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Schizophrenia Research

A neuropsychological investigation into violence and mental illness

Ian Barkatakia,*, Veena Kumaria,b, Mrigendra Dasc, Mary Hillc, Robin Morrisb,

Paul O’Connellc, Pamela Taylorc, Tonmoy Sharmad

aDepartment of Psychological Medicine, Institute of Psychiatry, London, United KingdombDepartment of Psychology, Institute of Psychiatry, London, United Kingdom

cBroadmoor Special Hospital, Crowthorne, Berkshire, United KingdomdClinical Neuroscience Research Centre, Dartford, Kent, United Kingdom

Received 26 May 2004; received in revised form 31 July 2004; accepted 1 August 2004

Available online 11 September 2004

Abstract

Previous research has reported cognitive impairment in patients with schizophrenia and antisocial personality disorder

(APD), the two psychiatric illnesses most implicated in violent behaviour. Previous studies have focused on either group

exclusively, and have been criticized for procedural inadequacies and sample heterogeneity. The authors investigated and

compared neuropsychological profiles of individuals with APD and violent and nonviolent individuals with schizophrenia in a

single investigation. The study involved four groups of subjects: (i) individuals with a history of serious violence and a

diagnosis of APD, (ii) individuals with a history of violence and schizophrenia, (iii) individuals with schizophrenia without a

history of violent behaviour and (iv) healthy control subjects. All study groups were compared on a neuropsychological battery

designed to assess general intellectual function, executive function, attention, and processing speed. Cognitive deficits were

more widespread among individuals with schizophrenia regardless of history of violence, compared with those with APD.

Significant impairment in patients with APD was limited to processing speed. Violent individuals with schizophrenia

demonstrated poorer performance than their nonviolent schizophrenia peers on a measure of executive function. Different

cognitive impairments are manifested by individuals with APD and schizophrenia with violent behaviours, suggesting

differences in underlying pathology. Furthermore, cognitive impairment appears to be more a feature of schizophrenia than of

violent behaviour, although there is evidence that a combination of schizophrenia and violent behaviour is associated with

greater cognitive deficits.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Violence; Aggression; Antisocial personality disorder; Schizophrenia; Neuropsychology

0920-9964/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.schres.2004.08.001

* Corresponding author. PO58, Section of Cognitive Pharma-

cology, Division of Psychological Medicine, Institute of Psychiatry,

De Crespigny Park, Demark Hill, London SE5 8AF, United

Kingdom. Tel.: +44 207 848 0702; fax: +44 207 848 0646.

E-mail address: [email protected] (I. Barkataki).

1. Introduction

There is an undoubted significant if small associ-

ation between psychosis and violent behaviour

74 (2005) 1–13

I. Barkataki et al. / Schizophrenia Research 74 (2005) 1–132

(Angermeyer, 2000; Tiihonen et al., 1997). The

relationship between personality disorder and violence

is much less clear, because of confounding between

measures of personality and of antisocial behaviour,

but personality disorders are heavily over-represented

in prison populations, even if antisocial personality

disorder (APD) per se is excluded (Fazel and Danesh,

2002). Furthermore, among people who have commit-

ted the most serious violence, many are co-morbid for

psychosis and/or personality disorder and the two

disorders most frequently implicated in violent behav-

iour are APD and schizophrenia (Taylor et al., 1998).

Neurobiological studies have suggested that certain

structural neural abnormalities are associated with

violent behaviour in mentally ill patients (Chesterman

et al., 1994). The two neural regions that have been

consistently cited in relation to violent behaviour in

both APD and schizophrenia in neuroimaging studies

are the prefrontal cortex and the limbic system (Das et

al., 2002). The prefrontal cortex (PFC) mediates

executive function and social conduct, in addition to

exerting an inhibitory influence on certain behaviours,

such as aggression (Damasio, 1995). Furthermore,

neuroimaging studies examining this region have

reported structural abnormalities in both schizophre-

nia (Buchanan et al., 1998) and APD samples (Raine

et al., 2000). The other implicated region is the limbic

system, an area involved in the processing of external

emotional stimuli and relaying it into emotional

response (Aggleton, 1992), and studies have demon-

strated abnormal limbic structure and function in both

schizophrenia (Chesterman et al., 1994) and APD

(Laakso et al., 2001). At the neurobiological level,

increases in violent behaviour has been linked with

reductions in serotonin (Soderstrom et al., 2001;

Volavka, 1999), reductions in dopamine (Berman

and Coccaro, 1998) as well as increases in testoster-

one (Book et al., 2001). Substance abuse is also

widely reported to exacerbate violent behaviour

(Reiss et al., 1994; Bushman and Cooper, 1990), via

its influence and interaction with neurochemical

agents such as serotonin (Virkkunen and Linnoila,

1993) and GABA (Miczek et al., 1997).

