Memory, Sleep, and Dreaming: Experiencing Consolidation (original) (raw)
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Memory reactivation and consolidation during sleep
Learning & Memory, 2004
Do our memories remain static during sleep, or do they change? We argue here that memory change is not only a natural result of sleep cognition, but further, that such change constitutes a fundamental characteristic of declarative memories. In general, declarative memories change due to retrieval events at various times after initial learning and due to the formation and elaboration of associations with other memories, including memories formed after the initial learning episode. We propose that declarative memories change both during waking and during sleep, and that such change contributes to enhancing binding of the distinct representational components of some memories, and thus to a gradual process of cross-cortical consolidation. As a result of this special form of consolidation, declarative memories can become more cohesive and also more thoroughly integrated with other stored information. Further benefits of this memory reprocessing can include developing complex networks of interrelated memories, aligning memories with long-term strategies and goals, and generating insights based on novel combinations of memory fragments. A variety of research findings are consistent with the hypothesis that cross-cortical consolidation can progress during sleep, although further support is needed, and we suggest some potentially fruitful research directions. Determining how processing during sleep can facilitate memory storage will be an exciting focus of research in the coming years.
Neuron, 2004
will be covered: (1) early work in this area-a brief history; (2) some important general considerations on this topic; (3) REM sleep deprivation studies in animals; (4) cognitive capacities of humans with greatly suppressed We discuss several lines of evidence refuting the hypothesis that procedural or declarative memories are or absent REM sleep; (5) recent human studies on procedural memory and sleep; (6) the "replay" of patterns of processed/consolidated in sleep. One of the strongest arguments against a role for sleep in declarative mem-neural activity of waking in subsequent sleep in animals; (7) "other factors" that dispute a role for sleep in memory ory involves the demonstration that the marked suppression or elimination of REM sleep in subjects on processing; and (8) a proposed function for sleep. antidepressant drugs or with brainstem lesions produces no detrimental effects on cognition. Procedural A Revisiting of This Issue memory, like declarative memory, undergoes a slow, Although possibly not recognized outside of the sleep time-dependent period of consolidation. A process field, the role of sleep in memory processing is not a has recently been described wherein performance on new issue, but is one that was thoroughly examined in some procedural tasks improves with the mere pasthe 1960s to 1970s. There was a wealth of research in sage of time and has been termed "enhancement." animals, and to a lesser extent in humans, devoted to Some studies, but not others, have reported that the this topic (for review, see McGrath and Cohen, 1978; consolidation/enhancement of perceptual and motor Horne and McGrath, 1984; Smith, 1985; Horne, 1988). skills is dependent on sleep. We suggest that consoli-Current interest represents a second wave. Most of the dation or enhancement, initiated in waking with task early work in this area in both animals and humans acquisition, could in some instances extend to sleep, examined the effects of REM sleep deprivation on prebut sleep would serve no unique role in these proviously learned material. As later discussed in detail, the cesses. In sum, there is no compelling evidence to results of numerous studies on this subject, involving support a relationship between sleep and memory various manipulations across species, were divided. consolidation. There were as many reports that failed to describe a link between sleep and memory as there were those that claimed such a relationship (Horne and McGrath, Born, J., and Gais, S. (2000). REM sleep deprivation: The wrong paradigm leading to wrong conclusions. Behav. Brain Sci. 23, analogous to processes shown for declarative memo-912-913. ries. Consolidation (as stabilization) begins with task Brashers-Krug, T., Shadmehr, R., and Bizzi, E. (1996). Consolidation initiation, and unless disrupted by competing events, in human motor memory. Nature 382, 252-255.
The Journal of …, 2011
Memory consolidation benefits from sleep. In addition to strengthening some memory traces, another crucial, albeit overlooked, function of memory is to erase irrelevant information. Directed forgetting is an experimental approach consisting in presenting "to be remembered" and "to be forgotten" information that allows selectively decreasing or increasing the strength of individual memory traces according to the instruction provided at learning. This paradigm was used in combination with functional MRI to determine, in humans, what specifically triggers at encoding sleep-dependent compared with time-dependent consolidation. Our data indicate that relevant items that subjects strived to memorize are consolidated during sleep to a greater extent than items that participants did not intend to learn. This process appears to depend on a differential activation of the hippocampus at encoding, which acts as a signal for the offline reprocessing of relevant memories during postlearning sleep episodes.
