What “reactivation” actually means in a sleeping brain
Reactivation is the idea that the brain replays patterns of activity from a recent waking experience while you sleep. In the rat reaching study, groups of neurons that had fired together during practice fired together again during sleep, and this replay was coordinated with muscle activity [1]. That coordination matters because a motor skill is not just a thought pattern; it is a link between neural commands and the muscles that carry them out.
In the human study, reactivation was induced rather than simply observed. Participants learned to control electrical activity in specific arm muscles to move a cursor to different locations, and each location was paired with a unique sound. Half of those sounds were played again during slow-wave sleep. After sleep, movements that had been cued during sleep were performed more quickly and efficiently than uncued movements [2]. The sound acted as a reminder that brought back the associated muscle-control memory.
Why slow-wave sleep is the clearer stage for motor execution
The human evidence points most directly to slow-wave sleep. When sounds were played during slow-wave sleep, the benefit showed up in how quickly and efficiently people executed the cued movements after waking [2]. This is a narrow but useful result: it concerns the execution of a newly learned action, not just general improvement on a well-practiced skill.
REM sleep is harder to pin down. A review of imagery training in athletes notes that REM-atonia—the near-paralysis of voluntary muscles during REM—largely abolishes voluntary muscle activity [3]. That does not mean REM is irrelevant to motor memory, but it does mean that any muscle-related replay during REM is not simply a rehearsal of overt movement. The rat study found coordinated reactivation across both REM and slow-wave sleep [1], so the two stages may contribute in different ways rather than one being the sole sleep stage for motor learning.
Lucid dreaming shows the link between dreamed movement and muscle signals
Lucid dreaming offers a different window into sleep and movement. In a lucid dream, a person becomes aware they are dreaming and can intentionally simulate motor tasks with mental imagery. Studies report promising performance improvements after lucid-dreaming practice, and similarities have been observed in brain activity, eye movements, muscle activity, and autonomic responses compared with physical practice [4]. This supports the idea that the sleeping brain can engage motor-related systems, but it is not the same as the targeted reactivation used in the slow-wave sleep experiment.
The lucid-dreaming evidence also comes with practical caveats. Lucid dreams are rare, training is limited, and control over the dream is difficult. The authors note that placebo effects and increased motivation after lucid-dreaming practice should be investigated in future studies [4]. So lucid dreaming is a promising route for extending mental practice into sleep, but it is not yet a reliable training method.
What this means for rapid motor skill learning
The practical answer is that sleep can do more than rest the body; it can actively strengthen the connection between a neural command and its muscular output. In the human study, the benefit was specific to movements that had been cued during slow-wave sleep, which suggests that reactivation helped consolidate the execution part of the skill rather than just making people generally faster [2]. The rat study goes further by showing that neural replay and muscle activity are coordinated during sleep and that this coordination is associated with better learning of a skilled reaching task [1].
The scope matters. The human demonstration used a myoelectric feedback task in a laboratory, with sounds played during slow-wave sleep, so it shows that targeted reactivation can improve execution of a novel action under those conditions [2]. The rat findings involve a skilled reaching task and coordinated reactivation across REM and slow-wave sleep [1]. Neither result means that every night of sleep automatically teaches a new motor skill, or that REM and slow-wave sleep play identical roles. The evidence supports a real contribution from sleep reactivation to motor execution, with slow-wave sleep currently the clearest stage for that effect in humans.
Sources used in this answer
Neural ensemble reactivation in rapid eye movement and slow-wave sleep coordinate with muscle activity to promote rapid motor skill learning
In rats learning a skilled reaching task, neural ensemble reactivation during REM and slow-wave sleep was coordinated with muscle activity and was associated with enhanced motor skill learning.
Memory Reactivation during Sleep Improves Execution of a Challenging Motor Skill
In humans learning a myoelectric feedback task, playing task-associated sounds during slow-wave sleep led to faster and more efficient execution of the cued movements after sleep compared with uncued movements.
Imagery Training in REM Sleep and Lucid Dreaming and the Optimisation of Motor Memory Consolidation in Athletes: A Narrative Review
A narrative review notes that REM-atonia largely abolishes voluntary muscle activity, which constrains how muscle activity can accompany neural reactivation during REM sleep.
Extending mental practice to sleep: Enhancing motor skills through lucid dreaming
Lucid-dreaming motor practice has shown promising performance improvements and similarities to physical practice in brain activity, eye movements, and muscle activity, but placebo effects, motivation, and practical challenges remain to be resolved.