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Lateralized abnormality in the EEG of persistently violent psychiatric inpatients
BIOL PSYCHIATRY 1991;30:363-370
363
Lateralized Abnormality in the EEG of Persistently Violent Psychiatric Inpatients A. Convit, P. Czobor, and J. Volavka
Twenty-one consecutive right-handed male psychiatric inpatients treated on a unit designed for the management of violent behavior were given computerized EEGs. We recorded their violent behaviors, the number of staff interventions needed to control their behavior, and their medications. The number of instances of violence as well as the number of staff interventions were related to increased delta band activity and to decreased alpha band activity in the temporal and the parietooccipital areas. These relationships were independent of the current medications and of the length of stay on the special unit. Furthermore, our results demonstrate that violence is very significantly related to the hemispheric asymmetry in EEG for the frontotemporal derivations. With increased levels of violence there was a greater level of delta power in the left compared with the right.
Introduction Soon after the introduction of EEG into clinical practice, there were reports linking abnormal brain waves and violent behavior; this literature has bee= reviewed (Volavka 1990). With few exceptions (Williams 1969; Yeudall et al 1987), authors linking EEG abnormality and aggressive behavior have not reported on lateralization or localization. Furthermore, with the exception of Williams (1969), no attempt has been made to relate the persistence of violent behavior to the EEG findings. "*Villiamsfound increased amounts of slow activity over the frontotemporal ~-~as of habio_~al!y ag~essive offenders. Most of the literature to date has used visual assessment of the EEG, and this method of assessment is somewhat unreliable. However, even authors using reliable computerized EEG analyses have reported inconsistent findings. Some of these findings have included generalized slowing of EEG activity in aggressive boys (Surwillo 1980), frontocentral increase of delta activity associated with self-reported history of aggressive behavior in adult male drug abusers (Fishbein et al 1989), or no distinguishing EEG characteristic between violent and nonviolent psychiatric inpatients (Milstein 1988). Researchers utilizing neuropsychological measures or imaging techniques have found clear evidence linking violent behavior and brain dysfunction. Localization of this dysfunction has varied. Some investigators have reported diffuse abnormalities (Bryant et al 1984; Lewis et al 1988; Lewis et al 1985; Convit et al 1988a; Krakowski et al 1989).
From the Nathan Kline Institute for Psychiatric Research, Kirby Forensic Psychiatric Center, and Manhattan Psychiatric Center, New York, ~Y. Address reprint requests to: Kirby Forensic Psychiatric Center, Research Department, Ward's Island, New York, NY 10035 Received September 27, 1990; revised March 14, 1991.
© 1991 Society of Biological Psychiatry
~3223D1/$03.50
364
BIOL PSYCHIATRY 1991;30:363-370
A. Convit et al
Others have localized findings to the temporal lobes (Mark and Ervin 1970; Devinsky and Bear 1984; Hamstra 1986; Monroe 1986; Will 1986) or the frontal lobes (Tancredi and Vo!kow 1988; Yeudall et al 1987; Valzelli 1973). There has been one report on the lateralization of the abnormalities (Yeudall et al 1987). The dominant hemisphere has been the one most frequently incriminated (Nachshon 1983, 1988; Hare and McPherson 1984). Most studies have dichotomized violence and looked only at group differences between those classified as violent and nonviolent. The extent of violence on a continuum has not been evaluated. This study seeks to explore the relationship between the degree of violence and the levels of slowed EEG activity and asymmetry. Although there is no consensus as to which part of the brain is affected in violence, our reading of the literature has led us to hypothesize that if such a localization exists, it is likely to be in the anteri~i' portion of the dominant hemisphere. Furthermore, we hypothesize that the amount of violent behavior in psychiatric inpatients will be associated with EEG slow activity in that part of the brain.
Method
Subjects The subjects studied were violent psychiatric inpatients from a 1300-bed state facility in New York City, serving a predominantly poor inner-city population. In this state hospital, patients who are repeatedly violent and who cannot be managed on their home wards are transferred to the Intensive Psychiatric Service (IPS). The IPS uses a combination of behavioral and psychopharmacological strategies to treat the violent behavior and the psychiatric symptoms. As a general rule, patients are transferred back to their home wards in 5-7 weeks. In some cases, patients stay longer because their violent behavior had by that time not been well controlled or because their symptoms continue, and their home wards want them more stabilized psychiatrically before they take them back. The subject sample consisted of 21 consecutive male patients transferred to the IPS. Although handedness was not used as a selection criteria, all patients were right-handed. The patient sample had a mean age of 33 (SD = 9. | , range .z.l .-.5...~. /. ,. . .l n e y a mean age of first psychiatric hospitalization of 17 years (SD = 6.5, range 6-33). The mean duration of stay in the IPS was 48.1 days (SD = 26, range 15-110). With a single exception, patients were receiving neuroleptic medications on the day of the EEG recording. To make medication dose comparable across subjects we converted the doses of medications into chlorpromazine equivalents. The majority of the patients were receiving haloperidol with two patients receiving chlorpromazine, two Navane, and one prolixin hydrochloride. On the day of the EEG subjects were receiving an average of 2015 _ 650 mg chlorpromazine equivalents with a range of 0-3000. Procedures
Patients were evaluated by two psychiatrists who by consensus assigned them DSM-II1 diagnoses. Fifteen patients were classified as schizophrenic, five as mood disorder, and one as personality disorder. When the patients had been on a given dose of medications for longer than 5 days and their clinical condition permitted it they were given an EEG by one of the investigators (AC). As a rule the EEG was recorded during the second or third week of stay in the IPS.
