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Secrets of sleep revealed

PUBLISHED: 10:06 10 August 2010 | UPDATED: 11:55 16 September 2010

They are always alert, full of energy, and youthful-looking - those maddening individuals who could sleep soundly through an earthquake and wake up rested and refreshed.

They are always alert, full of energy, and youthful-looking - those maddening individuals who could sleep soundly through an earthquake and wake up rested and refreshed.

Now scientists are discovering why some people close themselves off to the world after falling asleep while others are rudely awakened by the slightest bump in the night.

Experts in the US believe a sensory gateway in the brain called the thalamus plays a key role in blocking out sound during sleep.

The effect can be seen in brief bursts of electrical activity generated by the brains of sleepers, known as “sleep spindles”.

“The more sleep spindles your brain produces, the more likely you'll stay asleep, even when confronted by noise,'' said researcher Dr Jeffrey Ellenbogen, from Harvard Medical School in Boston.

Boosting sleep spindles through behavioural techniques, drugs or electronic devices might help light sleepers have a restful night, the scientists believe. But how this can be achieved is not yet clear.

The effect was seen in recordings of the brain wave patterns of 12 volunteers asked to endure noisy nights in a sleep laboratory.

For the first night, the volunteers were allowed to sleep undisturbed in quiet surroundings. Over the next two nights they were subjected to an array of disturbing noises, including a telephone ringing, people talking, and mechanical sounds of the sort frequently heard in hospitals.

During sleep, brain waves become slow and organised, said Dr Ellenbogen. Sleep spindles are brief bursts of faster-frequency waves which stand out against the calm background.

They are generated by the thalamus, a checkpoint in the brain through which all kinds of sensory information pass apart from smell signals, said the scientists.

Volunteers who produced more sleep spindles during the quiet night were better able to tolerate the subsequent noisy nights, the study found.

“The thalamus is likely preventing sensory information from getting to areas of the brain that perceive and react to sound,'' said Dr Ellenbogen. “And our data provide evidence that the sleep spindle is a marker of this blockade. More spindles means more stable sleep, even when confronted with noise.

The findings are published in the latest issue of the journal Current Biology.

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