Environmental deprivation contributes in important ways to the development of a wide range of psychiatric disorders. Isolation rearing of rodents, a model for environmental deprivation in humans, consistently produces hyperlocomotion, which provides a measurable parameter to study the underlying mechanisms of early adverse psychosocial stressors. Male Sprague-Dawley rat pups were separated from dams at postnatal (PN) day 20 and reared either in groups of three or in isolation. On PN 38, locomotion was assessed in the open field. On PN 46, rats were killed and gene expression patterns examined in the medial prefrontal cortex (mPFC). Isolation-reared rats displayed increased locomotor activity and decreased resting time in the open field. Specific gene expression patterns in the mPFC were associated with both isolation rearing and hyperlocomotive behavior in the open field. Genes involved in these expression patterns included immediate early genes (IEGs) and genes that regulate cell differentiation and apoptosis. The study of these genes could provide important insights into how abnormal early psychosocial events affect brain function and behavior.