Lateralized EEG and Violence
B1OLPSYCHIATRY
365
1991 ;30: 3 6 3 - 3 7 0
Detection and Classification of Violent Behavior All patients studied were by definition violent: they had met the criteria for admission to the IPS as described above. Once on the IPS, their violent and agitated behaviors were measured by inspecting the chart progress notes and the change shift reports using a highly reliable method. Details on the reliability of the violence detection method have been published elsewhere (Convit et al 1988b). All incidents were classified using the scale for the Assessment of Aggressive and Agitated Behaviors (Brizer et al 1987) into four categories: physical assault against another person, verbal assault (threatening someone with bodily harm), assault against property, and agitation (nonfocused shouting or markedly increased psychomotor activity). Because agitation can be nonspecific and does not involve overt and direct violence we excluded agitation from the analyses. The measure of violent behavior used was therefore the sum of physical, property, and verbal assault. We will refer to this sum as violent behavior or violence. The subjects had an average of 5.3 -4-- 9 instances of violent behavior during their stay in the IPS, with an average of 0.11 instances per day. The range was between 0 and 37. The patient's violent behavior does not occur in a natural setting. The IPS is staffed with personnel who have special training in management of violent behavior and who will frequently intervene before behaviors escalate to physical violence. For each of the instances of violent and agitated behaviors the staff intervention was recorded. The staff interventions were classified into four categories: verbal intervention, PRN medication given, patient placed in seclusion, and patient placed in a camisole. When more than one intervention was used, the more restrictive one was the one coded for that event (if a patient received an injection and was placed in seclusion, the seclusion was the one coded for the event). The staff interventions, although not a direct measure of violent behavior, are clinically quite relevant: they indicate the perceived potential dangerousness of a given situation. The dangerousness was felt to be more immediate when the staff intervened physically than when their intervention was limited to talking to the patient. For this reason we excluded from the analyses instances when verbal intervention alone was used; we used the sum of the nonverbal interventions. From now on this sum will be referred .t .O. . .
i;l~
b t l~l l_p-l y_ 1 _ .
, , :l l.l .l k. .~.l . .
V l ~ | l t ,~l't~. J.l l .
, , TJ t~l t,l ~. ~ , oO ,u,t kl | ~; ,, ~~, t~o* o
lho,-I la~a~
a n a v e r a g e~
'v~. f gu ~ - - .1 9. . ,t . . .i n. t .~ .r v. e.~.n t. i .o n . ,. ~.
. .
over
their stay in the 1PS, with an average of 0.12 interventions per day. The range was between 0 and 52. The number of staff interventions was larger than the number of instances of violent behavior. The staff deemed some instances of agitation as having the potential to progress to violence and hence intervened nonverbally.
Computerized Electroencephalogram Recordings were monopolar and used the International 10/20 Placement System referenced to linked earlobes. An electrode cap was used. One of three electrode cap sizes was used in order to optimize the electrode placement for each subject. The EEG was recorded in all cases by the first author while the patient was in the IPS, generally during the third week. EEG amplifiers with a time constant of 0.3 were used. The EEG was collected in 2.4 second epochs with only those epochs that were considered artifact-free on the monitor screen accepted. Eight bipolar derivations were created by computation from the earreferenced monopolar recordings: F7-T3, F8-T4, C3-Cz, C4-Cz, T3-T5, T4-T6, P3-O1, and P4-O2. From each of these bipolar derivations, relative power was computed using
366
B1OLPSYCHIATRY
A. Convit et al
1991;30:363-370
Hamming windows for each of the four frequency bands: delta (1.5-3.5 Hz), theta (3.57.5 Hz), alpha (7.5-12.5 Hz), and beta (12.5-25 Hz). The computed relative powers were then log-transformed to achieve a Gaussian distribution. The significance of the logtransformed values was assessed by computing Z scores relative to age norms. The Z scores expressed the deviation of the re!ative powers from that of the predictive age normative values in number of standard deviations. Detailed descriptions of these computations, their rationale, and reference to the age norms are published elsewhere (John et al 1988). The computations described above yielded a total of 32 EEG Z scores: each of the four frequency bands in the eight bipolar derivations computed. Because we were interested in differences between the two hemispheres, we computed an asymmetry score as follows:
L=
Lbd -- Rbd
Lbd + Rt,a'
where Lbd is the power spectrum value in frequency band b derivation d from the left hemisphere, and Rbd is the power spectrum value in frequency band b derivation d from the right hemisphere. Asymmetry scores were computed for each of the four pairs of derivations for each of the four frequency bands, giving us a total of 16 asymmetry scores.
