Aggression, psychopathy and free will from a cognitive neuroscience perspective

This article considers the notion of free will in the context of aggression and psychopathy research. The philosophical literature is very briefly considered to determine under what assumptions free will can be considered to exist. However, as the issue of free will is very difficult to address directly, the prime focus of this article is on issues raised in the philosophical debate, that may be empirically tractable and that are relevant to the understanding of psychopathy. Specifically, the following issues are considered: (1) The distinction between automatic and controlled processing; (2) Impairment related to automatic processing in individuals with psychopathy; and (3) Impairment related to controlled behavior in individuals with psychopathy. It is concluded that, while there is not a direct mapping of the automatic versus controlled processing dichotomy on to the reactive versus instrumental aggression dichotomy, some overlap can be considered. As such, it is possible to consider that certain episodes of reactive aggression might be considered to occur in the absence of free will. However, instrumental aggression, at least from a compatibilist perspective, must involve free will.

The impact of processing load on emotion

This event-related fMRI study examined the impact of processing load on the BOLD response to emotional expressions. Participants were presented with composite stimuli consisting of neutral and fearful faces upon which semi-transparent words were superimposed. This manipulation held stimulus-driven features constant across multiple levels of processing load. Participants made either (1) gender discriminations based on the face; (2) case judgments based on the words; or (3) syllable number judgments based on the words. A significant main effect for processing load was revealed in prefrontal cortex, parietal cortex, visual processing areas, and amygdala. Critically, enhanced activity in the amygdala and medial prefrontal cortex seen during gender discriminations was significantly reduced during the linguistic task conditions. A connectivity analysis conducted to investigate theories of cognitive modulation of emotion showed that activity in dorsolateral prefrontal cortex was inversely related to activity in the ventromedial prefrontal cortex. Together, the data suggest that the processing of task-irrelevant emotional information, like neutral information, is subject to the effects of processing load and is under top-down control.

Heightened sensitivity to facial expressions of emotion in borderline personality disorder

Individuals with borderline personality disorder (BPD) have been hypothesized to exhibit significant problems associated with emotional sensitivity. The current study examined emotional sensitivity (i.e., low threshold for recognition of emotional stimuli) in BPD by comparing 20 individuals with BPD and 20 normal controls on their accuracy in identifying emotional expressions. Results demonstrated that, as facial expressions morphed from neutral to maximum intensity, participants with BPD correctly identified facial affect at an earlier stage than did healthy controls. Participants with BPD were more sensitive than healthy controls in identifying emotional expressions in general, regardless of valence. These findings could not be explained by participants with BPD responding faster with more errors. Overall, results appear to support the contention that heightened emotional sensitivity may be a core feature of BPD.

Impaired recognition of fear facial expressions in 5-HTTLPR S-polymorphism carriers following tryptophan depletion

RATIONALE

Genotype at the 5' promoter region (5-HTTLPR) of the serotonin transporter has been implicated in moderating the effects of acute tryptophan depletion on neurocognitive functioning. Acute tryptophan depletion has been associated with the processing of fear-relevant cues, such as emotional expressions, but the effect of genotype at the 5-HTTLPR has not been assessed.

OBJECTIVE

The present study investigated the effects of acute tryptophan depletion on the recognition of standardized facial expressions of emotions in healthy volunteers classified as ll homozygotes or s carriers.

MATERIALS AND METHODS

A double-blind between-groups design was used with volunteers randomly selected to ingest capsules containing an amino acid mixture specifically lacking tryptophan, or placebo capsules containing lactose. 5 h after capsule ingestion, subjects were required to identify anger, disgust, fear, happiness, sadness, and surprise expressions that progressed from neutral to each full emotional expression in 5% steps.

RESULTS

Tryptophan depletion significantly impaired the recognition of fearful facial expressions in s carriers but not ll homozygotes. This impairment was specific to fear expressions. No significant differences in the recognition of other expressions were found. Free tryptophan levels were correlated with fear recognition in s carriers but not ll homozygotes.

CONCLUSIONS

The effects of acute tryptophan depletion on the processing of emotional expressions varies as a function of genotype at the 5-HTTLPR. Depletion impairs the recognition of fear in s carriers but not ll homozygotes. This finding reinforces the importance of considering genotype when assessing the behavioral effects of pharmacologic modulation.

