Functional connectivity via the dorsolateral prefrontal cortex in the late phase of rest periods predicts offline learning

The relationship between offline learning gains and functional connectivity (FC) has been investigated in several studies. They have focused on average motor task performance and resting-state FC across subjects. Generally, individual differences are seen in both offline learning gain and neurophysiological profiles in resting-state FC. However, few studies have focused on the relationship between individual differences in offline learning gain and temporal characteristics of resting-state FC. The present study aimed to clarify this relationship between the two profiles. Thirty-four healthy right-handed participants performed a force-controlled motor task. Electroencephalography was performed during the 15-minute wakeful rest period between tasks. The results revealed a significant correlation between offline learning gain and FC between the contralateral dorsolateral prefrontal cortex (DLPFC) and contralateral primary motor cortex (M1), and ipsilateral primary somatosensory cortex (S1) during late phase of the rest interval. These results are consistent with the findings of previous studies showing the FC between M1, which is necessary for awake offline learning, and DLPFC, which is related to motor control. Additionally, sensory feedback related to force control may be caused by the interaction between contralateral DLPFC and ipsilateral S1. Our study shed light on the temporal profiles of resting-state FC associated with individual differences in offline learning.

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 (F_4,60 = 0.316, p = 0.866), but showed differences in offline learning, which were only evident after 7 days (F_1,14 = 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.

Effects of acute cardiovascular exercise on motor memory encoding and consolidation: A systematic review with meta-analysis

Emerging evidence indicates that acute bouts of cardiovascular exercise promote motor memory formation. In this preregistered meta-analysis (CRD42018106288) we synthesize data from 22 studies published until February 2020, including a total of 862 participants. We calculated standardized mean differences (SMDs) with 95 % confidence intervals (CIs) to assess exercise effects on motor memory encoding and consolidation, respectively. The pooled data indicate that exercise mainly benefits the consolidation of memories, with exercise prior to motor practice improving early non-sleep consolidation (SMD, 0.58; 95 % CI, 0.30-0.86; p < 0.001), and post-practice exercise facilitating sleep-dependent consolidation (SMD, 0.62; 95 % CI, 0.34-0.90; p < 0.001). Strongest effects exist for high exercise intensities, and motor task nature appears to be another relevant modulator. We demonstrate that acute cardiovascular exercise particularly promotes the consolidation of acquired motor memories, and exercise timing, and intensity as well as motor task nature seem to critically modulate this relationship. These findings are discussed within currently proposed models of motor memory formation and considering molecular and systemic mechanisms of neural plasticity.

Beyond the mean reaction time: Trial-by-trial reaction time reveals the distraction effect on perceptual-motor sequence learning

Perceptual-motor sequences can be learned quickly under distraction, often demonstrated by the mean reaction time (RT) change in a serial reaction time (SRT) task. However, any arbitrary mean RT can arise from one of many distinct trial-by-trial RT patterns. It is surprising that previous sequence learning studies have hinged only on the mean RT metrics while little is known about the distraction effect on its trial-by-trial processes. In an SRT task with or without distraction, we found that initially learning a fixed repeating sequence without distraction was expressed by a micro-online learning process where reaction time (RT) progressively improved within learning blocks as adults continuously performed the SRT task. Such online RT improvements, however, vanished when the SRT task was performed under distraction. Despite the detrimental effect of distraction on micro-online RT improvements, we observed offline enhancements in RT following rest intervals of 3 min that emerged to secure sequence learning under distraction. We reasoned that distraction may exert influence on the micro-online and offline learning by mediating the engagement of explicit and implicit memory. Given the offline RT change under distraction, a short rest between learning blocks may be a key player in early perceptual-motor sequence learning under distraction. We thus suggest that future studies investigating the distraction effect on sequence learning need to control the length of rest between learning blocks, while previous research with equivocal interpretations of the distraction effect failed to do so.

Top-down control: A unified principle of cortical learning

Cognitive control of the brain flexibly maps incoming sensory information onto execution of actions appropriate for the current goal. Learning is a process that enables the brain to estimate current states of the world by extracting its spatiotemporal structure and generate goal-directed motor outputs through selective association of events or movement refinement. Accumulating evidence suggests that top-down control from higher-order brain areas modulates downstream neural activity and changes local computations that are critical for the execution of learned behavior. Recent technological advances in multi-site recordings and optogenetic approaches are beginning to reveal more direct evidence of top-down cognitive control by monitoring and perturbing activity of top-down inputs and observing its causal consequences on behavior and downstream neural dynamics. Here I highlight that learning-related changes in neural circuits in distinct domains of learning converge onto a unified principle; namely recruitment of top-down control whether it involves sensory, motor or offline learning. Recruitment of top-down control may reflect experience-dependent adaptation and integration of internal models for refined state estimation and goal-directed optimal behavior.

Serial practice impairs motor skill consolidation

Recent reports have revealed that motor skill learning is impaired if two skills are practiced one after the other, that is before the first skill has had the time to become consolidated. This suggests that motor skills should be practiced in isolation from one another to minimize interference. At the moment, little is known about the effect of practice schedules high in contextual interference on motor skill consolidation. In Experiment 1, we investigated whether a serial practice schedule impairs motor skill consolidation. Participants had to learn two distinct sequences of finger movements (A and B) under either a blocked practice schedule or a serial practice schedule before being retested the following day. A control group also practiced Sequence A only. Our results revealed that a blocked practice schedule led to no interference between the sequences, whereas a serial practice schedule impaired the consolidation of Sequence B. In Experiment 2, we investigated the origin of the interference caused by a serial practice schedule by replacing the physical practice of Sequence A with either the observation of a model performing Sequence A or by asking participants to produce random finger movements. Our results revealed that both tasks interfered with the consolidation of Sequence B. Thus, we suggest that a serial practice schedule impairs motor skill consolidation through a conflict in the brain networks involved in the acquisition of the cognitive representation of the sequence and its execution.