The relationship in children between the inattention and impulsivity components of attention deficit and hyperactivity disorder and psychopathic tendencies

Personality and Individual Differences 30 (2001) 1175±1187

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The relationship in children between the inattention and impulsivity components of attention de®cit and hyperactivity disorder and psychopathic tendencies E. Colledge, R.J.R. Blair * University College London, Institute of Cognitive Neuroscience, Alexandra House, 17 Queen Square, London, WC1N 3AR, UK Received 27 November 1999; received in revised form 27 March 2000

Abstract This study investigated the relationship between the inattention and impulsivity components of Attention-De®cit-Hyperactivity Disorder (ADHD) and psychopathic tendencies in children with emotional and behavioural diculties. Teachers rated 71 children on the Psychopathy Screening Device (Frick & Hare, 2000: Frick, P. J., & Hare, R. D. (2000). The psychopathy screening device. Toronto: Multi-Health Systems (in press)), the DuPaul's ADHD rating scale (DuPaul, 1991: DuPaul, G. J. (1991). Parent and teacher ratings of ADHD symptoms: Psychometric properties in a community-based sample. Journal of Clinical Child Psychology, 20, 245±253), and the Conners' Abbreviated Symptoms Questionnaire (Conners, 1973: Conners, C. K. (1973). Rating scales for use in drug studies with children. Pharmacotherapy of children [Special Issue]. Psychopharmacology Bulletin, 24±84). Signi®cant inter-correlations between teachers' ratings of children's inattention and impulsivity and psychopathic tendencies were found. There were signi®cant inter-correlations between teachers' ratings of the inattention and impulsivity components of ADHD and the Callous and Unemotional (C/UN) and Impulsivity and Conduct (I/CP) problems components of psychopathy. Further analysis revealed that the inter-correlations between these four components were mainly due to the association between the impulsivity component of ADHD and the antisocial behaviour (I/CP) component of psychopathy. The inattention component of ADHD was not related to either of the psychopathy risk measures. Equally, the distinguishing factor of the psychopathy (C/UN) was not related to either of the ADHD measures. A categorical analysis of the data revealed a higher than chance level of comorbidity of ADHD and psychopathic tendencies. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Psychopathy; Attention-de®cit-hyperactivity disorder (ADHD); Psychopathy Screening Device (PSD)

* Corresponding author. Tel.: +44-20-7679-1162; fax: +44-20-7813-2835. E-mail address: [email protected] (R.J.R. Blair). 0191-8869/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0191-8869(00)00101-X

