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Falling Asleep, Explained: The Flip-Flop Switch Model

Ever wondered how to fall asleep? If you’ve ever had trouble falling asleep, you’ve probably pondered how the brain falls into sleep. Modern science can help answer questions about how the brain switches into sleep. And while this knowledge may not help you nod off at night, it can help provide a better understanding of the processes that control our circadian rhythms and offer insight into disorders that impact wakefulness, like narcolepsy.

The brain is essentially an electrical system, with circuits that switch on and off to cue wakefulness or sleep. Scientists call this transition between slumber and consciousness “sleep state switching.” One model used to explain sleep state switching is the flip flop switch model, in which neurons effectively switch on and off to inhibit sleep or arousal, keeping you conscious during periods of wakefulness and helping you remain asleep once you drift into dreamland.

In most people, this switch helps keep slumber at bay in situations that aren’t conducive to sleep—like when you’re in a meeting or behind the wheel. In people with narcolepsy or those experiencing chronic exhaustion, however, this switch doesn’t function properly. This causes them to spontaneously transition into sleep even when they’d rather stay awake.

Exploring The Flip Flop Switch

Let’s take a closer look at how the brain’s toggle switch transitions between sleep states. Though it sometimes seems as though falling asleep takes ages, we actually move between waking and sleep and different stages of sleep within a few seconds.

Sleep and wakefulness are distinct states—you cannot be both asleep and awake, because one state effectively inhibits the other. That’s why scientists use the term “flip flop switch,” a phrase that describes an electrical feedback loop with circuits running in opposite directions. Flip flop circuits avoid transitional states; that is, they’re either on or off, which mirrors our scientific understanding of sleep.

The neurons involved in this switch are located deep inside the brain. Orexin is a neurotransmitter produced in the hypothalamus that regulates arousal and wakefulness. Neurotransmitters are the brain’s messengers, and this one tells the brain to remain awake.

That is, until a “switch” engages to cause the brain’s ventrolateral pre-optic nucleus (VLPO) to begin secreting neurotransmitters GABA and galanin. These messengers calm the brain and induce sleepiness by inhibiting orexin neurotransmitters that keep you awake, reversing the wakefulness switch and cueing sleep.

Switching during sleep

Sleep state switching can also help explain how we move between different stages of sleep. Recent research suggests that the switch occurs in an area near base of the brain called the mesopontine tegmentum. There, neurons regulate the change between REM and NREM.  In this model, both virtual switches include neurons that produce the neurotransmitter GABA. The switch that activates REM also contains glutamatergic neurons.

While the flip flop switch model may not assist with falling asleep, it offers insight into how the brain regulates sleep and arousal. Habits that promote a healthy brain, like regular exercise, eating a diet rich in healthy fats and antioxidants, and getting plenty of sleep, can help keep this switch, and your own circadian clock, in good working order.

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