Proof of Entrainment

It’s funny how you sometimes get the best results when you least expect them. Since the Neurosky EEG made an appearance I’ve been curious as to just what might be achieved with a single EEG electrode on the forehead (frontal lobe). I’ve done a few trials and had mixed results. I haven’t found this particularly surprising, as I’ve had mixed results with almost everything I’ve done with the EEG.

This afternoon I felt like a nice, basic delta session and a spur-of-the-moment EEG recording. I chose the NP2 Delta Session, customised to higher noise volume and reduced smoothness, scaled it down to 45 minutes and settled down with BioExplorer running the 3D spectrum, reference and ground to left and right ears respectively, one channel of the PN Pendant connected just below the hairline. My Procyon was providing the lightshow, with the AS mapping set to blue/green.

I enjoyed my 45 minutes away and checked the EEG recording. After reducing the spectrum analyser sensitivity to better show the larger-than-alpha delta, and narrowing the displayed frequency range from 0-30Hz to 0-10Hz, I was gratified to see a recording that showed strong correspondence to the course of the session. Seeing a good alpha response is not unusual. Seeing the bulk of activity drop down through theta and dwell beautifully in the 2-3Hz range, before ramping back up was a rare delight.

I have gone to great lengths to make it clear that the EEG doesn’t always show the expected signals in the expected places. Simple one-to-one correspondences between session and EEG are the exception rather than the rule, but when it happens it really boosts confidence in the underlying principles that justify AVS as a therapeutic and personal development tool. I still don’t know what matters – whether EEG-recordable signals have any great importance in the effectiveness of AVS – but knowing with certainty that entrainment really does happen sometimes, even down to delta, detectable even far, far away from the audio/visual centres of the brain, does weaken any argument that “AVS doesn’t work”.

In terms of the original line of enquiry – it looks as though the forehead may be just fine for general “proof of entrainment” testing.


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  • Dean Walker  On December 5, 2009 at 2:19 am

    Hi Craig,

    I use neurofeedback myself (2 channel pendant EEG & BioExplorer) & have used AVS in the past (Orion originally, now Procyon). Measuring the EEG at the back of the head I have seen the signature of my Orion tracking from 8Hz through to 12Hz as a diagonal line (albeit rather broken) on the BioExplorer 2D scrolling spectrum analyzer. So I know the signal does show up on the EEG. However I also know that the EEG is quite susceptible to electrical interference – particularly 50Hz, but also to whatever is floating around out there. Laptop transformers seem to be the worst offenders! It occurred to me that you might be seeing electrical interference on the EEG from the wires & circuitry in the glasses, particularly when measuring from the forehead. Is this possible? Hopefully this isn’t the case. Not sure how you would control for it.

    Also have you tried using BioExplorer to drive the AVS using Audiostrobe? A few years ago I experimented by creating a series of short wav files, each encoded with audiostrobe for a specific frequency (e.g. 9.5Hz, 9.6Hz, 9.7Hz etc). I could then use the expression evaluator in BioExplorer to selectively play one of these files (in a loop if I recall correctly) based on the dominant frequency. The idea is to let the EEG guide the feedback (so for example, play the 9.5Hz file when the dominant frequency is 9.4Hz to lead the alpha to a healthier higher level). It did work in terms of guiding the feedback. However I didn’t really pursue it fully though as Vipassana meditation caught my interest around then and fiddling with BioExplorer seemed at the time like the antithesis of the quiet mind I was looking the cultivate.

    Great website BTW.

    • CraigT  On December 5, 2009 at 7:47 am

      Hi Dean,
      Thanks for stopping by and the kind words.
      Yes, interference is a nuisance, fortunately it’s mostly 50Hz (or 60Hz depending on country) and relatively easily avoided. Electrode connection noise is my biggest problem, and why I’m tending to use the nice hairless forehead rather than more conventional placements these days. I haven’t specifically excluded intereference from the glasses, however I would expect it to be more consistent than the signals I do measure – as you have observed, EEG tends to be quite disjointed, and that’s what I’m seeing on the forehead.
      The trouble with back-of-head is that it’s directly over the visual cortex, and seeing evidence of the stimulus there is almost a given – as far as I’m concerned, entrainment is only indicated when a corresponding signal is seen over an area of the brain that is not directly associated with the sense being stimulated.
      I haven’t used the BioExplorer neurofeedback features, as use MindWorkstation Enterprise, which has very nice integration with BioExplorer. Early on I was uing AVS to deal with depression, and this would have been very helpful, but since I have had the EEG I’ve had no particular dysfunction to address – it’s all been recreational/experimental, so there have been no specific frequencies I’ve wished to train to.
      I know what you mean about EEG work “spoiling the moment”.

  • Dean Walker  On December 5, 2009 at 2:13 pm

    I have found that applying a little paste to part the hair first makes it much easier to get a good connection. Also makes it easier to apply the electrode, particularly when juggling with a mirror at the same time!

    MindWorkstation rings a bell… I’ve just read the specs and it looks quite impressive, but a bit too expensive for my budget I think. Have you tried the EEG driven stimulation yet? Sounds like a much better solution than my bodge!

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