Discrimination of behaviorally irrelevant auditory stimuli in stage II sleep

In sleep, the brain responds to significant stimuli such as one's own name or loud tones. It is, however, not yet known whether in sleep, the brain's response can vary systematically with change in an irrelevant stimulus. Here, we varied the intensity of a 1000 Hz tone and recorded the neural response of the participants by using electroencephalography. The P200 component of the auditory-evoked potential increased linearly and significantly with intensity in wake and in stage II sleep. Pattern classification confirmed that there is information about tone intensity in the poststimulus period, especially in the period corresponding to the P200. The sleeping brain is capable of discriminating the fine aspects of a stimulus that is of no significance to the individual.