Gutwein, B. M., Fishbein, W. 1980. Paradoxical sleep and memory (I): Selective alterations following enriched and impoverished environmental rearing. Brain Research Bulletin 5(1), 9-12.

Mice were reared in either enriched (EE), social control, (SE), or impoverished (IE) environments for 30 days. Environmental enrichment results in a significant and selective increase in paradoxical sleep (PS, or REM sleep) and also enhances recall of a multiple-trial, brightness discrimination task 28 days after training. Conversely, impoverished (IE) reared mice exhibit a decrease in PS and impaired task performance relative to socially housed (SE) controls. These results support the hypothesis that PS plays an integral role in the maintenance and stability of long-term memory.