Sleep & Brain Waves: How The Brain Coordinates Sleep
Quick Summary
Sleep is an active process. Far from being a passive shutdown, sleep is a highly organized, active state that is necessary for maintaining physical and mental health.
During sleep your brain follows a specific blueprint. Your brain cycles through a structured pattern called "sleep architecture," moving between Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) stages.
Chemicals control the switch. A complex balance of brain chemicals, or neuromodulators, dictates whether you feel alert or drowsy.
Two forces determine sleep timing. Your sleep is governed by the interaction between "sleep pressure" (how long you've been awake) and your circadian rhythm (your internal body clock).
We often imagine sleep as a passive "off" switch, a blank void where nothing happens until the alarm rings. However, looking at the science of how the brain works reveals that sleep is actually a highly organized, actively regulated process (Tubbs, Dollish, Fernandez, & Grandner, 2019). It is a dynamic period where the brain engages in critical work to repair the body and process the day's events.
To improve your sleep, it helps to understand the machinery behind it. This article explains the biological nuts and bolts of your nightly slumber, from brainwaves to neurochemistry.
So, how do scientists actually define this state we call ‘sleep’?
What Exactly Is Sleep?
Sleep is a naturally recurring and reversible state defined by reduced consciousness, relative stillness, and being less responsive to the world around you (Tubbs et al., 2019). This definition distinguishes it from other unconscious states like comas or anesthesia because sleep follows a natural rhythm and you can be woken up from it.
To observe this state, scientists rely on electroencephalography (EEG), a method that records the electrical activity of the brain. By watching these electrical shifts, researchers can see that the brain isn't just resting; it is following a specific script.
But before examining sleep, we need a baseline: what does the brain look like when you are awake?
How Does the Brain Behave When We're Awake?
When you are actively awake, your brain generates high-frequency, low-amplitude electrical signals known as beta waves (12-30 Hz) (Tubbs et al., 2019). This fast, chaotic pattern reflects the fact that your brain is processing multiple, unrelated things at once - from listening to a conversation to planning your dinner.
When you close your eyes and relax, this activity slows down into alpha waves (8.5-12 Hz), which signals a state of wakefulness without focused attention (Tubbs et al., 2019). During this time, your system is flooded with arousal/wake-promoting chemicals like serotonin and dopamine, and your heart rate and blood pressure remain responsive to the world around you.
As you drift off, your brain doesn't just slide into a single "sleep mode." There’s actually different “sleep modes” that occur in regular patterns. So, how is the night organized in terms of these patterns?
What Is Sleep Architecture?
Sleep architecture is the term used to describe the structural organization of sleep, which consists of a predictable pattern of brainwave changes that create specific stages of sleep (Tubbs et al., 2019).
Rather than staying in one state, your brain cycles through two distinct types of sleep - Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) - multiple times each night. This structured blueprint ensures that different physiological needs, from physical repair to memory processing, are met in a specific order.
The night begins with NREM sleep.
So what happens during this phase?
What Happens During NREM Sleep?
NREM sleep dominates the first half of the night and involves a progressive decrease in brainwave frequency and an increase in amplitude (Tubbs et al., 2019). As you move deeper into NREM, your brain activity slows down, your neurons start firing in a more coordinated way, and your body temperature and heart rate drop.
NREM is divided into three stages. What characterizes the first step or stage?
What Is Stage 1 Sleep?
Stage 1 Sleep is the brief transition from wakefulness to sleep, accounting for about 5% of total sleep time (Tubbs et al., 2019). During this phase, the brain begins producing theta waves (4-7 Hz), though some alpha activity remains. It is a very light sleep; while your brain might filter out background noise, it will still respond to significant triggers, such as hearing your name called (Tubbs et al., 2019).
Once you settle in, you move to the next level. So what defines Stage 2?
What Is Stage 2 Sleep?
Stage 2 Sleep acts as a bridge between light and deep sleep, making up roughly 45% to 55% of the night (Tubbs et al., 2019). While theta waves continue in stage 2, this stage is defined by two unique electrical patterns: K-complexes, which are large waves that may help filter out sensory disturbances, and sleep spindles, which are rapid bursts of activity (12-15 Hz) (Tubbs et al., 2019). While researchers are still debating their exact function, these features are thought to support memory consolidation (the process of strengthening memories) and protect the continuity of sleep.
