Mice and humans share sleep disorders - fundamental mechanisms of sleep are similar regardless of species

Currently the researchers at the University of Helsinki are investigating the link between sleep deprivation and inflammation, how parents influence their small children's sleep and how teenagers could find the tools for better sleep.

First the good news: according to studies, most Finns sleep between seven and eight hours per night. This is the recommended amount, and the median amount of sleep most people need. Our individual, genetically determined need for sleep varies between four and ten hours.

And the bad news?

“It seems that our employed populace is increasingly suffering from minor, occasional insomnia symptoms,” says Tiina Paunio, professor of psychiatry at the University of Helsinki.

While the exact reason of the occasional insomnia is unknown, Paunio posits that it has to do with changes in the work environment: people bring work home and often work on their emails late into the evening. This is detrimental to sleep.

Lack of sleep causes inflammation

Lack of sleep has many effects.

“I could talk about the negative effects for a solid week,” says Docent Tarja Stenberg, who has studied the physiology of sleep.

The initial effects are familiar to everyone. They target the central nervous system, with the primary symptom being tiredness. Sleep deprivation also lowers both mood and performance.

“The decreased performance is particularly apparent in tasks that require long concentration and feature many simultaneous tasks that burden the attention span. Night-time supervision work or operating in traffic are tasks in which tiredness can lead to disaster,” says Stenberg.

Other physiological effects will become apparent within a short time span if insufficient sleep continues. In Stenberg’s research, sleeping four hours per night for a week resulted in significant changes in insulin resistance and fat metabolism among young, healthy research subjects. Such changes could in the long term lead to health problems.

Problems resulting from short periods of sleep deprivation will correct themselves, but epidemiologic studies have found that a long-term lack of sleep is a significant risk factor for type 2 diabetes, cardiovascular disease, memory disorders and depression.

“We have come to the conclusion that the underlying reason for these health problems is a low-level inflammation, which develops at a very early stage of sleep deprivation in both humans and mice,” explains Stenberg.

The inflammation also manifests in the brain, even though usually the blood-brain barrier prevents the entry of inflammations into the brain.

Sleep is the same across species

At the moment, Stenberg’s team is using animal models to discover which processes inside the brain cause the inflammation, and how significant this is for a variety of neurological and psychological disorders, such as Alzheimer’s disease and depression.

For this purpose, they have developed a mouse model for depression by switching litters of mice to different mothers for some time. This trauma at a young age caused changes in the brains of the mice, which influenced their sleep in adolescence and adulthood. The research is part of Olena Santangeli’s dissertation, which will be submitted for examination in April.

“Sleep is a factor that is very easily disrupted, and we found that the mice had similar sleep disorders to humans with depression, such as an increase in REM sleep,” Stenberg explains.

REM sleep is the stage between deep and light sleep. During REM sleep, the body’s temperature, pulse and breathing are irregular and the autonomic nervous system is engaged. Most dreaming takes place during REM sleep.

Animal models have been found to be useful in sleep studies in general. Vilma Aho from Stenberg’s group, established that the sleep of zebrafish is astoundingly similar to that of humans.

“It seems that the fundamental mechanisms of sleep are the same irrespective of species.”

Sleep and the child’s development intertwine

Researchers are also interested in the sleep of human children and adolescents. Professor Tiina Paunio has been studying the sleep of babies and children for five years now. The project involves 1,700 families, and it seeks to determine how behaviour modelled by the parents and the family atmosphere influence the sleep of the children, and how sleep influences their development.

“In general, it seems that sleep and development are intertwined. Sleep influences development, but development also influences sleep,” says Paunio.

“It’s good for a child to sleep a lot, but certain developmental stages are characterised by sleep disruptions. This means that the child is processing learned information, which results in fragmentary sleep. It is a passing phase.”

With teenagers, external temptations often override the models and wishes established by the parents. Researchers estimate that up to half of all adolescents sleep too little. However, the need for sleep is also an individual characteristic among teenagers, and it varies.

“We know that the sleep pattern shifts to a later time during adolescence. Teenagers tolerate tiredness well, and there are many temptations vying for their attention in the evenings. They have to have to learn self-control to get to bed on time,” says Professor Anu-Katriina Pesonen, who studies adolescent sleep.

She has also studied learning during sleep by measuring the sleep spindles, or cyclic alternating patterns, meaning the sequences of small activations in the brain during sleep, in the brains of adolescents. Such sleep spindles have been associated with the consolidation of learning during sleep.

Tools for sound sleep

The goal of Pesonen’s other research project is to offer young people tools for managing their sleep patterns.

In 2016, all teenagers between the ages of 16 and 17 in Helsinki were invited to participate in a research project intended to motivate them to get better sleep. A fifth of those invited participated in the study.

“Most sleep instructions are very authoritarian: don’t do this, do this, just go to bed! That is not a particularly effective way of changing someone’s behaviour,” Pesonen points out.

Instead, the goal is to support the teenagers’ own observations of the impact sleep has on their wellbeing.

“Sleep is the time of the day when we think the least and on which we compromise the most. Everything we do during the day seems more valuable than the passive night-time, but when we understand the significance of sleep, we begin to value it more.”

Sleep and mental health are closely linked

“The way that I think about it is that a person who’s prone to anxiety is susceptible to insomnia, but sleep problems also increase the risk of depression,” says Professor Tiina Paunio.

In addition to depression, nearly every other psychological disorder is associated with sleep problems. In bipolar disorder and schizophrenia, this manifests as unpredictable sleep patterns, and in post-traumatic stress disorder, as recurring nightmares.

“The treatment of psychiatric patients should focus more on the impact their medication may have on sleep and how sleep deprivation influences individual health and wellbeing,” states Paunio.

In addition to the duration of sleep, Paunio is interested in the microstructures of sleep, the cycles of the stages of sleep and brain activity during sleep. These can help researchers find biomarkers, which may offer insight into the individual’s future health.