Statistical Analyses We conducted three types of analyses: (1) First, we explored the relationship of the EEG variables to the violence variables using multiple regre,sion analyses. Because one can assume that the more violent subject stayed in the IPS longer, or if the patients stayed there for other reasons, the longer the subject was in IPS the more he had a chance to display violent behavior, we used the duration of stay in the IPS as one of the independent variables in the multiple regression analyses. The duration of stay in the IPS, the sum of violence, and the sum of interventions served as independent variables in the multiple regression models. Each EEG frequency band (n = 4) for each derivation (n = 8, four for each hemisphere) was used as the dependent variable in 1 of 32 multiple regressions. For each of the 32 multiple regression analyses, we evaluated the overall signif.cance of the model, the multiple, R, the partial regression coefficients, and the structural parameters of the model (constant and slopes of individual variables). (2) Secondly, we carried out explanatory post hoc con'elations between the violencerelated variables and the EEG variables found to be important in the multiple regressions above. (3) Lastly, to more specifically localize the EEG abnormality, we computed for each frequency band (n = 4) a laterality index for corresponding pairs of derivations for each hemisphere (n = 4) and related it to the violence variables. Each of these laterality indices was used as the dependent variable in 1 of 16 additional multiple regression analyses.
Lateralized EEG and Violence
BIOL P S Y C H I A T R Y 1991 ;30:363-370
367
Table 1. Multiple Regression Analyses of EEG Variables Band
Derivation
Delta
Right R 2
Left R 2
[L - R/L + R] R 2
F-T
NS
0.37 °
0.73 b
T-T
0.38 ~
0.45 ~
0.64 b
NS
NS
NS
P-O
0.44 a
0.47 °
NS
F-T
NS
NS
NS
T-T
NS
0.44 ~
NS
C--CZ
NS
NS
NS
0.41 ~
0.49 °
NS
C-CZ
Alpha
P-O ~p < 0.05. bp < 0.001.
It could be argued that the more violent a patient is, the higher his medication dose is likely to be. We also know the medications may have an effect on the EEG. We examined whether this variable was related to the EEG variables by calculating its correlations with each of the EEG variables.
Results In the multiple regression analyses we found that the sum of violent behaviors as well as the sum of the staff interventions explained a statistically significant amount of the variance of the relative power of delta and alpha in most derivations over both hemispheres (Table 1). The portion of explained variance ranged between 31% and 49%. The duration of stay did not exert an independent influence on the EEG variables. Furthermore, the violence and the interventions appeared to be independent of the duration of stay. Detailed tables of these analyses can be obtained from the authors. Post hoc correlations between the EEG variables and the two violence variables are shown in Table 2. Note that most of the statistically significant correlations were restricted to the left hemisphere. The delta activity was positively correlated with the violence variables. In contrast, the alpha activity is negatively related to the violence variables.
Table 2 . P ¢ a r s o n ' s Variables
r ~ ~!~,ct
Moment
C ~
i~tions (Post Hoc) between EEG and Violence
Right hemisphere
Left hemisphere
Frequency bands
Dependent variables
Delta
F-T
0.37
0.31
0.57 ~
0.53 b
T-T
0.40
0.30
0.52 b
0.42
C-CZ
0.43
0.39
0.42
0.39
P-O
0.36
0.26
0.47 b
Alpha
ap < 0.01. ~p < 0.05.