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1. Introduction There are two main diagnoses of childhood disorder that are associated with high levels of externalising and undercontrolled (i.e., age inappropriate) behaviour: Attention-De®citHyperactivity Disorder (ADHD), and conduct disorder (CD). ADHD is de®ned as, ``a persistent pattern of inattention and/or hyperactivity-impulsivity that is more frequent and severe than is typically observed in individuals at a comparable level of development'' (American Psychiatric Association DSM-IV, 1994). CD is de®ned as ``a repetitive and persistent pattern of seriously anti-social behaviour usually criminal in nature'' (American Psychiatric Association DSM-IV, 1994). The reported prevalence rates for both ADHD and CD vary substantially across studies. Thus, DuPaul (1991), in a review of the literature, reported rates for ADHD that varied from 1 to 20%. Factors that can in¯uence prevalence rates include, for example, the speci®c diagnostic criteria used (Wolraich, Hannah, Baumgaertel & Feurer, 1998) or the age of the participants assessed (August, Braswell & Thuras, 1998). As regards CD, DSM-IV has suggested prevalence rates ranging from 6 to 16% for males and 2 to 9% for females. Factors that in¯uence prevalence rates for CD include social status and risk behaviours, such as class A drug use (Booth & Zhang, 1997). In addition, to the substantial di€erences in reported prevalence rates for ADHD and CD across studies, these disorders appear to be highly comorbid. Indeed, there are reports of an overlap of between 30 and 90% (e.g., Hinshaw, 1987; see also, Biederman, Newcorn & Sprich, 1991; Mannuzza, Klein, Konig & Giampino, 1989; Shapiro & Gar®nkel, 1986; Szatmari, Boyle & O€ord, 1989; Taylor, Schachar, Thorley & Weiselberg, 1986; Werry, Reeves & Elkind, 1987). With speci®c reference to antisocial behaviour, Vitelli (1996) examined the prevalence of CD and ADHD in a juvenile delinquent prison population and found a prevalence rate of 63% for CD, 41% for ADHD and signi®cant comorbidity. However, according to Vitelli, CD was the only signi®cant predictor of adult criminality. The reason for the high comorbidity of ADHD and CD has excited considerable empirical and theoretical work. A number of studies have compared the performance on cognitive tasks of individuals with ADHD alone, CD alone, comorbid ADHD and CD and comparison populations without disorder (e.g., Matthys, van Goozen, de Vries, Cohen-Kettenis & van Engeland, 1998; Oosterlaan, Logan & Sergeant 1998; Leung & Connolly, 1996; Schachar & Tannock, 1995). The ®ndings of these studies have been inconsistent. Some studies have reported that the comorbid individuals perform similarly to the individuals with ADHD (e.g., Osterlaan et al., 1998) while others have reported that the comorbid individuals perform more similarly to the individuals with CD (e.g., Leung & Connolly, 1996). Schachar and Tannock (1995) found that co-morbid individuals shared features with both disorders. In a review of the literature, Hinshaw (1987) argued that ``sucient evidence exists for considering the domains of hyperactivity/attention de®cits and conduct problems/aggression as partially independent'' (p. 459). A similar position was backed by Pennington and Ozono€ (1996) who reported that individuals with CD alone did not show the impairment in executive functioning that is characteristic of individuals with ADHD. Lynam (1996) focused speci®c attention on the children who are comorbid for ADHD and CD, considering them a special population that he termed `¯edgling psychopaths'. In addition, he proposed that the individuals who present with both ADHD and CD might present with more

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of the impulsivity component of ADHD and that this `impulsivity' might underpin both the ADHD and CD. In contrast, he suggested that those individuals only meeting criteria for ADHD might manifest more of the inattention component of ADHD. In an interesting study in line with Lynam's position, Babinski, Hartsough and Lambert (1999) examined the relationship between childhood conduct problems, hyperactivity-impulsivity and inattention in predicting adult criminal activity. They found that both early conduct problems and hyperactivity-impulsivity were signi®cant predictors of later criminal involvement. However, a child's level of inattention did not predict his/her later criminal involvement. It must be remembered, however, that there are potentially many reasons for why a child might present with antisocial behaviour (Blair & Frith, 2000; Frick, 1995). These range from the sociological (e.g., Booth & Zhang, 1997), to `empathic' dysfunction (e.g., Blair, 1995; Blair & Frith, 2000; Gibbs, 1987) or executive dysfunction (e.g., Mott, 1993; Pennington & Bennetto, 1993). Since ADHD is known to be associated with executive dysfunction (e.g., Pennington & Ozono€, 1996), it is possible that the comordid cases of ADHD and CD may represent those individuals with ADHD whose executive dysfunction has prompted the display of antisocial behaviour. It is certainly clear that the presentation of antisocial behaviour can follow executive dysfunction (e.g., Blair & Cipolotti, 2000; Burgess & Wood, 1990; Pennington & Bennetto, 1993). There appear to be other individuals whose antisocial behaviour is due to `empathic', or other emotional dysfunction (e.g., Blair, 1997; Frick, 1995; Patrick, 1994). A form of behavioural disorder following `empathic' dysfunction is considered to be psychopathy (e.g., Blair, 1995; Frick, 1995; Hare, 1991). Individuals with psychopathy form a far more homogeneous and selective group than those meeting criteria for CD or its adult antisocial behaviour based equivalent, Antisocial Personality Disorder (APD). Thus, for example, while 50± 80% of inmates meet criteria for APD, only 15±20% meet criteria for psychopathy (Hart & Hare, 1997). Psychopathy can be indexed behaviourally in children using the Psychopathy Screening Device (PSD, Frick & Hare, 2000) and in adults by using the Revised Psychopathy Checklist (PCL-R, Hare, 1991). Both scales index a strikingly similar syndrome. Factor analysis indicates that both the PSD and PCL-R capture two dimensions present in a psychopathic personality construct. The Impulsivity/Conduct Problems (I/CP) factor comprises of overt behavioural characteristics such as impulsivity, poor impulse control (e.g., becomes angry when corrected), and delinquent behaviours (e.g., Frick, O'Brien, Wootton & McBurnett, 1994; Harpur, Hare & Hakstian, 1989). This factor is highly correlated with traditional measures of conduct problems, such as the DSM-IV de®nition of Conduct Disorder (Frick, 1995). The Callous/Unemotional (C/UN) factor captures such characteristics as lack of guilt, lack of empathy, and super®cial charm, which are considered primary in clinical description of psychopathy (Cleckley, 1976; Hare, 1970). Previous studies using the Psychopathy Screening Device have shown that children with psychopathic tendencies perform poorly on the same neuro-cognitive tasks that cause adult psychopathic individuals dif®culty (e.g., Blair, 1997, 1999; O'Brien & Frick, 1996). While many studies have shown that ADHD and CD are highly comorbid, no previous study has examined comorbidity between the inattention and impulsivity components of ADHD and psychopathic tendencies. The aim of the present study was to investigate measures of ADHD and psychopathic tendencies in a population of children classi®ed as having Emotional and Behavioural Diculties.

