Psychobiological Approach Understanding Human Behaviour

Introduction
This paper examines the psychobiological approach pertaining to conduct disorder (CD) of human behaviour, with particular emphasis on how such information can increase our understanding of youths representing the under socialized aggressive subtype of CD. Although much of the information is preliminary and fraught with methodological shortcomings, literature from the neuro anatomical, biochemical, psycho physiological and pharmacological arenas is reviewed. The theoretical framework offered by Gray, Quay's application of this model to CD, and the empirical strategies used to evaluate assumptions of bio-behavioural systems are outlined.
The utility of considering psycho biologically based behavioural propensities when developing a treatment plan is discussed. A growing body of research has provided conceptual advances in our understanding of the relationship between clinical diagnostic categories or behavioural dimensions and various indices of psychobiological functioning. Included in this focus on the biological underpinnings of deviations in behavioural propensities is the under socialized aggressive subtype of conduct disorder (UACD). This paper will outline the biological correlates of this syndrome in which instrumental Cosmides and J. Tooby, 2000, 25-147) no defensive or proactive) aggression plays a major role, focusing on the evidence available from the biochemical, psycho physiological, neuro anatomical, and neuro behavioural study.
Support for the presence of the under socialized aggressive syndrome comes from the consistency with which it has been isolated in multivariate studies over the past several decades (Quay, 1986, 63-98). Characteristics of UACD include serious and persistent physical aggression, deception, violation of property rights and societal norms, disturbed interpersonal relationships, and school adjustment problems (Kazdin, 1987a; Quay, 1986). The DSM III-R (American Psychiatric Association, 1987) solitary type is roughly akin to the empirically derived UACD, although the former lacks somewhat in operational criteria used to describe its distinctiveness from other DSM III-R subtypes (e.g., group and undifferentiated). Researchers continue to debate the utility of investigating individual differences in aggressive versus dichotomous diagnostic categories (Plomin, Nitz, & Rowe, 1990).
In addition, narrowly defined areas of behaviour (narrow-band syndromes) may provide a better basis for detecting specific etiologist and prescribing specific treatments compared to focusing on the global distinction between broad-band under controlled and over controlled behaviour (Darwin, 1872, 36-199).
Although an assumption that biological differences could underlie differences in behaviour may suggest a view of biological determinism, in no way should the evidence be construed as such. Behaviour genetic researchers have asserted and provided evidence that psychopathology is both polygenic and "poly environmental" (Ekman, 1994, 268-87)
Anything short of adopting the concept of genotype-environment interaction and correlation likely disregards the complexity of the task at hand. Patterson's (1982) work reflects the genotype-environment interaction orientation, in that environmental factors (permissive or excessively punitive parents) may have different effects on individuals of different genotypes (aggressive children). Patterson's work also implicates a causal relationship between parental behaviours and subsequent child aggression. The genotype-environment correlation represents the notion that children with a genetic predisposition toward aggressiveness may seek out situations that reinforce this behaviour.In this context, empirical evidence appears to support a bio psycho social model of investigation and explanation.

Psychobiology of Conduct Human Behaviour Disorder
The current body on the biological basis of CD includes perspectives representing neuro anatomy, neurochemistry, psychophysiology, pharmacology, and behavioural paradigms that may reflect systems of neuropsychological functioning. Much of the evidence is preliminary, and should not be viewed as offering firm conclusions. Instead, it has provided a framework in which to pursue more methodologically refined investigations. A review of this literature is offered to increase the awareness of the biological perspective and to stimulate further research (Darwin, 1872, 36-199).
The neuro anatomical perspective attempts to delineate the location of the brain areas which are part of the systems involved in behaviours associated with CD. The neuro chemical approach focuses on the role of neurotransmitters that play a functional role in the neuronal circuitry underlying CD. Psycho physiological measures provide an index of autonomic nervous system functioning, which is responsible for the control of involuntary bodily functions. Pharmacological studies may provide additional information on the underlying biological systems involved in CD and their responsively to modification. Behavioural studies which document an individual's cognitive, learning, motivational, and attention style e.g., in the context of response characteristics under certain experimental paradigms which may reflect response "styles" to environmental situations) may provide insight into the functioning of certain biological subsystems (Izard, 1992, 561-565).

