Sleep is the cornerstone of early development. At approximately 10-12 weeks of age, the first signs of the circadian rhythm begin to develop and become evident with increased nighttime sleep. The change in the total 24-hour sleep duration decreases as the baby grows, gradually adapting to the circadian sleep rhythm. Daily sleep duration in newborns decreases to 16-17 hours, 14-15 hours at 16 weeks of age, and 13-14 hours at 6 months of age. As the baby grows, the need for daytime sleep decreases, resulting in a shift towards more nighttime sleep patterns. In recent years, studies examining the effects of music, especially on newborns, have increased. Music is a complex auditory stimulus consisting of various components such as melody, rhythm, timbre, and harmony. When adults listen to music, these components are perceived as a phenomenological whole, but they are processed separately through a complex dual cortical and subcortical regions. Since the adult human brain does not have a single musical center, the neural substrates supporting musical perception and production vary depending on the musical task. Neuroimaging studies in neonates or infants have reported inconsistent results regarding cortical activation in response to musical stimuli. While two studies showed weak bilateral responses to musical stimuli, results from a functional magnetic resonance imaging (fMRI) study used to measure brain activity in 1- to 3-day-old neonates hearing excerpts of Western tone music and modified versions of the same excerpts suggest that the infant brain shows hemispheric specialization in right-lateralized auditory cortex activity for processing music in the early postnatal hours, and that the neural architecture underlying music processing in neonates is sensitive to changes in tone key as well as differences in consonance and dissonance. It has been found that infants can maintain distinct memory traces for polyphonic music and show a high preference for polyphonic music from 3 months onwards. Marie and Trainor (2014) hypothesize that this high-volume advantage may be mediated at the level of the auditory nerve at birth. In general, the presence of immature mismatch negativity (MMN) occurs when there is an occasional change or deviant stimulus in a continuing standard stimulus sequence. Again, this more complex MMN-like response to polyphonic stimuli has been reported to have a longer developmental trajectory than the MMN elicited by a single tone stimulus. Early musical involvement is very important for the auditory system, which mostly matures in the first 6 months after birth. Polyphonic lullabies, known in the literature as polyphony consisting of sounds or music, are music played especially during the rapid development period (0-4 years) of infants and children. When the literature was examined, no randomized controlled studies were found that revealed the effects of polyphonic lullabies and piş piş sounds on the transition to sleep and sleep duration in healthy newborns. It was thought that the research results would provide strong evidence to support the development of approaches to improving sleep in newborns.