After Stage 2, the brain enters its most restorative phase. What occurs in deep sleep?
What Is Stage 3 (Slow Wave Sleep)?
Stage 3, or Slow Wave Sleep (SWS), is the deepest stage of NREM, characterized by high-amplitude, low-frequency delta waves (around 1 Hz) (Tubbs et al., 2019). This stage is vital for discharging "sleep pressure" (the drive to sleep that builds up during the day) and is when the body releases the majority of its growth hormone for physical repair (Tubbs et al., 2019). It is very difficult to wake someone from this stage, and the time spent here drops off dramatically as the night goes on.
After the deep restoration of NREM, the brain shifts gears entirely. What makes the next stage so different?
Why Is REM Sleep Called "Paradoxical"?
REM sleep is often called "paradoxical sleep" because the brain's electrical activity speeds up to resemble that of an awake, alert person, yet the body remains completely paralyzed (Tubbs et al., 2019). Occurring in episodes that make up about 25% of the night, this is the stage where vivid, emotional dreaming takes place.
During REM, levels of acetylcholine - a chemical associated with wakefulness - surge to match or exceed daytime levels (Tubbs et al., 2019). Despite this mental storm, the brainstem sends signals to shut down the nerve cells that control your muscles, causing atonia, a temporary paralysis of the muscles (Tubbs et al., 2019). The only exceptions are the diaphragm for breathing and the muscles controlling the eyes, which dart back and forth (which is where the name “rapid eye movement sleep” comes from).
This REM stage is also linked to emotional regulation. Functional imaging shows that the limbic regions of the brain, which process emotion, are highly active during REM dreams (Desseilles, Dang-Vu, Sterpenich, & Schwartz, 2011; Rothbaum & Mellman, 2001).
We know what happens during these stages, but which parts of the brain are pulling the levers?
Which Brain Structures Coordinate Sleep?
Sleep is not controlled by a single switch but by a network of brain regions working together (Tubbs et al., 2019).
The Brainstem: This structure controls vital functions like breathing and heart rate. It also houses a network of cells that act like a power switch, pumping out chemicals like serotonin and dopamine to wake up the cerebral cortex, the brain's outer layer responsible for conscious thought (Tubbs et al., 2019).
The Hypothalamus: This region contains the suprachiasmatic nucleus (SCN), the master clock that keeps your body on a 24-hour schedule. It also produces orexin and histamine, chemicals that help maintain wakefulness (Tubbs et al., 2019).
The Thalamus: Acting as a sensory gatekeeper, the thalamus blocks most incoming information (like sound or touch) during sleep to prevent you from waking up (Tubbs et al., 2019).
The Cerebrum: The largest part of the brain, responsible for memory and thought. Its massive network of neurons generates the brainwaves measured by EEG (Tubbs et al., 2019).
These structures communicate using chemical messengers.
So what are the key chemical messenger molecules involved?
What Brain Chemicals Control Wakefulness and Sleep?
Specific chemicals, or neuromodulators, drive the transitions between being awake and being asleep (Tubbs et al., 2019). On the wakefulness side:
Orexin (Hypocretin): Produced in the hypothalamus, this is a primary wake-promoting agent. A lack of orexin is the main cause of the sleep disorder narcolepsy (Tubbs et al., 2019).
Histamine: Also from the hypothalamus, this chemical promotes wakefulness.
Norepinephrine, Dopamine, and Serotonin: These are "arousal" chemicals that are high during the day and decrease significantly during sleep.
Acetylcholine: This chemical promotes wakefulness but is also the fuel for REM sleep, driving the high brain activity seen in that stage (Tubbs et al., 2019).
On the other side of the equation, several key chemicals and signals work to reduce alertness and help you fall and stay asleep:
GABA (gamma-aminobutyric acid): As the brain's primary inhibitory chemical, GABA acts like a brake pedal, actively suppressing the arousal centers that keep you awake. Many sleep medications work by enhancing GABA's calming effects.