F-T
Intervention r
-0.31
Violence r
-0.24
Intervention r
Violence r
0.36
-0.55 ~
-0.50 b
T-T
- 0.40
- 0.32
- 0.56 a
- 0.47 b
C-CZ
- 0.46 b
- 0.40
- 0.56 ~
- 0.52 b
P--O
- 0.34
- 0.23
- (~\54 a
- 0.44 b
368
31OL PSYCHIATRY 1991;30:363-370
A. Convit et al
We repeated the multiple regressions using the lateralization indices as the dependent variables and the length of stay in IPS and the two violence measures as the independent variables. Eight such regressions were carded out: four derivations each for the delta and alpha bands. We found that the significant relationship between laterality index and the violence variables was restricted to the frontotemporal areas. The sum of violent acts committed by each patient and the number of times the staff had to intervene explained a very large portion of the variance of the lateralization of delta for the frontotemporal and temporal derivations. These relationships were independent of the length of stay in IPS. The significance for the overall models were 0.0001 with 73% of the variance explained and 0.0005 with 64% of the variance explained for the frontotemporal and temporal derivations, respectively. The laterality computation implies a relative excess of delta activity over the left frontotemporal area. In order to study the possible confounding effect of medication with regard to the above relationships, correlation coefficients were calculated between each of the EEG variables and the chlorpromazine equivalents. The number of significant positive findings was under the chance level of 5%, and therefore these relationships were not interpreted.
Discussion Our findings indicate that independent of which measure of violence is used, a higher level of violence is accompanied by a larger power in delta. Elevation of the level of delta band activity or slowing of the EEG in violent patients had been reported in the literature (Fishbein et al 1989; Surwillo 198C). This increase of delta activity may be related to the structural impairments of the brains of our violent patients. Such structural abnormalities have been detected in violent individuals by other methods (Heinrichs 1989; Wood 1984). On the basis of the literature we hypothesized that there would be a relationship between lateralization of the EEG and the amount of violc~ce. Our results indeed demonstrated such a relationship. We found that the amount of violence is highly significantly related to the EEG hemispheric asymmetry for the frontotemporal derivations. For an increased level of violence there is greater level of power of delta band activity in the left hemisphere when compared with the right hemisphere. Our findings should be viewed as preliminary. We performed a large number of analyses with a relatively small subject sample size. These results are in agreement with reports demonstrating left hemisphere structural (Tancredi and Volkow 1988) and functional impairments (Tancredi and Volkow 1988; Yeudall et al 1987; Hamstra 1986; Will 1986) in violent individuals. The findings we report may not generalize to women, to patients who are not persistently violent, or to nonpsychiatric patients. There have been reports of abnormalities in the EEGs of psychotic patients (Multct et al 1986; Mukundan 1986). To improve on the generalizability of the findings to schizophrenics, we are conducting another EEG study using violent schizophrenics and age-matched nonviolent schizophrenics of both sexe~,.
References Brizer D, ConvitA, KrakowskiM, VolavkaJ (1987): Reportingviolence:A comparisonof routine ward reports with a new rating scale. Hosp Commun Psychiatry 38:769-770. Bryant ET, Scott ML, GoldenCJ, Tori CD (1984): Neuropsychologiealdeficits,learningdisability, and violent behavior. J Consult Clin Psychol 52:523-324.
Lateralized EEG and Violence
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Convit A, Jaeger J, Lin SP, Meisner M, Volavka J (1988a): Predicting assaultiveness in psychiatric inpatients: A pilot study. Hosp Community Psychiatry 39:429-434. Convit A, Isay D, Gadioma R, Volavka J (1988b): Underreporting of physical assaults in schizophrenic inpatients. J Nerv Ment Dis 176:507-5~9. Devinsky O, Bear D (1984): Varieties of aggressive behavior in temporal lobe epilepsy. Am J Psychiatry 1~ 1:651-656. Fishbein D, Herning R, Pickworth WB, Haertzen CA, Hickey JF, Jaffe JH (1989): EEG and brainstem auditory evoked response potentials in adult male drug abusers with self-reported histories of aggressive behavior. Biol Psychiatry 26:595-611. Hamstra B (1986): Neurobiological substrates of violence: An overview for forensic clinicians. J Psychiatry Law Fall/Winter, 349-374. Hare RD, McPherson L (1984): Violent and aggressive behavior by criminal psychopaths, lnt J Law Psychiatry 7:35-50. Heinrichs RW (1989): Frontal cerebral lesions and violent incidents in chronic neuropsychiatric patients. Biol Psychiatry 25:174-178. John ER, Prichep LS, Fridman J, Easton P (1988): Neurometrics: Computer-assisted differential diag~.osis of brain dysfunctions. Science 239:162-169. Krakowski M, Convit A, Jaeger J, Volavka (1989): Neurological impairment in violent schizophrenic inpatients. Am J Psychiatry 146:849-853. Lewis DO, Pincus JH, Bard B, et al (1988): Neuropsychiatric, psychoeducational, and family characteristics of 14 juveniles condemned to death in the United States. Am J Psychiatry. 