Neuropsychological studies examining cognitive

functioning in violent groups have supported neuro-

biological findings. Numerous reviews of antisocial

behaviour and neuropsychological function have

frequently cited the causal relationship between neural

dysfunction and violence (reviews: Brower and Price,

2001; Morgan and Lilienfeld, 2000; Golden et al.,

1996; Yeudall, 1977). These studies have generally

reflected the cognitive deficits that can be representa-

tive of certain types of neuropathology such as

executive function deficits reflecting PFC impairment,

but Jones (1992) proposed multiple neuropsychopa-

thological factors contributing to violent behaviour

including reduced inhibition, as well as impairment in

memory, attention and concentration.

Neuropsychological assessments of schizophrenia

populations have demonstrated deficits in a wide

range of cognitive domains including impairments in

attention, cognitive processing speed and IQ (reviews:

Sharma and Antonova, 2003; Goldberg and Gold,

1995). Schizophrenia has been linked to poor per-

formance on several aspects of executive functioning

using tests of working memory (Pantelis et al., 1997),

inhibition (Perlstein et al., 1998), and strategy

formation and planning (Morris et al., 1995). Within

the schizophrenia population, those with violent

histories are found to demonstrate impaired perform-

ance than those without a violent history on the

Wechsler Adult Intelligence Scale (WAIS) (Krakow-

ski et al., 1989) and Luria–Nebraska tests (Adams et

al., 1990). One study that directly compared non-

aggressive and aggressive (co-morbid APD) schizo-

phrenia groups (Rasmussen et al., 1995) reported the

aggressive group to perform poorly than the non-

aggressive group on tasks of frontal functioning with

the reverse being true for reaction time tasks.

Unlike schizophrenia, investigations of APD and

psychopathy (a closely related condition) do not show

significant differences in general intellectual perform-

ance in comparison to healthy groups (Walsh, 1991;

Miller, 1987; Prentice and Kelly, 1963). However,

these groups still exhibit deficits in executive function

across a range of tasks especially on those indexing

response inhibition and cognitive flexibility (Dolan

and Park, 2002; Morgan and Lilienfeld, 2000;

Lapierre et al., 1995; Devonshire et al., 1988;

Gorenstein, 1982). Furthermore, performance on tests

of impulsivity and emotional response have been cited

as particularly impaired in APD (Dinn and Harris,

2000; Lapierre et al., 1995). Overall, the literature

consistently reports that APD groups display PFC-

related deficits in executive function, inhibitory

control and emotional recognition. However, these

I. Barkataki et al. / Schizophrenia Research 74 (2005) 1–13 3

findings are controversial, as other studies have been

unable to find deficits on putatively PFC tasks

(Crowell et al., 2003; Hare, 1984) or have reported

deficits in some tasks but not others (Dinn and Harris,

2000). Published neuropsychological investigations of

APD and schizophrenia with violence have, however,

focused exclusively on either group, and there are as

yet no direct comparisons.

The current study compares neuropsychological

performance in individuals with APD and a history of

severe violence, those with schizophrenia who had

been similarly violent, non-violent individuals with

schizophrenia, and healthy control subjects, character-

izing the cognitive impairments associated with

violence in patients with these mental disorders. The

principal hypotheses were: (i) relative to the healthy

control subjects, subjects in all clinical groups will

show impaired neuropsychological performance; (ii)

individuals with APD will demonstrate impairment on

executive function and speed of processing tasks

(related to dorsolateral prefrontal cortex function) but

will not display deficits on tasks of attention and

general intellectual functioning; (iii) the non-violent

individuals with schizophrenia will show impairment

in processing speed, attention and general intellectual

functioning, in addition to executive functioning; (iv)

individuals with schizophrenia who have also been

violent will display a greater range and magnitude of

deficits than any other groups on cognitive measures,

especially in executive functioning.

