Is There a Neurofeedback Tsunami? (It is Synchrony.)

R. Adam Crane BCIA Senior Fellow, BCIAEEG, NRNP Diplomate

I think so and its name is Synchrony. Synchrony training is of great interest to many Neurofeedback practitioners. However, there seems to be a number of opinions about what synchrony means. We hope to add to the confusion by explaining our views. We will also explain why we feel synchrony training is an important part of Neurofeedback’s present and an even more important part of its future.

As multiple channel Neurofeedback systems come into fashion synchrony strategies will become critically important to this field. Stroebel, Fehmi, Green and others came to the view that there was a special relationship between EEG Synchrony and quality of some mind states in the early 70’s.


This insight came as a result of measuring the synchrony present as unusually gifted individuals demonstrated relatively high orders of perception and self-regulation.Not many are aware that the Nobel Laureate Francis Crick, coming from the traditional neuroscience “Binding” theory of consciousness, is reported to have speculated that EEG Synchrony may be an accessible and practically usable signature of consciousness. To quote from his book Astonishing Hypothesis, ” Both German groups suggested that these 40hz oscillations might be the Brain’s answer to the binding problem. They proposed that the neurons symbolizing all the different attributes of a single object (shape, color, movement, etc.) would bind these attributes to each other by firing together in synchrony.”

Now, Crick is limiting his investigation to visual awareness or “consciousness”. His notion is that synchronous firing is a way different types of neurons bind their different perceptions producing the phenomenon of consciousness. Others are signing on to this speculation. I doubt they are aware of the work that inspired the same kind of insight by early biofeedback researchers.

Our considerable experience with synchrony training has convinced us that it has substantial applications with problem patients including Alpha P and Minus types. However, we believe that synchrony will play an even greater role in Performance / Life Enhancement training. The value of right / left hemispheric synchrony training is widely recognized but less is known about rear /frontal. It is a reasonable hypothesis that rear / frontal is at least as important and relates to perception of the principle, the idea, the vision, if you will, and then the bringing of that vision into the real world, via the frontal lobes.

Our views are based on clinical observations and obviously hypothetical as much more controlled research needs to be done. As we all know there is almost no funding available for such research so we are forced to use our clinical observations as a practical way of arriving at our working hypothesis until society realizes the incredible value of what we are working on and provides adequate research funding.

There are several versions of what synchrony is when it comes to EEG feedback. Let me try to tell you how we are looking at it. Also, some of you will find the following technical jargon daunting as I do. I’m quite dependent on the assistance and interpretation of our technical team (Stroebel, Caldwell and Pitchittino). In 1986 when we first decided to take on the task of creating the first and hopefully the best computerized NeuroFeedback training system in the world, we were told by some well trained technical people that we would never be able to deliver true NeuroFeedbacik synchrony on four brain quadrants within one second epochs. Others including Chuck Stroebel and Les Fehmi said it could be done and by 1989 we had done it.

We put together a form of synchrony, which from our point of view has been exceptionally successful. Some say we just got lucky but that luck was founded on John Pitchittino and Sam Caldwell’s brilliant execution of Chuck Stroebel’s algorithm. Because our philosophy is to try to integrate into our software all ideas that we believe have merit, we wound up with four types of synchrony in the DOS software and have introduced a fifth version in the new CapScan Windows Solution. Our intention has always been to make all valid synchrony algorithms available so practitioners can do their own experimentation and decide for themselves what works best.

There are several ways of looking at synchrony. Obviously, the system which comes closest to matching the kind of synchrony created by the human brain is most valuable. Some feel that synchrony may be seen as same frequency even if the angle of the sine wave is 180 degrees out of phase. Others add making the amplitude equal as synchrony criteria. This does not seem to us to be intuitive because it is not as close as other techniques to what actually happens in nature. Still, we provide the option of experimenting with it.

We think the best way to arrive at synchrony includes relative coherence of the sine wave. This implies the activation of the energy and other potentials yielded by the laws of resonance. This kind of synchrony, harnessing the power of resonance, is similar to the coherent synchrony that makes AC current travel farther than DC, or a sense of beauty when two notes from different instruments harmonize, or the proverbial bridge to collapse if the Roman soldiers did not break step. Pitchittino uses the example of two children swinging on swings side by side at the same frequency and holding hands at the same time. They have to be together. Just swinging at the same frequency is not enough.

The four types of synchrony included in the Prism 5 DOS software may be described as:

Same Dominant Frequency: EEG signals from adjacent sites are scored as synchronous when dominant frequencies are equal.

Equal Frequency Equal Phase: EEG signals from adjacent sites are scored as synchronous when both dominant frequency and dominant phase are equal.