145:584589. Lewis DO, Moy E, Jackson LD, et al (1985): Biopsychosocial characteristics of children who later murder: A prospective study. ~m J Psychiatry 142:1161-1167. Mark VH, Ervin FR (1970): Violence and thc Brain. New York: Harper & Row. Milstein V (1988): EEG topography in patients with aggressive violent behavior. In Moffitt T, Mednick S (eds), Biological Contributions to Crime Causation. Dordrecht: Martinus Nijhoff, pp 40-52. ~?lonroe RR (15~6~: Episodic behavioral disorders and limbic ictus. In Doane B, Livingston K (eds), The Limbic System: Functional Organization and Clinical Disorders. New York: Raven, pp 251-266. Mukudan, CR (1986): Computed EEG in schizophrenia. Biol. Psychiatry 21:i225-1228. Muller HF, Achim A, Laur A, Buchbinder A (1986): Topography and possible physiological significance of EEG amplitude variability in psychosis. Acta Psychiatr Scand 73(6):665-675. Nachshon I (1983): Hemisphere dysfunction in psychopathy and behavior disorders. In Myslobodsky M (ed), Hemisyndromes: Psychobiology, Neurology, Psychiatry, New York: Academic, pp 389---414. Nachshon I (1988): Hemisphere function in violent offenders. In Moffitt TE, Mednick SA (eds), Biological Contributions to Crime Causation. Dordrecht: Martinus Nijhoff, pp 55-67. Surwillo WW (1980): The electroencephalogram and childhood aggression. Aggressive Behav 6:918. Tancredi LR, Volkow N (1988): Neural substrates of violent behavior: Implications for law and public policy. Int J Law Psychiairy ! 1:13-49. Valzelli L (1973): The isolation syndr~ ~e in mice. Psychopharmacologia 31:305-320. Volavka J (1990): Aggression, electroen~ephalograpby, and evoked potentials: A critical review. Neuropsychiatry, Neurop~,chol Behav Neurol (in press). Will TE (1986): Temporal lobe neuropsychological dysfunction among violent psychiatric inpatients. Dissert Abstr Int 49(3):923-924. Williams D (1969): Neural factors related to habitual aggression----Consideration of differences between those habitual aggressives and others who have committed crimes of violence. Brain 92:503-520. Wood RL (1984): Behavior disorders following severe brain injury: Their presentation and psy-
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chological management. In Brooks N (ed), Closed Head It!jury: Psychological, Social, and Family Consequences. New York: Oxford University Press. Yeudali LT, Fedora O, Frcmm D (1987): A neuropsyehosocial theory of persistent criminality: Implications for assessment and treatment. In Rieber RW, (ed), Advances in Forensic Psychology and P~ychiatry Norwood, NJ: Ablex, pp 119-191.
363
Lateralized Abnormality in the EEG of Persistently Violent Psychiatric Inpatients A. Convit, P. Czobor, and J. Volavka
Twenty-one consecutive right-handed male psychiatric inpatients treated on a unit designed for the management of violent behavior were given computerized EEGs. We recorded their violent behaviors, the number of staff interventions needed to control their behavior, and their medications. The number of instances of violence as well as the number of staff interventions were related to increased delta band activity and to decreased alpha band activity in the temporal and the parietooccipital areas. These relationships were independent of the current medications and of the length of stay on the special unit. Furthermore, our results demonstrate that violence is very significantly related to the hemispheric asymmetry in EEG for the frontotemporal derivations. With increased levels of violence there was a greater level of delta power in the left compared with the right.
Introduction Soon after the introduction of EEG into clinical practice, there were reports linking abnormal brain waves and violent behavior; this literature has bee= reviewed (Volavka 1990). With few exceptions (Williams 1969; Yeudall et al 1987), authors linking EEG abnormality and aggressive behavior have not reported on lateralization or localization. Furthermore, with the exception of Williams (1969), no attempt has been made to relate the persistence of violent behavior to the EEG findings. "*Villiamsfound increased amounts of slow activity over the frontotemporal ~-~as of habio_~al!y ag~essive offenders. Most of the literature to date has used visual assessment of the EEG, and this method of assessment is somewhat unreliable. However, even authors using reliable computerized EEG analyses have reported inconsistent findings. Some of these findings have included generalized slowing of EEG activity in aggressive boys (Surwillo 1980), frontocentral increase of delta activity associated with self-reported history of aggressive behavior in adult male drug abusers (Fishbein et al 1989), or no distinguishing EEG characteristic between violent and nonviolent psychiatric inpatients (Milstein 1988). Researchers utilizing neuropsychological measures or imaging techniques have found clear evidence linking violent behavior and brain dysfunction. Localization of this dysfunction has varied. Some investigators have reported diffuse abnormalities (Bryant et al 1984; Lewis et al 1988; Lewis et al 1985; Convit et al 1988a; Krakowski et al 1989).