Heightened sensitivity to facial expressions of emotion in borderline personality disorder

Individuals with borderline personality disorder (BPD) have been hypothesized to exhibit significant problems associated with emotional sensitivity. The current study examined emotional sensitivity (i.e., low threshold for recognition of emotional stimuli) in BPD by comparing 20 individuals with BPD and 20 normal controls on their accuracy in identifying emotional expressions. Results demonstrated that, as facial expressions morphed from neutral to maximum intensity, participants with BPD correctly identified facial affect at an earlier stage than did healthy controls. Participants with BPD were more sensitive than healthy controls in identifying emotional expressions in general, regardless of valence. These findings could not be explained by participants with BPD responding faster with more errors. Overall, results appear to support the contention that heightened emotional sensitivity may be a core feature of BPD.

They know the words, but not the music: Affective and semantic priming in individuals with psychopathy

Previous work has indicated dysfunctional affect-language interactions in individuals with psychopathy through use of the lexical decision task. However, it has been uncertain as to whether these deficits actually reflect impaired affect-language interactions or a more fundamental deficit in general semantic processing. In this study, we examined affective priming and semantic priming (dependent measures were reaction times and error rates) in individuals with psychopathy and comparison individuals, classified according to the psychopathy checklist revised (PCL-R) [Hare, R.D., 1991. The Hare Psychopathy Checklist-Revised. Multi-Health Systems, Toronto, Ont] Individuals with psychopathy showed significantly less affective priming relative to comparison individuals. In contrast, the two groups showed comparable levels of semantic priming. The results are discussed with reference to current models of psychopathy.

Differentiating among prefrontal substrates in psychopathy: neuropsychological test findings

Frontal lobe and consequent executive dysfunction have long been related to psychopathy. More recently, there have been suggestions that specific regions of frontal cortex, rather than all of frontal cortex, may be implicated in psychopathy. To examine this issue, the authors presented 25 individuals with psychopathy and 30 comparison individuals with measures preferentially indexing the orbitofrontal cortex (OFC; object alternation task), dorsolateral prefrontal cortex (DLPFC; spatial alternation task), and anterior cingulate cortex (ACC; number-Stroop reading and counting tasks). The individuals with psychopathy showed significant impairment on the measure preferentially sensitive to OFC functioning. In contrast, the 2 groups did not show impairment on the measures preferentially sensitive to the functioning of the DLPFC or ACC. These results are interpreted with reference to executive dysfunction accounts of the disorder.

Divergent patterns of aggressive and neurocognitive characteristics in acquired versus developmental psychopathy

An analogy is often drawn between patients with personality changes following orbitofrontal cortex lesions and individuals with developmental psychopathy. We present patient CL, who had acquired psychopathy following an orbitofrontal cortex lesion. Unlike previous studies, CL was assessed on a valid and reliable measure of psychopathy and was compared with controls and patients with developmental psychopathy on measures of instrumental (re)learning, extinction, emotional processing, and social cognition. The results provide further support for the notion that acquired and developmental forms of psychopathy are associated with dissociable neurocognitive deficits that leave each at different levels of risk for reactive and instrumental aggression.

Applying a cognitive neuroscience perspective to the disorder of psychopathy

Four models of psychopathy (frontal lobe dysfunction, response set modulation, fear dysfunction, and violence inhibition mechanism hypotheses) are reviewed from the perspective of cognitive neuroscience. Each model is considered both with respect to the psychopathy data and, more importantly, for the present purposes, with respect to the broader cognitive neuroscience fields to which the model refers (e.g., models of attention with respect to the response set modulation account and models of emotion with respect to the fear dysfunction and violence inhibition mechanism models). The paper concludes with an articulation of the more recent integrated emotion systems model, an account inspired both by recent findings in affective cognitive neuroscience as well as in the study of psychopathy. Some directions for future work are considered.

Instrumental learning and relearning in individuals with psychopathy and in patients with lesions involving the amygdala or orbitofrontal cortex

Previous work has shown that individuals with psychopathy are impaired on some forms of associative learning, particularly stimulus-reinforcement learning (Blair et al., 2004; Newman & Kosson, 1986). Animal work suggests that the acquisition of stimulus-reinforcement associations requires the amygdala (Baxter & Murray, 2002). Individuals with psychopathy also show impoverished reversal learning (Mitchell, Colledge, Leonard, & Blair, 2002). Reversal learning is supported by the ventrolateral and orbitofrontal cortex (Rolls, 2004). In this paper we present experiments investigating stimulus-reinforcement learning and relearning in patients with lesions of the orbitofrontal cortex or amygdala, and individuals with developmental psychopathy without known trauma. The results are interpreted with reference to current neurocognitive models of stimulus-reinforcement learning, relearning, and developmental psychopathy.

