Confirming and extending previous observations, the researchers showed that prolonged social isolation leads to a broad array of behavioral changes in mice. These include increased aggressiveness towards unfamiliar mice, persistent fear, and hypersensitivity to threatening stimuli. For example, when encountering a threatening stimulus, mice that have been socially isolated remain frozen in place long after the threat has passed, whereas normal mice stop freezing soon after the threat is removed. These effects are seen when mice are subjected to two weeks of social isolation, but not to short-term social isolation—24 hours—suggesting that the observed changes in aggression and fear responses require chronic isolation.

http://www.caltech.edu/news/how-social-isolation-transforms-brain-82290

(http://www.autoadmit.com/thread.php?thread_id=3979292&forum_id=2#36069975)