Adenosine: This chemical acts as the brain's sleep pressure gauge. It steadily builds up in your system the longer you are awake, increasing your body’s ‘drive’ for sleep. Caffeine keeps you alert by temporarily blocking adenosine's effects.
Melatonin: Often called the "hormone of darkness," melatonin is released by the pineal gland when it gets dark. It doesn't act as a sedative but rather as a timer, signaling to your entire body that it is biologically nighttime and time to wind down for sleep.
Galanin: This chemical works as a partner to GABA, helping to suppress the brain's arousal systems and maintain a stable, uninterrupted state of sleep.
Chemicals explain how we sleep, but what determines when we sleep?
What Is the Two-Process Model of Sleep?
The timing of your sleep is governed by the interaction of two physiological systems: Sleep Propensity (Process S) and the Circadian System (Process C) (Tubbs et al., 2019).
Sleep Propensity (Process S): This is the homeostatic drive for sleep. It builds up the longer you are awake, likely due to the accumulation of adenosine, a chemical byproduct of cellular energy use (Tubbs et al., 2019).
Circadian System (Process C): This is your internal 24-hour rhythm, controlled by the SCN. It uses light signals from the eyes to sync your body's internal schedule with the 24-hour day (Tubbs et al., 2019).
Sleep onset, or the "sleep gate," occurs when the pressure from Process S becomes strong enough to overpower the alerting signal from Process C (Tubbs et al., 2019).
So that’s a lot of information. But understanding this biology offers clues for better sleep. What can we do with this information?
Clinical Comment: What Are The Practical Takeaways?
If you go online you’ll read lots of “tips”. So we’ve put a few key ones here to help you separate fact from internet hype. But in essence, the best ways to keep your circadian rhythm healthy involve managing your exposure to key environmental cues that act as “zeitgebers” - especially light, food, and activity - to send strong, consistent signals to your master clock. We would also add that, while having a strong circadian rhythm is going to help sleep, the body clock isn’t typically a major factor in chronic insomnia for most people.
Protect Your Sleep Drive: Fundamentally, sleeplessness will result from inadequate “Process S”. Things that interfere with Process S? Since "Process S" relies on building up pressure over time, anything that interferes with building that pressure can potentially result in more difficulty sleeping. These can include, but are not limited to: Sleeping in, trying to “catch up” on sleep, long naps during the day, sleeping too long, and getting up late and going to bed early.
Use Light to Your Advantage: Your circadian system (Process C) relies on light to set its time. Get bright light in the morning to wake up your brain and dim the lights in the evening to prepare for sleep.
Respect the "Wind Down": Your brain activity needs to slow from Beta to Alpha before you can enter Stage 1. Give yourself time to relax before bed to make this shift easier. That relaxation can be in bed or out of bed, the main thing is it’s relaxing and pleasant.
Don’t ‘Try’ To Sleep. It Makes Things Worse: It’s common for people experiencing insomnia-type sleep problems to start to believe they must do certain things to make sleep happen - that if they just try hard enough, they can make sleep happen through intention and effort. It’s important to note that, at a basic level, this kind of goal directed and effortful behaviour engages the neurochemicals norepinephrine, dopamine, and serotonin - the same neurochemicals we noted above that drive arousal and wakefulness. So trying harder to sleep is going to result in alertness and wakefulness, the opposite brain state that we need to be in to sleep, and this will likely leave a person more awake and frustrated. Over time this grows into anxiety as a person begins to worry “what’s wrong with me”, “why can’t I make this sleep-thing happen”.
Concerned about your sleep? We always advocate talking to your primary care health provider in the first instance.
You can also talk to a NZ sleep clinic like The Better Sleep Clinic for sleep help. Whether it’s an Auckland sleep clinic, Wellington sleep clinic, Christchurch sleep clinic, Hamilton sleep clinic, New Plymouth sleep clinic or anywhere in NZ, we can help. We specialise in the recommended treatments for circadian rhythm disorders such as delayed sleep phase as well as treatments for other sleep disorders such as insomnia treatment - CBT for insomnia.
