sleep cycle

The sleep cycle of humans is regulated through a series of 90-minute ultradian cycles that occur across the night. These cycles alternate between non-rapid eye movement (non-REM) and rapid eye movement (REM) sleep. At the beginning of the night, the cycles consist more of non-REM sleep, which includes stages one through four, with stages three and four being the deepest. As the night progresses, the proportion of REM sleep increases in each cycle. REM sleep is associated with dreams and has different roles in learning and unlearning compared to non-REM sleep, which is also crucial for memory consolidation 1.

Each sleep cycle is initiated with light non-REM sleep, progresses into deep non-REM sleep, and then finishes with a lighter REM stage. Throughout the night, our sleep architecture changes, with deep non-REM sleep dominating the early parts of sleep and REM sleep becoming more prevalent in the later cycles. This shift has implications on learning, memory, and how one feels upon waking. Waking up at the end of a cycle may be more refreshing than waking during a deep stage 2.

The exact ratios of REM and non-REM sleep can vary from person to person, with some individuals finding they function well on different amounts of total sleep 3. Moreover, there are a variety of factors, such as light exposure, darkness, body temperature, and food intake, that can influence the quality of sleep and help regulate these cycles 4.

The sleep cycle is also intricately linked with our circadian rhythm, which dictates the oscillation of sleep and wakefulness roughly every 24 hours in sync with the Earth's rotation. Sleep pressure builds throughout the day as adenosine accumulates in the brain, making us feel sleepy. The desire to sleep is influenced by the convergence of this sleep pressure and our circadian time point 5.

Understanding the structure of our sleep cycles and the factors at play can inform better sleep habits and lead to more effective rest 6.

In Understanding and Using Dreams to Learn and to Forget | Huberman Lab Podcast #5, Andrew Huberman investigates the role of dreaming in both learning and forgetting. Key points covered in this episode include:

• The Importance of Sleep Cycles: Huberman emphasizes the critical nature of non-REM and REM sleep cycles for brain health and function.
• Learning and Forgetting: How sleep, and particularly REM sleep, facilitates learning new information and unlearning or "forgetting" irrelevant information.
• Dreams and Neuroplasticity: Dreams are not just random; they have a structure that reflects our waking experiences and are related to the concept of neuroplasticity, the brain's ability to change and adapt.
• Trauma and REM Sleep: Huberman discusses therapies for trauma that relate to REM sleep and the importance of this sleep phase in processing and overcoming traumatic experiences.

These topics are elaborated on within the context of how various factors—such as the use of substances like alcohol and cannabis—affect sleep cycles and, by extension, the benefits of dreaming. Huberman also provides practical tips on improving sleep quality and understanding the phenomena associated with sleep, such as sleep paralysis and nightmares. The broader implications for emotional well-being and performance are also discussed, highlighting the crucial role that consistent, high-quality sleep plays in overall health and cognitive function.

Sleep is separated into two main types: non-rapid eye movement sleep (non-REM) and rapid eye movement sleep (REM).

Non-REM Sleep:

• Stages: Non-REM is further subdivided into four stages, known as stages one through four, increasing in the depth of sleep, where stages one and two are lighter and stages three and four are deeper. Each stage has distinct brain activity.

  • Stage One: As you start to fall asleep, slow rolling eye movements occur, and your brain starts to slow down from wakefulness with some people experiencing hypnagogic jerks.

  • Stage Two: Characterized by sleep spindles, which are short bursts of electrical activity, indicating a further slowing of brainwave frequency from that of wakefulness.

  • Stage Three and Four (Deep Sleep): The brain's activity slows down significantly, heart rate drops, and the cortex experiences synchronized firing and silence of brain cells. This is a very unique brain state, different from any waking state 1 2 3.

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      1

      Brain Waves Unleashed

      00:25:31
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      2

      Sleep Stages

      00:18:55
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      4

      Sleep Structure Explained

      00:06:43
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      5

      Overnight Brain Transformation

      00:55:47
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      6

      Sleep Stages

      00:26:45
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      7

      Understanding Sleep Phases

      00:06:57

REM Sleep:

• REM sleep involves rapid, horizontal eye movements and is when dreaming occurs 4. It's a period when the brain simulates future options through dreams as if experiencing them in reality 5.

  • Throughout the night, non-REM and REM sleep alternate in cycles, usually every 90 minutes. Notably, the balance between non-REM and REM sleep changes as the night progresses. The first half of the night is dominated by non-REM (deep) sleep, while the second half has more REM sleep 4.

Each sleep stage plays a different role for the brain and body, with all stages being important for overall health 6. The 90-minute cycle repeats several times throughout a night's sleep, resulting in approximately four to five REM periods in a healthy night's sleep. A perfect night's sleep duration is about seven and a half to eight hours, with a steady progression through the sleep stages 7.

