How does sound influence our sleep?
This quora question just got my attention and here is my contribution in an attempt to answer it. There are different studies representing different ways on how sound might influence one’s sleep or processes that occur during one’s sleep: I will discuss 1) a study covering how sound can increase skill learning, 2) a study on how sound can interfere with our sleep and memory performance, 3) and a third study discussing a possible noise protective mechanism.
- A recent study by Antony et al.  about learning during sleep (that has gotten quite a lot of attention on blogs recently) elegantly showed how playing sounds during sleep can enhance skill learning. Actually this is quite a simplification, because the sounds weren’t mere sounds, but melodies that represented a sequence that was learned before sleep. So you can see the sequence of sounds as linked to a certain behavioral movement, i.e. procedural skill (in this example a sequence of piano button presses). There were 2 learned sequences (represented in blue and red in the picture below) and one baseline sequence. The blue sequence (melody) was played during sleep. As can be seen from part b of the picture, performance was improved for all sequences after sleep, but even more markedly for the cued sequence.
I do want to note this doesn’t mean one should just start playing all sorts of music or auditory books during sleep… in this study there is a pretty straightforward relation between the learned material beforehand and the melody used to reactivate the learned material, as well as the brain network, mostly activity in the premotor cortex involved in this skill. When learning material and brain activity networks get more complex, it could become more difficult to reactivate such memories during sleep. Also the study applies to procedural memory, although a sleep study using odor cues also showed that similarly declarative memory can be enhanced .
- The study by Van Der Werf et al.  sheds another light on sound during sleep. This study uses sound to disrupt our sleep without us even realizing it and reveals how this can interfere with our memory performance (as well as some brain mechanisms that might explain this). This study used a mild acoustic perturbation setup, i.e. when people spent a certain amount of time in slow wave sleep (one of the deeper stages of sleep characterized by slow waves in the EEG signal) a beeping noise was emitted that gradually increased in amplitude until the person returned to a more shallow sleep stage (thus the sound stopped so people wouldn’t be awoken). By using this setup sleep duration, as well as sleep efficiency could remain intact, while only manipulating the amount of time spent in the deeper stages of sleep. People with more shallow sleep, revealed decreased performance on a subsequent declarative memory task.
- Since sleep seems to have such an important function in maintaining our physical and psychological functioning, while from an evolutionary perspective being a very vulnerable state, there must be some mechanisms at play that on the one hand protect our sleep (keep our sleep stable), but on the other hand not too stable so we can be aroused when in “danger”. Dang-Vu et al.  propose a potential role for spindles (http://en.wikipedia.org/wiki/Sleep_spindle a spindle being a high-frequency burst of activity that can be seen in the EEG signal mainly during stage 2, one of the more superficial stages of sleep) with regard to sleep stability in the face of noise. During a first silent night (figure A) spontaneous spindle rate for each individual was determined. Figure C reveals that people with a higher spindle rate during the first night, had a higher sleep stability in the face of noise. Figure B reveals different arousal thresholds for different types of stimuli (thus some types of stimuli result in arousal more easily than others). Although the authors don’t elaborate more on this, this might be interesting in the sense of a possible “gating” mechanism, that allows certain sounds to be processed at a lower noise level than other (maybe less relevant) noises.
If there is one thing these studies show, than it’s that there are a lot of things going on during our sleep and sound can definitely influence these processes. There are however different ways by which sound can influence these processes.
 Antony, J. W., Gobel, E. W., O’Hare, J. K., Reber, P. J., & Paller, K. A. (2012). Cued memory reactivation during sleep influences skill learning. Nature neuroscience.
http://www.nature.com/neuro/journal/vaop/ncurrent/full/nn.3152.html (not freely accessible)
 Rasch, B., Büchel, C., Gais, S., & Born, J. (2007). Odor cues during slow-wave sleep prompt declarative memory consolidation. Science, 315(5817), 1426–1429.
 Der Werf, Van, Y. D., Altena, E., Schoonheim, M. M., Sanz-Arigita, E. J., Vis, J. C., De Rijke, W., & Van Someren, E. J. W. (2009). Sleep benefits subsequent hippocampal functioning. Nature neuroscience, 12(2), 122–123.
 Dang-Vu, T. T., McKinney, S. M., Buxton, O. M., Solet, J. M., & Ellenbogen, J. M. (2010). Spontaneous brain rhythms predict sleep stability in the face of noise. Current biology, 20(15), R626–7.