Sleep Team Helsinki conducts research on basic mechanisms of sleep and wakefulness. We are also interested in sleep pathologies, including effects of restricted sleep on brain and body and connections between sleep and depression.

The research consists of four main lines: sleep homeostasis, the effects of sleep and sleep loss on human health, mechanisms of sleep and depression and zebra fish as an animal model of sleep research

Homeostatic regulation of sleep

Sleep homeostasis means simply that after a period of prolonged wakefulness, we sleep longer (measured as duration of the sleep period) and deeper (measured as increase in EEG slow wave activity). Almost everybody has personal experince of the functioning of this process! The two-process mathematical model of sleep regulation accurately describes the magnitude by which sleep is increased after different periods of wakefulness.

But how does brain keep count of how long we have been awake, or in other words, what are the molecular mechanism of sleep homeostasis? That is the basic research question of our group.

We have discovered that one of the key sites for sleep homeostasis regulation is the basal forebrain (BF), in humans Nucleus Basalis Meynert. During prolonged wakefulness, adenosine and nitric oxide concentrations increase first in this structure and later in the cortex.

Lesioning of the basal forebrain cholinergic cells prevents the induction of sleep homeostasis:  after a period of prolonged wakefulness, NREM sleep and delta power do not increase, neither adenosine and nitric oxide concentrations.

Surprisingly, the increase in nitric oxide was mediated through inducible nitric oxide synthase, which normally is activated only by inflammation, suggesting that prolonged wakefulness activates the immune system.

Read more about homeostatic regulation of sleep and look at the publications.


Effects of restricted sleep on human health and performance

Too short or bad quality sleep affects performance and mood next day. Epidemiological studies evidence connections between short/bad quality sleep and several common diseases. However, the mechanisms by which sleep loss contributes to development of these conditions is not well understood.

We have investigated the consequences of short/bad quality sleep in epidemiological cohorts and conducted experimental sleep restrictions in healthy volunteers. The epidemiological cohorts offer an opportunity to identify individuals, who have sleeping problems and compare them to those, who report good sleep quality. The participants report of their actual health condition and sleep behavior in their normal living conditions, providing relevant information to analyze correlations between diseases and sleep. The experimental designs offer a tightly controlled conditions with possibility to EEG recordings and frequent sample collection, as well as performance tests.

Comparing results obtained from different approaches gives a more comprehensive idea about the consequences of sleep insufficiency and development of associated pathologies.

Read more about experimental sleep restriction


Sleep and depression

Sleep and depression are intimately connected, but are there common molecular mechanisms to regulate these conditions?  We have been particularly interested in the early phases of depression and the development/assessment of sleep problems in that phase.

We have tried to identify molecules that are involved both in development of depression and sleep regulation, and developed and used animal models to clarify this question. Most of the studies have been performed in collaboration with Professor Tiina Paunio.

Read more about sleep and depression


zebra fish as an animal model for sleep research

Sleep in mammals, including humans, is defined by features in EEG. But how to define sleep in species where the central nervous system either is different from that of mammals, or is not accessible for EEG electrodes? Behvioral criterion of sleep include immobility and decreased reactivity for stimulation. During sleep, most animals are immobile, but are all immobile animals sleeping? Clearly no.

We set up a measurement system that allowed us to study stimulation responses in zebra fish larvae during spontaneous behavior and after sleep restriction. Sleep restriction was conducted using a procedure that is natural for this species: swimming against constant water flow.

Read more about validation of sleep homeostasis in zebra fish larvae