From the Nathan Kline Institute for Psychiatric Research, Kirby Forensic Psychiatric Center, and Manhattan Psychiatric Center, New York, ~Y. Address reprint requests to: Kirby Forensic Psychiatric Center, Research Department, Ward's Island, New York, NY 10035 Received September 27, 1990; revised March 14, 1991.
© 1991 Society of Biological Psychiatry
~3223D1/$03.50
364
BIOL PSYCHIATRY 1991;30:363-370
A. Convit et al
Others have localized findings to the temporal lobes (Mark and Ervin 1970; Devinsky and Bear 1984; Hamstra 1986; Monroe 1986; Will 1986) or the frontal lobes (Tancredi and Vo!kow 1988; Yeudall et al 1987; Valzelli 1973). There has been one report on the lateralization of the abnormalities (Yeudall et al 1987). The dominant hemisphere has been the one most frequently incriminated (Nachshon 1983, 1988; Hare and McPherson 1984). Most studies have dichotomized violence and looked only at group differences between those classified as violent and nonviolent. The extent of violence on a continuum has not been evaluated. This study seeks to explore the relationship between the degree of violence and the levels of slowed EEG activity and asymmetry. Although there is no consensus as to which part of the brain is affected in violence, our reading of the literature has led us to hypothesize that if such a localization exists, it is likely to be in the anteri~i' portion of the dominant hemisphere. Furthermore, we hypothesize that the amount of violent behavior in psychiatric inpatients will be associated with EEG slow activity in that part of the brain.
Method
Subjects The subjects studied were violent psychiatric inpatients from a 1300-bed state facility in New York City, serving a predominantly poor inner-city population. In this state hospital, patients who are repeatedly violent and who cannot be managed on their home wards are transferred to the Intensive Psychiatric Service (IPS). The IPS uses a combination of behavioral and psychopharmacological strategies to treat the violent behavior and the psychiatric symptoms. As a general rule, patients are transferred back to their home wards in 5-7 weeks. In some cases, patients stay longer because their violent behavior had by that time not been well controlled or because their symptoms continue, and their home wards want them more stabilized psychiatrically before they take them back. The subject sample consisted of 21 consecutive male patients transferred to the IPS. Although handedness was not used as a selection criteria, all patients were right-handed. The patient sample had a mean age of 33 (SD = 9. | , range .z.l .-.5...~. /. ,. . .l n e y a mean age of first psychiatric hospitalization of 17 years (SD = 6.5, range 6-33). The mean duration of stay in the IPS was 48.1 days (SD = 26, range 15-110). With a single exception, patients were receiving neuroleptic medications on the day of the EEG recording. To make medication dose comparable across subjects we converted the doses of medications into chlorpromazine equivalents. The majority of the patients were receiving haloperidol with two patients receiving chlorpromazine, two Navane, and one prolixin hydrochloride. On the day of the EEG subjects were receiving an average of 2015 _ 650 mg chlorpromazine equivalents with a range of 0-3000. Procedures
Patients were evaluated by two psychiatrists who by consensus assigned them DSM-II1 diagnoses. Fifteen patients were classified as schizophrenic, five as mood disorder, and one as personality disorder. When the patients had been on a given dose of medications for longer than 5 days and their clinical condition permitted it they were given an EEG by one of the investigators (AC). As a rule the EEG was recorded during the second or third week of stay in the IPS.
Lateralized EEG and Violence
B1OLPSYCHIATRY
365
1991 ;30: 3 6 3 - 3 7 0
Detection and Classification of Violent Behavior All patients studied were by definition violent: they had met the criteria for admission to the IPS as described above. Once on the IPS, their violent and agitated behaviors were measured by inspecting the chart progress notes and the change shift reports using a highly reliable method. Details on the reliability of the violence detection method have been published elsewhere (Convit et al 1988b). All incidents were classified using the scale for the Assessment of Aggressive and Agitated Behaviors (Brizer et al 1987) into four categories: physical assault against another person, verbal assault (threatening someone with bodily harm), assault against property, and agitation (nonfocused shouting or markedly increased psychomotor activity). Because agitation can be nonspecific and does not involve overt and direct violence we excluded agitation from the analyses. The measure of violent behavior used was therefore the sum of physical, property, and verbal assault. We will refer to this sum as violent behavior or violence. The subjects had an average of 5.3 -4-- 9 instances of violent behavior during their stay in the IPS, with an average of 0.11 instances per day. The range was between 0 and 37. The patient's violent behavior does not occur in a natural setting. The IPS is staffed with personnel who have special training in management of violent behavior and who will frequently intervene before behaviors escalate to physical violence. For each of the instances of violent and agitated behaviors the staff intervention was recorded. The staff interventions were classified into four categories: verbal intervention, PRN medication given, patient placed in seclusion, and patient placed in a camisole. When more than one intervention was used, the more restrictive one was the one coded for that event (if a patient received an injection and was placed in seclusion, the seclusion was the one coded for the event). The staff interventions, although not a direct measure of violent behavior, are clinically quite relevant: they indicate the perceived potential dangerousness of a given situation. The dangerousness was felt to be more immediate when the staff intervened physically than when their intervention was limited to talking to the patient. For this reason we excluded from the analyses instances when verbal intervention alone was used; we used the sum of the nonverbal interventions. From now on this sum will be referred .t .O. . .