2. Methods

2.1. Subjects

Initially, 64 participants were recruited into the

study, but 6 were excluded due to withdrawal of

consent or nonparticipation. The final sample con-

sisted of incarcerated patients with a history of

violence diagnosed with APD (APD: n=14) or

schizophrenia (VS: n=13), schizophrenia patients

without violent history (NVS: n=15) and healthy

control subjects (n=15). The violent patient samples

were recruited from Broadmoor Special Hospital and

the Denis Hill unit of the Bethlem Royal Hospital.

The NVS group was recruited from South London and

Maudsley Trust Hospitals, London and control sub-

jects were recruited from general public advertise-

ments in the South London Press.

Inclusion into the study required all subjects to be

male, right handed, between 18 and 45 years of age,

speak English as their first language, be free of current

substance abuse (tested by urine analysis), and have

no history of neurological conditions or head injury.

Entry to the APD group required a DSM-IV diagnosis

of antisocial personality disorder, no co-morbid

diagnosis of schizophrenia and a history of violent

behaviour that would score 4 for seriousness of

offence on the Gunn and Robertson Scale for

violence, indicative of a fatal or near fatal act of

violence against another (Gunn and Robertson, 1976).

Both VS and NVS were required to fulfill the DSM-

IV criteria for schizophrenia and could not have co-

morbid diagnosis of APD. The VS group also had to

show similar violent history as described for the APD

group while the NVS group was required to have no

significant history of violence. In addition to the

overall inclusion criteria, the control group had to

have no previous psychiatric diagnoses without any

significant history of violence.

Groups were matched according to age, ethnicity

and socio-economic background. Subjects were also

matched for number of years in education, which seems

to have resulted in comparable levels of estimated

verbal IQ as measured by the National Adult Reading

Test (Nelson and Willison, 1991). Duration of incar-

ceration was also matched for APD and VS groups.

Medication information at study entry was recorded

and neuroleptic dosage was converted into chlorpro-

mazine dosage equivalents where applicable (Table 1).

For certain tasks, the total sample number is reduced

due to equipment failure or nonparticipation and these

instances are stated in Table 2. All participants

provided written informed consent. The protocol for

this study was approved by the ethics committees of the

Institute of Psychiatry and Maudsley Hospital, London

and Broadmoor Hospital Berkshire.

2.2. Clinical ratings

Diagnoses for violent groups were based on

classification by respective treating consultants at

secure units, using the Structured Clinical Interview

for DSM-IVAxis I disorder (SCID, First et al., 1995)

for the VS group, and the Structured Clinical Inter-

Table 1

Patient demographic and clinical characteristics

Control

(N=15),

mean (S.D.)

APD

(N=14),

mean (S.D.)

NVS

(N=15),

mean (S.D.)

VS

(N=13),

mean (S.D.)

F df P

Age 32.1 (7.47) 33.5 (10.45) 34.5 (7.49) 34.5 (4.94) 0.29 3,53 0.834

NART score (estimated IQ) 106.9 (16.09) 96.3 (9.69) 98.9 (13.40) 96.4 (13.93) 1.97 3,53 0.130

Violence score* 0.50 (0.85) 6.57 (1.34) 1.20 (1.32) 6.15 (1.46) 89.56 3,53 b0.001

Duration of illness (years) N/A N/A 11.2 (7.58) 12.2 (7.32) 0.114 1,26 0.739

PANSS

Positive symptoms 12.0 (3.96) 10.8 (4.87) 0.544 1,26 0.467

Negative symptoms 20.1 (5.40) 17.9 (5.24) 1.209 1,26 0.282

General psychopathology N/A N/A 32.7 (5.82) 23.8 (5.64) 16.97 1,26 b0.001

Total 64.8 (12.23) 52.9 (13.11) 6.22 1,26 0.02

PCL: SV total score N/A 16.29 (1.68) N/A 8.31 (3.17) 68.05 1,25 b0.001

Dosage of neuroleptic—chlorpromazine

equivalents (mg/day)

N/A N/A 567.0 (323.52) 426.7 (227.61) 1.42 1,20 0.247

NART=National Adult Reading Test; PANSS=Positive and Negative Symptom Scale; PCL: SV=Psychopathy Checklist: Screening Version;

APD=antisocial personality disorder; NVS=non-violent schizophrenia VS=violent schizophrenia; N/A=not applicable.

Significant findings indicated by bold text.

