Social isolation
Rats have a specific social organization within colonies. In social isolation models, pups which are placed in separate cages after being weaned show behavioural changes as adults and altered neural development. These changes remain after being re-introduced into the colony in adulthood. The behavioural deficits caused include neophobia, a larger response to new stimulus, locomotor hyperactivity, and increased aggression. Social isolation rats' inability to habituate to new environments may be caused by an increased mesolimbic dopaminergic activity.