i;l~
b t l~l l_p-l y_ 1 _ .
, , :l l.l .l k. .~.l . .
V l ~ | l t ,~l't~. J.l l .
, , TJ t~l t,l ~. ~ , oO ,u,t kl | ~; ,, ~~, t~o* o
lho,-I la~a~
a n a v e r a g e~
'v~. f gu ~ - - .1 9. . ,t . . .i n. t .~ .r v. e.~.n t. i .o n . ,. ~.
. .
over
their stay in the 1PS, with an average of 0.12 interventions per day. The range was between 0 and 52. The number of staff interventions was larger than the number of instances of violent behavior. The staff deemed some instances of agitation as having the potential to progress to violence and hence intervened nonverbally.
Computerized Electroencephalogram Recordings were monopolar and used the International 10/20 Placement System referenced to linked earlobes. An electrode cap was used. One of three electrode cap sizes was used in order to optimize the electrode placement for each subject. The EEG was recorded in all cases by the first author while the patient was in the IPS, generally during the third week. EEG amplifiers with a time constant of 0.3 were used. The EEG was collected in 2.4 second epochs with only those epochs that were considered artifact-free on the monitor screen accepted. Eight bipolar derivations were created by computation from the earreferenced monopolar recordings: F7-T3, F8-T4, C3-Cz, C4-Cz, T3-T5, T4-T6, P3-O1, and P4-O2. From each of these bipolar derivations, relative power was computed using
366
B1OLPSYCHIATRY
A. Convit et al
1991;30:363-370
Hamming windows for each of the four frequency bands: delta (1.5-3.5 Hz), theta (3.57.5 Hz), alpha (7.5-12.5 Hz), and beta (12.5-25 Hz). The computed relative powers were then log-transformed to achieve a Gaussian distribution. The significance of the logtransformed values was assessed by computing Z scores relative to age norms. The Z scores expressed the deviation of the re!ative powers from that of the predictive age normative values in number of standard deviations. Detailed descriptions of these computations, their rationale, and reference to the age norms are published elsewhere (John et al 1988). The computations described above yielded a total of 32 EEG Z scores: each of the four frequency bands in the eight bipolar derivations computed. Because we were interested in differences between the two hemispheres, we computed an asymmetry score as follows:
L=
Lbd -- Rbd
Lbd + Rt,a'
where Lbd is the power spectrum value in frequency band b derivation d from the left hemisphere, and Rbd is the power spectrum value in frequency band b derivation d from the right hemisphere. Asymmetry scores were computed for each of the four pairs of derivations for each of the four frequency bands, giving us a total of 16 asymmetry scores.
Statistical Analyses We conducted three types of analyses: (1) First, we explored the relationship of the EEG variables to the violence variables using multiple regre,sion analyses. Because one can assume that the more violent subject stayed in the IPS longer, or if the patients stayed there for other reasons, the longer the subject was in IPS the more he had a chance to display violent behavior, we used the duration of stay in the IPS as one of the independent variables in the multiple regression analyses. The duration of stay in the IPS, the sum of violence, and the sum of interventions served as independent variables in the multiple regression models. Each EEG frequency band (n = 4) for each derivation (n = 8, four for each hemisphere) was used as the dependent variable in 1 of 32 multiple regressions. For each of the 32 multiple regression analyses, we evaluated the overall signif.cance of the model, the multiple, R, the partial regression coefficients, and the structural parameters of the model (constant and slopes of individual variables). (2) Secondly, we carried out explanatory post hoc con'elations between the violencerelated variables and the EEG variables found to be important in the multiple regressions above. (3) Lastly, to more specifically localize the EEG abnormality, we computed for each frequency band (n = 4) a laterality index for corresponding pairs of derivations for each hemisphere (n = 4) and related it to the violence variables. Each of these laterality indices was used as the dependent variable in 1 of 16 additional multiple regression analyses.