* As measured by Gunn and Robertson Scale.


view for DSM-IV personality disorders (SCID II, First

et al., 1997) for the APD group. Diagnoses for

schizophrenia in the NVS group were made by trained

research psychiatrists (MD, PC) using clinical inter-

view, DSM-IV criteria and the SCID. Clinical inter-

view and the SCID nonpatient version (SCID NP,

Spitzer et al., 1995) were used in order to screen

controls to ensure they did not suffer from undiag-

nosed personality disorder or mental illness.

The Psychopathy Checklist: Screening Version

(Hart et al., 1995) was used to assess the level of

antisocial/psychopathic trait in the violent groups at

study entry, and was used to assess the degree of

psychopathy in the APD group and also to ensure that

VS subjects did not have high levels of co-morbid

psychopathic trait. While APD and psychopathy are

associated, as they are both characterized by aggres-

sive antisocial behaviour and are linked to heightened

impulsivity, they are not synonyms. While most

individuals with psychopathy will have APD, only a

small proportion of those fulfilling the APD criteria

and characterized by additional defective affective

experience will meet the criteria for psychopathy.

Subjects in the VS and NVS groups were assessed

for schizophrenia subtype and were rated for sympto-

matology using the Positive and Negative Symptom

Scale (PANSS) (Kay et al., 1987). As pure antisocial

personality disorder is relatively rare, APD subjects

were additionally assessed for co-morbid personality

disorders.

Among the schizophrenia groups (NVS, VS)

diagnosis included paranoid (n=21), undifferentiated

(n=5), disorganised (n=1) and residual (n=1) subtypes.

The VS and NVS groups did not significantly differ on

schizophrenia subtype. Within the APD group, 8

subjects had co-morbid antisocial and borderline

personality disorders, 3 had co-morbid antisocial,

borderline and paranoid personality disorders, 1 had

antisocial, borderline and histrionic personality disor-

ders, 1 had antisocial, paranoid, avoidant and depend-

ant personality disorders, and 1 had antisocial

personality disorder without other co-morbid disorders.

None of the APD group were on current anti-

psychotic medication. Within the schizophrenia

groups, 2 individuals were currently not on any

medication (NVS: n=1, VS: n=1), 10 were on

conventional antipsychotic medication (NVS: n=4,

VS: n=6) and 16 subjects were on atypical antipsy-

chotics (NVS: n=10, VS: n=6).

2.3. Details of index offences in violent groups

The index offences that constituted a factor in

admission to a secure hospital or hospital unit were

able 2

europsychological performance in subject groups and analysis of variance

(continued on next page)


T

N

WAIS =Wechsler Adult Intelligence Scale; EGT =Executive Golf Task; WCST =Wisconsin Card Sorting Task; TOL =Tower of London Task;

CPT =Continuous Performance Task; AMIPB = Adult Memory and Information Processing Battery; ES =Effect size; ns =non significant.

Significant findings indicated by bold text.aReduced sample size: control subjects n=12, APD n=12, NVS n=15, VS n=11 (main effect df=3,46).bReduced sample size: control subjects 14, APD 12, NVS 14, VS 13 (main effect df=3,50).cReduced sample size: control subjects 15, APD 13, NVS 15, VS 13 (main effect df=3,52).dReduced sample size: control subjects 15, APD 12, NVS 15, VS 13 (main effect df= 3,51).

*Superior performance is indicated by lower score on these tasks.

Table 2 (continued)


collated for the groups with violent history. There were

11 individuals whose index offence was homicide (6

APD, 5 VS), 5 with attempted murder (3 APD, 2 VS),

7 with wounding (3 APD, 4 VS), 2 with robbery (1

APD, 1 VS) and 2 (1 APD, 1 VS) classified as

demonstrating dother type of serious violenceT.

2.4. Neuropsychological assessment

Participants completed a neuropsychological bat-

tery of tests designed to assess general intellectual

functioning, memory, executive/frontal function, atten-

tion, and information processing speed as follows.

2.4.1. General intellectual functioning

A short form of the Wechsler Adult Intelligence

Scale 3rd edition (WAIS III) (Wechsler, 1997)

suggested by Blyler et al. (2000) was employed to

yield Verbal IQ (VIQ), Performance IQ (PIQ) and

Full-Scale IQ (FSIQ) measures.

2.4.2. Memory

Verbal memory was assessed using the Logical

Memory I and II subscales from the Wechsler

Memory Scale 3rd Edition (WMS III) (Wechsler,

1998) to test immediate and delayed auditory recall.