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2. Method 2.1. Design This experiment involved a correlational design. The measures were the children's verbal IQ and teacher's ratings of the children's behavioural diculties as indexed by the Psychopathy Screening device (Frick & Hare, 2000), Dupaul's ADHD rating scale (DuPaul,1991) and the Abbreviated Symptoms Questionnaire (Conners, 1973). 2.2. Participants The participants were all male, aged between 9 and 16 years, and attended special schools for children with Emotional and Behavioral Diculties (EBD schools). The mean age was 13.0 years (SD=2.3). They all had Statements under the Education Act of 1993 as too problematic for mainstream education. All the children whose parents did not object for them to participate were investigated (N=71). 2.3. Procedure and measures 2.3.1. General procedure Each participant's vocabulary was tested using the British Picture Vocabulary Scale (BPVS; Dunn, Dunn, Whetton & Burley, 1997). The testing was carried out on an individual basis by the experimenter, in a quiet room allocated for the purpose by the school. The BPVS includes a standard format of verbal instruction and two practice items. Prior to testing the experimenter made sure that the participant understood the instructions and felt comfortable to go ahead with the testing. Subsequent to the administration of the BPVS to the child, the Psychopathy Screening Device (Frick & Hare, 2000), the DuPaul's ADHD rating scale (DuPaul, 1991), and the Conners' Abbreviated Symptoms Questionnaire (Conners, 1973) were ®lled in for that child by both that child's form teacher and another teacher, or in the case of boarding students, by their residential social worker. 2.4. British Picture Vocabulary Scale (BPVS) The BPVS was used to measure the participant's verbal intelligence quotient (IQ). The BPVS measures receptive vocabulary for standard English. Vocabulary has been considered to be the best single measure of academic achievement (Smith, Smith & Dobbs, 1991). Importantly, the BPVS is not dependent on the child's ability to read. The BPVS was carried out in order to determine whether there were signi®cant associations between the children's IQ/mental age and their level of behavioural problems as revealed by teacher's report. 2.5. Teacher questionnaire A teacher questionnaire based on three sources was administered. The components were: the Psychopathy Screening Device, (PSD, Frick & Hare, 2000), the ADHD rating scale (DuPaul, 1991) and the Abbreviated Symptoms Questionnaire (ASQ) (Conners, 1973).

