29 March 2012

Continuous Sleep Favorable In Long Term Memory Consolidation and Enhancement

Memory Consolidation is a process where the brain stabilizes a memory trace after the initial acquisition. Memory is usually acquired during conscious periods through learning or experience.

Consolidation is distinguished into two specific processes, synaptic consolidation, which occurs within the first few hours after learning, and system consolidation, where hippocampus-dependent memories become independent of the hippocampus over a period of weeks to years. Recently, a third process has become the focus of research, reconsolidation, in which previously consolidated memories can be made labile again through reactivation of the memory trace.

Based on studies and observation, rapid eye movement (REM) sleep is crucial in the overnight learning in humans by the re-organization of novel information in the hippocampal and cortical regions of the brain. REM sleep elicits an increase in neuronal activity following an enriched or novel waking experience, thus increasing neuronal plasticity and therefore playing an essential role in the consolidation of memories.

Sleep disturbance negatively impacts the memory consolidation and enhancement that usually occurs with a good night's sleep, according to a study published in the open access journal PLoS ONE.

In their abstract, the authors state, "A growing literature supports a role for sleep after training in long-term memory consolidation and enhancement. Consequently, interrupted sleep should result in cognitive deficits. Recent evidence from an animal study indeed showed that optimal memory consolidation during sleep requires a certain amount of uninterrupted sleep. Sleep continuity is disrupted in various medical disorders."

Video: Sleep-Dependent Consolidation of Memory

Improvement of a skill can be enhanced by ongoing training, but it can even continue afterwards through off-line processes. Sleep is a complex state that has been shown to promote off-line memory consolidation and its underlying plastic processes. Only over the past decade has sleep become recognized as a state favorable for brain plasticity.

It is becoming widely accepted that sleep is crucial for cementing long-term memory, so in this new study, the researchers went a step further to investigate whether these beneficial effects only arise after some minimum amount of continuous sleep. The authors, led by Ina Djonlagic at Brigham and Women's Hospital in Boston, found that patients with sleep apnea, which leads to sleep disturbances, showed significantly lower overnight improvement and plateau performance for a newly learned motor task than seen for the control group. Both groups had comparable initial learning performance during the training phase, suggesting that the overnight sleep disturbance was likely related to the subsequent poorer performance.

"Optimal overnight memory consolidation in humans requires a certain amount of sleep continuity independent of the total amount of sleep" conclude the authors.


Public Library of Science
Increased Sleep Fragmentation Leads to Impaired Off-Line Consolidation of Motor Memories in Humans
Brigham and Women's Hospital
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