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Sleep Spindles: Definition and Importance

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Sleep spindles are bursts of brain activity that typically occur during Stage 2 of Non-Rapid Eye Movement (NREM) sleep. They are recorded by an Electroencephalogram (EEG), a device used to track and assess neurological patterns. Spindle records are documented in the form of waves. The spindle wavelengths are measured in Hertz (Hz). Hertz is a measuring unit for frequency.

Sleep spindles are believed to play an important role in neuronal plasticity and memory consolidation. Neuronal plasticity refers to the nervous system’s ability to alter its activity based on internal and external factors. Memory consolidation is how the information you learn turns into long-term memories.

What is a Sleep Spindle according to Science?

A sleep spindle, according to science, is a burst of brain activity that occurs during sleep. Spindles typically appear during Stage 2 of the Non-Rapid Eye Movement (NREM) phase, which is also the second stage of the full sleep cycle. They last for about .5-1.5 seconds and have a frequency of around 11-16 Hertz.

There are two types of spindles, slow frontal and fast centroparietal. Slow spindles are around 12 Hertz, while fast spindles are around 14 Hertz. Slow spindles occur around the brain’s frontal cortical area, and fast spindles occur over the parietal and central areas.

The factors that affect sleep spindles are sleep deprivation, circadian rhythms, and age.

Sleep deprivation means that you did not get enough hours of sleep. Adults should get between 7 and 9 hours of rest every night. If you don’t, you can become sleep-deprived, affecting the number of spindles that appear.

Circadian rhythms are natural physiological changes that follow a 24-hour cycle. For example, the body releases more melatonin, a sleep hormone, when it is dark outside. Melatonin is specifically associated with increased sleep spindle activity.

Lastly, age is known to impact sleep spindles. Research has found that sleep spindles are lower in elderly individuals than young adults.

Furthermore, lowered spindle density has been linked to cognitive decline. For example, scientists found that sleep spindle density decreased in patients with Alzheimer’s disease.

What is the Connection between Sleep Spindles and Sleep Quality?

The connection between sleep spindles and sleep quality is that spindles may significantly impact sleep continuity. Sleep continuity is the ability to remain asleep as you progress through sleep cycles.

Continuity is important for sleep quality because it means your rest is uninterrupted. The more interrupted your sleep is, the worse your sleep quality will be.

How are Sleep Spindles Measured?

Sleep spindles are measured using an Electroencephalogram (EEG). The EEG is a device used to document brain activity while sleeping.

During an EEG test, electrodes are placed around the person’s scalp to detect any changes in brain activity. The information the electrodes detect is recorded in the form of waves.

These waves are measured using the frequency unit Hertz (Hz). A hertz equals one cycle per second. Spindles typically last for 0.5-1.5 seconds and measure around 11-16 Hertz.

Once the EEG test is complete, a sleep specialist reviews the wave patterns and checks for irregularities.

What Stage can Sleep Spindles be seen at?

Sleep spindles can be seen at the second stage of the sleep cycle. There are four sleep stages in a sleep cycle. The second stage is called N2, and it is part of the Non-Rapid Eye Movement (NREM) phase.

Stage N2 lasts around 30-60 minutes and is considered a light sleep. During N2, the body temperature continues to drop, breathing slows, and the muscles relax further.

What are the causes of Sleep Spindles?

Sleep spindles are caused by the interaction of neurons from the brain’s thalamic reticular nucleus and thalamocortical networks. Spindles are a natural brain activity that typically happens during Stage N2 of Non-REM sleep.

Spindles start to appear during infancy, around 4-6 weeks of age. However, the number of spindles can decrease in older adults.

What are the Reasons for Unusual Sleep Spindles?

The reasons for unusual sleep spindles are age, pain, epilepsy, coma, and dyslexia. We list these below.

  1. Age
  2. Pain
  3. Epilepsy
  4. Coma
  5. Dyslexia

1. Age and Sleep Spindles

Age can cause unusual sleep spindles because the density and amplitude of the wavelengths decrease as people get older. Furthermore, the number of spindles the individual experiences also drops. The drop in spindles may also be a precursor to cognitive decline, as those with Alzheimer’s disease are found to have decreased spindle activity.

