Age-related decline of sleep-dependent consolidation

Sleep-dependent memory consolidation is observed following motor skill learning: Performance improvements are greater over a 12-h period containing sleep relative to an equivalent interval without sleep. Here we examined whether older adults exhibit sleep-dependent consolidation on a sequence learning task. Participants were trained on one of two sequence learning tasks. Performance was assessed after a 12-h break that included sleep and after a 12-h break that did not include sleep. Older and younger adults showed similar degrees of initial learning. However, performance of the older adults did not improve following sleep, providing evidence that sleep-dependent consolidation is diminished with age.     

Children's initial sleep‐associated changes in motor skill are unrelated to long‐term skill levels

Sleep is considered to support the formation of skill memory. In juvenile but not adult song birds learning a tutor's song, a stronger initial deterioration of song performance over night‐sleep predicts better song performance in the long run. This and similar observations have stimulated the view of sleep supporting skill formation during development in an unsupervised off‐line learning process that, in the absence of external feedback, can initially also enhance inaccuracies in skill performance. Here we explored whether in children learning a motor sequence task, as in song‐learning juvenile birds, changes across sleep after initial practice predict performance levels achieved in the long run. The task was a serial reaction time task (SRTT) where subjects had to press buttons which were lighted up in a repeating eight‐element sequence as fast as possible. Twenty‐five children (8–12 years) practised the task in the evening before nocturnal sleep which was recorded polysomnographically. Retrieval was tested on the following morning and again 1 week later after daily training on the SRTT. As expected, changes in response speed over the initial night of sleep were negatively correlated with final performance speed after the 1‐week training. However, unlike in song birds, this correlation was driven by the baseline speed level achieved before sleep. Baseline‐corrected changes in speed or variability over the initial sleep period did not predict final performance on the trained SRTT sequence, or on different sequences introduced to assess generalization of the trained behaviour. The lack of correlation between initial sleep‐dependent changes and long‐term performance might reflect that the children were too experienced for the simple SRTT, possibly also favouring ceiling effects in performance. A consistent association found between sleep spindle activity and explicit sequence knowledge alternatively suggests that the expected correlation was masked by explicit memory systems interacting with skill memory formation.     

Sleep-dependent consolidation of procedural motor memories in children and adults: the pre-sleep level of performance matters

In striking contrast to adults, in children sleep following training a motor task did not induce the expected (offline) gain in motor skill performance in previous studies. Children normally perform at distinctly lower levels than adults. Moreover, evidence in adults suggests that sleep dependent offline gains in skill essentially depend on the pre-sleep level of performance. Against this background, we asked whether improving children's performance on a motor sequence learning task by extended training to levels approaching those of adults would enable sleep-associated gains in motor skill in this age group also. Children (4-6 years) and adults (18-35 years) performed on the motor sequence learning task (button-box task) before and after ~2-hour retention intervals including either sleep (midday nap) or wakefulness. Whereas one group of children and adults, respectively, received the standard amount of 10 blocks of training before retention intervals of sleep or wakefulness, a further group of children received an extended training on 30 blocks (distributed across 3 days). A further group of adults received a restricted training on only two blocks before the retention intervals. Children after standard training reached lowest performance levels, whereas in adults performance after standard training was highest. Children with extended training and adults after reduced training reached intermediate performance levels. Only at these intermediate performance levels did sleep induce significant gains in motor sequence skill, whereas performance did not benefit from sleep in the low-performing children or in the high-performing adults. Spindle counts in the post-training nap were correlated with performance gains at retrieval only in the adults benefitting from sleep. We conclude that, across age groups, sleep induces the most robust gain in motor skill at an intermediate pre-sleep performance level. In low-performing children sleep-dependent improvements in skill may be revealed only after enhancing the pre-sleep performance level by extended training.     