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2.6. Psychopathy screening device The Psychopathy Screening Device (PSD; Frick & Hare, 2000) is a 20-item scale. Two teachers completed the PSD for each participating child; the main class teacher and the school's headteacher. In the case of the residential boys, their form teacher and their residential social worker completed the PSD. The PSD is designed to measure the characteristics of psychopathy in a way that is analogous to the Revised Psychopathy Checklist for adults (PCL-R; Hare, 1991). A study of the PSD revealed a similar two-factor structure to that identi®ed by analysis of the PCL-R (Frick et al., 1994). A rapidly burgeoning research literature attests to the validity of this measure; children with psychopathic tendencies identi®ed by the PSD, show similar cognitive pro®les to adult psychopathic individuals (e.g., Blair, 1999; Frick et al., 1994; O'Brien & Frick, 1996). For each of the 20 items on the Psychopathy Screening Device, the teachers could rate the participants with a score of between 0 and 2. 0 referred to the fact that the statement was `not true at all', 1 referred to the statement being `sometimes true', and 2 referred to statements that were `de®nitely true'. Five items were inversely scored prior to the totalling of each statement to obtain the ®nal PSD score. A ®nal score of up to 40 could be obtained. The participants' score for each item was the average assigned by the two teachers. Pearson's correlations of the ratings of the two teachers were 0.65 for total PSD score, 0.62 for the Callous/Unemotional factor and 0.51 for the Impulsiveness/Conduct Problems factor. 2.7. DuPaul's ADHD Rating Scale The ADHD rating scale (DuPaul, 1991) consists of 14 items. It is designed to measure the two components of ADHD: impulsivity coupled with hyperactivity and inattention coupled with hyperactivity. A study of the ADHD rating scale has indeed revealed a two factor structure (DuPaul, 1991). A growing research literature attests to the validity of this measure (e.g., Power et al., 1998; Danforth & DuPaul, 1996; Francis, 1993; DuPaul, 1991). Each item on the questionnaire can be rated on a scale from 0 to 3 for its applicability to the child (0=`not at all', 1=`just a little', 2=`pretty much', and 3=`very much'). A ®nal score of up to 42 can be obtained. The participant's score for each item was the average assigned by the two raters. Pearson's correlations of the ratings of the two teachers (or a teacher and a residential social worker) were 0.55 for total DuPaul score, 0.57 for Factor 1 (Impulsivity/Hyperactivity) and 0.56 for Factor 2 (Inattention/Hyperactivity). 2.8. The Conners Abbreviated Symptom Questionnaire The Conners Abbreviated Symptom Questionnaire (ASQ; Conners 1973) consists of 10 items. Each item is rated on a scale from 0 to 3 for its applicability to the child. A maximum score that can be obtained for this measure is 30. The ASQ is widely regarded as a measure of ADHD and has been frequently used in the empirical literature (e.g., Buitelaar, van der Gaag, Swaab-Barneveld & Kuiper, 1996; Zentall & Barack, 1979). The participants' score for each item was the average assigned by the two teachers. Pearson's correlations of the ratings of the two teachers were 0.38.

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3. Results A correlational analysis was used to observe the relationships between the children's age, IQ, mental age, teacher's ratings of the children's attentional and hyperactive diculties and psychopathic tendencies (see Table 1). This revealed signi®cant correlations between total ADHD score, whether measured by the DuPaul or Conners questionnaires, and total PSD score. Moreover, there were signi®cant correlations between both the Impulsive-Hyperactive and InattentiveHyperactive factors of the DuPaul measure and Factor 1 (Callous/Unemotional; C/U) and Factor 2 (Impulsive/Conduct Problems; I/CP) of the PSD. It should be noted also that there were highly signi®cant correlations between ratings on the DuPaul's ADHD rating scale, and its constituent factors, and scores on Conners' ASQ. Neither age nor IQ nor mental age was correlated with any of the PSD or ADHD scores. Because of the high inter-correlations between the constituent components of both the ADHD and PSD measures, we examined the inter-relationships between the constituent factors of the ADHD rating scale (D.Imp-hyper and D.Inatt-hyper) and the constituent factors of the PSD (C/UN and I/CP) using partial correlations. Following partialling out the impulsivity-hyperactive component of ADHD, the correlations between the inattentive component of ADHD and the C/UN and I/CP components of the PSD were no longer signi®cant (r=0.002 and r=0.025, n.s., respectively; see Table 2a). However, following partialling out the inattentive component of ADHD, the correlations between the impulsivity-hyperactive component of ADHD and the C/UN and I/CP factors of the PSD remained signi®cant (r=0.286, p<0.05 and 0.407, p<0.001 respectively; see Table 2b). These results suggest that the association between the ADHD and PSD measures is primarily mediated by the ADHD pathology associated with impulsiveness rather than that associated with inattention. Following partialling out the I/CP component of the PSD, the correlations between the C/UN component of the PSD and the impulsive and inattentive components of the ADHD rating scale were Table 1 A correlational analysis of subject characteristics and the components of ADHD and psychopathic tendenciesa Age BPVS Age BPVS Mental age PSD total PSD (C/UN) PSD (I/CP) DuPaul total D.Imp-hyper D.Inat-hyper a