Biochemical Studies
Neurotransmitters and neuro hormones have long been implicated in the regulation of several behavioural systems that in turn regulate the interaction of the organism with its external environment. Although many more neurotransmitters are known to exist, nore pinephrine (NE) and serotonin (5HT) have been implicated most often in the CD literature. Neuro hormones such as cortisol and testosterone also have been implicated in aggressive behaviour. Details of neuro chemical functioning in the context of various psychobiological models of personality and psychopathological disorders in children are provided by McBurnett (1992, 63).
Neurotransmitters (NTs) play a key role in transmitting information across cells, and can be classified as either excitatory (causing nerve cells to "fire") or inhibitory (reducing the responsively of nerve cells to incoming stimulation). The activity of a NT itself is regulated in many ways, and although the location of the cell bodies for NT systems has been identified, the axons from the cell bodies project across and throughout the brain. Furthermore, a neuron using one NT connects with neurons using other NTs, resulting in a direct interaction among the noradrenergic, dopaminergic, and serotonergic systems. The balance among the three systems likely plays an important role in how behaviour is regulated and expressed (Lazarus, 1991, 819-834). It is important to note that existing technology does not allow for a direct measure of NT activity. Body fluids (LeDoux, 1995, 45-189) cerebrospinal fluid or CSF, blood plasma, urine), enzymes (Schachter and Singer, 1962, 379-399) chemical substances that can induce changes in NTs without being changed themselves), platelets, drug probes which stimulate receptors for certain NTs, and brain imaging techniques all provide an indirect measure of NTs and their metabolites. Each technique poses particular challenges, advantages, and drawbacks.

Psycho physiological Studies
Involuntary bodily functions are under the regulation of the autonomic nervous system (ANS), which is divided into the sympathetic and parasympathetic system. Stimulation of the sympathetic portion typically produces, among other things, a rise in blood pressure, acceleration of the heart, and changes in the electrical conductance of the skin. These peripheral indices of sympathetic nervous system activity are usually measured at rest and in response to stimuli with varying evocative properties.
With regard to heart rate, several studies have found that youths with CD exhibit lower resting levels compared to controls and subjects without CD. Prospective longitudinal studies also have found that low heart rate was predictive of later aggressive criminal behaviour and criminal convictions (Scherer, 2003, 563-571).
Several studies have found lower responsively to stimuli as measured by skin conductance changes in variously defined youths with CD compared to controls, although measures of resting levels have yielded less consistent results. Garralda, Connell, and Taylor (1991, 14-29) found that children with CD showed increased reactivity, relative to emotional disorder and control group, when they were instructed to imagine pleasant situations. They also showed decreased responding to neutral but high intensity stimulation and to withdrawal of stimulation in silence periods.
Studies measuring electrical brain activity in response to stimulus events (event-related potentials, or ERPs) have suggested that certain components of the typical wave pattern may differ in children with conduct problems. These components are expressed in direction, amplitude, and latency of the electrical response following the stimulus event. Research comparing adolescents with and without CD have shown the former to exhibit higher P300 amplitudes to warning signals (Zajonc, 1985, 15-21) and a longer latency of N2 evoked peaks (Zajonc, 1985, 15-21). Components of the ERP may be predictive of adult criminality (Scherer, 2003, 563-571) although developmental factors still need to be considered.
Most of the above evidence suggests that anomalies in the modulation of biological arousal mechanisms may play a role in the expression of childhood psychopathology (Garralda et al., 1991). Further research with children representing various developmental levels and behavioural and emotional disorders is clearly needed to specify this relationship.

Behavioural Studies
The empirical literature reviewed so far, although not without its methodological limitations, suggests there may be a correspondence between aggressive behaviour characterizing the youth with CD and various neurophysiologic indices. Such a model would be strengthened by convergent evidence for these individuals exhibiting differences in learning and performance patterns that relate back to underlying biological systems. Theoretical and empirical work presented by Gray (1982, 1987) have been very influential in developing a line of research exploring the relationship between emotions, behaviour and performance within the context of instrumental learning paradigms. Since space prohibits a detailed description of Gray's model, the reader is referred to a well-articulated review by McBurnett (1992).
