Researchers split 70 young adults into two groups - one that got to sleep overnight and one that had to stay awake, Daily Mail reported Wednesday.
Both groups were required to look at positive images containing items such as puppies and flowers, and both at neutral images featuring furniture and dinner plates.
The participants' memories of the images were then tested 12 hours later, after either a period of sleep or staying awake, with the positive memories stronger for the sleepers.
"Results showed sleep enhances our emotionally positive memories," said professor Rebecca Spencer of the University of Massachusetts.
Spencer believes the results could also have significant implications for treating post-traumatic stress disorder.