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I saw a TED talk about researchers playing pulsating pink noise while a test subject is in Stage 3 Non-REM / Slow Wave / Deep sleep and observing an increase in Delta wave EEG activity. This seems to indicating that the burst frequency of the pink noise is matching the dominant frequency of the Delta waves. (Skip to 5:00 to hear a sample of the sound)

My question: While a spectral analysis shows a range of brain wave frequencies, and many sources define a range such as "0.5-4 Hz", I'd like to find a more precise dominant frequency of Delta waves.

The video inspired me to write my own small computer program to make my laptop play a similar pulsating pink noise pattern on the table next to my bed last night. I arbitrarily chose 1 Hz as the pulse frequency, and the following pattern:

30 min silent (to give me time to wind down and fall asleep)
  60 min sound
33 min silent
  54 min sound
40 min silent
  45 min sound
49 min silent
  37 min sound
57 min silent
  30 min sound
30 min silent

So roughly 5x 90-minute sleep cycles with an increasing ratio of silence to noise to mimic the ratio of REM to NREM as the night progresses. I've read that REM is characterized by un-synchronized brain waves and NREM is where you see large amplitude synchronized Delta waves which the sound experiment is trying to help stimulate. Tonight I will wear my FitBit bracelet with heart rate and sleep stage tracking to see if the readings match the sound schedule.

Bonus Questions:

  • How credible is the hypothesis that playing sounds can affect the quality of sleep?
  • Would a different sound than pulsating pink noise work better?
  • Does the phase matter?
  • Also, I couldn't help but notice that Deep NREM sleep seems to be the only time you see a single large amplitude frequency dominate on EEG and it's suspiciously close to the average Resting Heart Rate of 60 bpm...are Delta waves and heart rate related?

Image Source: https://www.ncbi.nlm.nih.gov/books/NBK10996/ enter image description here

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  • $\begingroup$ don't try to mess with your sleep. all phases of sleep have important things going on in them. $\endgroup$
    – honi
    Jan 17, 2018 at 4:54

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Periklis Y. Ktonas and Atul P. Gosalia performed such an analysis. It was published in 1981 under the heading "Spectral Analysis vs. Period-Amplitude Analysis of Narrowband EEG Activity: A Comparison Based on the Sleep Delta-Frequency Band"

The bins were quite wide but their analysis showed peak power spectrum moved between 0.84 and 1.96 Hz at different times.

I think the paper would serve you well, as it highlights the difficulty in achieving what you have set out to achieve. The frequency is not constant, even over short timescales. It depends for the most part on a balance between the intrinsic, basal polarity of thalamocortical neurons, and the effect of synchronising, inhibitory input from the reticular nucleus. The latter is in turn subject to cortical feedback. There are huge numbers of neurons involved. The period between bursts, and the number of action potentials per burst, is quite variable.

Perhaps it might be possible to set up a device that alters the round in real time, based on the EEG measurement.

With regards to your 'bonus' questions:

(1) The video posted does show an effect on the thalamic rhythm, which is surprising, as it had been thought that in deep sleep, sound has no effect on the thalamocortical circuit, since it is gated at the thalamus. This shows the plausibility of the hypothesis. However, the video does not provide any evidence that this alteration in rhythm is beneficial. It is possible that it is not and this possibility should be eliminated.

(2) Clearly the sound has an effect on the rhythm, so it seems entirely plausible that there is an optimal sound to maximise the effect.

(3) It will be hard to organise the phase, given the continuous, rapid shifts in period, unless done in combination with EEG in real-time.

(4) I am not aware of any research attempting to correlate thalamic rhythms with heart beat, although it would be quite easy to do. However it is highly unlikely there is a correlation, since the thalamocortical period has a lot of variation moment to moment, whereas the heart rhythm does not. Also the thalamocortical rhythm is generaly somewhat faster.

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  • $\begingroup$ Thank you for the excellent response (even if I'm a little disappointed to hear it). What do you make of the part of the TED talk where the presenter showed EEG readings that did in fact respond to sound? $\endgroup$
    – Dustin
    Jan 18, 2018 at 2:12
  • $\begingroup$ OK, I have to admit that I haven't seen that effect before. There is a clear response to the sound in the wave. My statement that sound "has no effect on the thalamus" is incorrect, so I will edit it. But I think what you should look for is evidence that this artificial alteration of the rhythm is beneficial. You could be having the opposite effect to that intended. It would be interesting to compare the effect on rhythm shown with the effect of the sound of wind blowing through trees, or water babbling down a stream, so if you get that far, do share your results ;-) $\endgroup$
    – Nobody
    Jan 21, 2018 at 7:35
  • $\begingroup$ * Well, strictly, you should look for evidence that it isn't beneficial, of course ;-) $\endgroup$
    – Nobody
    Jan 21, 2018 at 7:44
  • $\begingroup$ Heh yes well causality and health benefits are notoriously hard to prove - plus I don't have an EEG. So far I've lowered the pink noise pulses to 0.8 Hz and tried it for a few nights. While it's impossible to say whether I've felt any different the next morning due to placebo, I do think I had/remembered more dreams which is surprising since SWS is supposed to be dreamless. The other thing is that on nights where I have a hard time falling asleep the sound can be distracting, like disembodied breathing. On normal nights I'll wake up and notice it playing but fall back asleep without issue. $\endgroup$
    – Dustin
    Jan 23, 2018 at 1:05
  • $\begingroup$ I thought you might be interested in this, a Nature news feature last week: nature.com/articles/d41586-018-02391-6 $\endgroup$
    – Nobody
    Mar 3, 2018 at 11:14

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