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Biomedical subjects

Matthew P Walker

Publications and source records attributed to Matthew P Walker.

17 recordsLinked to original sources
PubMed2006

Sleep facilitates consolidation of emotional declarative memory.

Both sleep and emotion are known to modulate processes of memory consolidation, yet their interaction is poorly understood. We examined the influence of sleep on consolidation of emotionally arousing and neutral declarative memory. Subjects completed an initial study session involving arousing and neutral pictures, either in the evening or in the morning. Twelve hours later, after sleeping or staying awake, subjects performed a recognition test requiring them to discriminate between these original pictures and novel pictures by responding "remember,""know" (familiar), or "new." Selective sleep effects were observed for consolidation of emotional memory: Recognition accuracy for know judgments of arousing stimuli improved by 42% after sleep relative to wake, and recognition bias for remember judgments of these stimuli increased by 58% after sleep relative to wake (resulting in more conservative responding). These findings hold important implications for understanding of human memory processing, suggesting that the facilitation of memory for emotionally salient information may preferentially develop during sleep.

Adult↗
PubMed2006

Sleep, memory, and plasticity.

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.

Animals↗
PubMed2005

The functional anatomy of sleep-dependent visual skill learning.

Learning of procedural skills develops gradually, with performance improving significantly with practice. But improvement on some tasks, including a visual texture discrimination task, continues in the absence of further practice, expressly during periods of sleep and not across equivalent waking episodes. Here we report that the brain activation revealed significantly different patterns of performance-related functional activity following a night of sleep relative to 1 h post-training without intervening sleep. When task activation patterns after a night of sleep were compared with activation patterns without intervening sleep (1 h post-training), significant regions of increased signal intensity were observed in the primary visual cortex, the occipital temporal junction, the medial temporal lobe and the inferior parietal lobe. In contrast, a region of decreased signal intensity was found in the right temporal pole. Corroborating these condition differences, correlations between behavioural performance and brain activation revealed significantly different patterns of performance-related functional activity following a night of sleep relative to those without intervening sleep. Together, these data provide evidence of overnight bi-directional changes in functional anatomy, differences that may form the neural basis of sleep-dependent learning expressed on this task.

Adult↗
PubMed2005

It's practice, with sleep, that makes perfect: implications of sleep-dependent learning and plasticity for skill performance.

Although there is no consensus regarding the functions of sleep, one exciting hypothesis is that sleep contributes importantly to learning and memory. Over the last decade, several studies have provided substantive evidence supporting the role of sleep in memory processing. This article focuses on sleep-dependent learning and brain plasticity in humans, specifically in the development of skill performance that is the foundation of many sports actions. The different forms and stages of human memory are discussed, then evidence of sleep-dependent skill learning and associated sleep-dependent brain plasticity is described. In conclusion, a consideration of the fundamental importance of sleep in real-life skill learning is provided.

Brain↗
PubMed2005

Memory consolidation and reconsolidation: what is the role of sleep?

Memory consolidation and reconsolidation reflect molecular, cellular and systems-level processes that convert labile memory representations into more permanent ones, available for continued reactivation and recall over extended periods of time. Here, we discuss the complexities of consolidation and reconsolidation, and suggest they should be viewed not as all-or-none phenomena, but as a continuing series of biological adjustments that enhance both the efficiency and the utility of stored memories over time and in response to changing needs of the organism. As such, consolidation and reconsolidation might be better thought of as memory organization and reorganization. A rapidly growing body of evidence suggests that many of these processes are optimally engaged during sleep.

Animals↗
PubMed2005

A refined model of sleep and the time course of memory formation.

Research in the neurosciences continues to provide evidence that sleep plays a role in the processes of learning and memory. There is less of a consensus, however, regarding the precise stages of memory development during which sleep is considered a requirement, simply favorable, or not important. This article begins with an overview of recent studies regarding sleep and learning, predominantly in the procedural memory domain, and is measured against our current understanding of the mechanisms that govern memory formation. Based on these considerations, I offer a new neurocognitive framework of procedural learning, consisting first of acquisition, followed by two specific stages of consolidation, one involving a process of stabilization, the other involving enhancement, whereby delayed learning occurs. Psychophysiological evidence indicates that initial acquisition does not rely fundamentally on sleep. This also appears to be true for the stabilization phase of consolidation, with durable representations, resistant to interference, clearly developing in a successful manner during time awake (or just time, per se). In contrast, the consolidation stage, resulting in additional/enhanced learning in the absence of further rehearsal, does appear to rely on the process of sleep, with evidence for specific sleep-stage dependencies across the procedural domain. Evaluations at a molecular, cellular, and systems level currently offer several sleep specific candidates that could play a role in sleep-dependent learning. These include the upregulation of select plasticity-associated genes, increased protein synthesis, changes in neurotransmitter concentration, and specific electrical events in neuronal networks that modulate synaptic potentiation.