The development of psychopathy

The current review focuses on the construct of psychopathy, conceptualized as a clinical entity that is fundamentally distinct from a heterogeneous collection of syndromes encompassed by the term 'conduct disorder'. We will provide an account of the development of psychopathy at multiple levels: ultimate causal (the genetic or social primary cause), molecular, neural, cognitive and behavioral. The following main claims will be made: (1) that there is a stronger genetic as opposed to social ultimate cause to this disorder. The types of social causes proposed (e.g., childhood sexual/physical abuse) should elevate emotional responsiveness, not lead to the specific form of reduced responsiveness seen in psychopathy; (2) The genetic influence leads to the emotional dysfunction that is the core of psychopathy; (3) The genetic influence at the molecular level remains unknown. However, it appears to impact the functional integrity of the amygdala and orbital/ventrolateral frontal cortex (and possibly additional systems); (4) Disruption within these two neural systems leads to impairment in the ability to form stimulus-reinforcement associations and to alter stimulus-response associations as a function of contingency change. These impairments disrupt the impact of standard socialization techniques and increase the risk for frustration-induced reactive aggression respectively.

The role of the amygdala and rostral anterior cingulate in encoding expected outcomes during learning

Successful passive avoidance learning is thought to require the use of learned stimulus-reinforcement associations to guide decision making [Baxter, M.G., Murray, E.A., 2002. The amygdala and reward. Nature Reviews. Neuroscience 3, 563-573]. The current experiment investigated the neural correlates of successful passive avoidance learning in 19 healthy adults. Behaviorally, subjects showed a distinct pattern of performance: early indiscriminate responding to stimuli (pre-criterion performance), followed by relatively rapid learning before a plateau of successful performance (post-criterion performance). Neural responses to post-criterion correct responses were compared with neural responses to both incorrect responses and pre-criterion correct responses. Post-criterion correct responding was associated with increased activation in regions including rostral anterior cingulate, insula, caudate, hippocampal regions, and the amygdala.

Deficits on a probabilistic response-reversal task in patients with pediatric bipolar disorder

OBJECTIVE

Patients with bipolar disorder become hyperhedonic when manic and anhedonic when depressed; therefore, it is important to test whether patients with bipolar disorder show deficits on behavioral paradigms exploring reward/punishment mechanisms.

METHOD

A probabilistic response-reversal task was administered to 24 bipolar children and 25 comparison subjects.

RESULTS

Patients made more errors during probabilistic reversal, took longer to learn the new reward object, and were less likely to meet the learning criterion.

CONCLUSIONS

Children with bipolar disorder may have a reversal learning deficit.

Responding to the emotions of others: dissociating forms of empathy through the study of typical and psychiatric populations

Empathy is a lay term that is becoming increasingly viewed as a unitary function within the field of cognitive neuroscience. In this paper, a selective review of the empathy literature is provided. It is argued from this literature that empathy is not a unitary system but rather a loose collection of partially dissociable neurocognitive systems. In particular, three main divisions can be made: cognitive empathy (or Theory of Mind), motor empathy, and emotional empathy. The two main psychiatric disorders associated with empathic dysfunction are considered: autism and psychopathy. It is argued that individuals with autism show difficulties with cognitive and motor empathy but less clear difficulties with respect to emotional empathy. In contrast, individuals with psychopathy show clear difficulties with a specific form of emotional empathy but no indications of impairment with cognitive and motor empathy.

Response reversal and children with psychopathic tendencies: success is a function of salience of contingency change

BACKGROUND

Previous work has inconsistently reported difficulties with response reversal/extinction in children with psychopathic tendencies.

METHOD

We tested the hypothesis that the degree of impairment seen in children with psychopathic tendencies is a function of the salience of contingency change. We investigated the performance of children with psychopathic tendencies on a novel probabilistic response reversal task involving four conditions with gradated reward-punishment contingencies (100-0, 90-10, 80-20 and 70-30; i.e., for the 100-0 contingency, responding to one object is always rewarded while responding to the other is always punished).

RESULTS

In line with predictions, the impairment seen in the children with psychopathic tendencies was an inverse function of the salience of the contingency change.

