Motor Memory Consolidation Research Articles

Performance-Dependent Consolidation of Learned Vocal Changes in Adult Songbirds.

Motor skills learned through practice are consolidated at later time, which can include nighttime, but the time course of motor memory consolidation and its underlying mechanisms remain poorly understood. We investigated neural substrates underlying motor memory consolidation of learned changes in birdsong, a tractable model system for studying neural basis of motor skill learning. Previous studies in male zebra finches and Bengalese finches have demonstrated that adaptive changes in adult song structure learned through a reinforcement paradigm are initially driven by a cortical-basal ganglia circuit, and subsequently consolidated into downstream cortical motor circuitry. However, the time course of the consolidation process, including whether it occurs offline during nighttime or online during daytime, remains unclear and even controversial. Here, we provide in both species experimental evidence of virtually no consolidation of learned vocal changes during nighttime. We demonstrate instead that the consolidation occurs during daytime and the amount of consolidation is strongly correlated with the amount of learning, suggesting online, performance-dependent mechanisms of consolidation of learned vocal changes. Moreover, by using computer simulations based on our experimental results, we demonstrate that such online, performance-dependent consolidation can account for the contradicting conclusions concerning the time course of consolidation process reached by previous studies. These results thus reconcile a controversy in the study of vocal motor consolidation in songbirds, and illustrate the neural substrates through which newly learned motor skills initially implemented by cortical-basal ganglia circuits become encoded in the cortical motor circuitry.SIGNIFICANCE STATEMENT Motor skills learned through repetitive practice become stable and are consolidated into cortical motor circuits. We investigate neural substrates of this "motor memory consolidation" in adult songbirds, which produce songs that are complex motor skills learned and maintained through repetitive vocal practice. We demonstrate that learned changes in song acoustic structure are consolidated into the cortical motor circuits predominantly during daytime, but not during nighttime, depending on ongoing song performance. These consolidation mechanisms reconcile seemingly contradicting results of previous studies regarding the time course of vocal learning consolidation, and provide fundamental insights into the process through which learned performance of complex motor skills is consolidated and encoded in in motor circuits.

The role of nocturnal sleep on the retention, adaptability, and relearning rate of a motor skill

Aim: The influence of sleep on the adaptability and relearning rate during learning of complex motor skills is still unknown, limiting the comprehension of the sleep role in motor memory consolidation. Thus, we aimed to investigate the nocturnal sleep influence on retention, adaptability, and relearning rate of the dart-throwing task. Methods: Sixty healthy adults were divided into two groups: SLEEP and WAKE. Both groups practiced an under-arm dart-throwing task. However, WAKE practiced in the morning and performed a retention phase in the evening, and SLEEP practiced in the evening and performed a retention phase in the morning of the next day. The practice and retention phases were separated by 12 h in both groups. There were analyses regarding retention (retention test), adaptability (delayed transfer test), and relearning rate (savings). Results: Both groups improved their performance across the acquisition phase and maintained it in the retention test. The groups did not demonstrate adaptability and did not demonstrate a significant difference in relearning rate. Conclusion: We conclude that nocturnal sleep did not modulate the consolidation of motor memories related to ballistic discrete motor skills.

Motor memory consolidation in children: The role of awareness and sleep on offline general and sequence-specific learning

Abstract Study aim: The purpose of this study was to investigate the role of sleep and awareness on consolidation of general and Sequence-Specific learning in children. Material and methods: Male participants (n = 48, 10 to 12 years old) were assigned to one of four groups based on awareness and sleep. Acquisition phase took place in the morning (wake groups, 8 ± am) or in the evening (sleep groups, 8 ± pm) followed by a 12 hours retention interval and a subsequent delayed retention test (1 week). Children in the explicit groups were informed about the presence of the sequence, while in the implicit groups were not informed about it. For data analysis in consolidation of general sequence learning and Sequence-Specific Consolidation phases, 2 × 2 × 2 and 2 × 2 × 3 ANOVA with repeated measures on block tests were used respectively. Results: The data provides evidence of offline enhancement of general motor learning after 12 hours which was dependent on sleep and awareness. Moreover, the information persistence after 1-week was significant only in sleep groups. The results also indicated that consolidation of sequence-specific learning was only observed after 12 hours in element duration and it was related to sleep and awareness. Conclusions: The results revealed that sleep wasn’t only an essential factor in enhancement of off-line sequence learning task after 12 hours in children, but performance of the children was dependent on awareness and sleep.