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Table 1. Multiple Regression Analyses of EEG Variables Band
Derivation
Delta
Right R 2
Left R 2
[L - R/L + R] R 2
F-T
NS
0.37 °
0.73 b
T-T
0.38 ~
0.45 ~
0.64 b
NS
NS
NS
P-O
0.44 a
0.47 °
NS
F-T
NS
NS
NS
T-T
NS
0.44 ~
NS
C--CZ
NS
NS
NS
0.41 ~
0.49 °
NS
C-CZ
Alpha
P-O ~p < 0.05. bp < 0.001.
It could be argued that the more violent a patient is, the higher his medication dose is likely to be. We also know the medications may have an effect on the EEG. We examined whether this variable was related to the EEG variables by calculating its correlations with each of the EEG variables.
Results In the multiple regression analyses we found that the sum of violent behaviors as well as the sum of the staff interventions explained a statistically significant amount of the variance of the relative power of delta and alpha in most derivations over both hemispheres (Table 1). The portion of explained variance ranged between 31% and 49%. The duration of stay did not exert an independent influence on the EEG variables. Furthermore, the violence and the interventions appeared to be independent of the duration of stay. Detailed tables of these analyses can be obtained from the authors. Post hoc correlations between the EEG variables and the two violence variables are shown in Table 2. Note that most of the statistically significant correlations were restricted to the left hemisphere. The delta activity was positively correlated with the violence variables. In contrast, the alpha activity is negatively related to the violence variables.
Table 2 . P ¢ a r s o n ' s Variables
r ~ ~!~,ct
Moment
C ~
i~tions (Post Hoc) between EEG and Violence
Right hemisphere
Left hemisphere
Frequency bands
Dependent variables
Delta
F-T
0.37
0.31
0.57 ~
0.53 b
T-T
0.40
0.30
0.52 b
0.42
C-CZ
0.43
0.39
0.42
0.39
P-O
0.36
0.26
0.47 b
Alpha
ap < 0.01. ~p < 0.05.
F-T
Intervention r
-0.31
Violence r
-0.24
Intervention r
Violence r
0.36
-0.55 ~
-0.50 b
T-T
- 0.40
- 0.32
- 0.56 a
- 0.47 b
C-CZ
- 0.46 b
- 0.40
- 0.56 ~
- 0.52 b
P--O
- 0.34
- 0.23
- (~\54 a
- 0.44 b
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31OL PSYCHIATRY 1991;30:363-370
A. Convit et al
We repeated the multiple regressions using the lateralization indices as the dependent variables and the length of stay in IPS and the two violence measures as the independent variables. Eight such regressions were carded out: four derivations each for the delta and alpha bands. We found that the significant relationship between laterality index and the violence variables was restricted to the frontotemporal areas. The sum of violent acts committed by each patient and the number of times the staff had to intervene explained a very large portion of the variance of the lateralization of delta for the frontotemporal and temporal derivations. These relationships were independent of the length of stay in IPS. The significance for the overall models were 0.0001 with 73% of the variance explained and 0.0005 with 64% of the variance explained for the frontotemporal and temporal derivations, respectively. The laterality computation implies a relative excess of delta activity over the left frontotemporal area. In order to study the possible confounding effect of medication with regard to the above relationships, correlation coefficients were calculated between each of the EEG variables and the chlorpromazine equivalents. The number of significant positive findings was under the chance level of 5%, and therefore these relationships were not interpreted.
Discussion Our findings indicate that independent of which measure of violence is used, a higher level of violence is accompanied by a larger power in delta. Elevation of the level of delta band activity or slowing of the EEG in violent patients had been reported in the literature (Fishbein et al 1989; Surwillo 198C). This increase of delta activity may be related to the structural impairments of the brains of our violent patients. Such structural abnormalities have been detected in violent individuals by other methods (Heinrichs 1989; Wood 1984). On the basis of the literature we hypothesized that there would be a relationship between lateralization of the EEG and the amount of violc~ce. Our results indeed demonstrated such a relationship. We found that the amount of violence is highly significantly related to the EEG hemispheric asymmetry for the frontotemporal derivations. For an increased level of violence there is greater level of power of delta band activity in the left hemisphere when compared with the right hemisphere. Our findings should be viewed as preliminary. We performed a large number of analyses with a relatively small subject sample size. These results are in agreement with reports demonstrating left hemisphere structural (Tancredi and Volkow 1988) and functional impairments (Tancredi and Volkow 1988; Yeudall et al 1987; Hamstra 1986; Will 1986) in violent individuals. The findings we report may not generalize to women, to patients who are not persistently violent, or to nonpsychiatric patients. There have been reports of abnormalities in the EEGs of psychotic patients (Multct et al 1986; Mukundan 1986). To improve on the generalizability of the findings to schizophrenics, we are conducting another EEG study using violent schizophrenics and age-matched nonviolent schizophrenics of both sexe~,.
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