Results show that the emotional brain is not stable across the day, resulting in marked changes in emotional reactivity. Naps with REM sleep objectively and bi-directionally modify specific emotions. Individuals who took a 60 to 90 minute nap with REM sleep displayed increased receptiveness to happy facial expression following sleep. People who did not take a nap during the day displayed an amplified reaction to anger and fear.

"Social interactions are critically guided by, and indeed are predicated on the basis of, accurately recognizing emotional facial expressions," said Gujar. "Only through accurate recognition can cogent social judgments and subsequent actions be made. Nowhere are these accurate emotional face judgments more critical than in many professions that are associated with sleep curtailment, including emergency and resident medical staff, military personnel, and even new parents."