Plasma serotonin levels in young violent offenders: Aggressive responding and personality correlates

Reactive vs proactive aggression: A differential psychobiological profile? Conclusions derived from a systematic review

INTRODUCTION

Scholars have established subcategories of aggressive behavior in order to better understand this construct. Specifically, a classification based on motivational underpinnings makes it possible to differentiate between reactive and proactive aggression. Whereas reactive aggression is characterized by emotional lability, which means it is prone to impulsive reactions after provocation, proactive aggression is driven by low emotionality and high levels of instrumentality to obtain benefits. Some authors have conceived these two types as having a dichotomous nature, but others argue against this conceptualization, considering a complementary model more suitable. Hence, neuroscientific research might help to clarify discussions about their nature because biological markers do not present the same biases as psychological instruments.

AIM

The main objective of this study was to carry out a systematic review of studies that assess underlying biological markers (e.g., genes, brain, psychophysiological, and hormonal) of reactive and proactive aggression.

METHODS

To carry out this review, we followed PRISMA quality criteria for reviews, using five digital databases complemented by hand-searching.

RESULTS

The reading of 3993 abstracts led to the final inclusion of 157 papers that met all the inclusion criteria. The studies included allow us to conclude that heritability accounted for approximately 45% of the explained variance in both types of aggression, with 60% shared by both, especially, for overt and physical expression forms, and 10% specific to each type. Regarding allelic risk factors, whereas low functioning variants affecting serotonin transport and monoaminoxidase increased the risk of reactive aggression, high functioning variants were associated with proactive aggression. Furthermore, brain analysis revealed an overlap between the two types of aggression and alterations in the volume of the amygdala and temporal cortex. Moreover, high activation of the medial prefrontal cortex (PFC) facilitated proneness to both types of aggression equally. Whereas stimulation of the right ventrolateral (VLPFC) and dorsolateral (DLPFC) reduced proneness to aggression, inhibition of the left DLPFC increased it. Finally, psychophysiological and hormonal correlates in general did not clearly differentiate between the two types because they were equally related to each type (e.g., low basal cortisol and vagal variability in response to acute stress) CONCLUSIONS: This study reinforces the complementary model of both types of aggression instead of a dichotomous model. Additionally, this review also offers background about several treatments (i.e., pharmacological, non-invasive brain techniques…) to reduce aggression proneness.

Serotonin and aggressive behaviour in children and adolescents: a systematic review

OBJECTIVE

The role of serotonin (5-HT) in human aggression has been the subject of a large number of studies, mostly with adults. Meta-analyses indicate a small but significant inverse relationship between central nervous 5-HT availability and aggression, but genetically informed studies suggest two pathways: one to reactive aggression and the other to proactive aggression.

METHOD

We conducted a systemic review on central nervous 5-HT function in children and adolescents, with attention to the function of aggression.

RESULTS

In total, 675 articles were screened for relevance, with 45 reviewed. These included blood assays (e.g. plasma, 5-HIAA; platelet 5-HTR_2A ), epigenetic studies, retrospective PET studies and 5-HT challenge paradigms (e.g. tryptophan depletion). Overall, findings were mixed, with support both for negative and for positive associations of central nervous 5-HT function with aggression in children and adolescents.

CONCLUSION

We propose factors that may be blurring the picture, including problems in the conceptualization and measurement of aggression in young people, the lack of prospective designs and the bias towards clinical samples of boys. Research needs to account for variance in the both motivation for and implementation of aggression, and look to the behavioural economics literature to consider the roles of reward, vengeance and self-control more clearly.

The Point Subtraction Aggression Paradigm as a laboratory tool for investigating the neuroendocrinology of aggression and competition

A contribution to a special issue on Hormones and Human Competition.The ease of measuring steroids in saliva has led to an increase in investigating their role in competition and aggression in laboratory settings and using behavioral measures of aggression. We review here the Point-Subtraction-Aggression-Paradigm (PSAP) as a measure of costly aggression and we compare and contrast the PSAP to other aggression measures. We describe our use of the PSAP, highlighting how it can be modified to investigate a broad array of experimental questions. We review studies that have investigated neuroendocrine function and the PSAP, and we conclude that across studies the relationship between fluctuations in testosterone and PSAP aggression scores are directionally positive, and are likely specific to men. Investigations of other neuroendocrine measures and the PSAP are fewer, limiting conclusions that can be drawn for other hormones. We provide two versions of the PSAP that can be used with E-PRIME® software for researchers interested in this measure for their laboratories.

Sleep deprivation lowers reactive aggression and testosterone in men

The role of sleep deprivation in aggressive behavior has not been systematically investigated, despite a great deal of evidence to suggest a relationship. We investigated the impact of 33 h of sleep loss on endocrine function and reactive aggression using the Point Subtraction Aggression Paradigm (PSAP) task. PSAP performance was assessed in 24 young men and 25 women who were randomly assigned to a sleep deprivation or control condition. Sleep deprivation lowered reactive aggression and testosterone (but not cortisol) in men, and disrupted the positive relationship between a pre-post PSAP increase in testosterone and aggression that was evident in rested control men. While women increased aggression following provocation as expected, no influence of sleep deprivation was found. This is the first experimental study to demonstrate that sleep deprivation lowers reactive aggression in men. Testosterone, but not cortisol, played a role in the relationship between sleep and reactive aggression in men.

