slow wave sleep

The brain puts the memories warehouse in order while we sleep

March 15, 2018

Science Daily/FECYT - Spanish Foundation for Science and Technology

During the hours of sleep the memory performs a cleaning shift. A study reveals that when we sleep, the neural connections that collect important information are strengthened and those created from irrelevant data are weakened until they get lost.

 

Throughout the day, people retain a lot of information. The brain creates or modifies the neural connections from these data, elaborating memories. But most of the information we receive is irrelevant and it does not make sense to keep it. In such a case, the brain would be overloaded.

 

So far there have been two hypotheses about how the sleeping brain modifies the neural connections created throughout the day: while one of them argues that all of them are reinforced during sleep hours, the other maintains that their number is reduced.

 

A group of scientists from the Ole Paulsen Laboratory, at the University of Cambridge (United Kingdom), has analyzed the mechanisms underlying the maintenance of memory during the phase of slow wave sleep -- the third phase of sleep without rapid eye movements in the brain during which there is more relaxation and a deeper rest.

 

"Depending on the experiences of a person and depending on their relevance, the size of their corresponding neuronal connections changes. Those that save important information are smaller and those that store the dispensable are larger," explains Ana González Rueda, main author of the study and researcher at the MRC Laboratory of Molecular Biology (LMB) in Cambridge.

 

According to the expert, in the event that all these links were reinforced equally during sleep, the brain would be saturated by an extreme overexcitement of the nervous system.

 

In the study, published in the Neuron journal, the researchers stimulated the neuronal connections of mice subjected to a type of anesthesia that achieves a brain state similar to the slow wave sleep phase in humans.

 

In the words of González Rueda, the stimulation was carried out 'blindly' because the information contained in each of the links was not known. "We developed a system to follow the evolution of a specific neuronal synapse and thus study what type of activity influences that these are maintained, grow or decrease."

 

What isthe maintenance of neural connections dependent on?

 

The results show that during slow wave sleep, the largest connections are maintained while the smaller ones are lost. This brain mechanism improves the signal-to-noise ratio -- important information remains and the dispensable is discarded -- and allows the storage of various types of information from one day to the next without losing the previous data. That is, those that have already been considered relevant are kept in that state without having to reinforce them. According to González Rueda, the brain "puts order" during the hours of sleep, discarding the weakest connections to ensure stronger and consolidated memories.

 

"Although the brain has an extraordinary storage capacity, maintaining connections and neuronal activities requires a lot of energy. It is much more efficient to keep only what is necessary," says the expert. "Even without maintaining all the information we receive, the brain spends 20% of the calories we consume."

 

This research is a first indication of the electro-physiological mechanism of sleep and opens new horizons thanks to the development of a new way of studying live synaptic plasticity.

 

The next objective of the experts is to research the consequences of this type of brain activity for the maintenance of certain information and to analyze new phases of sleep. "In addition to the analysis of the slow wave phase, it could be interesting to know what happens in the REM phase, during which dreams occur," concludes González Rueda.

https://www.sciencedaily.com/releases/2018/03/180315110640.htm

Sleep selectively stores useful memories: brain evaluates information based on future expectations

February 1, 2011

Science Daily/Society for Neuroscience

After a good night's sleep, people remember information better when they know it will be useful in the future, according to a new study in the Feb. 2 issue of The Journal of Neuroscience. The findings suggest that the brain evaluates memories during sleep and preferentially retains the ones that are most relevant.

 

"Our results show that memory consolidation during sleep indeed involves a basic selection process that determines which of the many pieces of the day's information is sent to long-term storage," Born said. "Our findings also indicate that information relevant for future demands is selected foremost for storage."

 

Some, but not all, of the volunteers were allowed to sleep between the time they learned the tasks and the tests. As the authors expected, the people who slept performed better than those who didn't. But more importantly, only the people who slept and knew a test was coming had substantially improved memory recall.

 

The researchers also recorded electroencephalograms (EEG) from the individuals who were allowed to sleep. They found an increase in brain activity during deep or "slow wave" sleep when the volunteers knew they would be tested for memory recall.

 

"The more slow wave activity the sleeping participants had, the better their memory was during the recall test 10 hours later," Born said. Scientists have long thought that sleep is important in memory consolidation. The authors suggest that the brain's prefrontal cortex "tags" memories deemed relevant while awake and the hippocampus consolidates these memories during sleep.

http://www.sciencedaily.com/releases/2011/02/110201172603.htm

Memory Links to 40 Winks

July 6, 2010

Science Daily/Washington University in St. Louis

When it comes to executing items on tomorrow's to-do list, it's best to think it over, then "sleep on it," say psychologists at Washington University in St. Louis.

 

People who sleep after processing and storing a memory carry out their intentions much better than people who try to execute their plan before getting to sleep. The researchers have shown that sleep enhances our ability to remember to do something in the future, a skill known as prospective memory.

 

Moreover, researchers studying the relationship between memory and sleep say that our ability to carry out our intentions is not so much a function of how firmly that intention has been embedded in our memories. Rather, the trigger that helps carry out our intentions is usually a place, situation or circumstance -- some context encountered the next day -- that sparks the recall of an intended action.

 

The researchers found that participants who tested in the morning following sleep overwhelmingly performed the prospective memory task better in the semantic category test, or context, than in the other two, and they found no such correlation in the group who tested sleepless.

 

The crux of the finding rests on the fact that the prospective memory instruction was given right after the semantic category practice. In this context, those who slept remembered the prospective memory intention better than in the other categories.

 

"Sleep promoted the remembering to do the prospective memory task when that one context was present, but not when some other context was present," McDaniel says. "That's because of temporal contiguity -- the fact that the participants were told to hit that 'Q' button right after they were exposed to the semantic category context.

 

"The idea is that the semantic category test is weakly associated with the prospective memory intention -- it's weakly floating around in the mind and becomes weakly associated with the prospective memory test," McDaniel says.

 

To return to the colleague and message analogy, because before sleeping you remembered you had a message to deliver to your colleague and you would see him in the conference room tomorrow, sleep enhances the likelihood that you will tell him in the conference room, but not in some other context, the office, elevator, the mail room, for example.

 

The researchers believe that the prospective memory process occurs during slow wave sleep -- an early pattern in the sleep cycle -- involving communication between the hippocampus and cortical regions. The hippocampus is very important in memory formation and reactivation and the cortical regions are keys to storing memories.

 

"We think that during slow wave sleep the hippocampus is reactivating these recently learned memories, taking them up and placing them in long-term storage regions in the brain," Scullin says. "The physiology of slow wave sleep seems very conducive to this kind of memory strengthening."

http://www.sciencedaily.com/releases/2010/06/100630162359.htm

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