The Effect of Voluntary & Forced Exercises and Different Off-line Periods on Implicit Motor Memory Consolidation

The Effect of Voluntary & Forced Exercises and Different Off-line Periods on Implicit Motor Memory Consolidation

Offline low-frequency rTMS of the primary and premotor cortices does not impact motor sequence memory consolidation despite modulation of corticospinal excitability

Motor skills are acquired and refined across alternating phases of practice (online) and subsequent consolidation in the absence of further skill execution (offline). Both stages of learning are sustained by dynamic interactions within a widespread motor learning network including the premotor and primary motor cortices. Here, we aimed to investigate the role of the dorsal premotor cortex (dPMC) and its interaction with the primary motor cortex (M1) during motor memory consolidation. Forty-eight healthy human participants (age 22.1 ± 3.1 years) were assigned to three different groups corresponding to either low-frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS) of left dPMC, rTMS of left M1, or sham rTMS. rTMS was applied immediately after explicit motor sequence training with the right hand. Motor evoked potentials were recorded before training and after rTMS to assess potential stimulation-induced changes in corticospinal excitability (CSE). Participants were retested on motor sequence performance after eight hours to assess consolidation. While rTMS of dPMC significantly increased CSE and rTMS of M1 significantly decreased CSE, no CSE modulation was induced by sham rTMS. However, all groups demonstrated similar significant offline learning indicating that consolidation was not modulated by the post-training low-frequency rTMS intervention despite evidence of an interaction of dPMC and M1 at the level of CSE. Motor memory consolidation ensuing explicit motor sequence training seems to be a rather robust process that is not affected by low-frequency rTMS-induced perturbations of dPMC or M1. Findings further indicate that consolidation of explicitly acquired motor skills is neither mediated nor reflected by post-training CSE.

Sleep affects the motor memory of basketball shooting skills in young amateurs

Sleep has long been shown as important for memory processing and retention, and has recently been implicated in motor memory consolidation. However, it is not known whether sports skills, including basketball shooting skills, are also affected by sleep in young, healthy individuals. Therefore, we investigated whether sleep before and after basketball shooting skill training affected the acquisition and retention of shooting skills. This study included 19 healthy male subjects who participated in a basketball shooting skill training session (100 shots) and a retention test performed 2 days later (30 shots). The learning and retention indices were calculated using performance scores that evaluated each subject’s shooting skills. A wearable activity tracker was used to measure sleep parameters for 4 consecutive days, 2 days before and 2 days after training. We discovered the relationship between sleep duration before and after training and retention of shooting skills (sleep duration before training; p = 0.044, r = 0.467, sleep duration after training; p = 0.006, r = 0.606). The retention index for the subgroup with long sleep duration before and after training was significantly higher than that for the subgroup with short sleep duration before and after training, respectively (p = 0.021 for both). There was no significant relationship between learning index and each sleep parameter. Our results demonstrated that sleep duration before and after training was related to retention of shooting skills following basketball shooting skills training.