2.4.3. Executive function

Executive function was assessed using computer-

ized versions of the Executive Golf Task (EGT)

(Morris et al., 1999), Wisconsin Card Sorting Task

(WCST) (Heaton, 1993), the 3D computerized Tower

of London test (TOL) (Morris et al., 1995) and a pen

and paper version of the Stroop Colour–Word task

(Golden, 1978). The EGT measures spatial strategy

formation and working memory by making the subject

search through a set of locations on a computer screen

for a target location, and on subsequent searches

having to find new target locations without returning to

successful ones. Performance on this task was judged

by total number of errors made within each search and

between searches on a single trial, and by a methodical

strategy score; high scores indicate poor performance.

The WCST examines the ability to discern a rule

set, adhere to it and adjust to it in the event of a rule

change. During this task, a response card has to be

matched according to a given criteria (colour, shape,

number of shapes) to one of four stimulus cards that

are constantly displayed. However, in certain instan-

ces, the matching criteria is changed and the subject is

required to notice and adapt to the new rule. Perform-

ance on the WCST was measured according to the

number of perseverative errors made and categories

completed. Low numbers of perseverative errors made

indicated superior ability to adapt to new rules and a

high number of categories completed reflects profi-

ciency in concept formation.

The TOL investigates planning and spatial problem

solving ability. The task requires the manipulation of

several disks onto differently sized rods in order to

recreate a given configuration, across five levels of

increasing complexity. Performance on this task was


assessed on total number of moves above the possible

minimum taken to complete the task, with low number

of moves indicative of efficiency at problem solving.

Planning time taken between the start of the task and

the manipulation of the first disk and time taken for

subsequent execution of the task were also measured,

with quicker times signifying better performance.

The Stroop Colour–Word task tests the capacity to

suppress prepotent responses to stimuli as a measure

of inhibition. The task consists of three lists: a word

list of words in black ink that describe colour, a colour

list of differently coloured inks, and a colour–word list

of words describing colours, which is printed in a

colour of ink different to that colour described by the

word. Subjects are scored by the number of words

successfully read out in the last of these conditions. In

this task, high colour–word and T scores indicate

superior inhibitory ability, and high scores in the

colour list and word list (both combined into an

overall processing score) are indicative of better

processing speed.

2.4.4. Attention

The Continuous Performance Task—Identical

Pairs variant (CPT) (Cornblatt et al., 1988) was

used to gauge attention. In this computerized task,

subjects had to respond to identical consecutive four-

digit numbers by using a mouse to respond, while

ignoring nonconsecutive stimuli. Performance was

measured as the number of random errors commis-

sioned and by d-prime, a measure of vigilance

determined by how well an individual discriminates

Fig. 1. Order of neuropsycholog

between target and nontarget stimuli. Higher scores

indicate better performance.

2.4.5. Processing speed

Processing speed was measured by the informa-

tion processing subtests of the Adult Memory and

Information Processing Battery (AMIPB) (Coughlan

and Hollows, 1985). These are critically timed

number cancellation tasks which provide measures

of motor speed, of cognitive processing speed, and

processing accuracy. Processing speed was calculated

as the average of the adjusted scores derived from a

conversion table (Coughlan and Hollows, 1985),

which takes into account the total number of items

correctly cancelled within the time limit, and

performance on the motor speed task for both tasks.

Accuracy was calculated from the mean percentage

of correctly cancelled items on both scales. Motor

speed performance was assessed by the number of

cancelled items within a given time limit on a

separate noncognitive task.

Order of presentation of tests is given in Fig. 1.

The battery took approximately 2 h to administer

with a break given half way through (between tasks

5 and 6).

2.5. Statistical analysis

For categorical demographic data, chi-square tests

were used to analyze between group differences. One-

way analysis of variance (ANOVA) was used for all

other demographic and clinical variables.

ical battery administration.


The scores on Performance and Verbal IQ were

subjected to a 4 (Group: control subjects, APD,

NVS, VS)�2 (Measure: PIQ, VIQ) mixed-model

ANOVA. The scores on Logical Memory scales

were examined using a 4 (Group)�2 (Measure:

Logical Memory I score, Logical Memory II score)

mixed-model ANOVA. For both comparisons,

dGroupT was the between-subjects factor and

dMeasureT was the within-subjects factor. All other

cognitive tests were analyzed with a one-way

ANOVA with the score as the dependant variable

and Group as the independent factor. For significant

group effects, follow-up analysis of comparisons

between individual group pairs was conducted using

lower-order ANOVA with the two appropriate

groups as the between-subjects factor. For mixed-

model ANOVA, the Greenhouse–Geisser correction

was applied where appropriate.