Dominant Plus Average Sign: EEG signals from adjacent sites are scored as synchronous when dominant frequency and the sign (+ or – ) of the sum of the real and imaginary FFT components are the same.

Dominant Plus Phase Sign: EEG signals from adjacent sites are scored as synchronous when dominant frequency and the sign (+ or -)of the dominant frequency phase are equal.

Synchrony criteria for CapScan Windows (Uses a sliding scale for maximum flexibility):

Correlation Coefficient and Crosscorrelation

  • The Correlation Coefficient of the pair of input signals is a single value for each block, which always lies between -1 and 1.
  • Values near 1 represent a good correlation; the input signals are of similar shape.
  • Values near 0 mean that there is no correlation.
  • Values near -1 represent a good anti-correlation.
  • The result of Crosscorrelation is a full block for each signal-input block. Each one represents the correlation function. The first value is equal to the correlation coefficient; the other values are the correlation coefficients for the periodically shifted signals. The time shift is used as the abscissa of the correlation function.

Stroebel, Caldwell and Pitchittino’s version which we and most of our users are so happy with is the third choice (Dominant Plus Average Sign) available in the DOS CapScan. We do not yet have enough input from our users to have a feeling if the new Windows formula will equal or surpass Dominant Plus Average Sign.

The Dominant Plus Average Sign kind of Synchrony is defined as phase and coherency synchrony between the dominant frequency components from two channels, in a one-second epoch. The in – phase criterion is that the phase angles of the dominant frequency components lie in the same quadrant. To put it a bit more technically, the Prism 5 option three displays percentage of synchrony per quadrant pair as follows: Signal analysis is based on data derived from Fast Fourier Analysis on the signals from all four channels in successive one second intervals. Hamming weighting is applied in 128 time samples in each one-second interval. The resulting 64 frequencies, bins, are one cycle apart and are centered on integral frequencies. Alpha (9 – 13), Beta (14 – 29) and Theta (4 – 8) band measures are attained by selecting and stating the amplitude of the largest component in the defined frequency range. We have added the option of selecting individual bandwidths for synchrony training.

Adjacent signals (Phase 1, 2, 3, or 4) are considered synchronous in a given 1 second interval when the largest amplitude component in the spectrum of the first signal occurs at the same frequency as its counterpart for the second signal, and the FFT derived phase angles of the two dominant amplitude components lie in the same vector quadrant (i.e. 0 – 90, 90 – 180, 180 – 270. 270 – 360). We think this system falls closer than any other system we are aware of to the pattern that naturally happens with healthy human EEGs when synchronous.

Synchrony is calculated for each trial in each session and displayed in order to enhance pattern recognition.

I might add that we have developed averaging techniques, which we believe are useful and they provide synchrony updates on all four quadrants on a fast enough computer every 100 milliseconds. We believe these techniques perhaps combined with wavelet analytic strategies will allow us to achieve flicker fusion and beyond. In fact, we have a four channel compressed spectral array (water fall display) that is already running at 16 hz (flicker fusion) on some computers. The way that we provide audio feedback is to sound a different note from a four-note chord whenever a quadrant pair meets synchrony criteria. Two quadrant pairs yield a two note chord, all four a four note chord.

However, the original 1-sec updates still seem superior to most practitioners. It seems the sound is more comfortable coming at that speed than the extremely fast notes coming every tenth of a second. So we had to add a control for actually slowing down the updates as an option. Of course ten per second probably has an alpha driving effect.

There have been, so far, very few synchrony studies but I predict that they will be steadily growing as equipment makes it easier to do and our community becomes more aware of some of the implications of synchrony. Peniston and Kulkosky published a study in Advances in Medical Psychotherapy 1993, Volume 6. They used a Prism 5. They reported a significant increase in the percentages of brain channel pair synchrony over 20 sessions in the frontal and parietal occipital lobes of the cerebral cortex in Vietnam theatre veterans with combat-related PTSD symptoms. A twenty six-month follow up showed that four of the patients had a relapse of PTSD symptoms while 16 showed continued absence of symptoms.

“The mean amplitudes of alpha and theta brainwaves across the 20 trials of the abreactive imagery BWNT sessions displayed a statistically reliable interaction seen as a “cross-over” pattern, wherein theta waves gradually increase across trials and alpha waves decreased across trials. The aforementioned pattern is thought to identify a state of consciousness in which the patient is sensitive to hypnogogic imagery which relates symbolically to issues in the patient’s own life.”

We have long referred to this state of consciousness as a “window of opportunity”. The concept is that you cannot make insight happen anymore than you can force the breeze to come through the window. But you can keep the window open longer and thereby dramatically increase the chances of the breeze (insight) coming through. This insight often takes the form of hypnogogic imagery.

