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: Unsteady on your feet? Little touches could make all the difference

add to favorites email to friend print save as pdf

Related Stories

Feds: Don't expect winter to be polar vortex redux

12 minutes ago

(AP)—Federal forecasters don't expect a return of frequent cold blasts from the polar vortex this winter. Nor should the weather system that blocked rain from California last winter come back.

WASP has printer, will travel, to make houses

15 minutes ago

At Maker Faire Rome, an Italian 3D printer company is demonstrating a tall, portable machine that will bring 3D-printed dwellings to impoverished countries. WASP has been exploring low-cost solutions to ...

Cell architecture: Finding common ground

18 minutes ago

When it comes to cellular architecture, function follows form. Plant cells contain a dynamic cytoskeleton which is responsible for directing cell growth, development, movement, and division. So over time, changes in the cytoskeleton ...

Amphibians being wiped out by emerging viruses

55 minutes ago

Scientists tracing the real-time impact of viruses in the wild have found that entire amphibian communities are being killed off by closely related viruses introduced to mountainous areas of northern Spain.

Recommended for you

Cause of ageing remains elusive

8 minutes ago

A report by Chinese researchers in the journal Nature a few months ago was a small sensation: they appeared to have found the cause for why organisms age. An international team of scientists, headed by the ...

Newly discovered bacterial defence mechanism in the lungs

1 hour ago

A new study from Karolinska Institutet presents a previously unknown immunological mechanism that protects us against bacterial infections in the lungs. The study is being published in the American Journal of Respiratory an ...

Neutralising antibodies for safer organ transplants

22 hours ago

Serious complications can arise following kidney transplants. If dialysis is required within the first seven days, then the transplanted organ is said to have a Delayed Graft Function (DGF), and essentially ...

User comments : 0