0.453

Mental PSD age total 0.046 0.229

0.069 0.007 0.031

PSD (C/UN) 0.087 0.077 0.018 0.874

PSD (I/CP) 0.062 0.008 0.002 0.952 0.726

DuPaul total 0.098 0.053 0.164 0.715 0.555 0.706

D.Imp-hyper D.Inat-hyper Conners 0.116 0.032 0.129 0.728 0.570 0.729 0.967

0.051 0.101 0.170 0.673 0.513 0.661 0.975 0.904

0.080 0.152 0.027 0.624 0.458 0.635 0.909 0.889 0.884

BPVS: Verbal IQ test; PSD total: Score on the Psychopathy Screening Device; C/UN: callous/unemotional factor score; I/CP: impulsivity/conduct problems factor score; DuPaul total: Total score on the DuPaul ADHD rating scale; D.Imp-hyper: Impulsive-hyperactive subtype score on DuPaul ADHD rating scale; D.Inat-hyper: Inattentive-hyperactive subtype score on DuPaul ADHD rating scale, Conners Abbreviated Symptoms Questionnaire score. =sig at p<0.0001, two-tailed.

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Table 2 A partial correlational analysis of the components of ADHD and psychopathic tendenciesa (a) A partial correlational analysis of the Dupaul ADHD ratings and PSD (I/CP) factor controlling for PSD (C/UN) factor and mental age PSD (I/CP) D.Imp-hyper D.Inat-hyper PSD (I/CP) D.Imp-hyper

0.569 0.864

0.503

(b) A partial correlational analysis of the DuPaul ADHD ratings and PSD (C/UN) factors controlling for PSD (I/CP) factor and mental age PSD (C/UN) D.Imp-hyper D.Inat-hyper PSD (C/UN) D.Imp-hyper

0.099

0.074 0.814

(c) A partial correlational analysis of the PSD ratings and the D.Imp-hyper component of DuPaul's ADHD rating scale, controlling for D.Inat-hyper component and mental age PSD (C/UN) PSD (I/CP) D.Imp-hyper PSD (C/UN) PSD (I/CP)

0.579

0.286 0.407

(d) A partial correlational analysis of the PSD ratings and the D.Inat-hyper component of DuPaul's ADHD rating scale, controlling for D.Imp-hyper component and mental age PSD (C/UN) PSD (I/CP) D.Inat-hyper PSD (C/UN) PSD (I/CP)

0.528

0.002 0.025

a

C/UN: callous/unemotional factor score; I/CP: impulsive/conduct problem factor score; D. Imp-hyper: Impulsivehyperactive subtype score on DuPaul ADHD rating scale; D. Inat-hyper: Inattentive-hyperactive subtype score on DuPaul ADHD rating scale. =sig at p<0.05, two-tailed, =sig at p<0.001, two-tailed, =sig at p<0.0001, two-tailed.

no longer signi®cant (r=0.099 and r=0.074, n.s., respectively; see Table 2c). However, following partialling out the C/UN component of the PSD, the correlations between the I/CP component of the PSD and the impulsive and inattentive components of the ADHD rating scale remained signi®cant (r=0.569 and 0.503, p<0.0001, see Table 2d). These results suggest that the association between the ADHD and PSD measures is primarily mediated by the pathology linked to impulsiveness that is associated with both disorders. However, the association between these measures does not seem to be due to an association between ADHD and the a€ective interpersonal disturbance (the C/UN factor) linked to psychopathy. Following the correlational analyses presented above, we also conducted a categorical analysis to investigate prevalence rates for the disorders and the level of comorbidity within our study population. This revealed that 27/71 children reached criteria for a diagnosis of ADHD according

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to DuPaul's (1991) ADHD rating scale while 22/71 children scored high (25+) on the PSD. Out of the 33 children who reached criteria for either ADHD or psychopathic tendencies, 16 reached criteria for both disorders (i.e., there were 11 children who only met the criteria for ADHD and 6 children who only met the criteria for psychopathic tendencies). Two chi square analyses were attempted to identify whether there were signi®cantly larger numbers of individuals who were comorbid for both disorders than would be expected by chance. These revealed that the incidence of comorbidity compared to psychopathy alone was greater than would be expected by chance 2 (1df)=5.167, p<0.025. However, the incidence of comorbidity compared to ADHD alone was not signi®cantly greater than would be expected by chance 2 (1df)<1; n.s. 4. Discussion This present study is, as far as we are aware, the ®rst to investigate the relationship between the inattentive and impulsivity components of ADHD and psychopathic tendencies in children. This study revealed signi®cant inter-correlations between teacher's ratings of children's ADHD and psychopathic tendencies. In addition, there were signi®cant inter-correlations between teacher's ratings of the attentional and impulsivity components of ADHD and the Callous and Unemotional (C/UN) and Impulsive and Conduct Problems (I/CP) components of Psychopathy. Interestingly, partial correlations revealed that the intercorrelations between these four components were principally due to the association between the impulsivity impairment associated with ADHD and the antisocial behaviour (I/CP) component of psychopathy. Finally, a categorical analysis revealed a higher than would have been predicted by chance level of comorbidity of ADHD and psychopathic tendencies. The highly signi®cant inter-correlation between teacher's ratings of children's inattention and impulsivity and psychopathic tendencies was in line with previous work investigating the comorbidity of ADHD and Conduct Disorder (CD). This work has reported comorbidity rates for ADHD and CD of between 30 and 90% (e.g., Hinshaw, 1987; see also, Biederman et al., 1991; Mannuzza et al., 1989; Shapiro & Gar®nkel, 1986; Szatmari et al., 1989; Taylor et al., 1986; Werry et al., 1987). The DSM de®nition of CD is highly correlated with the I/CP component of psychopathy (Frick, 1995). While there were signi®cant intercorrelations between ADHD and psychopathic tendencies in the current study, the partial correlational analyses conducted on the components of ADHD and Psychopathy revealed that the relationship between these two disorders may be complex. They indicated that the association between ADHD and psychopathic tendencies was primarily due to the intercorrelation of the impulsivity component of ADHD and the I/CP component of psychopathy. It should be noted that this intercorrelation is not simply due to an overlap of items for the two components. These items are listed in Table 3. While both components make reference to engaging in risky activities all the other items are somewhat di€erent. The ®nding of an intercorrelation of the impulsivity component of ADHD and the I/CP component of psychopathy is interesting because it is both in line with, and extends, previous research. Thus, for example, Babinski et al. (1999) found that both early conduct problems and hyperactivity-impulsivity were signi®cant predictors of later criminal involvement, both alone and in combination. However, the symptoms of inattention did not seem to contribute to the risk for

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Table 3 Comparison of impulsivity items in DuPaul's ADHD rating scale and psychopathy screening device Imp/Ha DuPaul

I/CP PSD

Often ®dgets or squirms in seat Has diculty remaining seated Has diculty waiting for turn in groups Often blurts out answers to questions Has diculty playing quietly Often talks excessively Often interrupts or intrudes on others Often engages in physically dangerous activities without considering consequences

