Neuroscientists Discover How the Brain Learns While We Sleep
Changes in brainwave frequency are linked to mastering a skill during sleep.
Posted November 11, 2013
Scientists have known for decades that the brain requires sleep to consolidate learning and memory. At the annual meeting of the Society for Neuroscience in San Diego on November 10, 2013, sleep researchers from Brown University presented groundbreaking new research that helps explain the specifics of how the sleeping brain masters a new task.
“It's an intensive activity for the brain to consolidate learning and so the brain may benefit from sleep perhaps because more energy is available, or because distractions and new inputs are fewer,” said study corresponding author Yuka Sasaki, a research associate professor in Brown University’s Department of Cognitive, Linguistic and Psychological Sciences.
My roommate plays the piano for a few hours everyday. Over the past few months I have heard him improve steadily. Every morning he seems to play better than the night before. How does sleep lead to the improvement of motor skills?
Sleep is beneficial for a wide range of learning and memory. The Brown researchers used a finger-tapping motor-sequence task much like you would use when typing quickly on a keyboard or playing the piano to discover specifically what happens when motor learning takes hold in the brain.
Humans are designed to spend about one-third of our lives sleeping, which adds up to about 8 hours a night. By the time you are 60, ideally you will have slept for 20 years—5 of those years will be spent in REM sleep, dreaming. This ratio of one hour of sleep for every two hours of wakefulness is hardwired into our biology and necessary for both our survival and optimal performance.
There are four sleep stages that occur in a cycle about every 90 minutes during the night. Each sleep stage is associated with different brainwaves linked to various states of consciousness, learning, and creativity. If you’d like to read more on this please check out Chapter 11 of The Athlete’s Way titled “The Sleep Remedy.”
Changes in Brainwaves Consolidate Learning and Memory
There is mounting evidence that during sleep the brain employs various combinations of neural oscillations — also known as brainwaves — to consolidate learning in a specific brain region and then connects that learning to other parts of the brain using a different brainwave frequency.
In August 2013, the Brown researchers reported in the Journal of Neuroscience that two specific brainwave frequencies called fast-sigma and delta, were directly associated with learning a finger-tapping task similar to the skillset needed to type or play the piano.
The researchers at the Brown Sleep Lab found significant improvements to the speed and accuracy on the task after a few hours of sleep. Spontaneous delta and fast-sigma brainwaves significantly increased in the supplementary motor area (SMA), which is a region in both hemispheres near the top-middle of the brain. The increased spontaneous oscillations in the SMA correlated with performance improvement and were specific to slow-wave sleep stage also known as “deep sleep."
"The mechanisms of memory consolidations regarding motor memory learning were still uncertain until now," said Masako Tamaki, a postdoctoral researcher at Brown University and lead author of the study. Adding, "We were trying to figure out which part of the brain is doing what during sleep, independent of what goes on during wakefulness. We were trying to figure out the specific role of sleep."
Sigma and Delta Brainwaves are a Dynamic Duo for Learning
The results of the Brown study are revolutionary, largely because the scientists used a cutting edge blend of advanced technologies which included: magnetic and electronic encephalography, magnetic resonance imaging (MRI) and polysomnography. This combination allowed them to measure the brainwaves in specific brain regions within both a millimeter and millisecond of precision during distinct phases of sleep.
The Brown researchers conclude that sleep-dependent mastery of the finger-tapping motor-sequence resides in the SMA contralateral (on the opposite hemisphere) to the trained hand. This learning is mediated by spontaneous delta and fast-sigma oscillations, especially during slow-wave sleep.
“The new results show something similar with a visual task in which 15 volunteers were trained to spot a hidden texture amid an obscuring pattern of lines. It's a bit like an abstracted game of ‘Where's Waldo?’ but such training is not merely an academic exercise,” said Takeo Watanabe, who is also a professor of cognitive, linguistic, and psychological sciences at Brown. "Perceptual learning in general has been found to improve the visual ability of patients who have some decline of function due to aging," according to Watanabe.
What is the role of the supplementary motor area (SMA) in sleep learning?
The Brown researchers tracked 5 different oscillation frequencies in eight brain regions (four distinct regions on each of the brain's two sides). Sasaki said she expected the most significant activity to take place in the "M1" brain region, which governs motor control, but instead the significant changes occurred in the SMA on the opposite side of the trained hand. Many recent studies have found that the symmetry and connectivity of brain regions may be linked to optimal cognitive function and peak performance.
“The repeated significance of sigma oscillations, also known as sleep spindles, in both the visual task and the motor task may be important in figuring out a broader picture of how the brain consolidates learning during sleep,” according to the researchers.
The neuroscientists believe the two different brainwave frequency bands play different roles. The sigma frequency is believed to fortify the internal workings of a specific brain region, while the delta frequency is associated more with creating communication between brain areas.
Conclusion: Getting a Good Night's Sleep is Key to Learning and Memory
"Sleep is not just a waste of time," Yuka Sasaki concludes. The extent of reorganization that the brain accomplishes during sleep is suggested by the distinct roles the two brainwave oscillations appear to play. The authors conclude “that the delta oscillations appeared to govern the changes in the SMA's connectivity with other areas of the cortex, while the fast-sigma oscillations appeared to pertain to changes within the SMA itself.”
There are some pharmaceuticals used for sleep that have a negative effect on the time spent in slow-wave sleep. In particular, using benzodiazepines like Ativan, Valium, Klonopin reduces the time spent in deep sleep. Unfortunately, these substances (and other sedatives) may be effective for increasing the overall duration of sleep—and helping people fall asleep—but the payback is that they also deprive someone of the deep slow-wave sleep needed for optimal learning and memory.
Do you suffer from insomnia? Finding ways to improve sleep will help to optimize a lifespan of effective learning and memory. In Chapter 11 of The Athlete’s Way I offer specific tips for treating insomnia without medication.
One of the benefits of regular physical activity, and other healthier lifestyle choices, is they facilitate a better night’s sleep. Also, researchers are discovering the importance of keeping your sleep-wake cycle and circadian rhythms in sync with seasonal daylight patterns (as much as possible) and reducing nighttime exposure to specific types of artificial light.
For more on this topic, check out my Psychology Today blogs: