Can Deep Sleep Hold the Answers to Preserving Memory?

• Researchers examined 346 participants over 60 to determine how deep sleep affects memory.
• These participants completed two overnight sleep studies and were engaged for the next 17 years, to identify how the lack of sleep impacted recollection ability.
• Researchers found that for people over 60, just a one percent reduction in deep sleep per year could lead to a 27% increased risk of losing intellectual recall functions.

This study was published in ScienceDaily.

Sleep patterns have a significant impact on health and well-being. The amount and quality of sleep you receive can determine your mental health, longevity, and immune function. 

As researchers from Monash University have also recently discovered, sleep patterns are vital in later years, as older adults may be at greater risk of losing cognitive function when they cannot maintain deep sleep during the night.

What are Non-REM and REM Sleep?

Non-REM (NREM) sleep and Rapid Eye Movement (REM) sleep are the two main categories of sleep that make up the sleep cycle.

REM sleep is identifiable as the portion of rest marked by quick eye movements under the eyelids and is the sleep stage most closely linked with learning, memory, and mood regulation. NREM sleep is the phase of sleep not marked by rapid eye movements. This is a core portion of rest where the body experiences the most physical restoration and recovery.

Understanding the Basics of Sleep Cycles

As a cyclical process, the body goes through these levels of non-REM sleep at different points, before shifting gears to REM sleep. In this latter phase, brain activity is similar to wakeful hours, with typical signs of REM sleep being eye twitches during rest.

While REM sleep is the period where dreaming is commonly experienced, NREM or deep sleep has more therapeutic benefits for well-being. 

REM sleep first occurs around 90 minutes after falling asleep, and is the cycle where dreaming occurs.  However, NREM sleep kicks off right as you fall asleep, and will usually cycle through three stages, in roughly 90-minute intervals.

The first stage of NREM sleep is the switch from wakefulness to sleep, where the heartbeat, breathing, eye movements, and muscles relax. 

Stage 2 of NREM sleep is a period of light sleep before entering into deeper rest. In this stage, body temperature drops and eye movements stop, with brain wave activity slowing, accompanied by brief bursts of electrical activity.

The last stage of NREM sleep is crucial for a restful feeling in the morning. Slowed heartbeat, breathing, relaxed muscles, and slower brain waves mark this period.

Humans sleep most of their time in the slow wave cycle, with nearly 75-80% of rest taking place under NREM sleep. 

REM sleep takes up 20 to 25% of sleep time. However, a general trend is for sleep patterns and efficiency to decline with age.

What are the Links Between Sleep and Memory Loss? 

Sleep has been discovered to be a direct cause of age-related cognitive decline. Previous studies have found the changes in structure, timing, and continuity in sleep as the best-known risk factors of this condition, although the mechanisms are not fully understood.

According to Associate Professor Pase: “to date we have been unsure of the role of slow-wave sleep in the development of [memory loss]. Our findings suggest that slow-wave sleep loss may be a modifiable [cognitive] risk factor."

Findings suggest that when we wake more frequently at night, sleep less deeply, and wake early in the mornings, these disturbances can cause an increase in structures like the brain’s Aβ burden—a complex protein influencing brain activity.

The extent of the molecule’s function is still being researched. Still, early studies pair it with protective benefits against infections, leak repair in the blood-brain barrier, regeneration from injury, and regulation of synaptic function—a critical component for learning and memory processes.

To understand the link between sleep and age-related cognitive decline, researchers in this study adopted overnight polysomnographic (PSG) sleep studies and uninterrupted surveillance for incident dementia.

"We used these to examine how slow-wave sleep changed with aging and whether changes in slow-wave sleep percentage were associated with the risk of later-life [memory loss] up to 17 years later", says Pase.

Science Linking Sleep and Memory Loss 

Sleep has long been confirmed to contribute to several health conditions. Heart events, respiratory challenges, and low mood are just some of the diseases that have links to poor or inadequate sleeping habits.

Concerning memory, there have been several attempts to understand why sleep has such a strong influence on cognitive performance. One explanation is the sleep-based neuropsychological perspective, where sleep deprivation is tied to the ‘prefrontal vulnerability hypothesis’. Here, poor sleep is believed to impact cognitive performance following its impact on the prefrontal cortex, an essential region for working memory function.

Another explanation is that sleep deprivation can decrease hippocampus activation, resulting in challenges to memory retrieval even after one night of impaired sleep.

In one study examining the effects of extended sleep loss on memory, students were found to perform comparatively worse on working memory tasks after 36 hours of total sleep deprivation, compared to their execution while properly rested.

How to Improve Sleep

Appropriate sleep hygiene can significantly pay off for your memory and physical well-being. While sleep patterns may take a dip as we age, there are proven steps that can improve sleeping habits for enhanced cognitive and overall welfare.

Introduce consistency to your bedtime routine

Having dinner, going to bed, and waking up at the same time are not just helpful in getting your body used to a routine, but are also necessary for getting your sleep patterns in check.

Having a set time to fall asleep will shift your body into rest mode while guiding your body to wake up at the appropriate time when the required rest hours have been met.

Get the environment right

Deciding to head to bed early may only sometimes guarantee quickly falling into sleep. You can improve your sleep health and quality by keeping devices away from your sleeping area, maintaining a dark and quiet room, and keeping the temperature cool.

Limit alcohol and heavy meals before bed

While alcohol can have sedating effects, having these drinks in the system can cause challenges with insomnia and broken sleep during the wearing-off process. Likewise, consuming heavy foods can disrupt digestion and affect sleep quality.

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