Stages of sleep have distinct influence on process of learning and memory

Feb 25, 2009

Research on the sleeping brain has revealed some fascinating stage-dependent interactions between areas involved in formation and storage of long term memories. The study, published by Cell Press in the February 26th issue of the journal Neuron, may also provide a framework for further understanding the role of sleep in memory.

Mammalian sleep occurs in two discrete stages, slow wave sleep (SWS) and rapid eye movement (REM) sleep. One of the many ways in which SWS and REM sleep differ is in the level of synchronous firing in the hippocampus. Previous research has suggested that coordinated activity between the hippocampus (a brain area critical for memory formation) and the neocortex (where long-term memories are stored) may be critical for memory formation.

"Given the importance of synchrony and spike timing in synaptic plasticity, and given the putative role of sleep in learning and memory, a key question is whether consistent spike timing relationships exist across cortico-hippocampal circuits during sleep, and whether these differ in SWS versus REM sleep," explains senior study author, Dr. Athanassios G. Siapas from the California Institute of Technology. Dr. Siapas and colleagues used sophisticated recording and computational techniques to examine the activity of neurons in the hippocampus and prefrontal cortex in sleeping rats.

The researchers observed highly consistent directional interactions between the hippocampus and neocortex during SWS, but only during discrete bursts of activity in the hippocampus known as "ripples", suggesting that these bursts may represent a basic unit of information transfer. There was a non-linear relationship between the magnitude of hippocampal signals and the patterning of prefrontal responses, suggesting that variations in the strength of hippocampal bursts may lead to qualitatively different cortical responses.

Interestingly, the coupling between the hippocampus and prefrontal cortex was greatly reduced during REM sleep. Previous computational models of memory consolidation have supported a need for gradual transfer of memory traces from the hippocampus to the neocortex and for a reorganization of memory traces without external input. The current findings suggest that transfer and reorganization may be met by SWS and REM sleep, respectively.

The researchers went on to speculate that the disconnection between the hippocampus and prefrontal cortex during REM sleep may explain some of the persistent mysteries associated with REM sleep. "It's possible that the scarcity of coordinated cortico-hippocampal spiking during REM sleep may explain why the awake-like neural activity in the prefrontal cortex during REM does not interact strongly with the hippocampus and therefore why dreams are, on the whole, forgotten," offers Casimir Wierzynski, a graduate student in Dr. Siapas's lab and lead author of the paper.

Source: Cell Press

Explore further: Education, breastfeeding and gender affect the microbes on our bodies

add to favorites email to friend print save as pdf

Related Stories

REM sleep deprivation plays a role in chronic migraine

Jun 23, 2010

Reporting at the American Headache Society's 52nd Annual Scientific Meeting in Los Angeles this week, new research shows that sleep deprivation leads to changes in the levels of key proteins that facilitate events involved ...

Baby owls sleep like baby humans

Aug 02, 2013

Researchers at the Max Planck Institute for Ornithology and the University of Lausanne have discovered that the sleeping patterns of baby birds are similar to that of baby mammals. What is more, the sleep ...

Flies sleep just like us

Apr 19, 2013

(Phys.org) —Researchers at The University of Queensland have discovered that, like humans, flies sleep in stages of different intensities.

Recommended for you

Leeches help save woman's ear after pit bull mauling

8 hours ago

(HealthDay)—A pit bull attack in July 2013 left a 19-year-old woman with her left ear ripped from her head, leaving an open wound. After preserving the ear, the surgical team started with a reconnection ...

New pain relief targets discovered

19 hours ago

Scientists have identified new pain relief targets that could be used to provide relief from chemotherapy-induced pain. BBSRC-funded researchers at King's College London made the discovery when researching ...

Building 'smart' cell-based therapies

20 hours ago

A Northwestern University synthetic biology team has created a new technology for modifying human cells to create programmable therapeutics that could travel the body and selectively target cancer and other ...

User comments : 0

More news stories

Vietnam battles fatal measles outbreak

Vietnam is scrambling to contain a deadly outbreak of measles that has killed more than 100 people, mostly young children, and infected thousands more this year, the government said Friday.

Continents may be a key feature of Super-Earths

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...