A Dream Model: Reactivation and Re-encoding Mechanisms for Sleep-dependent Memory Consolidation
Cognitive Science, 2016
We humans spend almost a third of our lives asleep, and there is mounting evidence that sleep not only maintains, but actually improves many of our cognitive functions. Memory consolidation - the process of crystallizing and integrating memories into knowledge and skills - is particularly benefitted by sleep. We survey the evidence that sleep aids memory consolidation in various declarative and implicit memory tasks and review the basic neurophysiological structure of sleep with a focus on understanding what neural systems are involved. Drawing on machine learning research, we discuss why it might be useful for humans–and robots, perhaps–to have such an offline period for processing, even though humans are clearly capable of learning incrementally, online. Finally, we propose and simulate two mechanisms for use in computational memory models to accomplish sleep-based consolidation via either or both 1) re-encoding knowledge representations and 2) reactivating and strengthening recen...
The role of sleep in declarative memory consolidation: passive, permissive, active or none?
Current Opinion in Neurobiology, 2006
Those inclined to relish in scientific controversy will not be disappointed by the literature on the effects of sleep on memory. Opinions abound. Yet refinements in the experimental study of these complex processes of sleep and memory are bringing this fascinating relationship into sharper focus. A longstanding position contends that sleep passively protects memories by temporarily sheltering them from interference, thus providing precious little benefit for memory. But recent evidence is unmasking a more substantial and long-lasting benefit of sleep for declarative memories. Although the precise causal mechanisms within sleep that result in memory consolidation remain elusive, recent evidence leads us to conclude that unique neurobiological processes within sleep actively enhance declarative memories.
Sleep transforms the cerebral trace of declarative memories
Proceedings of The National Academy of Sciences, 2007
After encoding, memory traces are initially fragile and have to be reinforced to become permanent. The initial steps of this process occur at a cellular level within minutes or hours. Besides this rapid synaptic consolidation, systems consolidation occurs within a time frame of days to years. For declarative memory, the latter is presumed to rely on an interaction between different brain regions, in particular the hippocampus and the medial prefrontal cortex (mPFC). Specifically, sleep has been proposed to provide a setting that supports such systems consolidation processes, leading to a transfer and perhaps transformation of memories. Using functional MRI, we show that postlearning sleep enhances hippocampal responses during recall of word pairs 48 h after learning, indicating intrahippocampal memory processing during sleep. At the same time, sleep induces a memory-related functional connectivity between the hippocampus and the mPFC. Six months after learning, memories activated the mPFC more strongly when they were encoded before sleep, showing that sleep leads to longlasting changes in the representation of memories on a systems level.
