Sleep is a critical part of forming memories. Researchers found that increased sleep spindles can help form motor memory and improve task performance.
People spend about one third of their lives sleeping. Fingers glide across a phone screen or thoughts drift toward the day ahead, but soon, eyelids grow heavy, and sleep begins to take hold. During naps and nighttime sleep, the brain works to form memories.
Studies suggest that sleep spindles, bursts of brain wave activity, are associated with the consolidation of short-term and task-related information into long-term memory.1 A reduction in spindles is linked to neurodevelopmental, psychiatric, and degenerative disorders, while boosting spindle activity may improve memory and serve as a target for cognitive therapies.2,3
This motivated Dara Manoach, a neuropsychologist from Harvard Medical School, and her colleagues to explore where spindle changes occur in response to learning within the brain. In a recent study, published in the Journal of Neuroscience, Manoach and her team found that increased spindle frequency in brain areas involved in motor execution and planning improved task performance after a nap.4 These findings suggest that sleep spindles in these regions might be sensitive biomarkers of learning and sleep-dependent memory formation.
While sleep spindles occur throughout the brain, they tend to be more concentrated in specific regions. The researchers wanted to see if a motor test could boost spindle density in areas active during the task and if these increases predicted performance improvement after a nap.
First, they recruited 25 participants (21 to 42 years old) and trained them to perform a finger tapping motor sequence test (MST), which involved pressing numerically labeled keys in a particular sequence. The team used two types of brain activity recordings to detect the spatial changes in spindle frequency during a baseline nap, MST training, and a post-training nap. From these brain waves, the researchers counted the number, or density, of spindles per minute.
They found that the participants’ tapping performance correlated with increased sleep spindle density in regions of the brain associated with the task, but only during the nap following training—not at baseline. This suggests that learning a new task actively increases spindle density in task-related regions, rather than being simply a characteristic of individuals with naturally high spindle activity.
Moreover, the researchers observed that the rise in spindle density in motor execution areas of the brain predicted improvement after the nap. However, learning during training and performance improvement after the nap were not directly correlated, indicating that these are distinct processes.
There was a key difference between the two: Learning during the MST was associated with increased brain rhythms in movement execution areas during sleep, while post-nap performance was linked to increased brain rhythms in movement planning areas during sleep.
These findings demonstrate that spindle activity is influenced by learning and plays a crucial role in promoting the brain plasticity necessary for motor memory consolidation in specific regions. So, the next time a tough task comes up, just “sleep on it.” Sleep spindles will be hard at work.
