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What are Sleep Spindles?

By Matt Brady
Updated Mar 03, 2024
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Sleep spindles are waves of brain activity during sleep as seen on an electroencephalogram (EEG). They are also known as sigma bands or waves. These spindles are most evident during stage 2 sleep, occurring in bursts that last for roughly a second. Stage 2 is one of the deeper sleep stages, as opposed to lighter stages where individuals are still relatively aware of their external environment. Studies have shown that sleep spindles may help block out external noises, resulting in a sounder sleep.

Sleep spindles occur during stage 2 sleep, along with K-complexes. K-complexes look different than the wave-like patterns of spindles, appearing on EEGs as dramatic spikes. Spindles are caused by activity in the thalamus. It's suspected that when spindles occur, the thalamus is attempting to block brain signals—prompted from external stimuli such as the sound of a crying baby—from reaching other areas of the brain that might disturb sleep. Spindles begin appearing in sleep around the first six to eight weeks of life, after which they remain with the sleeper for life. Since stage 2 sleep comprises roughly half of a person's sleep, spindles make up a major part of our sleep pattern.

These spindles may be the key to a sound sleep. A study conducted by Harvard Medical School's Division of Sleep Medicine in the US showed that individuals with a greater frequency of spindles slept more soundly. Sleepers were subjected to a barrage of noises that commonly interrupt sleep—sounds of traffic, ringing phones, toilet flushes, etc. The study found that those who exhibited more spindles were better able to sleep through the noise, while those with fewer spindles slept less soundly. The study's data led to the conclusion that spindles may be the brain's way of deflecting noise and distractions during sleep.

If further studies prove that sleep spindles do indeed equal a better slumber, it would help to explain a lot about the way we sleep. It would explain why one person sleeps easily even through the most disruptive conditions, and why others wake up at the slightest sounds. Such a finding could also change the way we sleep; there may be efforts to attempt to artificially create these spindles. If such efforts were successful, they could be a revolutionary breakthrough for sleepers everywhere. In particular, insomniacs and light sleepers would stand to gain the most, able to perhaps finally settle in for a full night of sound sleep.

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Discussion Comments
By anon206932 — On Aug 18, 2011

this was very helpful. I am a polysomnography student and this site helps me a lot.

By anon176847 — On May 16, 2011

They should test the thalamus of new moms. It's amazing how you wake up to even the smallest noises your baby makes.

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