Neurocognitive Contributions to Motor Skill Learning: The Role of Working Memory

ABSTRACT

Researchers have begun to delineate the precise nature and neural correlates of the cognitive processes that contribute to motor skill learning. The authors review recent work from their laboratory designed to further understand the neurocognitive mechanisms of skill acquisition. The authors have demonstrated an important role for spatial working memory in 2 different types of motor skill learning, sensorimotor adaptation and motor sequence learning. They have shown that individual differences in spatial working memory capacity predict the rate of motor learning for sensorimotor adaptation and motor sequence learning, and have also reported neural overlap between a spatial working memory task and the early, but not late, stages of adaptation, particularly in the right dorsolateral prefrontal cortex and bilateral inferior parietal lobules. The authors propose that spatial working memory is relied on for processing motor error information to update motor control for subsequent actions. Further, they suggest that working memory is relied on during learning new action sequences for chunking individual action elements together.     

The effects of ageing and cognitive impairment on on‐line and off‐line motor learning

Skilled performance is a collective function of practice‐related experiences (online learning) and post‐practice memory consolidation during sleep (offline learning). This study examines the effects of ageing and cognitive impairment on the on‐ and offline learning of a point‐to‐point arm movement. In a 3‐day experiment, older adults (cognitively normal or impaired) and young adults (YAs) were randomly assigned to practice or no‐practice conditions. Changes in the dependent measures of movement time and timing error were analysed within and between conditions across days. The findings suggest that both age and cognitive function affect skill learning. YAs improved performance via both on‐ and offline learning whereas older adults with normal cognitive capacities appeared to learn the movement skill primarily in an online mode. Cognitive impairments were found to hinder both types of skill learning. Implications for motor skill acquisition and rehabilitation are briefly discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Consolidation of sensorimotor learning during sleep

Consolidation of nondeclarative memory is widely believed to benefit from sleep. However, evidence is mainly limited to tasks involving rote learning of the same stimulus or behavior, and recent findings have questioned the extent of sleep-dependent consolidation. We demonstrate consolidation during sleep for a multimodal sensorimotor skill that was trained and tested in different visual-spatial virtual environments. Participants performed a task requiring the production of novel motor responses in coordination with continuously changing audio-visual stimuli. Performance improved with training, decreased following waking retention, but recovered and stabilized following sleep. These results extend the domain of sleep-dependent consolidation to more complex, adaptive behaviors.     

Sleep in children improves memory performance on declarative but not procedural tasks

Sleep supports the consolidation of memory in adults. Childhood is a period hallmarked by huge demands of brain plasticity as well as great amounts of efficient sleep. Whether sleep supports memory consolidation in children as in adults is unclear. We compared effects of nocturnal sleep (versus daytime wakefulness) on consolidation of declarative (word-pair associates, two-dimensional [2D] object location), and procedural memories (finger sequence tapping) in 15 children (6-8 yr) and 15 adults. Beneficial effects of sleep on retention of declarative memories were comparable in children and adults. However, opposite to adults, children showed smaller improvement in finger-tapping skill across retention sleep than wakefulness, indicating that sleep-dependent procedural memory consolidation depends on developmental stage.     

A latent consolidation phase in auditory identification learning: time in the awake state is sufficient

Large gains in performance, evolving hours after practice has terminated, were reported in a number of visual and some motor learning tasks, as well as recently in an auditory nonverbal discrimination task. It was proposed that these gains reflect a latent phase of experience-triggered memory consolidation in human skill learning. It is not clear, however, whether and when delayed gains in performance evolve following training in an auditory verbal identification task. Here we show that normal-hearing young adults trained to identify consonant-vowel stimuli in increasing levels of background noise showed significant, robust, delayed gains in performance that became effective not earlier than 4 h post-training, with most participants improving at more than 6 h post-training. These gains were retained for over 6 mo. Moreover, although it has been recently argued that time including sleep, rather than time per se, is necessary for the evolution of delayed gains in human perceptual learning, our results show that 12 h post-training in the waking state were as effective as 12 h, including no less than 6 h night's sleep. Altogether, the results indicate, for the first time, the existence of a latent, hours-long, consolidation phase in a human auditory verbal learning task, which occurs even during the awake state.     