Book an assessment (no referral required) or, if you have a specific, question enquire about treatment, and get started addressing your sleep problems today.
Frequently Asked Questions About Sleep And The Brain
Q1: What are the main stages of sleep?
A1: The main stages of sleep are divided into two types: Non-Rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) sleep. NREM sleep is further broken down into three stages: Stage 1 (light sleep), Stage 2 (stable sleep), and Stage 3 (deep, slow-wave sleep). Your brain cycles through these NREM and REM stages multiple times each night (Tubbs et al., 2019).
Q2: What is the difference between NREM and REM sleep?
A2: The primary difference is in brain activity and muscle tone. During NREM sleep, your brain activity slows down progressively, and your body relaxes. In contrast, during REM sleep, your brain becomes highly active—similar to when you're awake—but your body's major muscles are temporarily paralyzed to prevent you from acting out your dreams (Tubbs et al., 2019).
Q3: How does my body know when it's time to sleep?
A3: Your body knows when to sleep based on the interaction of two systems: your homeostatic sleep drive (Process S) and your circadian rhythm (Process C). Your sleep drive, or "sleep pressure," builds the longer you are awake. Your circadian rhythm is your internal 24-hour clock that sends alerting signals during the day. You feel the strongest urge to sleep when your sleep pressure is high and your circadian alerting signals are low (Tubbs et al., 2019).
Q4: What part of the brain controls sleep?
A4: Sleep is not controlled by a single part of the brain but by a network of regions working together. Key structures include the brainstem, which produces arousal chemicals; the hypothalamus, which houses your internal body clock (the SCN); the thalamus, which acts as a sensory gatekeeper; and the cerebrum, which generates the brainwaves that define each sleep stage (Tubbs et al., 2019).
Q5: What brain chemicals control wakefulness?
A5: Specific chemicals, or neuromodulators, drive being awake (Tubbs et al., 2019). They are:
Orexin (Hypocretin): Produced in the hypothalamus, this is a primary wake-promoting agent. A lack of orexin is the main cause of the sleep disorder narcolepsy (Tubbs et al., 2019).
Histamine: Also from the hypothalamus, this chemical promotes wakefulness.
Norepinephrine, Dopamine, and Serotonin: These are "arousal" chemicals that are high during the day and decrease significantly during sleep.
Acetylcholine: This chemical promotes wakefulness but is also the fuel for REM sleep, driving the high brain activity seen in that stage (Tubbs et al., 2019).
Q6: What brain chemicals control sleep?
A6: Several key chemicals and signals work to reduce alertness and help you fall and stay asleep (Tubbs et al., 2019):
GABA (gamma-aminobutyric acid): As the brain's primary inhibitory chemical, GABA acts like a brake pedal, actively suppressing the arousal centers that keep you awake. Many sleep medications work by enhancing GABA's calming effects.
Adenosine: This chemical acts as the brain's sleep pressure gauge. It steadily builds up in your system the longer you are awake, increasing your body’s ‘drive’ for sleep. Caffeine keeps you alert by temporarily blocking adenosine's effects.
Melatonin: Often called the "hormone of darkness," melatonin is released by the pineal gland when it gets dark. It doesn't act as a sedative but rather as a timer, signaling to your entire body that it is biologically nighttime and time to wind down for sleep.
Galanin: This chemical works as a partner to GABA, helping to suppress the brain's arousal systems and maintain a stable, uninterrupted state of sleep.
References
Desseilles, M., Dang-Vu, T., Sterpenich, V., & Schwartz, S. (2011). Cognitive and emotional processes during dreaming: a neuroimaging view. Consciousness and Cognition, 20(4), 998–1008.
Rothbaum, B. O., & Mellman, T. A. (2001). Dreams and exposure therapy in PTSD. Journal of Trauma Stress, 14(3), 481–490.
Tubbs, A. S., Dollish, H. K., Fernandez, F., & Grandner, M. A. (2019). The basics of sleep physiology and behavior. In Sleep and Health (pp. 1–10). Elsevier Inc.
Written By The Better Sleep Clinic
Reviewed By Dan Ford, Sleep Psychologist
