Sleep readies synapses for learning

Findings offer insight into changes that occur in the brain during sleep

July 1, 2019

Science Daily/Society for Neuroscience

Synapses in the hippocampus are larger and stronger after sleep deprivation, according to new research in mice published in JNeurosci. Overall, this study supports the idea that sleep may universally weaken synapses that are strengthened from learning, allowing for new learning to occur after waking.

Sleep is thought to recalibrate synaptic strength after a day of learning, allowing for new learning to take place the next day. Chiara Cirelli and colleagues at the University of Wisconsin-Madison examined how synapses in the hippocampus, a structure involved in learning, changed following sleep and sleep deprivation in mice.

Consistent with previous studies in the cortex, the researchers observed that synapses were larger, and therefore stronger, after the mice were awake for six to seven hours compared to after they were asleep for the same amount of time. Additionally, the researchers found that the synapses were strongest when the mice were forced to stay awake and interact with new stimuli, compared to mice that stayed awake on their own. This is consistent with the hippocampus' role in learning, and suggests that synaptic changes take place when learning occurs, not merely from being awake.

https://www.sciencedaily.com/releases/2019/07/190701144310.htm

Excessive Sleepiness May Be Cause of Learning, Attention and School Problems

May 1, 2012

Science Daily/American Academy of Sleep Medicine

Children who have learning, attention and behavior problems may be suffering from excessive daytime sleepiness, even though clinical tests show them sleeping long enough at night, a new study reports.

Penn State researchers studied 508 children and found that those whose parents reported excessive daytime sleepiness (EDS) -- despite little indication of short sleep from traditional measurements -- were more likely to experience learning, attention/hyperactivity and conduct problems than children without EDS.

The culprits? Obesity, symptoms of inattention, depression and anxiety, asthma and parent-reported trouble falling asleep have been found to contribute to EDS even among children with no signs of diminished sleep time or sleep apnea.

"Impairment due to EDS in cognitive and behavioral functioning can have a serious impact on a child's development," said Susan Calhoun, PhD, the study's lead author. "When children are referred for neurobehavioral problems, they should be assessed for potential risk factors for EDS. Recognizing and treating EDS can offer new strategies to address some of the most common neurobehavioral challenges in young school-age children."

Calhoun said researchers were surprised that most of the children studied showed few signs of short sleep when tested, nor was short sleep associated with any of the learning, attention and behavior problems. She said parents and educators are good resources for determining if a child seems excessively sleepy in the daytime and the complaint should be taken seriously. Previous research found EDS prevalent in 15 percent of children from a general population sample.

http://www.sciencedaily.com/releases/2012/05/120501085700.htm

People learn while they sleep

September 27, 2011

Science Daily/Michigan State University

People may be learning while they're sleeping -- an unconscious form of memory that is still not well understood, according to a new study.

The findings are highlighted in the Journal of Experimental Psychology: General.

"We speculate that we may be investigating a separate form of memory, distinct from traditional memory systems," said Kimberly Fenn, assistant professor of psychology and lead researcher on the project. "There is substantial evidence that during sleep, your brain is processing information without your awareness and this ability may contribute to memory in a waking state."

In the study of more than 250 people, Fenn and Zach Hambrick, associate professor of psychology, suggest people derive vastly different effects from this "sleep memory" ability, with some memories improving dramatically and others not at all. This ability is a new, previously undefined form of memory.

"You and I could go to bed at the same time and get the same amount of sleep," Fenn said, "but while your memory may increase substantially, there may be no change in mine." She added that most people showed improvement.

Fenn said she believes this potential separate memory ability is not being captured by traditional intelligence tests and aptitude tests such as the SAT and ACT.

"This is the first step to investigate whether or not this potential new memory construct is related to outcomes such as classroom learning," she said.

It also reinforces the need for a good night's sleep. According to the National Sleep Foundation, people are sleeping less every year, with 63 percent of Americans saying their sleep needs are not being met during the week.

"Simply improving your sleep could potentially improve your performance in the classroom," Fenn said.

http://www.sciencedaily.com/releases/2011/09/110927124653.htm

Deep sleep maintains the learning efficiency of the brain

May 23, 2017
Science Daily/University of Zurich
For the first time, researchers have demonstrated the causal context of why deep sleep is important to the learning efficiency of the human brain. They have developed a new, noninvasive method for modulating deep sleep in humans in a targeted region of the brain.

Most people know from their own experience that just a single sleepless night can lead to difficulty in mastering mental tasks the next day. Researchers assume that deep sleep is essential for maintaining the learning efficiency of the human brain in the long term. While we are awake, we constantly receive impressions from our environment, whereby numerous connections between the nerve cells -- so-called synapses -- are excited and intensified at times. The excitation of the synapses does not normalize again until we fall asleep. Without a recovery phase, many synapses remain maximally excited, which means that changes in the system are no longer possible: Learning efficiency is blocked.

Causal connection between deep sleep and learning efficiency

The connection between deep sleep and learning efficiency has long been known and proven. Now, researchers at the University of Zurich (UZH) and the Swiss Federal Institute of Technology (ETH) in Zurich have been able to demonstrate a causal connection within the human brain for the first time. Reto Huber, professor at the University Children's Hospital Zurich and of Child and Adolescent Psychiatry at UZH, and Nicole Wenderoth, professor in the Department of Health Sciences and Technology at the ETH Zurich, have succeeded in manipulating the deep sleep of test subjects in targeted areas. "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," says Reto Huber.

Subjective sleep quality was not impaired

In the two-part experiment with six women and seven men, the test subjects had to master three different motoric tasks. The concrete assignment was to learn various sequences of finger movements throughout the day. At night, the brain activity of the test subjects during sleep was monitored by EEG. While the test subjects were able to sleep without disturbance after the learning phase on the first day, their sleep was manipulated in a targeted manner on the second day of the experiment -- using acoustic stimulation during the deep sleep phase. To do so, the researchers localized precisely that part of the brain responsible for learning the abovementioned finger movements, i.e., for the control of motor skills (motor cortex). The test subjects were not aware of this manipulation; to them, the sleep quality of both experimental phases was comparable on the following day.

Deep sleep disturbances impair learning efficiency

In a second step, researchers tested how the manipulation of deep sleep affected the motoric learning tasks on the following day. Here, they observed how the learning and performance curves of the test subjects changed over the course of the experiment. As expected, the participants were particularly able to learn the motoric task well in the morning. As the day went on, however, the rate of mistakes rose. After sleep, the learning efficiency considerably improved again. This was not the case after the night with the manipulated sleep phase. Here, clear performance losses and difficulties in learning the finger movements were revealed. Learning efficiency was similarly as weak as on the evening of the first day of the experiment. Through the manipulation of the motor cortex, the excitability of the corresponding synapses was not reduced during sleep. "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 explains.

In a controlled experiment with the same task assignment, researchers manipulated another region of the brain during sleep. In this case, however, this manipulation had no effect on the learning efficiency of the test subjects.

Use in clinical studies planned

The newly gained knowledge is an important step in researching human sleep. The objective of the scientists is to use this knowledge in clinical studies. "Many diseases manifest in sleep as well, such as epilepsy," Reto Huber explains. "Using the new method, we hope to be able to manipulate those specific brain regions that are directly connected with the disease." This could help improve the condition of affected patients.

Science Daily/SOURCE :https://www.sciencedaily.com/releases/2017/05/170523083345.htm