Wonder how do we exactly fall asleep? Think of your brain as an electrical system, which has ongoing circuits that can switch off or on, to induce sleep or wakefulness. The transitional phase between these two conditions is called sleep state switching – also known as the flip-flop switch model. In this model, the neurons switch off or on to prevent arousal or sleep, to keep you asleep or to keep you alert during the periods of wakefulness.
If you are struggling to fall asleep at night, then you probably have enough time to think about many things, starting from personal problems such as ex-partners to what to cook tomorrow and how to pass an exam. But did you ever wondered how do we fall asleep? What happens in those few seconds when we switch off and enter the world of dreams? And how is it possible that we are barely aware of it? Sleeping peacefully or staying wide awake depends mainly on the way a few small areas in our brain tend to function, but a lot of other factors can impact the stability of that well-established system, causing us to be sleepy or awake at inappropriate times.
Out of 24-hours we have at our disposal, we usually spend 16 hours awake, and sleep for the rest eight hours. It’s very interesting that only a small number of brain cells is in charge of that, so, today we will see what science has to say about it, and how exactly our brain falls asleep.
With many scientific achievements and discoveries over the past century, scientists were able to find out how exactly our brain falls asleep and to understand better how the entire process which controls our circadian rhythm functions. We can think about our brain as an electrical system, which has ongoing circuits that can switch off or on, to induce sleep or wakefulness. The transitional phase between these two conditions is called sleep state switching; one way to explain it is known as the flip-flop switch model. In this model, the neurons switch off or on to prevent arousal or sleep, and to keep you asleep once you fall into it, or to keep you alert during the periods of wakefulness.
For the majority of people who do not have any sleep-related problems or disorders, switch model is useful in regulating their sleep pattern, which is in accordant to their social obligations and daily functioning. In other words, this is what keeps us awake in situations where it is not appropriate to fall asleep, for instance, at a business meeting or in a restaurant. Patients who are diagnosed with narcolepsy or other sleep disorders have a problem with the way this switch functions. Since it does not switch properly, it gives them the ability to fall asleep anywhere and anytime, no rules, even when they would rather be awake.
Sometimes, falling asleep can turn into a real struggle, and it can last for hours, but the essential part of transitioning from wake to sleep phase lasts only a few seconds while getting to that point can take much longer. The ability to stay asleep or awake for a stable period of time is an outcome of mutual inhibition of two different groups of neurons. Wakefulness and sleep are two different states, and we cannot be both at the same time, even though only a few seconds is between them, they inhibit one another. That is why experts agreed to use the term flip-flop switch, which is otherwise used in electronics to describe the circuit with two stable states, but flip-flops do not have transitional stages, they are either on or off, which is basically how scientists understand our sleep and wake stages work.
The neurons which participate in the switching process are located deep in our brain; one of them is orexin. Orexin or hypocretin is in charge of regulating the arousal, wakefulness, and appetite, lack of in the brain can cause cataplexy, which is a type of narcolepsy. The human brain contains around 10-20.000 of neurons which produce orexin, and most of them are located in the lateral hypothalamus and perifornical area. Hypothalamus is a part of the brain in charge of different functions related to endocrine and nervous systems. Some of the duties of the hypothalamus that are related to the nervous system include control of circadian rhythm, inner clock and sleep-wake cycle, body temperature, hunger and thirst, emotional response, etc.
Now, let us go back to the core of things, orexin keeps us awake until the switch occurs and triggers the ventrolateral preoptic nucleus in our brain to start producing GABA and galanin neurotransmitters. Galanin is present in the brain, spinal cord, and gut, and it is involved in a few different functions, including sleep regulation. GABA is a neurotransmitter related to mood, and a lot of people take GABA supplements to enhance their sleep and mood. These two can calm the brain and prepare it for the state of sleep by blocking orexin, which use to keep us awake. By doing so, they reversed the cycle, or switched it, and induced sleep.
When talking about these things, we should make some things clear; neurons are the cells which are a part of the nervous system, to communicate with other cells they need to use neurotransmitters, which can pass their information to other cells like a carrier. Neurotransmitters are chemical compounds which tell neurons what to do, so in the spirit of today’s topic, if a group of sleep cells gets a message to stop their activity, they will stop, and the brain will also understand that message and start promoting wakefulness because those cells are now taking over, while the sleep cells are inhibited.
The model of sleep state switching can also be used to explain how we go from one stage of sleep to another. Some of the researchers claim that the switch occurs in the mesopontine tegmental area, which is located near the center of the brain. Right there, the neurons are regulating the switch between REM and NREM. In this case, while we are already sleeping, on both “sides,” we have neurons which produce the GABA neurotransmitter, but the switch in charge of triggering REM also has some glutamatergic neurons.
The flip-flop switch model is just a mechanism of how the switch happens, but by practicing some healthy habits, we can enhance the work of it, as well as our inner circadian clock.
Having a disbalance in your flip-flop switch is usually a sign of some other sleep-related disorders that follow destabilization of the switching process. For example, when the person is in the prolonged state of arousal, certain chemicals will start piling up in the brain and move the balance to the state of sleep, but chemicals are not the only ones in charge of triggering neurons. A lot of things around us, such as light, stress, or sound, can speed up or delay our sleep onset, but also some other conditions such as homeostatic sleep drive or circadian rhythm.
Here are some of the disorders that go hand in hand with changes in the flip-flop switch.
After we have seen what the consequences of irregular flip-flop switches can be, let us see now what we can do to prevent that from happening, and secure a healthier sleep routine that will enhance the quality of our life. These tips are all common sense advice, and the things we know we should practice, but somehow we always tend to avoid them, even though they are a part of sleep hygiene. Establishing healthy sleep hygiene sounds general and well-known, but a lot of people are not aware of what that means. Sleep hygiene implies a number of different habits and practices which should be followed on a daily basis to secure proper sleep quality and alertness during the daytime.