Effects of Adverse Early‐Life Events on Aggression and Anti‐Social Behaviours in Animals and Humans

Abstract

We review the impact of early adversities on the development of violence and antisocial behaviour in humans, and present three aetiological animal models of escalated rodent aggression, each disentangling the consequences of one particular adverse early-life factor. A review of the human data, as well as those obtained with the animal models of repeated maternal separation, post-weaning social isolation and peripubertal stress, clearly shows that adverse developmental conditions strongly affect aggressive behaviour displayed in adulthood, the emotional responses to social challenges and the neuronal mechanisms activated by conflict. Although similarities between models are evident, important differences were also noted, demonstrating that the behavioural, emotional and neuronal consequences of early adversities are to a large extent dependent on aetiological factors. These findings support recent theories on human aggression, which suggest that particular developmental trajectories lead to specific forms of aggressive behaviour and brain dysfunctions. However, dissecting the roles of particular aetiological factors in humans is difficult because these occur in various combinations; in addition, the neuroscientific tools employed in humans still lack the depth of analysis of those used in animal research. We suggest that the analytical approach of the rodent models presented here may be successfully used to complement human findings and to develop integrative models of the complex relationship between early adversity, brain development and aggressive behaviour.

Developmental stress and social phenotypes: integrating neuroendocrine, behavioural and evolutionary perspectives

“…Overall the evidence provided in the previous sections suggests that early life stress decreases measures of social motivation, reduces the expression of social behaviours, increases aggression and promotes the development of anti-social behaviours, but the specific consequences depend on the timing and nature of the stressor (11,14).…”

“…Maternal separation prior to weaning is a potent stressor in mammals. It is used as a proxy for deficient parental care and is akin to social isolation in older animals (11,70,92). Individuals exposed to this stress show significant deficits in social behaviours in adulthood.…”

“…In many cases exogenous GC treatments induce very similar effects on social behaviour as those mediated by social and other stressors(11). For example direct GC administration in juveniles immediately diminishes social exploration (14) and acute GC treatments in adulthood increase aggression (11,14,68,72).These above examples provide evidence for stress 'negatively' impacting on social behaviour, albeit in a potentially adaptive way. However, stressful situations can trigger an increase in social behaviours, promoting affiliative behaviours specifically, which is thought to link to increased group cohesion facilitating better coping in stressful conditions (73).…”

Hippocampal Plasticity during the Peripartum Period: Influence of Sex Steroids, Stress and Ageing

“…In support of this, restraint stress during the first weeks of lactation increased active nursing behavior in dams for the first two hours after stress compared with control dams (82). Clearly high maternal CORT or stress can adversely affect the offspring, for a review on the effects of early life stress and environment on offspring development see reviews in this issue (78, 84, 85). …”

Social instigation and repeated aggressive confrontations in male Swiss mice: analysis of plasma corticosterone, CRF and BDNF levels in limbic brain areas

“…8 Furthermore, most of the stress faced by humans occurs in a social context. 9 Although preclinical research has produced important descriptions of aggression and provided a solid basis for analysis of the neurobiology of aggressive behavior, the degree of similarity across species, neural systems, behavioral expression, and outcomes of aggression remain unclear.…”