Stemming from a series of experimental findings, Gray has proposed a modification in Eysenck's (1967) personality theory. Gray (1987) has emphasized the utility of viewing personality dimensions in terms of individual differences in conditionality and sensitivity to punishment versus reward. This has led to the proposal that behaviour is regulated primarily by two different but interacting conceptual brain systems: the behavioural inhibition system (BIS) and the behavioural activation (or reward) system (BAS).
The BIS is excited by signals of impending punishment, signals recently associated with the failure of a formerly expected reward to appear (Cannon, 1927, 10-124)
frustrative non reward), or arousing novel stimuli. Functionally, the BIS responds with outputs that inhibit ongoing behaviour, but also increases arousal, attention, and information processing of the stimuli. The resulting emotion is anxiety and frustration. Presumably, an individual with chronically hyper reactive BIS, relative to the BAS, would exhibit symptoms of anxiety, whereas an individual with a relative hypo reactive BIS would be predicted to show a marked lack of anticipatory anxiety and deficiencies in passive avoidance learning (Cosmides and J. Tooby, 2000, 25-147) i.e., reinforcement contingent upon not responding). In support of this notion, Hare (1970, 1978) has documented deficiencies in passive avoidance among "primary psychopaths" or individuals considered to exhibit antisocial personality disorder under the current diagnostic schema. Cleckley (1976) characterized these individuals as showing a marked incapacity for anxiety. Gray suggests that the anatomical locus of the BIS is in the septo-hippocampal system with neural circuits through the noradrenergic fibres of the locus coeruleus and the serotonergic fibres of the rapine nucleus.
Interacting with the BIS, the BAS mediates the learning and performance of active responses to either gain a reward (approach) or avoid an impending punishment (escape or active avoidance). Dopamine is considered to play a significant role, and the core anatomical components are suggested to be the medial forebrain bundle, lateral hypothalamus, and lateral septum.
Gray proposes, therefore, that individual differences in personality are jointly determined by the sensitivities of the two above systems. Shaping an individual's behaviour may be predicted by the conditions of reinforcement to which they are most sensitive, based on the relative functioning of the BIS and BAS. That is, will available reward or signals of punishment have a dominant influence over one's behaviour? A more prescriptive approach to treatment planning may evolve out of knowledge regarding the relative sensitivities of these two bio behavioural systems. A decision to reward non prohibited behaviour or punish prohibited behaviour may rest largely upon what is known about an individual's psycho biologically based behavioural propensities (Quay, 1987, 66-174).
A series of empirical studies have investigated Gray's framework in the context of psychopathological disorders in children and adolescents. Based on Gray's work, Quay (1988a, 1988b, 1988c) proposed that CD involves a persistently overactive reward system (BAS) that predominates over the BIS. That is, these children exhibit persistent reward-dominant behaviour. Quay also has proposed that an underactive BIS characterizes children with attention deficits, whereas the BIS would predominate over the BAS in anxious-withdrawn children. Thus, rather than working in tandem, one system may predominate across situations, resulting in less behavioural flexibility, so to speak.
Newman and his colleagues have focused on a model of "dis inhibitory" psychopathology, suggesting that under conditions that pit the probability of reward against the probability of punishment, psychopaths and extraverts show a greater tendency to respond to cues of reward (Newman, Patterson & Kosson, 1987, 145-149).
A computerized card-playing task was used consisting of 100 trials (cards) in which subjects chose either to see the next card or to stop playing. In the preprogrammed sequence, the probability of the next card being a winning card dropped from 90% to 0% per 10-card block. Money was immediately given or taken away from subjects depending upon whether the card "uncovered" was designated a "winner" or "loser." The dependent measure on this task was number of cards played. Preservative responding results in fewer earnings, due to the fact that the probability of winning decreases as the game is played.
The delay task operationally a differential reinforcement for low-rate responding (DRL) paradigm. Purported to examine disinhibition, the delay task provides dependent measures of the efficiency with which subjects respond to the delay requirements. Results provided strong support for the notion that children with CD are overly sensitive to reward and fail to inhibit responding in mixed incentive conditions. As a group, subjects with CD played more cards and lost more money than the group without CD. These differences emerged even after co varying for RBPC ratings of attention problems. Mixed results were obtained on the delay task, although subjects with CD were significantly less efficient during the last segment of the task (LeDoux, 1995, 45-189).