Motor Memory Consolidation after Augmented Variability Depends on the Space in which Variability is Introduced

Motor memories undergo a period of consolidation before they become resistant to the practice of another task. Although movement variability is important in motor memory consolidation, its role is not fully understood in redundant tasks where variability can exist along two orthogonal subspaces (the 'task space' and the 'null space') that have different effects on task performance. Here, we used haptic perturbations to augment variability in these different spaces and examined their effect on motor memory consolidation. Participants learned a shuffleboard task, where they held a bimanual manipulandum and made a discrete throwing motion to slide a virtual puck towards a target. The task was redundant because the distance travelled by the puck was determined by the sum of the left and right hand speeds at release. After participants practiced the task, we used haptic perturbations to introduce motor variability in the task space or null space and examined consolidation of the original task on the next day. We found that regardless of the amplitude, augmenting variability in the task space resulted in significantly better consolidation relative to augmenting variability in the null space, but was not different from a control group that practiced with no variability. This benefit of increasing task space variability relative to increasing null space variability was likely due to the fact that it did not disrupt the pre-existing coordination strategy. These results suggest that the effects of variability on motor memory consolidation depend on the interplay between the induced variability and the pre-existing coordination strategy.

Motor Learning Promotes the Coupling between Fast Spindles and Slow Oscillations Locally over the Contralateral Motor Network.

Recent studies from us and others suggest that traditionally declarative structures mediate some aspects of the encoding and consolidation of procedural memories. This evidence points to the existence of converging physiological pathways across memory systems. Here, we examined whether the coupling between slow oscillations (SO) and spindles, a mechanism well established in the consolidation of declarative memories, is relevant for the stabilization of human motor memories. To this aim, we conducted an electroencephalography study in which we quantified various parameters of these oscillations during a night of sleep that took place immediately after learning a visuomotor adaptation (VMA) task. We found that VMA increased the overall density of fast (≥12Hz), but not slow (<12Hz), spindles during nonrapid eye movement sleep, stage 3 (NREM3). This modulation occurred rather locally over the hemisphere contralateral to the trained hand. Although adaptation learning did not affect the density of SOs, it substantially enhanced the number of fast spindles locked to the active phase of SOs. The fact that only coupled spindles predicted overnight memory retention points to the relevance of this association in motor memory consolidation. Our work provides evidence in favor of a common mechanism at the basis of the stabilization of declarative and motor memories.

Encoding and consolidation of motor sequence learning in young and older adults

Sleep benefits motor memory consolidation in young adults, but this benefit is reduced in older adults. Here we sought to understand whether differences in the neural bases of encoding between young and older adults contribute to aging-related differences in sleep-dependent consolidation of an explicit variant of the serial reaction time task (SRTT). Seventeen young and 18 older adults completed two sessions (nap, wake) one week apart. In the MRI, participants learned the SRTT. Following an afternoon interval either awake or with a nap (recorded with high-density polysomnography), performance on the SRTT was reassessed in the MRI. Imaging and behavioral results from SRTT performance showed clear sleep-dependent consolidation of motor sequence learning in older adults after a daytime nap, compared to an equal interval awake. Young adults, however, showed brain activity and behavior during encoding consistent with high SRTT performance prior to the sleep interval, and did not show further sleep-dependent performance improvements. Young adults did show reduced cortical activity following sleep, suggesting potential systems-level consolidation related to automatization. Sleep physiology data showed that sigma activity topography was affected by hippocampal and cortical activation prior to the nap in both age groups, and suggested a role of theta activity in sleep-dependent automatization in young adults. These results suggest that previously observed aging-related sleep-dependent consolidation deficits may be driven by aging-related deficiencies in fast learning processes. Here we demonstrate that when sufficient encoding strength is reached with additional training, older adults demonstrate intact sleep-dependent consolidation of motor sequence learning.

Schizophrenia-associated variation at ZNF804A correlates with altered experience-dependent dynamics of sleep slow waves and spindles in healthy young adults.

