Scientists are closer to understanding why deep sleep is crucial for the brain’s ability to learn efficiently.
Researchers from the University of Zurich and the Swiss Federal Institute of Technology have discovered for the first time the causal context as to why deep sleep is crucial to the learning efficiency of the brain and developed a non-invasive method for modulating deep sleep in a targeted region of the brain.
“We have developed a method that lets us reduce the sleep depth in a certain part of the brain and therefore prove the causal connection between deep sleep and learning efficiency,” Reto Huber, professor at the University Children’s Hospital Zurich and of Child and Adolescent Psychiatry at UZH, said in a statement.
The researchers focally perturbed deep sleep in the motor cortex, while investigating the consequences on behavioral and neurophysiological markers of neuroplasticity arising from dedicated motor practice. They discovered that the capacity to undergo neuroplastic changes is reduced by wakefulness but restored during unperturbed sleep.
A single sleepless night can lead to difficulty in mastering mental tasks the following day. While we are awake we receive constant impressions of the environment, where synapses—connections between the nerve cells—are excited and intensified at times.
Perpetual increases in synaptic strength would render the brain highly insensitive to new inputs due to neurons losing their ability to fire selectively and synapses could not be further potentiated—saturating neural plasticity. The need for cellular maintenance and the removal of potentially neurotoxic waste would be enhanced, causing an unsustainable level of energy consumption.
According to the study, when slow waves are selectively perturbed in motor cortex, the restorative process is markedly attenuated, showing that deep sleep is a requirement for maintaining sustainable learning efficiency.
The researchers examined six women and seven men, who had to master three different motoric tasks during the study. The volunteers had their sleep manipulated at times while the researchers localized the part of the brain responsible for learning the finger movements they were tasked with for the control of motor skills.
The researchers were able to learn how the manipulation of deep sleep impacted the motoric learning tasks the next day.
The participants performed well in the morning after a deep sleep but struggled more as the day went on. After sleeping again, the participant’s efficiency increased. However, after a manipulated sleep performance, difficulties in learning the finger movements was noticeably weaker.
“In the strongly excited region of the brain, learning efficiency was saturated and could no longer be changed, which inhibited the learning of motor skills,” Nicole Wenderoth, a professor in the Department of Health Sciences and Technology at the ETH Zurich, said in a statement.
According to the study, there is a lack of causal evidence in humans due to the inability to sleep deprive one target area while keeping the natural sleep pattern intact.
“Many diseases manifest in sleep as well, such as epilepsy,” Huber said. “Using the new method, we hope to be able to manipulate those specific brain regions that are directly connected with the disease.”
The study was published in Nature Communications.