Migration, urban upbringing, low IQ, childhood trauma, and illicit drug use are well established risk factors for schizophrenia. Are these factors actually contributing to this risk via social defeat (SD) or social exclusion (SE) pathways? .Is there evidence for SD and SE experiences to sensitise mesolimbic pathways ? Selten JP, van der Ven E, Rutten BP and Cantor-Graae E review the current thinking and evidence.
Social Defeat hypothesis is mainly based on epidemiological studies that compared defeated and non defeated groups. The construct is studied using Social Comparison Scale, the Defeat Scale, Brief Core Schema Scale ,Self esteem scale etc.
A Swedish adolescent study showed that social deprivation at the individual level increased psychosis risk when most children at school were not deprived. However, deprivation at the individual level protected against psychosis when the majority of children at school were deprived. Same relationship was observed for foreign birth (proportion of children with 1 or 2 parents born abroad) and social fragmentation (the proportion of children who migrated into Sweden, moved into a different municipality between ages 8 and 16 years, or were raised in single-parent households). From this study Zammit et al proposed that the characteristic that defines a person as different from his environment may increase the psychosis risk.
Migrants from low-income countries and those with black skin colour are more at risk for schizophrenia than other migrants. This increased risk persists into the second generation. Minority position rather than the adverse circumstances during the migration process per se has a more determinant role.
It has also been shown that living in a neighborhood with a high proportion of residents of the own ethnic group is related to a lower risk for schizophrenia. Low own-group ethnic density is associated with higher risk . A Netherland study has shown that younger age at migration predicts a higher risk, indicating that duration and timing of SD might be important.
Child hood trauma is another risk factor for psychosis.Risk for psychotic symptoms at age 12 is associated with previous maltreatment by an adult or bullying by peers , but much less so with the experience of a lifetime accident .The difference might be the pathogenic influence of humiliation in the abusive experiences. Illicit drug use often lead to SD.SD may lead to drug use also. Apart from direct biological effects, SD can also be involved in the pathway to psychosis.Discriminated minorities ,whether ethnic and sexual also ,show an increase in psychosis further supporting the role of SD.
Social evaluative stress when studied using fMRI, showed that anterior cingulate cortex activity in individuals with urban upbringing history was more affected .This provides some preliminary evidence for SD as the mechanism underlying the association with urban upbringing and schizophrenia.Several animal studies show that social defeat paradigms can lead to hyperdopaminergic state. However extrapolating this to complex human social interactions have serious limitations.
Social defeat appears to be a common denominator for some of the established risk factors for schizophrenia.Chronic social defeat is limey to be toxic. Biological evidence for this is insufficient currently.
Summary of the article:
Selten JP, van der Ven E, Rutten BP, Cantor-Graae E. Schizophr Bull. 2013 Nov;39(6):1180-6