关于午睡研究的概述

适当的午睡可以缓解我们午后的疲劳感,提高午后心境状态、觉醒状态;对于进行了正常夜眠的个体而言,习惯性午睡行为并不是对夜眠不足的补偿;短时午睡对恢复正常体个体身心状态有着积极的效果;然而,越来越多的研究也发现,午睡对记忆也有一定的整合作用。午睡中慢波睡眠对陈述性记忆的整合起着重要作用,此外,二期睡眠纺锤波对陈述性记忆及程序性记忆的整合也起着一定的作用。利用午睡探讨睡眠对记忆的整合作用及机制,可能是未来研究的方向     

The beneficial effect of synchronized action on motor and perceptual timing in children

We examined the role of action in motor and perceptual timing across development. Adults and children aged 5 or 8 years old learned the duration of a rhythmic interval with or without concurrent action. We compared the effects of sensorimotor versus visual learning on subsequent timing behaviour in three different tasks: rhythm reproduction (Experiment 1), rhythm discrimination (Experiment 2) and interval discrimination (Experiment 3). Sensorimotor learning consisted of sensorimotor synchronization (tapping) to an isochronous visual rhythmic stimulus (ISI = 800 ms), whereas visual learning consisted of simply observing this rhythmic stimulus. Results confirmed our hypothesis that synchronized action during learning systematically benefitted subsequent timing performance, particularly for younger children. Action‐related improvements in accuracy were observed for both motor and perceptual timing in 5 years olds and for perceptual timing in the two older age groups. Benefits on perceptual timing tasks indicate that action shapes the cognitive representation of interval duration. Moreover, correlations with neuropsychological scores indicated that while timing performance in the visual learning condition depended on motor and memory capacity, sensorimotor learning facilitated an accurate representation of time independently of individual differences in motor and memory skill. Overall, our findings support the idea that action helps children to construct an independent and flexible representation of time, which leads to coupled sensorimotor coding for action and time.     

The impact of post-learning sleep vs. wakefulness on recognition memory for faces with different facial expressions

A beneficial effect of sleep after learning, compared to wakefulness, on memory formation has been shown in many studies using a variety of tasks. However, none of these studies has specifically addressed recognition memory for faces so far. The recognition of familiar faces, together with the extraction of emotional information from facial expression, is a fundamental cognitive skill in human everyday life, for which specific neural systems and mechanisms of processing have been developed. Here, we investigated the role of post-learning sleep for later recognition memory for neutral, happy, and angry faces. Twelve healthy subjects, after judging the emotional valence of the faces in the evening (learning phase), either slept normally in the subsequent night, with sleep recorded polysomnographically (sleep condition), or remained awake (wake condition) according to a cross-over design. Recognition testing took place in the second evening after learning, i.e. after a further night of regular sleep spent at home. Sleep after learning, compared to wakefulness, enhanced memory accuracy in recognition memory. This effect was independent of the emotional valence of facial expression. The response criterion at recognition testing did not differ between sleep and wake conditions. The amount of non rapid eye movement (NonREM) sleep during post-learning sleep correlated positively with memory accuracy at recognition testing, while time in REM sleep was associated with a speeded responding to the learned faces. Results suggest that face recognition, despite its dependence on specialized brain systems, nevertheless relies on the general neural mechanisms of sleep-associated memory consolidation.     

Offline consolidation of memory varies with time in slow wave sleep and can be accelerated by cuing memory reactivations

Memory representations are reactivated during slow-wave sleep (SWS) after learning, and these reactivations cause a beneficial effect of sleep for memory consolidation. Memory reactivations can also be externally triggered during sleep by associated cues which enhance the sleep-dependent memory consolidation process. Here, we compared in humans the influence of sleep periods (i) of 40min and (ii) of 90min without externally triggered reactivations and (iii) of externally triggered reactivations by an associated odor cue during a 40-min sleep period on the consolidation of previously learned hippocampus-dependent visuo-spatial memories. We show that external reactivation by an odor cue during the 40-min sleep period enhanced memory stability to the same extent as 90min of sleep without odor reactivation. In contrast, 40min of sleep without external reactivations were not sufficient to benefit memory. In the 90-min sleep condition, memory enhancements were associated with time spent in SWS and were independent of the presence or absence of REM sleep. These results suggest that the efficacy of hippocampus-dependent memory consolidation depends on the duration of sleep and particularly SWS. External reactivation cues can accelerate the consolidation process even during shorter sleep episodes.     