According to Andrew Huberman, sleep plays an essential role in the process of neuroplasticity, the brain's ability to change and adapt as a result of experiences. Dreams, which most commonly occur during REM sleep, are not directly mentioned in relation to neuroplasticity, but the state of the brain during REM sleep is believed to support learning and memory consolidation.

In an episode of the Huberman Lab podcast, Dr. Huberman notes that the neural changes associated with learning and experience, known as neuroplasticity, primarily occur during sleep, including REM sleep where most dreaming happens 1. Deeper rest during sleep is vital for the rewiring of neural connections and the consolidation of what is learned during wakefulness 2 1.

Furthermore, studies have shown that cues during sleep, such as tones played in the background, can enhance learning retention of tasks practiced while awake, indicating that sleep serves to reinforce and integrate new experiences and skills 3.

In summary, dreams are a part of the REM sleep experience, which contributes to the brain's neuroplastic mechanisms, particularly in enhancing the consolidation and integration of new information and experiences while we are asleep.

The Understanding and Using Dreams to Learn and to Forget dives into the intricacies of dreams and their connection to learning and forgetting, displaying the critical role of sleep in these processes:

• The Science of Dreams & Sleep:

  • Dreams are most abundant during REM (rapid eye movement) sleep, which associates with learning and forgetting.
  • The stages of sleep cycle through the night, with REM and non-REM (NREM) sleep alternating, each having unique brain activity patterns.

• Dreams & Neuroplasticity:

  • Neuroplasticity is the brain's ability to remodel itself based on experiences, which can occur during sleep and dreaming.
  • Dreams can reinforce learning by replaying experiences, consolidating memories, and integrating new information with existing knowledge.

• Forget to Learn:

  • Sleep, especially REM sleep, helps to weaken certain synapses, allowing outdated or less useful information to be forgotten. This "pruning" of unnecessary connections is important for making room for new learning.

• Lucid Dreaming:

  • Lucid dreaming, or being aware that you're dreaming while still in the dream state, was also discussed, with potential ways to increase the likelihood of experiencing lucid dreams.

This episode highlighted the continuous dialogue between waking life experiences and the mysterious world of dreams, emphasizing the significance of dreams in our cognitive and emotional lives. The concepts of neuroplasticity, memory consolidation, and the active forgetting process in shaping our learning and mental health are explored, providing insight into the powerful impact of our nocturnal brain activity.

To optimize sleep cycles, Andrew Huberman offers several strategies based on scientific research:

1. Morning Light Exposure:

   • Expose yourself to bright sunlight within the first 30 to 60 minutes after waking to help trigger an early release of cortisol, supporting wakefulness and focus throughout the day 1.

2. Afternoon Light:

   • Get outside for 10 to 30 minutes in the afternoon or evening without sunglasses to help regulate melatonin, which is crucial for initiating sleep 2.

3. Critical Sleep Timings:

   • There are three critical periods within the 24-hour cycle that you should focus on to optimize wakefulness and sleep. Leverage specific behavioral tools during these times to maintain alertness during the day and improve sleep at night 3.
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       Optimizing Morning Routine

       00:15:10
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       2

       Optimize Your Sleep

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       3

       Optimize Your Day

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       4

       Optimize Your Sleep

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       5

       Sleep Optimization Strategies

       01:11:44
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       6

       Optimizing Sleep

       01:04:09
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       7

       Sleep Cycles

       00:22:19
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       8

       Mastering Sleep Quality

       00:52:35

4. Avoiding Sleep Disruptors:

   • Do not consume caffeine in the hours leading up to bedtime and minimize exposure to artificial light in the evening. Cooling down your sleeping environment and dimming lights can promote better sleep conditions 4.

5. Supplements:

   • If needed and after consultation with a physician, consider supplements like magnesium threonate, apigenin, and theanine, which may improve the ability to fall and stay asleep 5.

6. Peak Wakefulness:

   • Be aware of a peak in alertness and wakefulness about an hour before bedtime, which is a natural occurrence. Understanding this can help you avoid anxiety about feeling awake late in the evening 6.

7. Sleep Duration and Quality:

   • Sleep needs are individualized, and there's no definitive evidence that 8 hours of sleep is superior to 6. Aligning your sleep with the natural 90-minute ultradian cycles can also improve sleep quality 7.

8. Sleep Quality Over Quantity:

   • Focus on improving sleep quality and mastering the transition into sleep to access deep, restorative states 8.

Implementing these tools consistently can drastically improve sleep quality, which lays the foundation for better mental health, physical health, and overall performance.