taking an afternoon nap increases learning capacity. A study tested two groups of subjects on a nondeclarative memory task. One group engaged in REM sleep, and one group did not (meaning that they engaged in NREM sleep). The investigators found that the subjects who engaged only in NREM sleep did not show much improvement. The subjects who engaged in REM sleep performed significantly better, indicating that REM sleep facilitated the consolidation of nondeclarative memories. A more recent study demonstrated that a procedural task was learned and retained better if it was encountered immediately before going to sleep, while a declarative task was learned better in the afternoon. Electrophysiological evidence in rats A 2009 study based on electrophysiological recordings of large ensembles of isolated cells in the prefrontal cortex of rats revealed that cell assemblies that formed upon learning were more preferentially active during subsequent sleep episodes. More specifically, those replay events were more prominent during slow wave sleep and were concomitant with hippocampal reactivation events. This study has shown that neuronal patterns in large brain networks are tagged during learning so that they are replayed, and supposedly consolidated, during subsequent sleep. There have been other studies that have shown similar reactivation of learning pattern during motor skill and neuroprosthetic learning. Notably, new evidence is showing that reactivation and rescaling may be co-occurring during sleep. Sleep in relation to school Sleep has been directly linked to the grades of students. One in four U.S. high school students admit to falling asleep in class at least once a week. Consequently, results have shown that those who sleep less do poorly. In the United States, sleep deprivation is common with students because almost all schools begin early in the morning and many of these students either choose to stay awake late into the night or cannot do otherwise due to delayed sleep phase syndrome. As a result, students that should be getting between 8.5 and 9.25 hours of sleep are getting only 7 hours. Perhaps because of this sleep deprivation, their grades are lower and their concentration is impaired. As a result of studies showing the effects of sleep deprivation on grades, and the different sleep patterns for teenagers, a school in New Zealand, changed its start time to 10:30 a.m., in 2006, to allow students to keep to a schedule that allowed more sleep. In 2009, Monkseaton High School, in North Tyneside,