Findings suggest that a biphasic sleep schedule not only refreshes the mind, but it can improve neurocognitive functioning as well.
SAN DIEGO—An hour-long nap can dramatically boost and restore your brain power, according to research presented at the 2010 Annual Meeting of the American Association for the Advancement of Science.
Conversely, the more hours we spend awake, the more sluggish our minds become, reported researchers from the University of California, Berkeley. The results support previous findings from the same research team that pulling an all-nighter—a common practice at college during midterms and finals—decreases the ability to cram in new facts by nearly 40%, due to a shutdown of brain regions during sleep deprivation.
“Sleep not only rights the wrong of prolonged wakefulness, but, at a neurocognitive level, it moves you beyond where you were before you took a nap,” said lead investigator Matthew P. Walker, PhD, Assistant Professor of Psychology and Neuroscience.
Sleep and Short-Term Memory Storage in the Brain
In the study, 39 healthy young adults were categorized into two groups—nap and no-nap. At noon, all participants were subjected to a rigorous learning task intended to tax the hippocampus. The groups performed at comparable levels.
At 2 pm, the nap group slept for 90 minutes, while the no-nap group stayed awake. Later that day, at 6 pm, participants performed a new round of learning exercises. Those who remained awake throughout the day became worse at learning. In contrast, those who napped did markedly better and actually improved in their capacity to learn.
These findings reinforce the researchers’ hypothesis that sleep is needed to clear the brain’s short-term memory storage and make room for new information, according to Dr. Walker.
Since 2007, Dr. Walker and other sleep researchers have established that fact-based memories are temporarily stored in the hippocampus before being sent to the brain’s prefrontal cortex, which may have more storage space.
“It’s as though the e-mail inbox in your hippocampus is full, and, until you sleep and clear out those fact e-mails, you’re not going to receive any more mail. It’s just going to bounce until you sleep and move it into another folder,” Dr. Walker said.
In their latest study, the researchers found that this memory-refreshing process occurs when nappers are engaged in a specific stage of sleep. EEG tests indicated that this refreshing of memory capacity is related to stage 2 non–rapid eye movement (REM) sleep, which takes place between deep sleep (non-REM) and the dream state (REM). Previously, the purpose of this stage was unclear, but the results offer evidence as to why humans spend at least half their sleeping hours in stage 2, non-REM, according to Dr. Walker.
“I can’t imagine Mother Nature would have us spend 50% of the night going from one sleep stage to another for no reason,” said Dr. Walker. “Sleep is sophisticated. It acts locally to give us what we need.”
Dr. Walker and his team next want to investigate whether the reduction of sleep experienced by people as they get older is related to the documented decrease in our ability to learn as we age. Finding that link may be helpful in understanding such neurodegenerative conditions as Alzheimer’s disease, Dr. Walker commented.
The Role of Sleep in Brain Development
In a separate study, Marcos Frank, PhD, Associate Professor of Neuroscience at the University of Pennsylvania School of Medicine in Philadelphia, presented information on early brain development and the importance of sleep during early life when the brain is rapidly maturing and highly changeable.
Building on his research that the brain during sleep is fundamentally different from the brain during wakefulness, Dr. Frank found that cellular changes in the sleeping brain may promote the formation of memories. “This is the first real direct insight into how the brain, on a cellular level, changes the strength of its connections during sleep,” said Dr. Frank.
For example, when an animal goes to sleep it’s like a switch is thrown, and everything is turned on that’s necessary for making synaptic changes that form the basis of memory formation, said Dr. Frank.
He and his colleagues used an animal model of cortical plasticity. They found that once the brain is triggered to reorganize its neural networks in wakefulness (by visual deprivation, for instance), intra- and intercellular communication pathways engage, setting a series of enzymes into action within the reorganizing neurons during sleep. The key cellular player in this process is the N-methyl-d-aspartate receptor (NMDA), which acts like a combination listening post and gate-keeper, noted Dr. Frank. It both receives extracellular signals in the form of glutamate and regulates the flow of calcium ions into cells.