Experimental manipulations of social isolation in rats and mice (e.g., isolated rearing) are a common means of elucidating the effects of isolation on social animals in general. Researchers have proposed isolated rearing of rats as an etiologically valid model of human mental illness.[10] Indeed, chronic social isolation in rats has been found to lead to depression-, anxiety-, and psychosis-like behaviors as well signs of autonomic, neuroendocrine, and metabolic dysregulation.[11][12][13] For example, a systematic review found that social isolation in rats is associated with increased expression of BDNF in the hippocampus, which is associated with increased anxiety-like symptoms. In another example, a study found that social isolation in rats is associated with increased brain-derived neurotrophic factor (BDNF) expression in the prefrontal cortex. This results in the dysregulation of neural activity which is associated with anxiety, depression, and social dysfunction.[14]
The effects of experimental manipulations of isolation in nonhuman social species has been shown to resemble the effects of perceived isolation in humans, and include: increased tonic sympathetic tone and hypothalamic-pituitary-adrenal (HPA) activation and decreased inflammatory control, immunity, sleep salubrity, and expression of genes regulating glucocorticoid responses.[15] However, the biological, neurological, and genetic mechanisms underlying these symptoms are poorly understood.