Sleep and Memory Consolidation
Sci Insigt. 2019; 31(3):107-115., 2019
Sleep occupies about one third of a person's life. It is a critical physiological process. It is essential for the formation and consolidation of memory. Deficiency, lack of sleep will obviously affect the body's cognitive function. With the development of society and changes in lifestyle, more and more of people suffer from lack of sleep. We herein review the research history of the relationship between sleep and memory and discuss the most relevant fields and corresponding research progress, introduce various mechanisms of sleep to consolidate memory, and clarify the effects of sleep problems on memory. So as to help people better weigh the pros and cons of sleep, improve the quality of life, and respond to growing competition struggling for pressure and aging.■
Studies of Learning during Sleep: Problems, Progress, and Perspectives
Neuroscience and Behavioral Physiology, 2020
Sleep is a quickly reversible state characterized by the absence of consciousness and reductions in activity and the ability to respond to external stimuli. Sleep plays an important role in memory consolidation and, therefore, learning processes. Current studies address the specifi c mechanisms accompanying memory consolidation at levels from molecules to whole-brain activity. These works and the theories based on them suggest processing of previously obtained information stored in short-term memory. The question "can de novo learning not based on previously acquired information occur during sleep?" has been controversial for many years. There are now two main theories for the important role of sleep in learning. The active consolidation theory holds that during sleep, the neuronal complexes in the cerebral cortex which encode new information are reactivated and reorganized for integration into long-term memory. The neuronal representations of these memories are potentiated and fi xed. Hippocampus-dependent memory is tightly linked with the processes of slow-wave sleep (NREM sleep) and sleep spindles [1-3]. The synaptic homeostasis theory focuses on the opposite process: an overall reduction in synaptic activity during sleep. Representations of important memory traces undergo minimal weakening, while other connections return to their initial levels. This leads to improvements in the signal:noise ratio in neuronal ensembles, readying the brain to work with the new information [4, 5]. These theories complement each other, but presuppose that the brain operates as an isolated system during sleep. They both indicate that memory consolidation will prevent the formation of new memories. However, the brain can also process incoming sensory signals during sleep, as complete isolation from the external environment would be an enormous evolutionary risk. Various studies, especially those reported in the last decade, have pointed to the possibility that several types of learning may occur. The mechanisms and limits of learning potential during sleep remain unclear, though the authors of these studies have tried to integrate their results into a modern understanding of the mechanisms of sleep and memory consolidation. The review presented here focuses on the most straightforward studies in the understanding of "learning in sleep": studies in which subjects must assimilate some kind of new information during sleep, this being refl ected in their reactions or behavior. Another approach to manipulating memory during sleep has become popular in recent years. This is directed not to the memorization of new information during sleep
Memory Processing during Sleep Mechanisms and Evidence from Neuroimaging Studies
Psychologica Belgica, 2004
A growing number of studies support the hypothesis that sleep participates in the off-line processing of recent memories. However, many determinants and outcomes of memory reprocessing during sleep remain to be identified. This review provides a summary description of the main behavioural, neurophysiological and hemodynamic features of sleep, with a special emphasis on sleep mechanisms deemed potentially important to support sleep-related brain plasticity and memory consolidation: PGO-waves, spindles and hippocampal rhythms. Next are presented brain imaging studies having demonstrated the reexpression and modulation of learning-related cerebral activity during posttraining sleep in humans. As a whole, functional neuroimaging results nowadays suggest that learning-dependent modulations in cerebral activity during human sleep reflect the offline processing of recent memory traces, which eventually leads to the plastic changes underlying the subsequent improvement in performance.
Sleep Selectively Enhances Memory Expected to Be of Future Relevance
Journal of Neuroscience, 2011
The brain encodes huge amounts of information, but only a small fraction is stored for a longer time. There is now compelling evidence that the long-term storage of memories preferentially occurs during sleep. However, the factors mediating the selectivity of sleepassociated memory consolidation are poorly understood. Here, we show that the mere expectancy that a memory will be used in a future test determines whether or not sleep significantly benefits consolidation of this memory. Human subjects learned declarative memories (word paired associates) before retention periods of sleep or wakefulness. Postlearning sleep compared with wakefulness produced a strong improvement at delayed retrieval only if the subjects had been informed about the retrieval test after the learning period. If they had not been informed, retrieval after retention sleep did not differ from that after the wake retention interval. Retention during the wake intervals was not affected by retrieval expectancy. Retrieval expectancy also enhanced sleep-associated consolidation of visuospatial (two-dimensional object location task) and procedural motor memories (finger sequence tapping). Subjects expecting the retrieval displayed a robust increase in slow oscillation activity and sleep spindle count during postlearning slow-wave sleep (SWS). Sleepassociated consolidation of declarative memory was strongly correlated to slow oscillation activity and spindle count, but only if the subjects expected the retrieval test. In conclusion, our work shows that sleep preferentially benefits consolidation of memories that are relevant for future behavior, presumably through a SWS-dependent reprocessing of these memories.