The rs1344706 polymorphism in ZNF804A is robustly associated with schizophrenia and schizophrenia is, in turn, associated with abnormal non-rapid eye movement (NREM) sleep neurophysiology. To examine whether rs1344706 is associated with intermediate neurophysiological traits in the absence of disease, we assessed the relationship between genotype, sleep neurophysiology, and sleep-dependent memory consolidation in healthy participants. We recruited healthy adult males with no history of psychiatric disorder from the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort. Participants were homozygous for either the schizophrenia-associated ‘A’ allele (N = 22) or the alternative ‘C’ allele (N = 18) at rs1344706. Actigraphy, polysomnography (PSG) and a motor sequence task (MST) were used to characterize daily activity patterns, sleep neurophysiology and sleep-dependent memory consolidation. Average MST learning and sleep-dependent performance improvements were similar across genotype groups, albeit more variable in the AA group. During sleep after learning, CC participants showed increased slow-wave (SW) and spindle amplitudes, plus augmented coupling of SW activity across recording electrodes. SW and spindles in those with the AA genotype were insensitive to learning, whilst SW coherence decreased following MST training. Accordingly, NREM neurophysiology robustly predicted the degree of overnight motor memory consolidation in CC carriers, but not in AA carriers. We describe evidence that rs1344706 polymorphism in ZNF804A is associated with changes in the coordinated neural network activity that supports offline information processing during sleep in a healthy population. These findings highlight the utility of sleep neurophysiology in mapping the impacts of schizophrenia-associated common genetic variants on neural circuit oscillations and function.

P 36. rTMS-induced offline-modulation of premotor-motor interaction after motor sequence learning does not affect consolidation

Introduction. The acquisition of novel motor skills depends on active training and further offline processing of the motor engram (i.e., consolidation). Previous studies suggest an essential role of post-training corticospinal excitability (CSE) for the induction of offline motor memory consolidation. Furthermore, it was shown that the interaction of the primary motor cortex (M1) and the premotor cortex (PMC) after training affects the consolidation process. In this study, we modulated the post-training interaction of M1 and PMC by applying inhibitory repetitive transcranial magnetic stimulation (rTMS) and investigated the effects on CSE and consolidation. Methods. 48 healthy, right-handed subjects (age 22.13 ± 3.2 a) were assigned to 3 groups. All participants practiced an explicit motor sequence learning task with their right hand. Immediately after training, participants received 1 Hz rTMS to either left M1, left PMC, or sham stimulation. Motor evoked potentials (MEP) were recorded before training and after rTMS. Task performance was retested eight hours after the end of stimulation to assess offline performance changes. Task performance was assessed using a performance index (PI) that integrated speed and accuracy of sequence execution. Consolidation was quantified as the difference of task performance at the end of the training session compared to the beginning of the retest (mean PI of 4 blocks each). Results. In terms of changes of MEP amplitudes, rmANOVA revealed an interaction of factors group*time ( p = 0.001). When applied to M1, rTMS induced a decrease of CSE compared to the pre-training assessments ( p = 0.007), whereas stimulation of the PMC led to an increase of MEP amplitudes ( p = 0.009). No relevant change of corticospinal excitability was seen after sham stimulation ( p = 0.862). Training performance did not differ between groups (group*block, p = 0.781) and all groups demonstrated significant offline-improvements at delayed retesting. However, there were no significant differences of consolidation between groups ( p = 0.456). Furthermore, correlation analysis revealed no significant association of CSE modulation and offline performance changes ( r = 0.101, p = 0.493). Discussion. The increase of CSE induced by post-training PMC demonstrated here differs from results of previous studies that applied inhibitory PMC stimulation at rest or before a training intervention, which resulted in decreased CSE. We, therefore, interpret our findings as further evidence of a state-dependent function of the PMC. Despite significant modulation of CSE by post-training rTMS of M1 and PMC, there was no behavioral effect on consolidation. This challenges the relevance of immediate post-training CSE changes as a key mechanism in terms of the induction of consolidation. Although proximal intracortical physiological mechanisms are still not excluded, they are not detected by changes in post-training corticospinal excitability.

