Friday, February 18, 2011

EEG Biofeedback Equipment & Techniques

A recent commenter asked for some starting points for EEG biofeedback and meditation.

It's a bit much to cover, and it's all really speculative at this point (and in fact that's what this blog is all about, exploring these possibilities), but based on what literature exists one might think it reasonable to focus on rewarding alpha and/or theta amplitudes and coherence.  Slow wave activity such as alpha and theta are found in greater quantities on the back of the head, as well as in the right hemisphere as opposed to the left, so this is where you would typically want to reward it.

For meditative purposes we would typically be using eyes closed biofeedback, eyes closed being the method used by arguably the most successful meditators (in terms of percent of adherents attaining enlightenment), the Theravada Buddhists.  With eyes closed, visual processing relaxes, and alpha wave amplitudes rise.

There is an existing protocol (with many small variations) called alpha-theta training that is highly relaxing and relatively meditative.  I think for many people, however, rewarding theta is going to lead them more into dreamy reverie than meditation.  The studies that show theta in advanced meditators is probably reflecting the fact that their dominant alpha rhythm has slowed into the theta range.  So my recommendation would be to concentrate on alpha, and although people may differ, I'd use a complete range of alpha like 8-12.

As a direct input for biofeedback, I find coherence a little difficult to make use of as the variation occurs slowly and so the feedback is sparce.  For an input like that you can use a feedback tone that changes frequency, but it's tricky to get the feedback to sound pleasing.  Coherence is likely pretty important, though.  My recommendation is to skip direct coherence measures and just reward total alpha from 2 symmetrical sites, one left hemisphere and one right.  Rewarding total alpha over 2 sites simultaneously encourages coherence between the sites as well as amplitude.

The prototypical 2 channel setup for alpha biofeedback would probably be on the parietals, P3 & P4 on the 10-20 system.  Other placements would include the occipitals, O1 & O2, and typically no farther forward than the centrals, C3 & C4.  But that's just what has been done.  Based on the post about Austin's article, I'd say the temporals would be an interesting placement, for example.  Based on the post about Goenka meditation, if you're practicing that kind of scanning vipassana, you might want to try O1 & O2 or T5 & T6.  I personally kind of like the idea of C3 & C4 as a central brain location.

For EEG Biofeedback equipment, there are any number of suppliers, but something like a 2 channel Pendant unit with Bioexplorer software is a relatively popular option for this type of thing.  Some resources can be be found from other people on the quest.