Rats are highly social animals whose welfare in laboratory settings depends critically on social housing, yet single housing remains common despite causing measurable psychological harm.
Social isolation causes measurable psychological suffering in rats equivalent in neurobiological terms to the social deprivation that causes harm in humans. Chronically isolated rats show behavioral despair, increased anxiety, and impaired cognitive function that persists even after socialization opportunities are restored. The scientific justification for single housing is often weak — many studies claiming social housing would confound results could be designed to accommodate group housing without compromising scientific validity. Institutions should treat social housing as the default and require genuine scientific justification for exceptions rather than treating isolation as a convenient baseline.