Ehlers, C. L., Kaneko, W. M., Owens, M. J. et al. 1993. Effects of gender and social isolation on electroencephalogram and neuroendocrine parameters in rats. Biological Psychiatry 33, 358-366.

Same-sex pairs were established and partners separated after 6 weeks. The effects of 6 weeks of [subsequent] social isolation on electroencephalographic (EEG) recordings and hypothalamic-pituitary-adrenal (HPA) functioning were studied. Separation resulted in significant sleep disturbances - as measured in EEG responses - and increase in HPA activity. Significant sex differences were noticed.