Trying to cram the brain with information during an "all-nighter" before taking a test is a ritual for many high school and college students.
But most brain scientists say putting in long hours trying to pack in facts and figures is counterproductive, disrupting the steady absorption that's key to long-term learning.
Still, recent research at the University of California, Berkeley, that involved brain scans of students taking law school prep courses shows that intensive training in reasoning skills actually does change the microscopic structure of the brain.
The results, reported in the issue of Frontiers in Neuroanatomy, show that the training improves students' reasoning ability by strengthening connections between the right and left hemispheres of the brain.
The changes were recorded in scans of 24 college students or recent grads before and after 100 hours of LSAT prep over a three-month period. Compared with brain scans of a matched group of 23 young adults who got no training, the trained students developed increased connectivity between the frontal lobes of the brain and between the frontal and parietal lobes.
Another study, done at the University of California, Los Angeles, shows that cramming that sacrifices a student's normal amount of sleep is usually counterproductive to good academic performance the next day.
Other research shows the average teen in ninth grade sleeps 7.6 hours a night, but by senior year, that snooze average falls to 6.9 hours. Yet the ideal amount of adolescent sleep is considered to be 8 to 9 hours a night.
For the UCLA study, published online in the journal Child Development, researchers asked 535 students from three Los Angeles area high schools to keep a diary for 14 days. They kept track of how many hours they studied, how long they slept and whether they had problems with a test or understanding something they were taught the following day in class.
The diaries showed that longer hours of study time was consistently associated with more academic problems because those longer hours with the books generally meant less sleep.
Scientists have long known that sleep is essential for memory formation, and that some portion of the sleep cycle is key for transferring short-term memories from the brain's hippocampus to the long-term memory of the neocortex.
The brain also seems to selectively sort through what's important to recall and trivia during sleep. And it appears to involve a kind of reverse filtering process.
Another group of UCLA researchers, writing for the online edition of Nature Neuroscience, showed that a key portion of the sleeping brain behaves as if it's remembering something, even under anesthesia.
While it had been known that the two brain regions exchange information, the UCLA team, working with mice, focused on a middleman structure called the entorchinal cortex. Working in mice, the team was able to decipher activity with the neurons of the entorchinal, the neocortex and the hippocampus at the same time during sleep.
The researchers found that the entorchinal cortex goes through waves of persistent activity as if it is remembering something even when the mice were getting no sensory input. These periods, lasting up to a minute or longer, seem to be driven by activity in the neocortex, not the hippocampus.
Mayank Mehta, the study's senior author and a professor of neurophysics, said the fact that this process occurs most of the time during sleep suggests that it operates as a way to unclutter memories and delete irrelevant information processed from the hippocampus to the neocortex during the day. This leaves the important memories more readily accessible.
Mehta also noted that Alzheimer's disease is known to begin in the entorchinal cortex and patients often have impaired sleep, so the findings may have implications for better understanding and treating that illness.