How does sound affect your inner clock? It seems that a mix of music and bird sounds before bedtime can signifcantly delay your circadian clock. However, due to the qualitiative complexity of sound and a lack of scientific investigation, many questions remain.

Evidence from birds and humans

It has been shown that acoustic stimulation in the late half of sleep advances the circadian clock of male (but not female) sparrows. At other times of day, sound failed to have a significant impact on their rhythms. Therefore, it is unclear whether the observed shift was really caused by the sound or whether the interruption of sleep triggered other factors that act as a zeitgeber .1

In a noteworthy study with humans, exposure to 1h of classical music with bird sounds on two consecutive evenings led to a mean 0.89h delay of the circadian clock. As subjects were required to remain seated at the given time both with and without music, an increase in locomotor activity could not be the reason for the delay.2

Still a lot unclear

While sound has been shown capable to delay the circadian clock in humans, the underlying neural mechanics are yet to be understood.2 Is it really sound itself or physiological responses, e.g. changes in heart rate or brainvwaves, that cause the shift? How do different factors like volume, pace and style (in music) or (emotional) association influence the impact of sound on circadian rhythm? There are many open questions for further research. Unfortunately, the number of studies are very limited and I could not even find a single study investigating the potential of sound to advance circadian clock in humans. A lot of question marks remain that will hopefully be answered in the future.

[1] Reebs, S. G. (2010). Acoustical Entrainment of Circadian Activity Rhythms in House Sparrows: Constant Light is not Necessary. Ethology, 80(1–4), 172–181.

[2] Goel, N. (2005). Late-night presentation of an auditory stimulus phase delays human circadian rhythms. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 289(1), R209–R216.