Adaptation, Physiological↗
PubMed2005

Sleep and memory: the ongoing debate.

The last 10 years have produced a wealth of scientific studies reporting a role for sleep in offline memory processing. Despite this evidence, debate continues to rage over the very existence of sleep-dependent learning and memory processing. We briefly review here the evidence in support of sleep's role in memory consolidation.

Brain↗
PubMed2004

Sleep-dependent learning and memory consolidation.

While the functions of sleep remain largely unknown, one of the most exciting and contentious hypotheses is that sleep contributes importantly to memory. A large number of studies offer a substantive body of evidence supporting this role of sleep in what is becoming known as sleep-dependent memory processing. This review will provide evidence of sleep-dependent memory consolidation and sleep-dependent brain plasticity and is divided into five sections: (1) an overview of sleep stages, memory categories, and the distinct stages of memory development; (2) a review of the specific relationships between sleep and memory, both in humans and animals; (3) a survey of evidence describing sleep-dependent brain plasticity, including human brain imaging studies as well as animal studies of cellular neurophysiology and molecular biology. We close (4) with a consideration of unanswered questions as well as existing arguments against the role of sleep in learning and memory and (5) a concluding summary.

Animals↗
PubMed2004

The influence of sleep on auditory learning: a behavioral study.

Evidence continues to support a role for sleep in delayed learning without further practice. Here we demonstrate the beneficial influence of sleep on auditory skill learning. Fifty-six subjects were randomly assigned to two groups, trained and tested on a pitch memory task three times across 24 h. The morning group was trained at 09.00 h, retested 12 h later that same day, and again after 12 h sleep. The evening group was trained at 21.00 h, retested 12 h immediately after sleep, and again 12 h later the next day. At retesting, both groups combined showed significant delayed learning only after sleep, but not across equivalent periods of wake, regardless of which came first. These data add to the growing literature describing sleep-dependent learning throughout sensory and motor domains.

Acoustic Stimulation↗
PubMed2003

Dissociable stages of human memory consolidation and reconsolidation.

Historically, the term 'memory consolidation' refers to a process whereby a memory becomes increasingly resistant to interference from competing or disrupting factors with the continued passage of time. Recent findings regarding the learning of skilled sensory and motor tasks ('procedural learning') have refined this definition, suggesting that consolidation can be more strictly determined by time spent in specific brain states such as wake, sleep or certain stages of sleep. There is also renewed interest in the possibility that recalling or 'reactivating' a previously consolidated memory renders it once again fragile and susceptible to interference, therefore requiring periods of reconsolidation. Using a motor skill finger-tapping task, here we provide evidence for at least three different stages of human motor memory processing after initial acquisition. We describe the unique contributions of wake and sleep in the development of different forms of consolidation, and show that waking reactivation can turn a previously consolidated memory back into a labile state requiring subsequent reconsolidation.

Fingers↗
PubMed2003

Metastatic disease of the spine: evaluation and treatment.

Treatment of patients with metastatic disease of the spine continues to be a challenging problem. Advances in imaging studies and surgical techniques have improved patient outcomes with operative intervention. However, the lack of a validated set of criteria to determine spinal instability makes patient selection for surgical intervention difficult. Multiple classification systems that assist surgeons in determining appropriate operative candidates have been proposed. We will review current information on the evaluation and treatment of metastatic disease of the spine and discuss classification systems that assist in determining appropriate operative candidates.

Algorithms↗
PubMed2002

Practice with sleep makes perfect: sleep-dependent motor skill learning.

Improvement in motor skill performance is known to continue for at least 24 hr following training, yet the relative contributions of time spent awake and asleep are unknown. Here we provide evidence that a night of sleep results in a 20% increase in motor speed without loss of accuracy, while an equivalent period of time during wake provides no significant benefit. Furthermore, a significant correlation exists between the improved performance overnight and the amount of stage 2 NREM sleep, particularly late in the night. This finding of sleep-dependent motor skill improvement may have important implications for the efficient learning of all skilled actions in humans.

Adolescent↗
PubMed2002

Cognitive flexibility across the sleep-wake cycle: REM-sleep enhancement of anagram problem solving.