Kdm3b haploinsufficiency impairs the consolidation of cerebellum-dependent motor memory in mice

Histone modifications are a key mechanism underlying the epigenetic regulation of gene expression, which is critically involved in the consolidation of multiple forms of memory. However, the roles of histone modifications in cerebellum-dependent motor learning and memory are not well understood. To test whether changes in histone methylation are involved in cerebellar learning, we used heterozygous Kdm3b knockout (Kdm3b+/−) mice, which show reduced lysine 9 on histone 3 (H3K9) demethylase activity. H3K9 di-methylation is significantly increased selectively in the granule cell layer of the cerebellum of Kdm3b+/− mice. In the cerebellum-dependent optokinetic response (OKR) learning, Kdm3b+/− mice show deficits in memory consolidation, whereas they are normal in basal oculomotor performance and OKR acquisition. In addition, RNA-seq analyses revealed that the expression levels of several plasticity-related genes were altered in the mutant cerebellum. Our study suggests that active regulation of histone methylation is critical for the consolidation of cerebellar motor memory.

A multi-representation approach to the contextual interference effect: effects of sequence length and practice

The present study investigated the long-term benefit of Random-Practice (RP) over Blocked-Practice (BP) within the contextual interference (CI) effect for motor learning. We addressed the extent to which motor sequence length and practice amount factors moderate the CI effect given that previous reports, often in applied research, have reported no long-term advantage from RP. Based on predictions arising from the Cognitive framework of Sequential Motor Behavior (C-SMB) and using the Discrete Sequence Production (DSP) task, two experiments were conducted to compare limited and extended practice amounts of 4- and 7-key sequences under RP and BP schedules. Twenty-four-hour delayed retention performance confirmed the C-SMB prediction that the CI-effect occurs only with short sequences that receive little practice. The benefit of RP with limited practice was associated with overnight motor memory consolidation. Further testing with single-stimulus as well as novel and unstructured (i.e., random) sequences indicated that limited practice under RP schedules enhances both reaction and chunking modes of sequence execution with the latter mode benefitting from the development of implicit and explicit forms of sequence representation. In the case of 7-key sequences, extended practice with RP and BP schedules provided for equivalent development of sequence representations. Higher explicit awareness of sequence structures was associated with faster completion of practiced but also of novel and unstructured sequences.

The effect of acute aerobic exercise on the consolidation of motor memories.

Acute aerobic exercise performed prior to training may assist with motor skill acquisition through enhancement of motor cortical plasticity. In addition, high-intensity exercise performed after training improves retention, although the mechanisms of this are unclear. We hypothesized that acute continuous moderate-intensity exercise performed post-motor training would also assist with motor skill retention and that this behavioral change would be positively correlated with neural markers of training-related cortical adaptation. Participants [n = 33; assigned to an exercise (EXE) or control (CON) group] completed a single visuomotor training session using bilateral wrist movements while movement-related cortical potentials (MRCPs) were collected. After motor training, the EXE group exercised for 20min [70% of heart rate reserve (HRR)] and the CON group read for the same amount of time. Both groups completed two post-training tests after exercise/rest: 10min and ~ 30min once heart rate returned to resting level in EXE. Retention and transfer tests were both completed 1 and 7days later. MRCPs measured training-related neural adaptations during the first visit and motor performance was assessed as time and trajectory to the target. The EXE group had better performance than CON at retention (significant 7days post-training). MRCP amplitudes increased from early to late motor training and this amplitude change was correlated with motor performance at retention. Results suggest that moderate-intensity exercise post-motor training helps motor skill retention and that there may be a relationship with motor training-related cortical adaptations that is enhanced with post-motor training exercise.

