Sleep deepening effect of steady pink noise

Abstract Sleep under a steady pink noise was studied by a hypnogram of EEG. A young male subject slept all night under a steady pink noise of 40, 50 or 60 dB(A) for 4 to 5 nights, and for 10 nights under unexposed conditions with 35 dB(A). The hypnogram showed a significant decrease in the proportion of REM and an increase in the proportion of stage 2, at 60 dB(A) of steady pink noise exposure. The proportion of stage 3 increased significantly at 40 and 50 dB(A) as compared with 35 dB(A). The average depth of a night's sleep at 60 dB(A), calculated postulating stage W, 1, 2, 3 and 4 to be 0·0, 1·0, 2·0, 3·0 and 4·0, respectively, and REM to be 1·5, was significantly deeper than that at 35 and 40 dB(A). These findings are all sleep deepening effects of a steady noise. A second experiments was carried out with four other subjects exposed to a night of 60 dB(A) of steady pink noise and a paired quiet night. All four subjects also showed a decrease in the proportion of REM and an increase in the proportion of stage 2 at this exposure level. No significant change in subjective sleep was observed in either experiment. An inhibition pulse from the cortex may suppress the activation of reticular formation, which could make sleep under a steady noise deeper. However, the meaning of a depressed proportion of REM under steady pink noise is not clear.