December 22, 2021 | by Claudia Lopez Lloreda, PennNeuroKnow

A new study found that activating memories through learning-associated sound cues during sleep improved the performance of a motor task.

Not every experience you have or fact that you encounter turns into a long-lasting memory. Many of these moments slip away, while others become stable, long-lasting memories in your brain. This process of stabilization, called memory consolidation, is influenced by many aspects that impact learning. One such factor is sleep, which is critical for the consolidation of a memory. But not all memories are the same, and scientists still wonder whether sleep could help improve a memory associated with a motor skill. A new study published in the Journal of Neuroscience found that activating a motor memory during sleep could improve performance of that motor skill¹.

So how can a motor memory be activated? The technique used in this study, called targeted memory reactivation (TMR), consists of presenting a sensory aspect of a recently learned memory, like a sound or smell, to “activate” a memory while the person sleeps. One analysis found that TMR improved declarative memory, the ability to remember facts and personal experiences. Additionally, they found that TMR during deeper, non-rapid eye movement (non-REM) sleep was more effective than during REM sleep². Another study found that learning-associated sound cues helped participants solve puzzles that they had left unsolved before sleep³.

But while TMR helped to improve declarative memory and problem solving, whether TMR could also improve motor skills had been a big question in the field. While some studies found that TMR improved a learned motor skill, like learning a finger tapping sequence, others found that activating motor memories had little effect on motor performance. Additionally, most of the motor skills tested relied on well-learned tasks that left little room for improvement, so the researchers in the new study decided to test a more complex task that emphasized action execution. 

To do this, the researchers trained and tested 20 participants in a complex motor task. They had to learn to control specific arm muscles to move a cursor on a computer to a particular target on the screen. With each of the eight different target locations, a unique sound was played — a bell or a dog’s bark for example — while the participants were being trained. After training, the participants learned to reliably flex and contract arm muscles to move the cursor to the target area associated with a specific sound.

Then the participants took a nap. During their approximately 60-minute nap, researchers played the same sounds that participants had learned to associate with certain targets in the task. In this case, they cued, or played, the sounds associated with about half of the targets. When the participants woke up, the researchers tested how well they performed for the targets that had been cued with sound while participants slept, which presumably activated the memory during sleep when the sound was played, versus the targets that had not been cued during sleep.

Participants showed an improved cursor control in the memories that were activated during their nap, with performance times on cued targets being faster than their performance times prior to sleeping and faster than those that had not been cued. On the other hand, movement towards targets that had not been cued were slower than before the participants went to sleep. Researchers also found that participants were able to move the cursor in a more direct and efficient way to the targets that were cued. These results suggest that re-activating motor memories, by presenting the learning-associated sound cue during sleep, strengthens the memories.

However, the improvement could be due to two things: participants could be remembering the task better or they could be executing it better. To pinpoint in what aspect participants were improving in, researchers looked at the time that it took the, to begin moving the cursor when they heard the sound associated with a target. The researchers identified that, for the cued targets, participants took less time moving the cursor, but the time it took for them to start participants was similar. Participants got better at controlling their muscles to move the cursor towards a specific target associated with a unique sound. This means that participants got faster and more accurate at the motor skill because they got better at the execution of the skill and not necessarily because they remembered better.

This new study reflects what other studies looking at memory activation during sleep have found: if a memory is re-activated it can be better consolidated. In this case, the researchers showed that memory activation during sleep can actually improve and enhance the performance of a motor skill learned previously. In fact, re-activation of these motor control memories may be necessary to strengthen memories and consequently the movements and motor skills learned. The authors suggest that this strategy could be used to help with rehabilitation in patients with injuries that impair movement. Activating certain motor memories while a patient sleeps could potentially help them recover and improve their daily lives. But beyond clinical applications, it may mean that getting better at a skill, be it throwing a baseball or driving a car, may just require a little sleep.

Images

Cover image. From Pixabay.

References

1. Cheng, L. Y., Che, T., Tomic, G., Slutzky, M. W., & Paller, K. A. (2021). Memory reactivation during sleep improves execution of a challenging motor skill. The Journal of Neuroscience. https://doi.org/10.1523/jneurosci.0265-21.2021
2. Hu, X., Cheng, L. Y., Chiu, M. H., & Paller, K. A. (2020). Promoting memory consolidation during sleep: A meta-analysis of targeted memory reactivation. Psychological Bulletin, 146(3), 218–244. https://doi.org/10.1037/bul0000223
3. Sanders, K. E., Osburn, S., Paller, K. A., & Beeman, M. (2019). Targeted memory reactivation during sleep improves next-day problem solving. Psychological Science, 30(11), 1616–1624. https://doi.org/10.1177/0956797619873344

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