Platelet poor plasma serotonin level in delinquent adolescents diagnosed with conduct disorder

OBJECTIVE

Accumulating data indicate the involvement of the serotonergic system in adolescent aggression. The aim of this study was to examine the platelet-poor plasma (PPP) serotonin (5-HT) levels among delinquent adolescent boys with conduct disorder (CD) in comparison with normal controls.

METHOD

PPP 5-HT levels were measured in 16 male delinquent CD adolescents from a correctional facility and in 14 normal male adolescent controls. Severity of aggressive behavior was assessed by the Child Behavior Checklist (CBCL) and the Overt Aggression Scale (OAS).

RESULTS

Delinquent CD adolescents had higher PPP 5-HT levels (about 3-fold) than the normal controls (27.68+/-32.29 vs. 7.76+/-4.23 ng/ml, respectively, p=0.027). In the delinquent CD adolescents a significant correlation was found between the PPP 5-HT levels and the CBCL and OAS aggressive scores (r=0.68, p=0.0034 and r=0.59, p=0.016, respectively).

CONCLUSIONS

Juvenile delinquency is associated with high PPP 5-HT levels. Modulation of 5-HT neurotransmission may have a role in the symptomatology and treatment of severe adolescent CD.

Serotonergic mediation of aggression in high and low aggressive chicken strains

Serotonin (5-HT) regulates aggressive behavior via binding to its receptors, such as 5-HT1A and 1B, in humans and rodents. Here we investigate the heritable components of 5-HT regulation of aggressiveness in chickens, utilizing 3 distinct genetic strains. In this study, we used 2 divergently selected strains (high and low group productivity and survivability, respectively; HGPS and LGPS) and a third strain, Dekalb XL (DXL), an aggressive out-group. Hens were paired within the same strain. At 24 wk of age, the subordinate of each pair received a daily i.p. injection of NAN-190 (0.5 mg/kg, a 5-HT1A antagonist), GR-127935 (0.5 mg/kg, a 5-HT1B antagonist), or saline (control) for 5 consecutive days. Frequency of aggressive behaviors was increased in the hens of DXL and LGPS treated with 5-HT1A antagonist and in the HGPS hens treated with 5-HT1B antagonist. The 5-HT1B antagonist-treated HGPS hens and 5-HT1A antagonist-treated LGPS hens also displayed increased feather pecking, but neither antagonist had an effect on feather pecking of DXL hens. This may suggest that multiple mediating factors alter feather pecking behaviors. Among the controls, LGPS hens have higher epinephrine levels than HGPS or DXL hens, indicative of the inferior stress-coping ability of LGPS hens. Treatment with 5-HT1B antagonist reduced epinephrine in LGPS hens but not in DXL or HGPS hens, suggesting a role of 5-HT1B in stress regulation in LGPS hens. The results provide evidence for different heritable serotonergic mediation of aggressive behaviors and stress coping in chickens.

Personality disorders and violence

PURPOSE OF REVIEW

To review the most recent literature on the relationship between personality disorders and violent behavior. The review does not aim to address the issue of a possible etiological connection between previously being the victim of violent acts and later developing a personality disorder.

RECENT FINDINGS

Recent data suggest that personality disorders, especially antisocial and borderline, are strongly related to the manifestation of violent acts. Substance abuse is another strong factor which could act either independently or additively. Biological factors seem to constitute a risk factor for violent behavior independently of personality. Although intelligence does not seem to be related to violence, some patients may manifest specific cognitive deficits. The ethical and legal questions posed by the above correlations are difficult to answer, and research has not yet provided enough data on this issue.

SUMMARY

The most recent data support the relationship between antisocial personality and violence, especially when substance abuse is also present, although the presence of confounding factors in the diagnostic criteria suggest caution in the interpretation of the literature.

Human proactive aggression: association with personality disorders and psychopathy

Aggressive behaviors can be divided into two categories: reactive and proactive. Reactive aggressive behaviors occur in response to a stimulus or provocation. Proactive aggressive behaviors occur without provocation and are goal directed. A number of findings have suggested that individuals displaying proactive aggression may be discerned from individuals not displaying proactive aggression on measures of personality, psychopathology and psychopathy as well as in aggressive histories and type and severity of aggressive behaviors committed. In this study, subjects were recruited from a large urban community and classified as proactive (n = 20), reactive-only (n = 20) or nonaggressive (n = 10) based on laboratory behavioral testing. Subjects were administered a battery of questionnaires and structured interviews pertaining to personality disorders and psychopathy. It was hypothesized that proactive aggressive subjects would show greater numbers of personality disorders and have greater psychopathy relative to reactive-only and nonaggressive subjects. These hypotheses were supported. These results suggest that proactive aggression may be identified in a laboratory-based task, and differences between proactive and reactive-only aggressors can be detected.