The effects of social housing on extinction of fear conditioning in rapid eye movement sleep-deprived rats.

Both human and animal research indicate that rapid eye movement sleep (REM) plays an important role in the processing of emotional information. REM is altered after fear conditioning in rats, but this alteration can be mitigated by exposure to a naïve conspecific. In addition, both the housing condition (isolated vs paired) and the experiences of rats' cagemates can influence the response to aversive events. Based on this prior work, the present study sought to determine the effects of social housing on the previously demonstrated impairment in the extinction of conditioned fear responses produced by REM deprivation. Rats were assigned to one of three housing conditions: housed with a naïve rat, housed with another fear-conditioned rat, or housed alone. The results demonstrated that rats housed with either a naïve or a fear-conditioned conspecific exhibited an impairment in the acquisition of extinction as a consequence of REM deprivation, as observed in previous studies. However, rats in the isolated condition demonstrated a trend toward an impairment only after continued extinction training. These results indicate that the effects of social housing on REM deprivation-induced impairments in learning and memory are subtle, but may explain some conflicting findings in the literature.