Effects of aging on priming and skill learning.

This study examined the effects of aging on 2 kinds of implicit memory; repetition priming and skill learning. In Experiment 1, older adults showed less improvement in the skill of reading inverted words than did young adults, but priming performance did not differ for the 2 age groups. Similarly, in Experiment 2, in a partial-word identification task, skill learning was observed only for young adults, whereas there was no age difference in priming. Experiments 1a and 2a, however, showed that when older adults were presented with more perceptual information than were young adults, the age deficit in skill learning was eliminated. These results indicate that skill learning is impaired under data-limited conditions, whereas priming is unaffected under these conditions. It is proposed that the age deficit in skill learning is related to a deficit in perceptual organization and reorganization.     

A matter of time: rapid motor memory stabilization in childhood

Are children better than adults in acquiring new skills (‘how‐to’ knowledge) because of a difference in skill memory consolidation? Here we tested the proposal that, as opposed to adults, children's memories for newly acquired skills are immune to interference by subsequent experience. The establishment of long‐term memory for a trained movement sequence in adults requires a phase of memory consolidation. This results in substantial delayed, ‘offline’, performance gains, which nevertheless remain susceptible to interference by subsequent competing motor experience for several hours after training, unless sleep is afforded in the interval. Here we compared the gains attained overnight (delayed gains) by 9‐year‐olds and adults after training on a novel finger‐to‐thumb movement sequence, with and without subsequent interference by repeating a different movement sequence. Our results show that, in 9‐year‐olds, but not in adults, an interval of 15 min. between the training session and interfering experience sufficed to ensure the expression of delayed, consolidation phase, gains. Nevertheless, in the 9‐year‐olds, as well as in adults, the gains attained with no interference were significantly larger. Altogether, our results show that while the behavioral expressions of childhood and adult consolidation processes are similar, procedural memory stabilizes, in the waking state, at a much faster rate in children. We propose that, in children, rapid stabilization is a mechanism whereby the constraints on consolidating new experiences into long‐term procedural memory are relaxed at the cost of selectivity.     

Goal orientation and self-efficacy in relation to memory in adulthood

The achievement goal framework (Dweck, 1986, American Psychologist, 41, 1040) has been well-established in children and college-students, but has rarely been examined empirically with older adults. The current study, including younger and older adults, examined the effects of memory self-efficacy, learning goals (focusing on skill mastery over time) and performance goals (focusing on performance outcome evaluations) on memory performance. Questionnaires measured memory self-efficacy and general orientation toward learning and performance goals; free and cued recall was assessed in a subsequent telephone interview. As expected, age was negatively related and education was positively related to memory self-efficacy, and memory self-efficacy was positively related to memory, in a structural equation model. Age was also negatively related to memory performance. Results supported the positive impact of learning goals and the negative impact of performance goals on memory self-efficacy. There was no significant direct effect of learning or performance goals on memory performance; their impact occurred via their effect on memory self-efficacy. The present study supports past research suggesting that learning goals are beneficial, and performance goals are maladaptive, for self-efficacy and learning, and validates the achievement goal framework in a sample including older adults.     

Sleep in children enhances preferentially emotional declarative but not procedural memories

Although the consolidation of several memory systems is enhanced by sleep in adults, recent studies suggest that sleep supports declarative memory but not procedural memory in children. In the current study, the influence of sleep on emotional declarative memory (recognition task) and procedural memory (mirror tracing task) in 20 healthy children (10-13 years of age) was examined. After sleep, children showed an improvement in declarative memory. Separate analysis with respect to the emotional stimulus content revealed that sleep enhances the recognition of emotional stimuli (p > .001) rather than neutral stimuli (p = .084). In the procedural task, however, no sleep-enhanced memory improvement was observed. The results indicate that sleep in children, comparable to adults, enhances predominantly emotional declarative memory; however, in contrast to adults, it has no effect on the consolidation of procedural memory.     

