Clue found in hunt for sound sleep

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, USA.

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.

Volunteers in a sleep laboratory were allowed to sleep undisturbed for one night in quiet surroundings. Over the next two nights they were subjected to noises, including a telephone ringing, people talking, and mechanical sounds.

Those who produced more sleep spindles during the quiet night were better able to tolerate the subsequent noisy nights.