During sleep, our perception of the environment decreases. However the extent to which the human brain responds to surrounding noises during sleep remains unclear. Researchers have now used brain imaging to study responses to sounds during sleep. They show that brain activity in the face of noise is controlled by specific brain waves during sleep. Researchers found that perception of the environment is not continuously reduced during sleep, but rather varies throughout sleep under the influence of particular brain waves.

Source: Brain waves control the impact of noise on sleep