A new study helps explain what happens in your brain while you are asleep that helps improve motor learning.
“The mechanisms of memory consolidations regarding motor memory learning were still uncertain until now,” said Masako Tamaki, Ph.D., a postdoctoral researcher at Brown University and lead author of the study.
“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.”
Using three different kinds of brain scans, the researchers were able to precisely quantify changes in some brain waves and the exact location of that changed brain activity in people as they slept after learning a sequential finger-tapping task. The task was a sequence of key punches akin to typing or playing the piano.
The results of experiments performed at Massachusetts General Hospital and then analyzed at Brown show that the improved speed and accuracy volunteers showed on the task after a few hours of sleep was “significantly” associated with changes in fast-sigma and delta brainwave oscillations in their supplementary motor area (SMA), a region on the top-middle of the brain.
These brainwave changes in the SMA occurred during a particular phase of sleep known as “slow-wave” sleep, according to the researchers.
While scientists have shown that sleep improves many kinds of learning, including the kind of sequential finger-tapping motor tasks addressed in this study, they haven’t been sure about why or how, according to corresponding author Yuka Sasaki, Ph.D., a research associate professor in Brown’s Department of Cognitive, Linguistic & Psychological Sciences.
It’s an intensive activity to consolidate learning, so the brain may benefit from sleep because more energy is available or because distractions and new inputs are fewer, she noted.
“Sleep is not just a waste of time,” she said.
For the study, the research team recruited 15 subjects. For the first three nights, nine of them slept at whatever their preferred bedtime was while their brains were scanned both with magnetoencephalography (MEG), which measures the oscillations with precise timing, and polysomnography, which keeps track of sleep phase.
By this time the researchers had good baseline measurements of the brain activity and subjects had become accustomed to sleeping in the lab, the researchers noted.
On the fourth day, the subjects learned the finger-tapping task on their non-dominant hand, so that it was purposely harder to learn. They then were allowed to go to sleep for three hours and were scanned with PSG and MEG.
Then the researchers woke them up. An hour later they asked the subjects to perform the tapping task.
A control group of six other subjects did not sleep after learning the task, but were also asked to perform it four hours later.
The researchers found that the subjects who had slept did the task faster and more accurately than those who did not.
On day five, the researchers scanned each volunteer with a magnetic resonance imaging machine, which maps brain anatomy, so that they could see where the MEG oscillations they had observed were located in each person’s brain.
The researchers tracked five 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 discovered that the significant changes occurred in the SMA on the opposite side of the trained hand.
What was especially important about the delta and fast-sigma oscillations was that they fit two key criteria: They changed substantially after the volunteers were trained in the task and the strength of that change correlated with the degree of the person’s improvement on the task, according to the researchers.
After performing the experiments, Sasaki, Tamaki and co-author Takeo Watanabe moved from the hospital to Brown, where they set up a new sleep lab. They have since begun a project to further study how the brain consolidates learning. In this case they’re looking at visual learning tasks.
“Will we see similar effects?” Sasaki asked. “Would it be with similar frequency bands and a similar organization of neighboring brain areas?”
To find out, some volunteers will just have to sleep on it.
The study appeared in the Journal of Neuroscience.
Source: Brown University