Brags about accomplishments Becomes angry when corrected Thinks he/she is more important than others Acts without thinking Blames others for mistakes Teases other people Does not keep same friends Engages in risky or dangerous activities Gets bored easily

criminal involvement. The current study complements this work by indicating that the impulsivity component of ADHD was associated with the I/CP component of psychopathy (i.e., the antisocial behavior component). In contrast, the inattentive component of ADHD, independent of its association with the impulsivity component of ADHD, was not associated with the I/CP component of PSD. Moreover, the current study extends the preceding work by indicating that the a€ective C/UN component of psychopathy was not associated with the components of ADHD independently of their association with the I/CP component of Psychopathy. The ®ndings of the partial correlations support previous suggestions that there are multiple developmental routes to the display of antisocial behaviour (e.g., Blair & Frith, 2000; Frick, 1995); see Fig. 1. They do not suggest that there is a common pathological basis to the two disorders or even to the impulsivity component of ADHD and the I/CP component of psychopathy. Rather they are consistent with the suggestion that one developmental route, perhaps associated with executive dysfunction (cf. Mott, 1993), involves a syndrome of impulsivity that is a risk factor for both ADHD and antisocial behavior (Route 1 in Fig. 1). A second route would involve disturbance to the neural systems that mediate empathy and fear (Blair, 1995; Frick, 1995; Route 2 in Fig. 1a). Such disturbance predisposes the individual to the callous and unemotional a€ective component of psychopathy and is also a risk factor for antisocial behaviour. In addition, it should be noted that these ®ndings augment those of Babinski et al. (1999), in suggesting that the pathology that underpins the inattention component of ADHD is not a risk factor for the display of antisocial behaviour and conduct problems. In the current study, 16/22 individuals who met criteria for psychopathic tendencies on the PSD (cut-o€ score=25; Blair, 1997), also met criteria for ADHD according to the DuPaul ADHD rating scale (1991). This is a signi®cantly higher comorbidity than would be expected by chance. Of course, given the selected nature of the present sample, this comorbidity could re¯ect a selection bias in the decision to send these particular children to Special Schools. But it is perhaps interesting to brie¯y consider a potential reason for the signi®cant comorbidity between ADHD and psychopathic tendencies and to place the above results in the context of recent anatomical ®ndings related to the pathologies of ADHD and psychopathy. It has been suggested that the impulsivity component of ADHD may be due to early dysfunction in a neural circuit that includes anterior cingulate (Swanson et al., 1998). In contrast, the inattention component of

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Fig. 1. A causal model of the potential relationship between ADHD and psychopathic tendencies.

ADHD has been attributed to dysfunction to a neural circuit that includes right frontal cortex (Swanson et al., 1998). Psychopathy has been related to dysfunction within a neural circuit that includes either the amygdala, orbitofrontal cortex or both (e.g., Blair, Morris, Frith, Perret & Dolan, 1999; Blair & Frith, 2000; Damasio, 1994; Hare, 1998). Interestingly, anterior cingulate, amygdala and orbitofrontal cortex are all richly interconnected (e.g., Amaral, Price, Pitkanen & Carmichael, 1992; Rolls, 1996). It could be expected that dysfunction in any one of these neural systems might disrupt the development of the connecting systems (see Karmilo€-Smith, 1998). In addition, it should be noted that a particular polymorphism of the dopamine 4 receptor gene has been linked to the development of ADHD (Swanson, Sunohara, Kennedy et al., 1998). Both anterior cingulate and amygdala are particularly rich in dopamine 4 receptors (Seeman & Van Tol, 1994). Thus, both the evidence on the interconnections of anterior cingulate and amygdala and the rich presence of dopamine 4 receptors in both regions might be linked to the high levels of comorbidity of ADHD, potentially particularly the impulsive form of ADHD, and CD/psychopathy. Interestingly, the inattention component of ADHD is associated with right frontal cortex. Right frontal cortex is not directly connected to the amygdala. Moreover, right frontal cortex is also not particularly rich in dopamine 4 receptors. The lack of association between this component of ADHD and CD/psychopathy may be linked to this relative independence of pathology. Fig. 1 represents this tentative speculation. We want to note that as the population studied was highly selected, co-morbidity with other problems is also likely. For example, ADHD is highly comorbid with emotional disorders and pervasive developmental disorders (e.g., dyslexia; Boetsch, Green & Pennington, 1996). In addition, ADHD is often associated with reduced verbal and performance IQ (Taylor, 1994). We cannot address co-morbidity with other disorders with the data available. While the presence of dyslexia is unlikely to in¯uence the results and we controlled for mental age in the analyses, it is possible that co-morbidity with anxiety disorders may have a€ected the results. However, it should be