Results offered by Daugherty and Quay (1991) provide additional support for the hypothesis of preservative responding for reward in conduct disorder. In this study, public school children in Grades 3 through 6 were screened using the RBPC. Four groups were identified, as defined by scores on the relevant scale CD, ADD, CD/ADDH, AW (anxious-withdrawn), and a normal control group. Tasks included a modified version of the card-playing task deemed more appropriate for younger children (Cosmides and J. Tooby, 2000, 25-147) referred to as the door-opening task), and the Gordon delay task. Consistent with Quay's hypothesis, subjects with a CD or CD/ADDH behaviour pattern (Cosmides and J. Tooby, 2000, 25-147) although not necessarily considered clinically significant) responded preservative for reward to a maladaptive degree (Scherer, 2003, 563-571) i.e., they lost rewards already won). The anxious-withdrawn subjects, as a group, chose to stop the task prior to the optimal interval; that is, they stopped too soon and did not receive as much money as they could have. No group differences were found on the delay task.
Daugherty, Quay, and Ramos (1991) found a similarly strong tendency for the group with CD to respond preservative on the door opening task, although group differences among subjects classified as RBPC-defined CD/ADDH, ADD, AW, and normal controls did not emerge. A unique feature of this study was the measurement of spontaneous eye-blinks during a 5-minute interview. Karson (1983) has suggested that eye-blink rate is a behavioural measure of central dopaminergic activity, and thus may provide a "window" into BAS activity. Although no group differences were found, eye-blinks were marginally related to CD subscale scores on the RBPC.
Kalantari, Yule, and Gardner (1990) have extended the findings of preservative responding to a small sample of preschool children in Iran. All 6 children rated by their teachers as having persistent behaviour problems played significantly more cards than the 6 children in the normal control group. In fact, all behaviour-disordered children played all cards and therefore lost all candy rewards, compared to only 2 normal control children.
Passive avoidance deficits have been documented among disinhibited individuals, in that they are deficient in learning to inhibit goal-directed behaviour in the presence of cues of reward. Scerbo et al. (1990) applied this paradigm to juvenile delinquents classified as psychopaths (CD) or non psycho paths. Specifically, subjects were instructed to respond to items designated as positive discriminative stimuli and to withhold responding to negative stimuli. Responses to negative items were considered passive avoidance (or commission) errors and resulted in loss of rewards. Failure to respond to positive stimuli were considered omission errors, but produced no consequences, as did withholding responses to negative stimuli.
The paradigm used by Scerbo et al. (1990) did not include a reward-only or punishment-only condition. The psychopathic or CD group made significantly more responses to the positive stimuli (Borod, 2000, 63-128) fewer errors of omission) than the non psychopathic group. The two groups did not differ on the number of incorrect responses to negative stimuli (commissions). Results were interpreted in the context of hyper responsively to rewards under conditions of mixed incentives in psychopathic-like adolescents.
Studies investigating the effects of coexisting psychiatric disorders have shed light on Gray's (1987) two-factor model, that antisocial behaviour is the product of both excessive reward-seeking behaviour and insufficient inhibition. Walker et al. (1991) formed four groups of clinic-referred boys with and without conduct disorder and anxiety disorder. As predicted by Gray's model, boys with CD and comorbid anxiety exhibited less social impairments (fewer school suspensions, fewer police contacts, fewer "fight most" and "meanest" peer nominations) than boys with CD alone. Additional research with these comorbid populations using similar paradigms described in previous sections of this paper would be very fruitful.

Conclusions
School personnel are frequently among the first individuals to face the challenges posed by students exhibiting chronic and severe conduct problems, of which aggression is among the most salient and disruptive symptom. Educators, counsellors, and school psychologists, in conjunction with parents and other health professionals, are often faced with decisions regarding how best to manage children and adolescents with CD in the school setting. A likely role of the school psychologist is to formally evaluate students referred for disruptive behaviours and to recommend/develop intervention strategies. Given the complexity of the problems associated with CD, it would seem prudent for the school psychologist to be aware of information pertaining to biological correlates of CD, so that a well-integrated intervention plan could be developed. Knowledge of the biological basis of CD also may assist in the development of treatment plans more consistent with what is known about how youths with CD respond to their environment.
