NEW YORK (Reuters Health) - Night owls and insomniacs are missing out on precious learning time, it seems. Researchers have found that sleep is vital to holding on to certain types of memory.

According to two reports in the December issue of Nature Neuroscience, getting a good night's sleep helps people retain some of what they learned that day. In experiments, investigators found that well-rested study participants were more adept at picking up new skills than their sleep-deprived counterparts were. Catching some Z's on the first night after learning the skills turned out to be crucial.

In one study, researchers at Harvard Medical School (news - web sites) in Boston, Massachusetts, had healthy young people learn a task in which they had to distinguish visual targets set in a distracting background on a computer screen. One group was allowed to sleep as normal the night after the test, while the other group stayed awake through the first night and day after learning the task. They were then allowed to sleep as long as they wanted during the next 2 nights before being re-tested.

This second series of tests revealed that while the first group's skills had improved, those who got no sleep the first night showed no improvement. This indicates that people cannot make up for that critical night of sleep by sleeping late on other days, Dr. Robert Stickgold told Reuters Health.

Sleep loss did not appear to make study participants forget what they learned, he noted. Instead, they seemed to miss out on a window of time in which sleep helps the brain mold information into lasting memories.

Sleep, Stickgold said, helps people ``deal with information overload.'' A growing body of research is showing that during the body's dormant state, the brain is busy establishing connections that lay down memories.

``There has to be a transformation of information to a form where it can be useful,'' Stickgold said. The type of memory his team tested is known as procedural memory--the type used in learning to play a piano or hit a baseball.

Other researchers, at the Medical University of Lubeck in Germany, found that the early stages of sleep were particularly important to learning. Steffen Gais and his colleagues found that study participants' skills improved after 3 hours of ''early'' sleep--known as slow-wave sleep. Skills did not improve when participants got only ``late'' (REM) sleep. However, improvements were greatest when participants got a full night's rest.

This, according to Gais and colleagues, suggests that while early sleep is essential to memory formation, later stages are also involved.

``It looks like all stages play subtly different roles,'' Stickgold said. This is why a restless or shortened night's sleep is as bad as a sleepless night. Moreover, Stickgold noted, sleeplessness likely affects all types of memory formation.

``We're only touching the tip of the iceberg with this research,'' he added.

SOURCE: Nature Neuroscience 2000;3:1237-1238, 1335-1339.