I'm not sure if this is the right place to ask this but Biology seemed to fit best.

I'm trying to find out what frequencies the brain responds to best while sleeping.

The reason for this is recently I attended a lecture where it was stated that the brain hears low frequencies/deep noises better, meaning fire alarms for example might not be as effective as we think.

However I remember there was an episode of The Big Bang Theory where they said high pitch noises are heard better while sleeping as a built in response to, for example, a baby crying. Now I know this is just a TV show but I presume they must have some basis for the remark since they do have science advisors, it also just seems to make more sense.

Does anyone know which is correct or better yet can point me in the direction of some research to help.

  • 2
    $\begingroup$ Just to point out that the big bang theory episode states that women are more likely to respond to high pitched sounds such as a baby crying. I have no idea if it is true but it makes perfect evolutionary sense. $\endgroup$
    – terdon
    Oct 1 '12 at 15:55
  • $\begingroup$ On a less serious sidenote: I know Francis Crick was an advocate of his brain@40Hz theory. / I would advocate for the Sceptics.SE site, which deals with scrutinizing notable sources... $\endgroup$ Oct 1 '12 at 16:13

Sleep as you may know is divided into 2 broad categories which are the REM (Rapid Eye movement) and NREM (non rapid eye movement). NREM is further divided into 3 stages (reference). You never know which stage of sleep you are in when you are subjected to a particular frequency of sound. Your response to different sounds differ in your different sleep cycles.

The present 3 stages in NREM sleep is an update by The American Academy of Sleep Medicine (AASM) in 2007 (reference).The original 4 stages in the Rechtschaffen and Kales (R&K) standardization of 1968 (reference) has been used to explain the effect of disturbances in different sleep cycles

Stage 1 is still the phase of sleep from which it is easiest to wake someone up.

People in Stage 2 sleep are unlikely to react to a light or a noise, unless it is extremely bright or loud.

During Stage 3, the muscles still have some tonus, and sleepers show very little response to external stimuli unless they are very strong or have a special personal meaning (for example, when someone calls your name, or when a baby cries within earshot of its mother).

Stage 4 is the stage of sleep that accomplishes most of the body’s repair work and from which it is most difficult to wake someone up (reference).

A study conducted to measure brain activity while sleeping subjects were subjected to varying degrees of sound found that some people did you wake up after being hit with 70db of sound while others woke up even at sounds between 40 - 50 db (reference). This could lead to new behavioral or drug therapies for people with sleep disorders.

A review on the affect of low frequency sound on sleep could not reach any significant conclusions warranting that more search needs to be conducted in the field.(reference).

You will be interested to know that different sounds have been found to wake up men and women. A list is available here. Differences between the sleep of men and women are listed in this article.


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