Patterns of behaviour are mediated by various neuro physiological mechanisms, regardless of the psychosocial origin of those patterns. This in no way minimizes the importance of interventions focusing on psychosocial factors, since they are integrally related to each other. However, it emphasizes the need to consider the body of literature pertaining to neuro anatomical, neuro chemical, psycho physiological, pharmacological, and neuro behavioural research as it relates to the symptoms and syndrome of CD. For example, how might an individual's and attention style is determined by neuro physiological processes? How might certain response styles in a controlled laboratory setting provide some insight into the functioning of certain biological systems? How might the above information be used to develop an intervention program specific to an individual's neuro physiological or neuro behavioural profile?
Considerable interest in these and related questions is reflected in a growing body of literature that has accumulated over the past decade. Methodological issues will need to be addressed by researchers investigating the etiology and maintenance of CD. Specific issues, among others, include how antisocial behaviour is defined (e.g., specific behaviours, narrow-band versus broad-band, subtypes, etc.); the effect of coexisting disorders (e.g., ADHD, anxiety, etc.) on an individual's functioning; the need to control for cognitive and demographic characteristics; the delineation of factors that may be consequences of behaviour problems rather than causes of them; and the indirect or peripheral measures of neuro physiological indices. In light of the limitations represented in the literature, no firm conclusions can be drawn about the psychobiology of CD.
Even if firm conclusions could be drawn, a biologically deterministic view-point should be vigorously discouraged. Delineation of biological markers of CD is likely to have extreme social implications and lead to many potential abuses of such information by those with sociopolitical agendas. Markers of CD should not be equated to markers for criminal behaviour, since most crime is not committed by individuals with CD or a history of CD (Damasio, 1994, 1102-5) Furthermore assert that "Identifying an individual as having high biological risk for antisocial conduct should never involve deprivation of opportunities or rights, but should involve enhancement of the opportunities to become successful, prosocial, and fully franchised members of society" (Scherer, 2003, 563-571).
With the above caveats in mind, the present literature has suggested many psychobiological characteristics of children and adolescents with CD. Measures of frontal-lobe functions have occasionally differentiated between youths with and without CD. Youths with CD have shown reduced ear asymmetry on a dichotic listening task, possibly suggesting a reduced role of language in mediating and regulating behaviour which may reflect left hemispheric functioning. Neurochemical studies, although frequently relying on peripheral measures, have strongly implicated the association between serotonergic and noradrenergic system functioning and aggressive/antisocial behaviour. The neuro hormones cortisol and testosterone also have been linked to CD. Several studies regarding sympathetic nervous system functioning have found that youths with CD, compared to youths without CD, exhibit lower heart rate levels, different patterns of stimulus responsively as measured by skin conductance, and different patterns of electrical brain activity in response to stimulus events.
Pharmacological studies have implicated potential drug therapies for youths with CD, although the lack of controlled studies and the nonspecific nature of the drug activity make interpretation difficult. Stemming largely from Gray's conceptual model of the nervous system and Quay's application of this model to child psychopathology, a body of literature has identified differences in conditionality and sensitivity to punishment and reward among youths with CD. Such differences based on the interaction between what is referred to as the behavioural inhibition and activation systems? Clearly suggest hypersensitivity of the youth with CD to reward and failure to inhibit responding in mixed incentive conditions i.e., cues for reward and punishment). Preliminary research using different groups co morbid for CD and anxiety have supported the notion that antisocial behaviour is the product of both excessive reward-seeking behaviour and insufficient inhibition. This behavioural line of research which focuses on instrumental learning characteristics and converges with neurophysiologic indices has clear treatment implications applicable to school settings. Shaping an individual's behaviour may be predicted by the conditions of reinforcement to which they are most sensitive, based on the relative functioning of two interacting bio behavioural systems and the behavioural propensities these systems modulate.

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