A recent study at the University of California, San Diego placed volunteers under certain sleep conditions and recorded their results on word–association tests in the morning and evening. They found that the group that did not nap mid–day had the lowest scores, while those who napped without REM sleep had slightly higher scores. A 40% increase in the evening test was observed among those who napped with REM sleep. The results suggest that having naps containing a significant amount of REM sleep increases performance levels in individuals.
New York Times- June 23, 2009; pages D6