June 11 (HealthDay News) -- Sleep is good for your memory, but the sleeping brain seems to store only the most useful information, researchers have found.

Using data from a group of 44 college students aged 18 to 22, the study findings showed that when a good night's rest follows a period of learning, sleep can preserve the most important memories for as long as four months.

The findings are scheduled to be presented Thursday at the Associated Professional Sleep Societies annual meeting, in Seattle.

Think of sleep as a period of memory consolidation, where the sleeping brain calculates what is most important about a memory and selects the best candidates for long-term memory, study author Jessica Payne, a postdoctoral fellow in psychology at Harvard Medical School in Boston, explained in a news release from the American Academy of Sleep Medicine.

"It may be that the chemical and physiological aspects of sleep underlying memory consolidation are more effective if a particular memory is 'tagged' shortly prior to sleeping," she said, adding that sleep seems to selectively preserve memories that are emotionally important and relevant to future goals.

SOURCE: American Academy of Sleep Medicine, news release, June 11, 2009