The American Physiological Society Press Release

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APS Contact: Donna Krupa

Email: dkrupa@the-aps.org

Phone: 301.634.7209

Twitter: @Phyziochick

Relationship Between Sleep and Memory:

Historical Perspective available in Physiological Reviews

BETHESDA, Md. (July 29, 2013) —It is evident to just about everyone that a good night’s sleep will improve your memory, a belief that been confirmed by scientific research conducted during the last century.  However, the underlying concepts of why it occurs have changed.  At first, initial inquiries into the physiological relationship between sleep and memory focused on rapid eye-movement (REM) sleep and the passive role for sleep enhancing memories by protecting them from interfering stimuli.  Now, current theories highlight an active role for slow-wave sleep (SWS) advancing memory consolidation along with the electrophysiological, neurochemical, and genetic mechanisms found in these processes.

Sleep and Memory Research: A Historical Perspective

A new review aims to comprehensively cover the field of “sleep and memory” research by providing a historical perspective on concepts and a discussion of more recent key findings.  The review covers the progress of research in this field of sleep and memory in its entireness, simultaneously taking into account the vastly differing approaches that have been adopted to clarify the mechanism causing memory to benefit from sleep.

This review also discusses sleep’s criti­cal role in memory consolidation, essential for any understanding of this physiological process.  Memory functions comprise three major sub­processes, i.e., encoding, consolidation, and retrieval. Dur­ing encoding, the perception of a stimulus results in the formation of a new memory trace, which is initially highly susceptible to disturbing influences and decay, or in other words forget­ting. During consolidation, the changeable memory trace is grad­ually stabilized possibly involving multiple waves of short and long-term consolidation processes, which serve to strengthen and integrate the memory into preexisting knowledge networks. During retrieval, the stored memory is accessed and recalled.

That review “About Sleep’s Role in Memory” is authored by Björn Rasch from the Institute of Psychology, Neuroscience Center Zurich and Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland; and Jan Born Institute of Medical Psychology and Behavioral Neurobiology, and Center for Integrative Neuroscience, University of Tuebingen, Tuebingen, Germany.  Their review with their commentary appeared earlier this year in the April 2013, edition of Physiological Reviews, published by the American Physiological Society to provide state of the art coverage of issues in the physiological and biomedical sciences for physiologists, neuroscientists, cell biologists, biophysicists, and clinicians with special interest in pathophysiology. The review is available online at http://bit.ly/15IfNo6.

Review Structure and Organization

The review is structured with eight sections.  They are, with a brief description:

1.  Introduction: A discussion of the core concepts of sleep and memory.

2.  Overview of Approaches and Concepts: A summary of evidence from behavioral studies in support of the notion that sleep aids memory consol­idation. Key experiments for the different theoretical ac­counts and concepts are described in chro­nological order.

3.  Memory Reactivations During Sleep: This section addresses the assumption that memories are reactivated during the consolidation phase is an integral part of standard consolidation theory as well as of the “active system consolidation” view of the memory function of sleep.

4.  Sleep-Specific Electrical Oscillations: A focus on sleep and sleep stages characterized by specific potential rhythms of brain activity. The authors review neocortical slow oscillations and SWA, thalamocortical spindles and hippocampal Sharp-Wave Ripple (SWR) which have been associated with processes of memory consolidation during SWS and might support the reactivation and redistribution of memory representations during this sleep stage.

5. Neuro-chemical Signaling And Memory Consolidation During Sleep: An examination of how sleep and sleep stages are characterized by a specific neurochemical environment of neurotransmitters and hormones), some of which contribute to memory consolidation by favoring processes of synaptic consolidation or processes of system consolidation.

6.  Genetic Approaches to Sleep-Dependent Memory Formation: The section discusses how the search for genes involved in sleep regulation has received a great boost in recent years with the discovery of quiet states in simple organisms like the fruit fly and worms that satisfy the criteria for sleep but that quest is tempered by the inability to identify sleep stages in these organisms.

7.  Developmental Aspects of Sleep-Related Brain Plasticity: This section highlights how human development enables understanding the mechanisms underlying sleep-dependent memory consolidation with a focus on how infants and children sleep longer and deeper.  Concurrently, in early life the brain exhibits particularly strong plasticity shaping memory systems and underlying neuronal circuit formation.

8.  Sleep-Dependent Memory Consolidation in the Immune System: Identification of the differences between memory formation in the immune system and in the central nervous system.

The state of current sleep and memory research

Newer research outcomes characterize sleep as a brain state optimizing memory consolidation, in opposition to the waking brain being optimized for encoding of memories. Consolidation originates from reactivation of recently encoded neuronal memory representations, which occur during SWS and transform respective representations for integration into long-term memory. Ensuing REM sleep may stabilize transformed memories. While elaborated with respect to hippocampus-dependent memories, the concept of an active redistribution of memory representations from networks serving as temporary store into long-term stores might hold also for non-hippocampus-dependent memory, and even for nonneuronal, i.e., immunological memories, giving rise to the idea that the offline consolidation of memory during sleep represents a principle of long-term memory formation established in quite different physiological systems.

More than ever, the value of sleep to overall health is being recognized by social and professional networks.  This review provides a needed insight on why sleep is essential to memory, an ability core to all facets of life. 

NOTE TO EDITORS: To schedule an interview with a member of the study team, please contact Donna Krupa at dkrupa@the-aps.org, @Phyziochick, or 301.634.7209. The article is available online at http://bit.ly/15IfNo6.

Physiology is the study of how molecules, cells, tissues and organs function in health and disease. Established in 1887, the American Physiological Society (APS) was the first U.S. society in the biomedical sciences field. The Society represents more than 10,500 members and publishes 15 peer-reviewed journals with a worldwide readership.