CONCLUSIONS

We suggest that this data is consistent with suggestions of subtle orbital frontal cortex impairment in children with psychopathic tendencies.

Boston naming test short forms: a comparison of previous forms with new item response theory based forms

Two new short forms of the Boston Naming Test (BNT) were developed using item response theory (IRT) with data from 206 elderly outpatients. We evaluated the diagnostic ability of 12 short forms among the full sample and in a sub-sample of 69 patients diagnosed with mild Alzheimer's disease (AD) either alone or in combination with vascular dementia (VD). The full BNT (reliability alpha = .90) identified 44% of the AD/VD patients as abnormal on naming. Our 30 item short form (alpha = .90) also identified 44% of the AD/VD patients as abnormal, with 93% agreement with the full BNT on abnormal AD/VD patient classifications. Our 15 item short form (alpha = .84) identified 48% of the AD/VD patients as abnormal, with 90% agreement with the full BNT's abnormal classifications. An adaptive 30/15 item version equaled the performance of the full 30 item test while requiring only 15 items for 75% of the patients with normal naming ability. This study illustrates the utility of IRT for developing neuropsychological assessment tools.

Deafness to fear in boys with psychopathic tendencies

The processing of the emotional signals of others is fundamental for normal socialization and interaction. Reduced responsiveness to the expressions of sadness and fear has been implicated in the development of psychopathy (Blair, 1995). The current study investigates the ability of boys with psychopathic tendencies to process auditory affect information. Boys with psychopathic tendencies and a comparison group, as defined by the Antisocial Process Screening Device (APSD: Frick & Hare, 2001), were presented with neutral words spoken with intonations conveying happiness, disgust, anger, sadness and fear and were asked to identify the emotion of the speaker based on prosody. The boys with psychopathic tendencies presented with a selective impairment for the recognition of fearful vocal affect. These results are interpreted with reference to amygdala dysfunction and components of the Integrated Emotion Systems model.

The roles of orbital frontal cortex in the modulation of antisocial behavior

This article considers potential roles of orbital frontal cortex in the modulation of antisocial behavior. Two forms of aggression are distinguished: reactive aggression elicited in response to frustration/threat and goal directed, instrumental aggression. It is suggested that orbital frontal cortex is directly involved in the modulation of reactive aggression. It is argued that orbital frontal cortex does not "inhibit" reactive aggression but rather may both increase or decrease its probability as a function of social cues present in the environment. Early dysfunction in this function of orbital frontal cortex may be linked to the development of Borderline Personality Disorder. Instrumental aggression is linked to a fundamental failure in moral socialization. However, the available data suggest that the amygdala, but not orbital frontal cortex, is required for functions such as aversive conditioning and passive avoidance learning that are necessary for moral socialization. Psychopathic individuals who present with significant instrumental aggression, are impaired in aversive conditioning and passive avoidance learning and show evidence of amygdala dysfunction. Orbital frontal cortex and the amygdala are involved in response reversal where instrumental responses must be reversed following contingency change. Impairments in response reversal are also seen in psychopathic individuals. However, it remains unclear whether impairment in response reversal per se is associated with antisocial behavior.

Effects of diazepam on facial emotion recognition

OBJECTIVE

There have been few studies of the pharmacologic modulation of facial emotion recognition. The present study aimed to replicate and extend the finding that recognition of facial anger was selectively impaired by diazepam. The hypothesis was that, in comparison with placebo, diazepam would impair the recognition of facial anger in healthy volunteers, but not the recognition of 5 other basic emotions: happiness, surprise, fear, sadness and disgust.

DESIGN

A randomized, counterbalanced, double-blind, placebo-controlled, within-subjects comparison of diazepam with placebo.

SETTING

A university psychopharmacology research unit.

PARTICIPANTS

Healthy male (n = 6) and female (n = 22) volunteers, aged 18-45 years.

PROCEDURES

Subjects were tested on 2 tasks following the administration of diazepam, 15 mg, and placebo on separate occasions. In the first "multimorph" task, images of facial expressions were morphed to produce continua between the neutral and full expressions of 6 basic emotions. Accuracy and identification thresholds were assessed for stimuli in which the intensity of expression gradually increased. In the second "emotional hexagon" task, facial expressions were morphed between pairs of emotions. Single images were presented, and accuracy and speed of response were assessed.

RESULTS

Diazepam produced broad impairments in response accuracy, recognition thresholds and response speed on the facial emotion tasks that were not limited to angry expressions.

