A Guide to Understanding Sleep Spindles

Sleep spindles are rapid bursts of brain activity that occur during NREM sleep. They help us sleep through the night and are essential for memory consolidation and learning.

By Nicole Gleichmann

Researchers are just beginning to unravel the mysteries of how humans benefit from sleep. One of the most interesting players in this realm is sleep spindles, which are rapid bursts of brain activity that occur when we’re sleeping.

Sleep spindles, also referred to as sigma waves or sigma bands, appear to be central in memory consolidation and learning potential. They may even play a central role in the pathology of certain psychiatric conditions, although further research is needed to clarify this connection.

In this article, we’re going to help you understand sleep spindles: what they are, what they do, and why they’re such an important part of our sleep cycle.

Understanding Sleep

When you go to sleep, your brain goes through a series of four stages: stages 1, 2, 3 and rapid eye movement (REM) sleep. Each of these stages is unique from the others in their brainwave activity as measured through electroencephalographic (EEG) readings.

Low frequency, or slow, brainwaves are associated with sedation and calm, while high frequency, or fast, brainwaves are indicative of higher states of mental and physical energy.

During stage 1 sleep, your brain waves begin to slow. They continue slowing during stage 2 sleep, with the addition of sleep spindles and K complexes, which are unique brain waves that serve a variety of functions.

Stage 3 sleep is the deepest stage of sleep, which is then followed by REM sleep. You dream during REM sleep, and while it is easier to wake someone during REM sleep than during stages 2 and 3, you tend to wake up in a fog, feeling groggy and tired.

What Are Sleep Spindles?

Sleep spindles are a unique type of brainwave that occurs during stage 2 sleep, one of the stages of Non-REM (NREM) sleep. They are bursts of activity that are fast and oscillatory as seen on an EEG. The frequency rapidly increases and decreases, leading to an EEG pattern that resembles an eye.

The sleep spindles observed in an EEG occur in the reticular nucleus of the thalamus when GABAergic neurons fire, resulting in oscillations of around 12-15 Hz that last between 0.5 and 2 seconds. This activity leads to spindles occurring globally throughout the brain and in specific regions.

What Do Sleep Spindles Do?

So, what, exactly, is the function of these brain activity bursts? While researchers are still working to understand exactly what it is they do, they appear to be involved in:

  • Memory consolidation and learning potential
  • Controlling sensory transmission
  • Cortical (a region of the brain) development
  • Psychiatric and other brain disorders

It is thought that different spindles may serve different functions; for example, fast sleep spindles of 13-15 Hz are thought to do something different from low-frequency spindles of 11-13 Hz. Location, too, may dictate what effects the spindles offer.

1. Sleep Spindles in Memory and Learning

Researchers have known for many years that sleep spindles are involved in memory consolidation during sleep. They play a role in moving memories from temporary to permanent storage, allowing improved recall and memory performance.

According to recent research, sleep spindles during rest may also support learning abilities while awake. A study conducted at the University of California Berkeley revealed that increased sleep spindle activity in napping participants was correlated with refreshed learning potential.

This study and others demonstrate the importance of sleep spindles in learning and memory; getting enough sleep at night and napping during the day can enhance both your ability to learn and your recall later.

2. Sleep Spindles in Sleep Quality

If you struggle to stay asleep during the night, waking at the slightest noise, it might be due to inadequate sleep spindle activity. In one study, researchers found that people who were more difficult to wake up produced more spindles than those who woke easily.

This study demonstrates that sleep spindles could be involved in altering our sensory transmission, essentially blocking our consciousness from the noise and activity occurring in the outside world.

Staying asleep during phase 2 sleep is of particular importance as humans spend nearly half of their time sleeping at night in stage 2 sleep. From here, we transition to the deep, restorative phase 3 sleep, so staying asleep until we accomplish this deep sleep is essential for optimal sleep quality.

Another piece of information supporting the role of sleep spindles in remaining asleep is the difference between sleep spindle frequency in the young and the elderly. As you age, your brain tends to produce fewer spindles, and your ability to stay asleep at night declines.

3. Sleep Spindles in Development

Sleep spindles don’t appear in EEGs until humans are six weeks of age. At this point, babies will begin to experience sleep spindles following muscle twitching during sleep. Early research in animals suggests that these spindle bursts may be involved in brain development.

In infants, spindles are associated with the rapid muscle tremors that occur during sleep. The interaction between these tremors and the spindle oscillations is involved in forming the cortical connections central to sensorimotor coordination.

4. Sleep Spindles in Disease

Sleep spindles may be a biomarker for certain neurological disorders, such as schizophrenia, epilepsy, and autism. In a study of 49 schizophrenics, it was found that they experienced certain spindle deficits when compared to both healthy controls and non-schizophrenic patients on antipsychotic medications.

While the research examining this connection is in its infancy, it may help scientists better understand what’s happening in the brain of those with a variety of difficult-to-treat conditions. This could be used in the future for both diagnostic and treatment purposes.

How Long Should You Sleep to Optimize Spindle Activity?

Sleep spindles may be the reason why it’s so important to get adequate sleep each night. Researchers have found that the highest spindle activity when we sleep occurs following the first six hours of sleep, meaning that those last one or two hours every night may be central for memory and learning. If you don’t get enough sleep during the night, take a nap! Napping offers an extra dose of sleep spindle activity.


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