[Social defeat and schizophrenia: Hypotheses, arguments, mechanisms]

There is growing evidence for a main role of environment in the occurrence of mental disorders such as a psychosocial risk factor, for example, childhood trauma, discrimination linked to minority status, or migrant status. One hypothesis is that social adversity factors influence the risk of schizophrenia through a common pathway: social defeat which could be defined as the impotence of a subject in the face of a situation of social adversity, with a consequential experience of devaluation on the social scale. This review proposes to explain the animal model of social defeat which provides an overview of the neurobiological consequences of chronic stress. Then, we expose this topic in humans, the assessment methods, and its psychopathological field. Finally, we expose epidemiologic and neurobiological evidences, in particular the dopaminergic sensitization process, which provide evidence of a significant role of social defeat in schizophrenia risk due to exposure to psychosocial factors. This etiopathogenic hypothesis has several issues. First, a common pathway to several environmental risk factors could allow an ethiopathogenic model more parcimonious for schizophrenia. It could also allow the assessment and prevention of adversity factors involved in social defeat so as to finally improve the outcome of subjects who have an individual risk for schizophrenia.