Additionally, the reduction in spindles can affect sleep quality because spindles are believed to help with sleep continuity. Therefore, older individuals may have more difficulty staying asleep through the night.

2. Pain and Sleep Spindles

Chronic pain may influence sleep spindles. Pain can also result in sleep disorders like insomnia that prevent the individual from getting sufficient rest.

Research has found that chronic pain could be linked to decreased spindle activity. Conversely, an increase in spindles has been associated with reduced pain.

However, pain’s effect on the spindle waves themselves is not known. Like aging, the decreased spindle activity means those with chronic pain could be more susceptible to waking up during the night.

3. Epilepsy and Sleep Spindles

Epilepsy is also linked to abnormal spindle activity. Epilepsy is a neurological disorder in which a person experiences periodic seizures.

Researchers have found that spindle wave density and power decreased before a seizure. Therefore, this suggests that these changes in spindle activity can reveal when a person is about to have a seizure.

Epilepsy and sleep are connected because sleep deprivation and poor sleep quality can escalate the prevalence of seizures.

4. Coma and Sleep Spindles

Sleep spindles do not normally appear in comatose patients. However, their appearance may help determine a positive outcome. For example, research suggests comatose patients who exhibit sleep spindles during an EEG test are more likely to awaken.

Although spindles may be a good indicator of recovering from a coma, this condition could still impair sleep quality down the road. Researchers have found that many post-comatose patients experience poor sleep quality and insomnia.

5. Dyslexia:

Dyslexia is a condition in which an individual has difficulty learning to read and process words. Dyslexia is also connected to sleep spindle activity. For example, a 2009 study found that children with dyslexia exhibited higher spindle density during Stage N2 of sleep, along with a higher frequency power.

Furthermore, researchers say that the increase in spindle activity is directly tied to the severity of dyslexia. They suggest that this increased spindle activity likely represents the brain working harder to process information.

What are sleep spindles important for?

Sleep spindles are important for neuronal plasticity and memory consolidation. Neuronal plasticity refers to the nervous system’s ability to alter its activity based on internal and external factors. Neuronal plasticity is vital for brain development from infancy through adulthood.

Memory consolidation refers to when information you learn turns into long-term memories. Healthy rest is an important contributor to memory consolidation since sleep is when memory consolidation occurs. Specifically, sleep spindles have been linked to memory processing and, therefore, play a vital role in learning.

Can you Increase Sleep Spindles?

Yes, you can increase sleep spindles.

Researchers in a 2017 study found that they were able to increase spindles by playing oscillating sounds. Additionally, some medications may increase spindle production, but experts say those same substances could negatively impact information processing while the individual is awake. Lastly, in-depth learning has also been found to boost the number of spindles a person experiences.

To increase sleep spindles, try learning in-depth information while awake or playing oscillating sounds while you rest.

What is the Relation between Sleep Spindles and K-Complexes?

A K-complex is a type of waveform seen on an EEG. K-complexes are high amplitude spike-and-rebound waveforms resulting from internal and external stimuli. While their specific purpose is unknown, scientists have several theories about why people experience them.

The first theory is that K-complexes help you wake up if the brain detects any dangerous stimuli. At the same, the K-complexes may help you stay asleep if the brain detects stimuli that are not dangerous.

The second theory is that K-complexes aid in memory consolidation by converting short-term memories into long-term ones. Thirdly, they hypothesize that K-complexes provide a way for the body’s nervous system to reboot in order to remain in a healthy state of balance.

The relationship between sleep spindles and K-complexes is that they both occur during Stage N2 of the sleep cycle. Furthermore, these wave patterns are considered vital roles in memory consolidation. While sleep spindles likely aid memory processing, K-complexes are believed to help convert short-term memories into long-term memories.

Jill Zwarensteyn

Jill Zwarensteyn


About Author

Jill Zwarensteyn is the Editor for Sleep Advisor and a Certified Sleep Science Coach. She is enthusiastic about providing helpful and engaging information on all things sleep and wellness.

Combination Sleeper