Sleep and memory are interlinked in the most conflicting manner possible. While sleep deprivation may lead to a significant impact on memory, like forgetfulness, mood swings, and irritation, a sound sleep is likely to enhance memory, as per recent studies.
History of Sleep and Memory
There is no denying the fact that sleep is the most vital tool for good health. Major disorders like diabetes, strokes, high blood pressure, heart diseases, etc., are linked to less sleep. In the midst of this behemoth of sleep-related causes and effects, a major breakthrough occurred when studies revealed how sleep can affect memory. While it was obvious that less sleep may lead to lack of brain power and a weak memory, the opposite was not something that struck researchers immediately. The first study to postulate this was undertaken in the 20th century by John Jenkins and Karl Dallenbach, when both declared that a sound sleep propagated better memory retention. A few decades down the line, further research unveiled the existence of sleep stages (NREM and REM) and their effects on memory. Since then, there has been no looking back, and the relationship between sleep cycles and learning has constantly been in question. Studies conducted by several experts prove that a sound sleep after learning helps remember the things learned better than what the person would've remembered if he had lesser sleep.
Evidence from Practical Research
Major case studies conducted at reputed universities like the Beth Israel Deaconess Medical Center (BIDMC) in Boston, University of Geneva, and the University of Notre Dame, among others, have confirmed that learning before sleeping instigates a better response from the brain.
Types of Memory
There are 2 types of memory - procedural (implicit) and declarative (explicit). The former refers to memory that stores motor skills, while the latter refers to storing facts and figures, and is further broken down into semantic and episodic memory. Experiments prove that learning a new skill and then having a good 7 - 8 hours of sleep helps remember the skill better.
Consider that student 1 stays up all night and completes reading a book, while student 2 studies a few facts from the same book and then has a refreshing sleep. In the morning, student 2 would be able to remember whatever he has learned, while student 1 is likely to get befuddled. This is the most common experiment undertaken by most researchers, and most of the time, it has been proven that a good sleep helps remember stuff better. Although further research is being undertaken in this area, it is almost an established theory, evident from various MRI scans, that sleep after learning activates the cerebellum, which is the component of the brain that controls motor skills. Also, scans reveal that sleep might slow down the component of the brain that deals with stress and tension. Thus, whatever information you have crammed up prior to sleeping, has been acquired, consolidated, and stored away so that you can recall it all easily the next day.
Infant Learning and Sleep
A good night's sleep helps infants with better motor coordination. If they are taught how to walk, talk, flex limbs, etc., and then put to sleep, they will remember and improve their skills once they wake up. This discovery is likely to be used for stroke rehabilitation and other motor neuron-related disorders.
The Relationship Between Sleep and Memory Enhancement
When a person sleeps, the brain actually forms new memories. Improved learning after sleeping can be attributed to the REM (rapid eye movement) stage. Here's when the brain acquires and processes the learned information that was absorbed prior to sleeping. All the newly acquired skills and learning are consolidated and processed in this stage, which is why sleep, post learning, is said to improve memory.
Sleep and Memory Consolidation
Memory consolidation occurs when the different regions of the brain connect with each other, like the hippocampus and cortex communication within the brain. Sleep helps strengthen this process, leading to an improved connection between the brain cells and other regions of the brain. Say, you learn to play the flute. An 8-hour sleep after 2 hours of practice ensures that whatever you have registered through your 5 senses has been absorbed by the brain cells and perceived by the neurons that form your brain. These neurons coordinate with each other, the brain cells get activated, and the skills learned are stored away in the memory. This is assumed to occur during the REM phase of sleep, which is why, when you wake up, whatever you learned is likely to remain fresh in your brain. This may not have happened if you had practiced for numerous hours without sleep, as lack of sleep makes the brain foggy and renders it inactive, thus, making you forget what was learned.
Sleep and Memory Loss
According to the University of California, Berkeley, lack of sleep may cause memory loss, especially among the elderly. While the body rests when you sleep, the brain is busy processing new and existing information. If there is no sleep, the brain is unable to function actively, and its normal functions are impaired. The brain cannot process memories or store them anywhere, which may result in loss of memory.
Extraordinary Brain Power While Sleeping
When you learn and sleep, the brain stores whatever you have learned into long-term memory storage, which helps you recall the same easily. It clears out toxins that may lead to neurological disorders. Surprisingly, and sub-consciously, it also helps take decisions. It creates new memories and also forges connections with previous memories, thus, helping you recall something you may have long-forgotten.
The long and short of it, thus, is the fact that, sleep after learning definitely improves memory. The sleep and memory connection has a lot of established scientific evidence, although experiments are still being conducted for more concrete proof. This does not mean that you are going to achieve super-sharp memory if you sleep for long. It requires you to learn something with complete concentration, and then have a refreshing sleep (even a good nap will do) so that the brain can do what it's supposed to.