Can laboratory animals violate behavioural norms? Towards a preclinical model of conduct disorder.

Conduct disorder (CD), a disturbance characterised by excess rates of aggression - often associated with callousness, lack of empathy and shallow/deficient affect - is extremely prevalent (2-10%) in the juvenile population. CD symptoms are quantitative rather than qualitative in nature whereby, rather than exhibiting abnormal behaviours, CD patients indulge in normal behaviours at abnormal rates. Although genetic and environmental factors contribute to CD aetiology, their precise contribution is yet to be determined. Experimental animal models may aid discriminating genetic vs. environmental effects and designing innovative therapeutic approaches. Here we discuss a theoretical framework potentially favouring the design of experimental models of CD. We suggest that the latter shall recapitulate the "norm violation" typical of the human disorder across the core domains involved in CD: aggression, callousness, empathy and emotionality. We first review how these domains have been operationalised in preclinical models; we then suggest that these experimental paradigms shall be combined with appropriate statistical tools to identify a subset of individuals consistently characterised by abnormal values in CD-relevant phenotypes.