Twenty-six years. That’s about the part of our lives we spend sleeping. Scientists have been trying to explain why we spend so much time sleeping since the ancient Greeks, but pinpointing sleep’s exact functions has proven difficult.
Over the past decade, there has been a surge of interest among researchers in the nature and function of sleep. New experimental models, coupled with technological advances and analytical techniques, give us a deeper insight into the sleeping brain. Here are some of the biggest recent breakthroughs in sleep science.
1. We know more about lucid dreaming
The neuroscientific study of dreams is no longer on the margins, but has now become mainstream.
In a 2017 study, American researchers woke their participants at regular intervals at night and asked them what was going through their minds before the alarm call. Sometimes participants could not remember any dreams. The research team then looked at what happened in the participant’s brain just before he woke up.
Participants’ recall of dream content was associated with increased activity in the posterior hot zone, a part of the brain closely linked to conscious awareness. Researchers were able to predict the presence or absence of dream experiences by monitoring this zone in real time.
Another exciting development in dream research is the study of lucid dreaming, where you are aware that you are dreaming. A 2021 study established two-way communication between a dreamer and a researcher. In this experiment, participants indicated to the researcher that they were dreaming by moving their eyes in a prearranged pattern.
The experimenter read math problems (what is eight minus six?). The dreamer might answer this question with eye movements. The dreamers were accurate and indicated that they had access to high-level cognitive functions. The researchers used polysomnography, which monitors body functions such as breathing and brain activity during sleep, to confirm that the participants were asleep.
These discoveries have dream researchers excited about the future of “interactive dreaming,” such as practicing a skill or solving a problem in our dreams.
Read more: While we dream, we can listen to the waking world – podcast
2. Our brains replay memories while we sleep
This year marks the centenary of the first demonstration that sleep improves our memory. However, a 2023 review of recent research found that memories formed during the day are reactivated while we sleep. Researchers discovered this using machine learning techniques to ‘decode’ the contents of the sleeping brain.
A 2021 study found that training algorithms to distinguish between different memories while awake makes it possible to see the same neural patterns reappear in the sleeping brain. Another study, also from 2021, found that the more often these patterns occur during sleep, the greater the benefit for memory.
In other approaches, scientists have been able to reactivate certain memories by replaying sounds associated with the memory in question while the participant slept. A 2020 meta-analysis of 91 experiments found that when participants’ memory was tested after sleep, they remembered more of the stimuli whose sounds were played during sleep, compared to control stimuli whose sounds were not replayed .
Research has also shown that sleep strengthens memory for key aspects of an experience, restructures our memories to form more coherent stories, and helps us come up with solutions to problems we’re stuck on. Science shows that sleeping on it all night really helps.
3. Sleep keeps our mind healthy
We all know that lack of sleep makes us feel bad. Laboratory studies of sleep deprivation, in which researchers keep willing participants awake all night, have been combined with functional MRI brain scans to paint a detailed picture of the sleep-deprived brain. These studies have shown that a lack of sleep severely disrupts the connectivity between different brain networks. These changes include a disruption of connectivity between brain areas responsible for cognitive control, and a strengthening of those involved in threat and emotional processing.
As a result, the sleep-deprived brain is worse at learning new information, worse 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 pervasive in poor mental health.
4. Sleep protects us from neurodegenerative diseases
Although we naturally sleep less as we age, mounting evidence suggests that sleep problems later in life increase the risk of dementia.
The accumulation of β-amyloid, a metabolic waste product, is one of the mechanisms underlying Alzheimer’s disease. Recently, it has become clear that deep, undisturbed sleep is good for flushing these toxins from the brain. Sleep deprivation increases the build-up of β-amyloid in parts of the brain involved in memory, such as the hippocampus. A longitudinal study published in 2020 found that sleep problems were associated with higher β-amyloid accumulation at a follow-up four years later. In another study published in 2022, sleep parameters predicted the rate of cognitive decline in participants over the next two years.
5. We can create sleep
The good news is that research is developing treatments to get a better night’s sleep and increase its benefits.
For example, the European Sleep Research Society and the American Academy of Sleep Medicine recommend cognitive behavioral therapy for insomnia (CBT-I). CBT-I works by identifying 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 to be recommended for treatment on the NHS by England’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 trials 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 is receiving funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 101028886.