Given the difference in symptoms between the

NVS and VS groups (see Table 1), any cognitive

variables differentiating these two groups were re-

evaluated using analyses of co-variance with the

PANSS general psychopathology scores as a cova-

riate. Any measure showing impaired performance in

all three APD, NVS, and VS groups relative to

healthy subjects was re-evaluated after co-varying for

Full-Scale IQ to estimate the variance it might share

with the general intellectual functioning. Statistical

analysis was conducted using SPSS v.10 with level of

significance maintained at p=0.05 unless specified

otherwise.

3. Results

3.1. Demographic and clinical variables

There were no significant differences between

groups on demographic variables (Table 1). Charac-

teristic variables that defined groups (i.e. PCL score

and violence rating) differed as did PANSS General

psychopathology score.

3.2. General intellectual functioning

Means and standard deviations for all neuro-

psychological variables, classified by subject groups,

and ANOVAs are presented in Table 2.

For PIQ and VIQ scores, there were statistically

significant group differences. PIQ/VIQ scores were

significantly lower in the NVS and VS groups than in

healthy participants. The APD group displayed a trend

for lower scores than the control group, but had higher

scores than the VS group. Examination of FSIQ

revealed significant group differences as both NVS

and VS groups showed significantly lower mean

FSIQ compared to the healthy participants. Moreover,

the APD group exhibited a trend towards having a

lower FSIQ than the control group. Although mean

FSIQ scores in the APD were not significantly

different from the NVS group, they were significantly

higher than those of the VS group.

3.3. Memory

For the scores on the Logical Memory I and II

scales, there were significant group differences. The

NVS and VS groups performed worse than the control

group. The APD group did not differ from control

group but performed significantly better than NVS

and VS subjects. In general, all groups had higher

immediate memory relative to delayed memory scores

(F=21.22, df=1,53, pb0.001), but no Group� Meas-

ure interaction was found.

3.4. Executive functioning

On the EGT task, there were no significant group

differences for within-search errors or for strategy score

but there were significant group differences in the

between-search error scores. The NVS and VS subjects

made significantly more between-search errors than

control subjects. The APD group made fewer between-

search errors than the VS groups but did not signifi-

cantly differ from NVS or healthy participants.

WCST scores also showed significant group differ-

ences. Both the NVS and VS groups made more

perseverative errors than the control group. The VS

and NVS groups also made more errors than APD

subjects. The difference between NVS and VS groups

was not diminished when PANSS general psychopa-

thology scores was co-varied for (F=5.119, df=1, 23,

p=0.033). For the WCST number of categories

completed, both NVS and VS groups performed worse

than the control group. The APD group showed

significantly better performance than the VS group


and a trend towards better performance than the NVS

group.

There were significant group differences in per-

formance on the Stroop processing score. Both NVS

and VS groups had significantly poorer (lower)

processing scores than the control group. Mean

processing scores in the APD group were similar to

NVS and control groups, but were significantly better

than the VS group. The NVS group showed signifi-

cantly better processing score than the VS group

although this effect was reduced and became non-

significant after co-varying for the PANSS general

psychopathology.

3.5. Attention

For the d-prime scores on the CPT, there were

significant group differences. Both NVS and VS

groups had significantly poorer (lower) scores than

the control group. Mean scores in the APD group

were similar to control subjects but they performed

significantly better than both NVS and VS groups.

3.6. Information processing and motor speed

AMIPB processing speed scores showed signifi-

cant group differences. In contrast to other neuro-

psychological measures, the APD group as well as the

NVS and VS groups demonstrated impaired perform-

ance relative to the control group. Significance for the

Group effect was reduced but not abolished after

controlling for differences in FSIQ (F=3.054, df=3,

50, p=0.037). No significant group differences were

found for AMPIB accuracy measure but there were

significant differences in motor speed, which revealed

the NVS and VS groups as slower than either control

or APD groups.

4. Discussion

The findings show that all patient groups (APD,

NVS and VS) exhibit some neuropsychological

dysfunction when compared with control subjects,

albeit of differing degrees. Overall, both violent and

nonviolent schizophrenia groups had global deficits

involving measures of general intellectual function-

ing, executive function, attention, and cognitive

processing speed compared with the healthy control

group. In contrast, the APD group generally per-

formed as well as the control group on cognitive

measures, with the notable exception of significantly

poorer performance on a measure of processing speed.