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noted that if this is the case, our observations of an association between the impulsivity components of ADHD and psychopathic tendencies are an underestimate of the situation outside of the special school setting. The presence of anxiety should be inversely related to psychopathic tendencies (Hare, 1991). In conclusion, the present paper examined the relationship between the attentional and impulsivity impairments associated with ADHD and the C/UN and I/CP components of psychopathy in children with Emotional and Behavioural Diculties. In line with previous work showing substantial comorbidity between ADHD and Conduct Disorder (e.g., Hinshaw, 1987), the current study showed that an individual child's level of impulsivity diculties was a signi®cant predictor of the conduct problem component of psychopathy. In line with suggestions that there are multiple developmental routes to conduct problems (e.g., Frick, 1995), the conduct problem component of psychopathy appeared to be independently related to both the impulsivity component of ADHD as well as the callous/ empathic component of psychopathy. Acknowledgements This work was supported by a Medical Research Council grant [ref. G9716841] and the Department of Health [Virtual Institute for Personality Disorders]. We thank the sta€ and pupils at Boxmoor House, Falconer, and Larwood schools. References Amaral, D. G., Price, J. L., Pitkanen, A., & Carmichael, S. T. (1992). Anatomical organization of the Primate Amygdaloid Complex. In J. P. Aggleton, The Amygdala. Neurobiological aspects of emotion, memory, and mental dysfunction (pp. 1±66). New York: Wiley-Liss, Inc. American Psychiatric Association (1994). Diagnostic and statistical manual of mental disorders. Washington, DC: American Psychiatric Association. August, G. J., Braswell, L., & Thuras, P. (1998). Diagnostic stability of ADHD in a community sample of school-aged children screened for disruptive behaviour. Journal of Abnormal Child Psychology, 26, 345±356. Babinski, L. M., Hartsough, C. S., & Lambert, N. M. (1999). Childhood conduct problems, hyperactivity-impulsivity, and inattention as predictors of adult criminal activity. Journal of Child Psychology, Psychiatry and Allied Disciplines, 40, 347±355. Biederman, J., Newcorn, J., & Sprich, S. (1991). Comorbidity of attention de®cit hyperactivity disorder with conduct, depressive, anxiety, and other disorders. American Journal of Psychiatry, 148, 564±577. Blair, R. J. R. (1995). A cognitive developmental approach to morality: Investigating the psychopath. Cognition, 57, 1±29. Blair, R. J. R. (1997). Moral reasoning and the child with psychopathic tendencies. Personality and Individual Di€erences, 22, 731±739. Blair, R. J. R. (1999). Responsiveness to distress cues in children with psychopathic tendencies. Personality and Individual Di€erences, 27, 135±145. Blair, R. J. R., & Cipolotti, L. (2000). Impaired social response reversal: A case of ``acquired sociopathy''. Brain (in press). Blair, R. J. R., & Frith, U. (2000). Neuro-cognitive explanations of the antisocial personality disorders. Criminal Behaviour and Mental Health (in press). Blair, R. J. R., Morris, J. S., Frith, C. D., Perret, D. I., & Dolan, R. J. (1999). Dissociable neural responses to facial expressions of sadness and anger. Brain, 122, 883±893. Boetsch, E. A., Green, P. A., & Pennington, B. F. (1996). Psychosocial correlates of dyslexia across the life span. Development and Psychopathology, 8, 539±562.

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