Sleep Care

Understanding How Sleep Affects Memory

When sleep is lost due to the fast pace of today’s world, feelings of fatigue and tiredness are common for many people.  However, another issue that accompanies lack of sleep often gets overlooked:  memory problems.  These can take several forms—from simply forgetting information that was learned recently, to having difficulties recalling thoughts, feelings and emotions that once easily came to mind.

Sleep Architecture and Types of Memory

To understand the relationship between sleep and memory, it is important to know a little about how we sleep at night and to look at the various types of memory.  When we lay down to sleep, the brain goes through cycles of sleep throughout the night, alternating between periods of “non-REM” (NREM) sleep (a portion of which is made up of a very relaxed sleep known as “slow wave sleep”) and REM sleep (where the brain generally does its dreaming during the night).  In the first half of the night, sleep cycles are composed primarily of NREM and have a higher percentage of slow wave sleep (SWS).  As the night goes on, this architecture changes so that in the last couple hours of sleep, the cycles are composes of roughly half NREM and half REM sleep, with little SWS present.

When we think of memory, we typically think of what researchers call declarative or episodic memories.  These are memories that can be verbally described—using nouns, verbs, etc.—and are fact based; i.e., that can be located in time and space.  These memories are usually explicit—meaning that they are concepts we can be consciously aware of.

In contrast to declarative memories, there are procedural, perceptual, and motor memories.  These memories are often implicit, in that they are concepts we are often not aware of consciously.  They can be things such as the “muscle memory” that athletes often develop when practicing a sport over and over again, or the moments of insight gained when a person comes back to a difficult problem after focusing on it for a long time, then taking a break.

The Relationship Between Sleep and Memory

Research investigating the relationship between sleep and memory has found that in the first half of the night—when slow wave sleep (SWS) is present in greater amounts—declarative and episodic memories are enhanced and strengthened.  This appears to be when the brain filters through the day’s information and determines what is important to keep for long-term storage.

As REM sleep takes over in the second half of the night, the information that was preserved early on gets connected to related material stored in long-term memory.  In this way, information is gathered during the day and then sorted and filed away at night for later recall. REM sleep also appears to play a critical role in the processing and storing of the more complex procedural, perceptual and motor memories. One of the theories for the purpose of dreaming is the ability of the mind to practice procedures and motor skills learned throughout the day.

An analogy can be useful to understanding this relationship.  Imagine a desk cluttered with lots of papers, some of which need to be put into a filing cabinet that is neatly organized.  During SWS in the first half of the night, the brain is predominantly sorting through the mess of papers, determining which ones need to be saved, and preparing them to be filed by sorting them into small stacks.  In the second half of the night—when REM sleep is greater—the long-term storage files are looked up and the small stacks of new papers are added to them.

Improving Memory With Better Sleep

Limiting the duration of sleep limits the amount of time available for the brain to categorize and store the information gathered throughout the day, inhibiting your ability to recall memories for later use. Sleep deprivation also limits the performance of over-worked neurons that have not had adequate rest to operate efficiently, causing additional limitations to the access of our memories.

A good starting point to improving memory through better sleep is developing good sleep hygiene, which for many people may take a focused effort given the busy demands of life in modern society.  Problems that can disrupt sleep—such as snoring and sleep apnea—should also be treated, usually be seeing your doctor or a sleep specialist.

While it can be limited in its effectiveness, researchers have found that electrical stimulation (when a person is sleeping) of the specific brain regions related to different types of memory has been associated with improved recall of those memories the next day.  For most people, however, getting a better night’s rest is the most effective way to improve their memory.

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