How Transitions Between Sleep and Wakefulness Are Produced

Numerous complex brain processes are involved in the wake-sleep transition. We tell you what happens when you fall asleep and what substances are involved.
How Transitions Between Sleep and Wakefulness Are Produced

Last update: 30 August, 2022

We don’t know everything about the transitions between sleep and wakefulness. Despite the fact that they’re vital and natural processes that occur with circadian periodicity, in reality, many people suffer alterations in this regard.

These conditions range from insomnia to less frequent disorders, such as narcolepsy. Knowing how the transitions between sleep and wakefulness (and vice versa) work could help us design appropriate interventions. This would improve the quality of life of those who suffer from sleep-related disorders.

Even in healthy individuals, transitions between sleep and wakefulness can be tricky. For instance, you probably often find it difficult to fall asleep, and then, in the morning, have trouble clearing your head and starting the day.

These transitions from one state to another are quite remarkable. In fact, your state of consciousness and your behavior is really different from when you’re awake to when you’re asleep. Furthermore, your brain also functions in different ways.

So what do we really know about these transitions?

Sleepy woman unable to sleep

How the transition from wakefulness to sleep occurs

Neural dynamics change markedly from wakefulness to sleep. Electroencephalograms measure wakefulness as a desynchronized activity. On the other hand, sleep is seen as a globally synchronized slow-wave activity. However, the transformation from one state to another isn’t drastic or instantaneous.

Recent research has found how the transition from wakefulness to sleep occurs. Its findings suggest that local slow waves appear during wakefulness and that sleep slow waves are rarely global. Their appearance seems to be related to the decrease in arousal. Thus, when cholinergic neuromodulation decreases, local slow waves appear. When it reduces further, these slow waves go global.

In addition, differences and changes in functional connectivity in the resting state have been found in the connection and neural activation patterns of separate brain regions. When neuromodulation decreases and the first slow waves appear, no changes are observed in this regard. When it’s reduced further (and the slow waves become global), the functional connectivity changes and the resting-state neural networks merge into a single, widely synchronized network.

This suggests that the transition from sleep to wakefulness is gradual and depends on chemical and electrical changes in the brain. Multiple neurotransmitters such as GABA, melatonin, and adenosine participate in these processes.

How the transition from sleep to wakefulness occurs

The transition from a dream state to a waking state also arouses great interest. Many chemical processes are involved in this transition. For example, norepinephrine, serotonin, and histamine produce cortical activation and promote states of alertness and wakefulness. The activity of their firing systems decreases during slow-wave sleep and is further reduced during REM sleep.

Recent findings have highlighted the role of hypocretin in sleep control. Research published in the journal, Nature has shown how this substance is fundamental in the transition from sleep to wakefulness and the role it plays in the stability of awakening.

Hypocretin-producing neurons (a group of brain cells) are located in the lateral hypothalamus. This study found that the electrical activity that arises from them favors awakening and is essential to maintaining wakefulness.

In the study, direct photostimulation was applied to these neurons in the brain of mice, verifying that it increased the probability of transition from slow-wave sleep or REM sleep to wakefulness. In addition, stimulation at higher frequencies reduced the latency to wakefulness, leading to faster awakening.

By confirming the direct relationship between the activity of these neurons and the transition from sleep to wakefulness, it’s suggested that they could also be involved in narcolepsy. Indeed, the loss of function of these neurons would make it impossible to sustain the stability of the arousal, causing a sudden need to sleep.

Woman in bed waking up

Prevention of sleep disorders

The above are just some of the findings concerning sleep regulation. However, more research is required in this regard.

Finally, understanding brain function during wakefulness and rest facilitates the design of more effective interventions to address sleep disorders. Given the fact that a large number of people are affected by them globally, it’s a task that should be given the utmost priority.

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