However, the APD group performed significantly

better than the VS group on measures of executive

function, and better than both NVS and VS groups

on measures of general intellectual function, atten-

tion and motor speed. There was no significant

difference between the NVS and VS groups on

neuropsychological measures, other than better per-

formance in the NVS than VS group on a measure of

executive function. Moreover, the nature of the

deficits observed here suggests that cognitive abil-

ities in the clinical groups are at the lower end of the

normal range rather than being indicative of severe

pathological dysfunction.

With regard to the proposed hypotheses, the first

hypothesis was supported in that there were signifi-

cant group differences on all measures, with the

healthy controls consistently showing superior per-

formance. Further examination of the results, how-

ever, confirmed that the difference was mainly

accounted for by higher scores in the control group

relative to the two schizophrenia groups. The second

hypothesis was not sustained. While it was true that

the violent men with APD performed as well on tests

of general intellectual function and attention as the

healthy subjects, and significantly better than the men

with schizophrenia on the latter, they were similarly

not distinguished by their performance on tests of

executive function. The third hypothesis was largely

confirmed. Relative to healthy participants, the

schizophrenia groups did show impairments in gen-

eral intellectual function, executive functions and

processing speed, but despite generally gaining lower

scores than the APD group, they rarely differed from

them significantly in these respects. The fourth

hypothesis was only partly confirmed. On tests of

general intellectual function, memory, attention, pro-

cessing speed, and some executive tasks the perform-

ance of the schizophrenia group with violent history

was indistinguishable from their nonviolent schizo-

phrenic peers. However, on two of the executive

function tests (Stroop, Wisconsin Card Sorting Task)

their performance was relatively impaired. The Stroop

result was confounded by levels of psychopathology,


but the error rate on the Wisconsin Card Sorting Task

was independent of the PANNS general psychopa-

thology score.

Contrary to the expectations, the APD group did

not show deficits in executive function compared to

control subjects or patients with nonviolent schizo-

phrenia, but did show impairment in processing

speed. The lack of observable significant impairment

in executive function does not support the theory that

dysfunction of the dorsolateral prefrontal cortex is a

core component of APD (Chesterman et al., 1994;

Das et al., 2002; Raine et al., 2000), and lends support

to the studies reporting executive functioning parity

between APD and healthy individuals (Crowell et al.,

2003; Hare, 1984). These studies advocate attribution

of antisocial behaviour in APD to emotional or

socialization factors rather than straightforward com-

promise of executive function, and suggest that

prefrontal cortical dysfunction can serve to facilitate

aggression and violence in APD, but is not an

essential prerequisite.

Interestingly, the novel finding of reduced process-

ing speed in individuals with APD in this study

suggests that the impulsive and risk-taking character-

istics of APD may be related to failure to appropri-

ately process data indicating the presence of danger in

adequate time. This deficit may also be responsible for

the irresponsibility and failure in foresight that are

characteristic of individuals with APD, as the inad-

equate processing of data may result in the individual

in making maladaptive decisions (inability to bthink it

through properlyQ), especially in scenarios where

thinking time available is brief (e.g. within confronta-

tional situations). There is also the possibility of a

specificity of effect to this particular type of task, as

performance on planning time within the TOL did not

differentiate between control and APD subjects.

Currently, there are no investigations focusing on

processing speed in APD, and the issue of processing

speed impairment being specifically related to APD

requires further research.

Deficits in information processing speed have

traditionally been associated with multiple sclerosis

(Rao, 1995), but studies of Parkinson’s disease

(Grossman et al., 2002) and head injury (Schmitter-

Edgecombe et al., 1992) have also found impairments

in this domain. Information processing in such

instances could consist of a sequence, which begins

with sensory input and ends with motor output. It can

be subdivided into three main components: automatic

processing (involuntary recognition of sensory input),

controlled processing (the conscious manipulation of

information) and motor programming (Vlaar and

Wade, 2003). As the APD group did not differ on

the motor speed component of the task, and they also

did not show deficits in the recognition aspects of

other tasks (see Results), it could be speculated that

this particular deficit was localised to the controlled

processing component. Contemporary research into

neural correlates of information processing speed

related to white matter (Posthuma et al., 2003) and

frontal lobe volumes (Schretlen et al., 2000), the latter

of which has previously been implicated in APD

function.