Flexible or 'fluid' cognitive processes are regarded as fundamental to problem solving and creative ability, requiring a specific neurophysiological milieu. REM-sleep dreaming is associated with creative processes and abstract reasoning with increased strength of weak associations in cognitive networks. REM sleep is also mediated by a distinctive neurophysiological profile, different to that of wake and NREM sleep. This study compared the performance of 16 subjects on a test of cognitive flexibility using anagram word puzzles following REM and NREM awakenings across the night, and waking performances during the day. REM awakenings provided a significant 32% advantage in the number of anagrams solved compared with NREM awakenings and was equal to that of wake time trials. Correlations of individual performance profiles suggest that REM sleep may offer a different mode of problem solving compared with wake and NREM. When early and late REM and NREM awakening data were separated, a dissociation was evident, with NREM task performance becoming more REM-like later in the night, while REM performance remained constant. These data suggest that the neurophysiology of REM sleep represents a brain state more amenable to flexible cognitive processing than NREM and different from that in wake, and may offer insights into the neurocognitive properties of REM-sleep dreaming.

Adolescent↗
PubMed2002

Clinical and neuropathological correlates of apolipoprotein E genotype in dementia with Lewy bodies.

Dementia with Lewy bodies (DLB) represents the second commonest cause of dementia in the elderly following Alzheimer's disease (AD). Whilst the presence of Lewy bodies is essential, DLB shares with AD the presence of senile plaques (SP), but neurofibrillary tangles (NFT) are not a necessary feature. The apolipoprotein E (APO E) epsilon4 allele is the most consistently associated genetic risk factor for AD and has also been shown to associate with DLB. We have therefore analysed the APO E epsilon4 allele in a large series of DLB cases coming to autopsy to: (1) determine if the epsilon4 allele describes a similar risk in DLB development as in AD and (2) determine how APO E epsilon4 allele status correlates with clinical and neuropathological findings in DLB, and in AD, as an indication of the role of APO E in underlying disease biology. Both DLB and AD share an increased epsilon4 allele frequency, though in DLB the epsilon2 allele frequency is not reduced and there is a relative lack of epsilon4 homozygotes. In contrast to previous studies, no association of the epsilon4 allele with age at onset or duration of disease was found in either disorders. In DLB cases, overall a significantly shorter duration of illness was observed when compared with AD cases, though no significant effect of the epsilon4 allele on disease onset or duration was seen. The survival rate was reduced by the presence of the epsilon4 allele in DLB, as with AD. No effect on SP or NFT counts was seen with the epsilon4 allele, though DLB cases showed a lower SP burden in addition to the expected lower NFT counts. This study demonstrates that DLB shares the APO epsilon4 allele with AD as a common risk factor, but that there are differences in the way the epsilon4 allele affects the phenotypic expression of disease.

Adult↗
PubMedDate not supplied

Sleep and the time course of motor skill learning.

Growing evidence suggests that sleep plays an important role in the process of procedural learning. Most recently, sleep has been implicated in the continued development of motor-skill learning following initial acquisition. However, the temporal evolution of motor learning before and after sleep, the effects of different training regimens, and the long-term development of motor learning across multiple nights of sleep remain unknown. Here, we report data for subjects trained and retested on a sequential finger-tapping task across multiple days. The findings demonstrate firstly that following initial training, small practice-dependent improvements are possible before, but not following the large practice-independent gains that develop across a night of sleep. Secondly, doubling the quantity of initial training does not alter the amount of subsequent sleep-dependent learning that develops overnight. Thirdly, the amount of sleep-dependent learning does not correlate with the amount of practice-dependent learning achieved during training, suggesting the existence of two discrete motor-learning processes. Finally, whereas the majority of sleep-dependent motor-skill learning develops during the first night of sleep following training, additional nights of sleep still offer continued improvements.

Adult↗
PubMedDate not supplied

Sleep-dependent learning and motor-skill complexity.

Learning of a procedural motor-skill task is known to progress through a series of unique memory stages. Performance initially improves during training, and continues to improve, without further rehearsal, across subsequent periods of sleep. Here, we investigate how this delayed sleep-dependent learning is affected when the task characteristics are varied across several degrees of difficulty, and whether this improvement differentially enhances individual transitions of the motor-sequence pattern being learned. We report that subjects show similar overnight improvements in speed whether learning a five-element unimanual sequence (17.7% improvement), a nine-element unimanual sequence (20.2%), or a five-element bimanual sequence (17.5%), but show markedly increased overnight improvement (28.9%) with a nine-element bimanual sequence. In addition, individual transitions within the motor-sequence pattern that appeared most difficult at the end of training showed a significant 17.8% increase in speed overnight, whereas those transitions that were performed most rapidly at the end of training showed only a non-significant 1.4% improvement. Together, these findings suggest that the sleep-dependent learning process selectively provides maximum benefit to motor-skill procedures that proved to be most difficult prior to sleep.

Adolescent↗