Normal aging and the dissociable prototype learning systems

Dissociable prototype learning systems have been demonstrated behaviorally and with neuroimaging in younger adults as well as with patient populations. In A/not-A (AN) prototype learning, participants are shown members of category A during training, and during test are asked to decide whether novel items are in category A or are not in category A. Research suggests that AN learning is mediated by a perceptual learning system. In A/B (AB) prototype learning, participants are shown members of category A and B during training, and during test are asked to decide whether novel items are in category A or category B. In contrast to AN, research suggests that AB learning is mediated by a declarative memory system. The current study examined the effects of normal aging on AN and AB prototype learning. We observed an age-related deficit in AB learning, but an age-related advantage in AN learning. Computational modeling supports one possible interpretation based on narrower selective attentional focus in older adults in the AB task and broader selective attention in the AN task. Neuropsychological testing in older participants suggested that executive functioning and attentional control were associated with better performance in both tasks. However, nonverbal memory was associated with better AN performance, while visual attention was associated with worse AB performance. The results support an interactive memory systems approach and suggest that age-related declines in one memory system can lead to deficits in some tasks, but to enhanced performance in others.     

Walking While Memorizing: Age-Related Differences in Compensatory Behavior

This study investigated predictions of the life-span theory of selection, optimization, and compensation, focusing on different patterns of task priority during dual-task performance in younger and older adults. Cognitive (memorizing) and sensorimotor (walking a narrow track) performance were measured singly, concurrently, and when task difficulty was manipulated. Use of external aids was measured to provide another index of task priority. Before dual-task testing, participants received extensive training with each component task and external aid. Age differences in dual-task costs were greater in memory performance than in walking, suggesting that older adults prioritized walking over memory. Further, when given a choice of compensatory external aids to use, older adults optimized walking, whereas younger adults optimized memory performance. The results have broad implications for systemic theories of cognitive and sensorimotor aging, and the costs and benefits of assistive devices and environmental support for older populations.     

Does a simultaneous memory load affect older and younger adults’ implicit associative learning?

This study investigated the effects of a simultaneous memory load on implicit associative sequence learning using the Triplets Learning Task (TLT). Participants in the Simultaneous condition held a secondary task memory load during the TLT, while those in the Sequential condition also performed both tasks, but successively, rather than simultaneously. Thus, the Simultaneous condition had a memory load during the TLT, while the Sequential condition did not. Probe blocks without the secondary task allowed separation of effects on learning from effects on its expression. Results revealed that the simultaneous memory load affected older, but not younger adults, by suppressing the expression of learning, not learning itself. Thus, older and younger adults can learn probabilistic associations while holding a simultaneous memory load, but the load can limit the extent to which older adults adapt their performance to environmental structure. Results are consistent with theories which propose that implicit associative learning does not call on limited capacity resources, and highlight the importance of distinguishing effects of dual tasks on the expression of learning from those on learning itself.     

Instructional support for novice law students: Reducing search processes and explaining concepts in cases

Reasoning about legal cases is a complex skill that imposes a high working memory load, especially for novice students. Not only do novices lack necessary conceptual knowledge, searching through the information sources that are used during reasoning can also be assumed to impose a high additional working memory load that does not contribute to learning. Therefore, this study investigated the effects of supporting novice law students' learning by (a) providing the meaning of important concepts in the case and (b) reducing the search process by providing a condensed (relevant articles only) rather than a complete civil code. Results show that performance on a test case (for which they had to use the complete civil code) was significantly better for participants who had used the condensed civil code during learning. Performance on a conceptual knowledge post‐test was significantly enhanced when students had received the concept explanations during learning. Copyright © 2010 John Wiley & Sons, Ltd.