Twenty-six years. Approximately this much of our lives is spent sleeping. Scientists have been trying to explain why we spend so much time sleeping since at least the ancient Greeks, but determining the exact functions of sleep has proven difficult.
Over the past decade there has been an increase in researchers’ interest in the nature and function of sleep. New experimental models, combined with advances in technology and analytical techniques, are allowing us to look deeper into the sleeping brain. Here are some of the biggest recent breakthroughs in sleep science.
1. We know more about lucid dreaming
Neuroscientific studies on dreaming are no longer on the sidelines but have become mainstream.
In a 2017 study, US researchers woke their participants at regular intervals throughout the night and asked them what was going through their minds before the alarm call. Sometimes participants did not remember having any dreams. The study team then looked at what was happening in the participant’s brain in the moments before they woke up.
Participants’ recall of dream content was associated with increased activity in the posterior hot region, an area of the brain closely linked to conscious awareness. By monitoring this region in real time, researchers were able to predict the presence or absence of dream experiences.
Another exciting development in dream research is the study of lucid dreams, in which you are aware that you are dreaming. A 2021 study established two-way communication between the dreamer and the researcher. In this experiment, participants signaled to the researcher that they were dreaming by moving their eyes in a predetermined pattern.
The researcher read math problems (What is eight minus six?). The dreamer can answer this question with eye movements. The dreamers were accurate, indicating that they had access to high-level cognitive functions. The researchers used polysomnography, which monitors bodily functions such as breathing and brain activity during sleep, to confirm that the participants were sleeping.
These discoveries have dream researchers excited about the future of “interactive dreaming,” like practicing a skill or solving a problem in our dreams.
Read more: We can listen to the waking world while dreaming – podcast
2. Our brain relives memories while we sleep
This year we celebrate the centennial of the first demonstration that sleep improves our memory. However, a review of recent research in 2023 showed that memories formed during the day are reactivated while we sleep. Researchers discovered this by using machine learning techniques to “decode” the contents of the sleeping brain.
A 2021 study found that training algorithms to distinguish different memories while awake made it possible to see the same neural patterns reemerge in the sleeping brain. A different study, also conducted in 2021, found that the more these patterns reappear during sleep, the greater the benefit to memory.
In other approaches, scientists have been able to reactivate specific memories by replaying sounds associated with that memory while the participant sleeps. A 2020 meta-analysis of 91 experiments found that when participants’ memory was tested after sleep, they remembered more of stimuli whose sounds were played back during sleep compared to control stimuli whose sounds were not played back.
Research has also shown that sleep strengthens memory for the most important aspects of an experience, restructures our memories to form more coherent narratives, and helps us find solutions to problems we’re stuck on. Science shows that sleeping on it actually works.
3. Sleep keeps our minds healthy
We all know that lack of sleep makes us feel bad. Laboratory sleep deprivation studies, in which researchers keep willing participants awake throughout the night, have been combined with functional MRI brain scans to paint a detailed picture of the sleep-deprived brain. These studies have shown that lack of sleep severely disrupts the connectivity between different brain networks. These changes include disrupted connectivity between brain regions responsible for cognitive control and strengthening of regions involved in threat and emotional processing.
As a result, the sleep-deprived brain is worse at learning new information, weaker at regulating emotions, and unable to suppress intrusive thoughts. Sleep loss can even make you less likely to help other people. These findings may explain why poor sleep quality is so common in poor mental health.
4. Sleep protects us against neurodegenerative diseases
Although we naturally sleep less as we get older, growing evidence suggests that sleep problems early in life increase the risk of dementia.
Accumulation of β-amyloid, a metabolic waste product, is one of the mechanisms underlying Alzheimer’s disease. It has recently been revealed that deep, uninterrupted sleep is good for removing these toxins from the brain. Sleep deprivation increases the rate of β-amyloid accumulation in memory-related parts of the brain, such as the hippocampus. A longitudinal study published in 2020 found that sleep problems were associated with a higher rate of β-amyloid deposition at a follow-up four years later. In a different study published in 2022, sleep parameters predicted the rate of cognitive decline in participants over the next two years.
5. We can design sleep
The good news is that research is developing treatments to help get a better night’s sleep and increase its benefits.
For example, the European Association for Sleep Research and the American Academy of Sleep Medicine recommend cognitive behavioral therapy (CBT-I) for insomnia. CBT-I works by identifying the thoughts, feelings, and behaviors that contribute to insomnia, which can then be modified to help promote sleep.
In 2022, a CBT-I app became the first digital therapy recommended for treatment on the NHS by the UK’s National Institute for Health and Care Excellence.
These interventions can also improve other aspects of our lives. A 2021 meta-analysis of 65 clinical studies found that improving sleep through CBT-I reduced symptoms of depression, anxiety, rumination, and stress.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Dan Denis receives funding from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement No. 101028886.