermal responding during the paragraph and block design tasks. Task differences were found in only one measure of electroder- mal activity - right-hand spontaneous fluctuations of all groups were greater during the paragraph than during the block trials. For tonic levels, paragraph and block trials were nearly identical. These results support earlier f'mdings that tonic and phasic electrodermal activity may be responsive to different activities. In this case, if Kilpatrick (1972) and Miller and Shmavonian (1965) are correct in their hypothe- sis that tonic and phasic electrodermal responses differentiate cognitive activity and stress, respectively, it might be suggested that although the two different types of tasks are similar in a 'cognitive' aspect (perhaps level of difficulty or amount of cognitive activity needed to complete the task), they may still be differentiated by the amount of stress that they elicit. Specifically, it may be that the paragraph trials were more stressful than the block trials. This would prompt greater sponta- neous activity. One might also speculate that this increased activity occurred in the right hand due to mediation by the left hemisphere, as would be predicted due to the verbal orientation of the task.
The major new finding of the present study was the significant difference found between the inhalant abuse group and the non-abuse group in heart rate responding to the scenes in the traffic film. The inhalant abuse group showed significantly greater heart rate deceleration while watching the scenes of traffic accidents than did the non-inhalant control group. Lacey and Lacey (1970) have indicated that a decrease in heart rate can be an indicant of increased environmental intake as a person becomes more attentive to certain external stimuli. In addition to these findings, Libby, Lacey and Lacey (1973) have found that the greater the interest level of the stimulus to the participant, the greater the amount of cardiac decelera- tion. Given these data, it might be assumed that the inhalant abusers were more attentive to the explicit scenes presented to them on the video monitor than were the non-abusing youths and the adults. This assumption is supported by a growing number of studies that demonstrate that high sensation-seeking individuals tend to seek out sensational stimuli and do not demonstrate high anxiety in these situations (Segal, 1973; Thorne, 1971 ; Zuckerman, 1974, 1977).
Kish (1973) suggests that anxious individuals would be more likely to avoid novel stimuli, preferring routine and predictable experiences, whereas high sensa- tion seekers, being less anxious, are more likely to approach novel stimuli. Zucker- man (1974, 1977) found that drug users, a group which certainly explores novel stimuli, tend to score high on sensation seeking scales. These findings, along with the present results, suggest that if inhalant abusers (as a specific group of drug
D.B. Smith et al. / EEG and autonomic responding 199
abusers) tend to be high sensation seekers, then they should be more interested in, and attentive to , the sensational scenes o f the accident scenes. Consequently, they would be expected to show a greater heart rate deceleration when compared to the control group due to both greater environmental intake during the task and a less- ened arousal response to the scenes.
The present results also revealed a significant difference between the adults and the two juvenile groups in heart rate response to the paragraph and block trials. In response to these tasks, the adults showed greater heart rate increase over the baseline measures then did the others. It may be that the adult group demonstrated greater cardiac acceleration due to a greater internal processing or rehearsal of these stimuli, whereas the juvenile groups were more oriented toward just visually pro- cessing the stimuli without at tempting as much cognitive rehearsal. This is sup- ported by the fact that the adults tended to be much more explicit and detailed in their responses to the paragraph trials, and tended to be faster at duplicating the block designs. It is also possible that the juveniles found the tasks more difficult and less familiar, and thus were required to spend more time visually scanning the
stimuli rather than rehearsing them. Future research will need to more carefully control for these possibilities.
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