CONCLUSIONS

The present study found that diazepam, 15 mg, impaired facial emotion recognition, but not selectively. In the emotional hexagon task, a reaction-time analysis suggested that the identification of facial anger might be differentially sensitive to variations in stimulus duration, complicating the interpretation of this paradigm.

Theory of mind and psychopathy: can psychopathic individuals read the 'language of the eyes'?

There have been suggestions that Theory of Mind (ToM) impairment might lead to aggressive behaviour and psychopathy. Psychopathic and matched non-psychopathic individuals, as defined by the Hare Psychopathy Checklist [The Hare Psychopath Checklist-Revised, 1991] completed the 'Reading the Mind in the Eyes' ToM Test [Journal of Child Psychology and Psychiatry, 1997;38:813]. This test requires the self-paced identification of mental states from photographs of the eye region alone. Results indicated that the psychopathic individuals did not present with any generalised impairment in ToM. The data are discussed with reference to the putative neural system mediating performance on this task and models of psychopathy.

Facial expressions, their communicatory functions and neuro-cognitive substrates

Human emotional expressions serve a crucial communicatory role allowing the rapid transmission of valence information from one individual to another. This paper will review the literature on the neural mechanisms necessary for this communication: both the mechanisms involved in the production of emotional expressions and those involved in the interpretation of the emotional expressions of others. Finally, reference to the neuro-psychiatric disorders of autism, psychopathy and acquired sociopathy will be made. In these conditions, the appropriate processing of emotional expressions is impaired. In autism, it is argued that the basic response to emotional expressions remains intact but that there is impaired ability to represent the referent of the individual displaying the emotion. In psychopathy, the response to fearful and sad expressions is attenuated and this interferes with socialization resulting in an individual who fails to learn to avoid actions that result in harm to others. In acquired sociopathy, the response to angry expressions in particular is attenuated resulting in reduced regulation of social behaviour.

Risky decisions and response reversal: is there evidence of orbitofrontal cortex dysfunction in psychopathic individuals?

This study investigates the performance of psychopathic individuals on tasks believed to be sensitive to dorsolateral prefrontal and orbitofrontal cortex (OFC) functioning. Psychopathic and non-psychopathic individuals, as defined by the Hare psychopathy checklist revised (PCL-R) [Hare, The Hare psychopathy checklist revised, Toronto, Ontario: Multi-Health Systems, 1991] completed a gambling task [Cognition 50 (1994) 7] and the intradimensional/extradimensional (ID/ED) shift task [Nature 380 (1996) 69]. On the gambling task, psychopathic participants showed a global tendency to choose disadvantageously. Specifically, they showed an impaired ability to show learning over the course of the task. On the ID/ED task, the performance of psychopathic individuals was not significantly different from incarcerated controls on attentional set-shifting, but significant impairments were found on response reversal. These results are interpreted with reference to an OFC and amygdala dysfunction explanation of psychopathy.

A comparison of the effects of a beta-adrenergic blocker and a benzodiazepine upon the recognition of human facial expressions

RATIONALE

Accumulating evidence from neuropsychological and neuroimaging research suggests that facial expressions are processed by at least partially separable neurocognitive systems. Recent evidence implies that the processing of different facial expressions may also be dissociable pharmacologically by GABAergic and noradrenergic compounds, although no study has directly compared the two types of drugs.

OBJECTIVE

The present study therefore directly compared the effects of a benzodiazepine with those of a beta-adrenergic blocker on the ability to recognise emotional expressions.

METHODS

A double-blind, independent group design was used with 45 volunteers to compare the effects of diazepam (15 mg) and metoprolol (50 mg) with matched placebo. Participants were presented with morphed facial expression stimuli and asked to identify which of the six basic emotions (sadness, happiness, anger, disgust, fear and surprise) were portrayed. Control measures of mood, pulse rate and word recall were also taken.

RESULTS

Diazepam selectively impaired participants' ability to recognise expressions of both anger and fear but not other emotional expressions. Errors were mainly mistaking fear for surprise and disgust for anger. Metoprolol did not significantly affect facial expression recognition.

CONCLUSIONS

These findings are interpreted as providing further support for the suggestion that there are dissociable systems responsible for processing emotional expressions. The results may have implications for understanding why 'paradoxical' aggression is sometimes elicited by benzodiazepines and for extending our psychological understanding of the anxiolytic effects of these drugs.