Somatosensory Targeted Memory Reactivation Modulates Oscillatory Brain Activity but not Motor Memory Consolidation

Previous research has shown that targeted memory reactivation (TMR) protocols using acoustic or olfactory stimuli can boost motor memory consolidation. While somatosensory information is crucial for motor control and learning, the effects of somatosensory TMR on motor memory consolidation remain elusive. Here, healthy young adults (n = 28) were trained on a sequential serial reaction time task and received, during the offline consolidation period that followed, sequential electrical stimulation of the fingers involved in the task. This somatosensory TMR procedure was applied during either a 90-minute diurnal sleep (NAP) or wake (NONAP) interval that was monitored with electroencephalography. Consolidation was assessed with a retest following the NAP/NONAP episode. Behavioral results revealed no effect of TMR on motor performance in either of the groups. At the brain level, somatosensory stimulation elicited changes in oscillatory activity in both groups. Specifically, TMR induced an increase in power in the mu band in the NONAP group and in the beta band in both the NAP and NONAP groups. Additionally, TMR elicited an increase in sigma power and a decrease in delta oscillations in the NAP group. None of these TMR-induced modulations of oscillatory activity, however, were correlated with measures of motor memory consolidation. The present results collectively suggest that while somatosensory TMR modulates oscillatory brain activity during post-learning sleep and wakefulness, it does not influence motor performance in an immediate retest.

Combining Observation and Physical Practice: Benefits of an Interleaved Schedule for Visuomotor Adaptation and Motor Memory Consolidation

Visuomotor adaptation to novel environments can occur via non-physical means, such as observation. Observation does not appear to activate the same implicit learning processes as physical practice, rather it appears to be more strategic in nature. However, there is evidence that interspersing observational practice with physical practice can benefit performance and memory consolidation either through the combined benefits of separate processes or through a change in processes activated during observation trials. To test these ideas, we asked people to practice aiming to targets with visually rotated cursor feedback or engage in a combined practice schedule comprising physical practice and observation of projected videos showing successful aiming. Ninety-three participants were randomly assigned to one of five groups: massed physical practice (Act), distributed physical practice (Act+Rest), or one of 3 types of combined practice: alternating blocks (Obs_During), or all observation before (Obs_Pre) or after (Obs_Post) blocked physical practice. Participants received 100 practice trials (all or half were physical practice). All groups improved in adaptation trials and showed savings across the 24-h retention interval relative to initial practice. There was some forgetting for all groups, but the magnitudes were larger for physical practice groups. The Act and Obs_During groups were most accurate in retention and did not differ, suggesting that observation can serve as a replacement for physical practice if supplied intermittently and offers advantages above just resting. However, after-effects associated with combined practice were smaller than those for physical practice control groups, suggesting that beneficial learning effects as a result of observation were not due to activation of implicit learning processes. Reaction time, variable error, and post-test rotation drawings supported this conclusion that adaptation for observation groups was promoted by explicit/strategic processes.

Reward Timing Matters in Motor Learning

Reward can improve motor learning and the consolidation of motor memories. Identifying the features of reward feedback that are critical for motor learning is a necessary step for successful integration into rehabilitation programs. One central feature of reward feedback that may affect motor learning is its timing – that is, the delay after which reward is delivered following movement execution. In fact, research on associative learning has shown that short and long reward delays (e.g., 1 and 6 s following action execution) activate preferentially the striatum and the hippocampus, respectively, which both contribute with varying degrees to motor learning. Given the distinct functional role of these two areas, we hypothesized that reward timing could modulate how people learn and consolidate a new motor skill. In sixty healthy participants, we found that delaying reward delivery by a few seconds influenced motor learning dynamics. Indeed, training with a short reward delay (i.e., 1 s) induced slow, yet continuous gains in performance, while a long reward delay (,i>i.e., 6 s) led to initially high learning rates that were followed by an early plateau in the learning curve and a lower endpoint performance. Moreover, participants who successfully learned the skill with a short reward delay displayed overnight consolidation, while those who trained with a long reward delay exhibited an impairment in the consolidation of the motor memory. Overall, our data show that reward timing affects motor learning, potentially by modulating the engagement of different learning processes, a finding that could be exploited in future rehabilitation programs.

