No probs, I have a quick look-see on WOS...OK here we go...
Siegel (2005)
Clues to the functions of mammalian sleep | Nature
We present evidence disputing the hypothesis that memories are processed or consolidated in REM sleep. A review of REM deprivation (REMD) studies in animals shows these reports to be about equally divided in showing that REMD does, or does not, disrupt learning/memory. The studies supporting a relationship between REM sleep and memory leave been strongly criticized for the confounding effects of every stressful REAL deprivation techniques. The three major classes of antidepressant drugs, monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants (TCAs), and selective serotonin reuptake inhibitors (SSRIs), profoundly suppress REM sleep. The MAOIs virtually abolish REM sleep, and the TCAs and SSRIs have been shown to produce immediate (40-85%) and sustained (30-50%) reductions in REM sleep. Despite marked suppression of REM sleep, these classes of antidepressants on the whole do not disrupt learning/memory. There have been a few reports of patients who have survived bilateral lesions of the pons with few lingering complications. Although these lesions essentially abolished REM sleep, the patients reportedly led normal lives. Recent functional imaging studies in humans have revealed patterns of brain activity in REM sleep that are consistent with dream processes but not with memory consolidation. We propose that the primary function of REM sleep is to provide periodic endogenous stimulation to the Brain which serves to maintain requisite levels of central nervous system (CNS) activity throughout sleep. REM is the mechanism used by the brain to promote recover from sleep. We believe that the cumulative evidence indicates that REM sleep serves no role in the processing or consolidation of memory.
Title: The case against memory consolidation in REM sleep
Author(s): Vertes RP, Eastman KE
Source: BEHAVIORAL AND BRAIN SCIENCES 23 (6): 867-+ DEC 2000
It has been hypothesized that REM (rapid eye movement) steep has an important role in memory consolidation. The evidence for this hypothesis is reviewed and found to be weak and contradictory. Animal studies correlating changes in REM steep parameters with learning have produced inconsistent results and are confounded by stress effects. Humans with pharmacological and brain lesion-induced suppression of REM steep do not show memory deficits, and other human steep-learning studies have not produced consistent results. The time spent in REM steep is not correlated with learning ability across humans, nor is there a positive relation between REM steep time or intensity and encephalization across species. Although steep is clearly important for optimum acquisition and performance of learned tasks, a major role in memory consolidation is unproven.
Title: The REM sleep - Memory consolidation hypothesis
Author(s): Siegel JM
Source: SCIENCE 294 (5544): 1058-1063 NOV 2 2001
The memory consolidation idea a persistent theory in sleep research and doesn't seem to disappear but there are good reasons to question it. Here's a recent paper that supports the memory consolidation theory...
Although the function of sleep remains elusive, there is compelling evidence to suggest that sleep plays an important role in learning and memory. A number of studies have now shown that sleep deprivation (SD) results in significant impairment of long-term potentiation (LTP) in the hippocampus. In this study, we have attempted to determine the mechanisms responsible for this impairment. After 72 h SD using the multiple-platform technique, we observed a reduction in the whole-cell recorded NMDA/AMPA ratio of CA1 pyramidal cells in response to Schaffer collateral stimulation. This impairment was specific to sleep deprivation as rats placed over a single large platform, which allowed sleep, had a normal NMDA/AMPA ratio. mEPSCs evoked by local application of a high osmolarity solution revealed no differences in the AMPA receptor function. NMDA currents recorded from outside-out patches excised from the distal dendrites of CA1 cells displayed a reduction in amplitude after SD. While there were no alterations in the glutamate sensitivity, channel open probability or the single channel conductance of the receptor, a crosslinking assay demonstrated that the NR1 and NR2A subunits of NMDA receptors were preferentially retained in the cytoplasm after SD, indicating that SD alters NMDAR surface expression. In summary, we have identified a potential mechanism underlying SD-induced LTP impairment. This synaptic alteration may underlie the cognitive deficits seen following sleep deprivation and could represent a target for future intervention studies.
Title: Sleep deprivation-induced alterations in excitatory synaptic transmission in the CA1 region of the rat hippocampus
Author(s): McDermott CM, Hardy MN, Bazan NG, Magee JC
Source: JOURNAL OF PHYSIOLOGY-LONDON 570 (3): 553-565 FEB 1 2006
and another...
Abstract: Although the functions of sleep remain largely unknown, one of the most exciting hypotheses is that sleep contributes importantly to processes of memory and brain plasticity. Over the past decade, a large body of work, spanning most of the neurosciences, has provided a substantive body of evidence supporting this role of sleep in what is becoming known as sleep-dependent memory processing. We review these findings, focusing specifically on the role of sleep in (a) memory encoding, (b) memory consolidation, (c) brain plasticity, and (d) memory reconsolidation; we finish with a summary of the field and its potential future directions.
Title: Sleep, memory, and plasticity
Author(s): Walker MP, Stickgold R
Source: ANNUAL REVIEW OF PSYCHOLOGY 57: 139-166 2006
I like the way this abstract calls this idea exciting - it's actually old hat and has been around for yonks. Siegel would probably accept that REM is important for plastcity and neural growth during the developmental phase, but loses it's importance once the brain is developed i.e. it is not essential for learning/memory in an adult.
edit: Now here's a study I didn't know of - quite interesting in that it makes a distinction between emotional learning and declarative learning. REM deprivation may affect just the emotional component of memory, whereas slow-wave affects declarative memory...
Background
Previous research indicates that hippocampus-dependent declarative memory benefits from early nocturnal sleep, when slow-wave sleep (SWS) prevails and cortisol release is minimal, whereas amygdala-dependent emotional memory is enhanced through late sleep, when rapid eye movement (REM) sleep predominates. The role of the strong cortisol rise accompanying late sleep for emotional memory consolidation has not yet been investigated.
Methods
Effects of the cortisol synthesis inhibitor metyrapone on sleep-associated consolidation of memory for neutral and emotional texts were investigated in a randomized, double-blind, placebo-controlled study in 14 healthy men. Learning took place immediately before treatment, which was followed by 8 hours of sleep. Retrieval was tested at 11 am the next morning.
Results
Metyrapone suppressed cortisol during sleep and blocked particularly the late-night rise in cortisol. It reduced SWS and concomitantly impaired the consolidation of neutral texts. Emotional texts were spared from this impairing influence, however. Metyrapone even amplified emotional enhancement in text recall indicating amygdala-dependent memory.
Conclusions
Cortisol blockade during sleep impairs hippocampus-dependent declarative memory formation but enhances amygdala-dependent emotional memory formation. The natural cortisol rise during late sleep may thus protect from overshooting emotional memory formation, a mechanism possibly pertinent to the development of posttraumatic stress disorder.
Title: Effects of cortisol suppression on sleep-associated consolidation of neutral and emotional memory
Author(s): Wagner U, Degirmenci M, Drosopoulos S, Perras B, Born J
Source: BIOLOGICAL PSYCHIATRY 58 (11): 885-893 DEC 1 2005
This could explain why there is little cognitive effect of REM deprivation.
This message has been edited by melatonin, 02-20-2006 05:41 PM
This message has been edited by melatonin, 02-20-2006 05:50 PM
This message has been edited by melatonin, 02-20-2006 05:50 PM
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