Information processing speed is just one of several

possible measures of impulsivity, and other neuro-

biological studies examining antisocial populations

have reported similar deficits in impulsivity using

different methods. There have been reports of

increased rate of error during motor inhibition tasks

in psychopathic (Lapierre et al., 1995) and APD

subjects (Dolan and Park, 2002) when compared to

normal controls, which has been attributed to increased

impulsivity characteristic of the disorders. Further-

more, a recent functional neuroimaging study examin-

ing impulsivity using a similar motor inhibition task

(Vollm et al., 2004) demonstrated PFC activation

during inhibition in controls and a displacement of

activation to the medial superior gyrus and anterior

cingulate in personality disordered subjects (including

APD), suggesting that impulsivity may be related to

PFC dysfunction and the use of alternative neural

pathways to deal with inhibitory demands. It has been

theorized that poor impulse control in APD is due to

impairment in the PFC (Horn et al., 2003) based on the

observations of reduced metabolism and grey matter

volume in this region (Raine et al., 1997, 2000).

The performance in the schizophrenia groups

demonstrated here supports prior findings of the

presence of widespread deficiencies in cognitive

function. In addition, a greater degree of impairment

was observed in violent compared to nonviolent

schizophrenia patients. This finding confirms certain

earlier findings of violent groups with schizophrenia

displaying impaired performance compared to non-

violent groups (Adams et al., 1990; Krakowski et al.,


1989). However, this impairment may only be

prevalent when the violent group with schizophrenia

does not have co-morbid psychopathy (as in the

current study), as there has been some indication that

the presence of a personality disorder of the antisocial

type may have a protective factor against certain

neuropsychological deficits normally found in schiz-

ophrenia (Rasmussen et al., 1995). Overall, these

results corroborate published reports of cognitive

deficits in intellectual function (Allen et al., 1998),

executive function (Adams et al., 1990; Bustini et al.,

1999), attention (Mirsky, 1988; Franke et al., 1994)

and cognitive processing (Perlstein et al., 1998) in

patients with schizophrenia. In addition, the findings

suggest that moderate cognitive impairment in schiz-

ophrenia is present regardless of the presence or

absence of violent behaviours, and the poor perform-

ance in executive function tasks implies the existence

of prefrontal cortex dysfunction.

Despite attempting to account for external factors

and potential confounding variables, this study has

some limitations. Although the violent mentally ill

sample in the current study is large compared to other

published research, we encountered a high attrition

rate in terms of total sample size as well as within

individual tests, and as a result the sample was

relatively small. The reasons for dropouts were

withdrawal of consent and noncooperation, as well

as logistic and circumstantial issues. The number of

subjects dropping out of the study was, however,

evenly distributed across the four study groups with

no apparent difference between those who dropped

out and those who remained in the study on the

demographic and estimated IQ variables.

Other limitations, with some potential for con-

founding in our results, include the use of APD

subjects with other co-morbid personality disorders,

the use of schizophrenia subjects with various

subtypes and symptoms and the possibility of

previous substance abuse in all groups. Finally, due

to the array of neuropsychological tasks and four

study groups investigated in this study, it was

necessary to perform many statistical comparisons,

which would normally necessitate a correction to the

alpha value to reduce potential type-one error.

However, we felt it would be more appropriate to

maintain the conventional level of significance in

order to examine the subtle but meaningful differences

between groups and report the effect sizes pertaining

to our proposed hypotheses.

In conclusion, this study demonstrated some level

of dysfunction in all three pathological groups.

Individuals with APD displayed marginal impairment

in cognitive processing speed, but not in executive

function, suggesting that an alternate hypothesis of the

pathogenesis of behaviors characteristic of these

patients is needed. Widespread cognitive deficits are

present in patients with schizophrenia both with and

without a history of violence, but deficits in executive

function are more pronounced in violent than non-

violent patients. These findings suggest that violence

in patients with schizophrenia and APD is linked to

different aspects of impaired neuropsychological

function. There is a need for additional research to

elucidate the factors and impairments that facilitate

violence in individuals with mental illness.

Acknowledgements

This study was funded by grants from The Zito

Trust and the Community Fund, UK, and the Stanley

Medical Research Institute, USA. Veena Kumari

holds a Wellcome Trust Senior Research Fellowship

in Basic Biomedical Science. We express our appre-

ciation to the staff of Broadmoor Special Hospital and

the Denis Hill Unit of the Royal Bethlem Hospital,

and to Ms. Catherine Hughes for assistance with this

study.

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