Sleep and memory: how they are connected and how they affect each other
Scientists and researchers have been studying the relationship between memory and sleep for over 100 years. The conclusion to date is that the process of retaining key memories and discarding redundant information occurs in both the non-rapid eye movement (NREM) and rapid eye movement (REM) stages of your sleep cycle.
Recent studies also show that insufficient or excessive sleep can affect memory processing and other cognitive processes. A good night's rest not only promotes good physical health, but also allows our brains to function properly, so getting the recommended amount of sleep each night is key to consolidating memories.
How are memory and sleep connected?
Sleep and memory share a complex relationship. Getting enough rest helps you process new information when you wake up, and sleeping after learning can consolidate that information into memories, allowing you to store it in your brain.
A healthy adult's sleep cycle consists of four distinct stages:
The first two stages are considered light NREM sleep
The third is deep (or “slow wave”) NREM sleep. These three stages prepare your brain to learn new information the next day. Not sleeping enough or not sleeping enough can reduce your learning abilities by up to 40%. During these NREM stages, the brain also sorts through your various memories from the previous day, filtering out important memories and eliminating other information. These selected memories will become more specific as deep NREM sleep begins.
This process will continue during the fourth stage, REM sleep. Emotional memories are also processed in the REM stage, which can help you cope with difficult experiences. Most dreams occur in REM sleep. The thalamus transmits input from your five senses to the cerebral cortex, a thin layer of the brain that interprets and processes information from your memories. The thalamus is largely inactive during the NREM stages, but when REM sleep begins, it will transmit images, sounds, and other sensations to the cerebral cortex that will then be incorporated into your dreams.
How does sleep deprivation affect brain function and memory?
Since the brain doesn't have enough time to create new pathways for newly learned information, sleep deprivation often affects how memories are consolidated. Other possible cognitive effects include problems learning and focusing, impaired decision-making skills, and poor emotional and behavioral control.
How much sleep we need depends largely on age. Studies have concluded that children experience stronger memory consolidation after a good night's sleep. However, too much sleep can also lead to cognitive impairment.
Some studies have found that sleep quality declines with age 7. This is associated with slow wave sleep. Slow waves are produced in an area of the brain known as the medial prefrontal cortex. The medial prefrontal cortex will deteriorate over time, and as a result, older adults typically sleep less during a normal sleep cycle and have a harder time processing memories.
Insomnia and memory loss
Since sleep is so important for the formation and consolidation of memories, some sleep disorders are associated with memory problems. Insomnia, defined as persistent difficulty initiating or maintaining sleep, is known to cause daytime cognitive impairment, including impaired memory function. Sleep disorders that lead to excessive daytime sleepiness, such as narcolepsy, can cause memory loss.
One disorder, sleep apnea, can actually promote memory loss. Sleep apnea is characterized by the temporary interruption of the airway during sleep that can cause people to feel as if they are suffocating. Heavy snoring and excessive daytime sleepiness are other common symptoms of sleep apnea.
More than 900 million people worldwide live with obstructive sleep apnea (OSA), a subtype of the disorder that occurs when a natural obstruction blocks the airway. OSA has long been linked to chronic depression. People with depression often have a difficult time processing memories related to their own experiences. People with OSA have also shown difficulty consolidating memory.
*Article compiled with data from the Sleep Foundation , validated by leading health media OneCare**The scientific data of the article has been edited by Dr. Anis Rehman , Endocrinologist & Metabolism Specialist