Acute exercise following skill practice promotes motor memory consolidation in Parkinson’s disease

Acute cardiovascular exercise has shown to promote neuroplastic processes supporting the consolidation of newly acquired motor skills in healthy adults. First results suggest that this concept may be transferred to populations with motor and cognitive dysfunctions. In this context, Parkinson’s disease (PD) is highly relevant since patients demonstrate deficits in motor learning. Hence, in the present study we sought to explore the effect of a single post-practice exercise bout on motor memory consolidation in PD.For this purpose, 17 patients with PD (Hoehn and Yahr: 1 – 2.5, age: 60.1 ± 7.9 y) practiced a whole-body skill followed by either (i) a moderate-intense bout of cycling, or (ii) seated rest for a total of 30 min. The motor skill required the participants to balance on a tiltable platform (stabilometer) for 30 s. During skill practice, participants performed 15 trials followed by a retention test 1 day and 7 days later. We calculated time in balance (platform within ± 5° from horizontal) for each trial and within- and between-group differences in memory consolidation (i.e. offline learning = skill change from last acquisition block to retention tests) were analyzed.Groups revealed similar improvements during skill practice (F4,60 = 0.316, p = 0.866), but showed differences in offline learning, which were only evident after 7 days (F1,14 = 5.602, p = 0.033).Our results suggest that a single post-practice exercise bout is effective in enhancing long-term motor memory consolidation in a population with motor learning impairments. This may point at unique promoting effects of exercise on dopamine neurotransmission involved in memory formation. Future studies should investigate the potential role of exercise-induced effects on the dopaminergic system.

Sleep following intense physical exercise stabilizes motor learning in typically developing boys

There is compelling evidence that sleep (N2, REM sleep, but also N3) supports the consolidation of motor memory in adults. Although children express higher levels of REM sleep and N3, it is still not understood why sleep does not benefit the consolidation of motor memory in children as in adults. Here, we aimed to manipulate sleep by daytime physical exercise in typically developing boys (N = 12; range 9–12 yrs) to test the impact on sleep and motor learning. The manipulation consisted of 1 h of intense ergometer exercise during the daytime before a night of restorative sleep. In a rest control condition, children were seated comfortably and listened to an audio drama. Motor learning was assessed with a visuomotor finger sequence tapping task; in both conditions learning took place before either exercise or rest. Prior to sleep in the sleep laboratory, motor memory was assessed as a baseline. Motor memory was again collected in the morning after a night of sleep in the lab. While there was no change in N3, we found prolonged REM sleep latency after physical activity compared to rest, corresponding to a prolonged first sleep cycle. With respect to motor learning, we found superior accuracy of motor performance after physical exercise compared to rest. Our findings suggest that physical exercise during the daytime stabilizes sleep-dependent motor learning.

Lateralized effects of post-learning transcranial direct current stimulation on motor memory consolidation in older adults: An fMRI investigation

Previous research has consistently demonstrated that older adults have difficulties transforming recently learned movements into robust, long-lasting memories (i.e., motor memory consolidation). One potential avenue to enhance consolidation in older individuals is the administration of transcranial direct current stimulation (tDCS) to task-relevant brain regions after initial learning. Although this approach has shown promise, the underlying cerebral correlates have yet to be revealed. Moreover, it is unknown whether the effects of tDCS are lateralized, an open question with implications for rehabilitative approaches following predominantly unilateral neurological injuries. In this research, healthy older adults completed a sequential motor task before and 6 h after receiving anodal or sham stimulation to right or left primary motor cortex (M1) while functional magnetic resonance images were acquired. Unexpectedly, anodal stimulation to right M1 following left-hand sequence learning significantly hindered consolidation as compared to a sham control, whereas no differences were observed with left M1 stimulation following right-hand learning. Impaired performance following right M1 stimulation was paralleled by sustained engagement of regions known to be critical for early learning stages, including the caudate nucleus and the premotor and parietal cortices. Thus, post-learning tDCS in older adults not only exerts heterogenous effects across the two hemispheres but can also disrupt ongoing memory processing.