“It is postulated that the increases in theta amplitude in conjunction with the decreases in alpha during the abreactive sessions seem to be correlated with the strong affective experiences of childhood and/or adulthood – particularly, past traumatic anxiety evoking events (i.e. abreactive imageries)… it is hypothesized that the more the synchronicity and amplitude of theta waves increase the deeper the patient is able to descend into the reverie (theta) state which activates anxiety-evoking imageries… the limbic system and both hemispheres are more synchronized and the increased theta and beta rhythms reflect a brain process which enables the patient to remember and/or relive the traumatic anxiety provoking event… It was as though the patient was capable of integrating past traumatic experiences by coping with previously unresolved conflicts represented in the essentially anxiety-free imageries and memories generated during the theta state of consciousness.”

“Levine, Herbert , Haynes and Stroebel found that meditators are able to produce high amplitude, synchronous beta, alpha and theta frequencies. The literature has indicated that during deep meditation, alpha, and theta frequencies become synchronous. Hypnogogic, dreamlike images have been found to occur during the theta and or reverie states. This work was reported by Budzynski and Stoyva, Green, Green and Walters, Folkes and Vogel. The combination of sensory and cognitive perceptions comprises the experiences of hypnogogic imagery. Green, Green and Walters associated this type of imagery with creativity and integrative experiences and Peniston and Kulkosky associated it with abreactive (i.e. traumatic-anxiety provoking) experiences. In order to experience vivid imaging, the subject should be in an alpha-theta mode for a sustained period of time.”

I would point out that Sue Wilson suggests that the first use of EEG feedback in Peak Performance with elite athletes is to deal with sub clinical PTSD. We say this is correct because these repressed fears are contaminating the “field of mind”. This is what we mean by “cleaning up the field of mind.”

Classic meditation models hold that quality of consciousness is enhanced in some proportion to the amount of repressed fear material that is pulled up from the unconscious and burned up, as it were, in the fires of consciousness, similar to the dramatic abreaction between Matt Damon and Robin Williams in the hit movie Good Will Hunting.

Following are two examples of how synchrony training apparently saved the day with an “alpha blocked” psychiatrist and an alpha minus psychologist I trained. The psychiatrist was actually an old friend who strangely seemed to have a tendency to cut you down suddenly during what you would think is a friendly, innocent conversation; and then turn his back and walk away leaving you smarting. Yet, equally strangely I was always glad to see him, perhaps sensing that this was some kind of game, which leads somewhere worthwhile. I had been trying for about ten years to persuade him to add EEG biofeedback to his existing traditional biofeedback practice. Finally, I got around to hooking him up and discovered that I could not assist him in having a decent alpha feedback experience because his alpha was quite low amplitude (about 3 ‘ 4 UV) and I assumed he was an Alpha P. Also, his Theta was quite high and I realized that in a way his behavior was a bit disassociative.

So, I decided to train him in synchrony for about thirty minutes. Then I switched him back to traditional alpha feedback and was delighted to see that he was now doing 12 – 15uV. There were witnesses to this event and they agreed that his whole affect had changed. His face had lit up and he smiled much more and seemed to be “high” in a healthy way. He said he felt much better and could hardly wait to begin offering EEG BioFeedback to his patients. He subsequently developed a successful Neurofeedback practice. Interestingly, upon finding out how much relative Theta he had, he commented that he had often felt frustrated when working with patients because he felt he was in a kind of trance and found it difficult to bring through into the therapy session all of the insights he was actually having. He felt that this kind of training was going to help with this long-term creativity problem.

Another example was a psychologist I was training at the University of Mexico. She appeared to be an Alpha Minus so I immediately put her into a ten-minute synchrony session. At the end of the session I saw that she had gone pretty deep so I gently brought her out and asked if she had enough for today. With some urgency she said that she would like to do more. She described things getting very dark and feeling she was in some kind of large tunnel but she wanted to go back. I could see that we were moving into an abreaction but since the room was filled with mental health professionals I thought it would be a good opportunity to show them something about synchrony training.

As I brought her out of the second session she was tearing but had a peaceful smile on her face. She said that she had come to the end of the tunnel and found herself looking at a magnificent stained glass window. I started to unhook her recognizing a classic archetypal abreaction shaping up and felt I did not have enough time to properly deal with it. She pleaded to go back and by now the other psychologists were amazed at what they saw. So, she went back in for another ten minutes of option 3 (Dominant Plus Average Sign) synchrony. At the end of this session she was freely weeping and had obviously had a profound experience. I gently asked if she wanted to talk about it and she said that she had crashed though the stained glass window into pure white light and she felt somehow changed in a beautiful way. She knew she had had an archetypal “near death” experience and felt it was very “healing”.

So, the question I continuously get asked is what is the practical application? Putting it in simple language; I would say the following. NFB is already a fast learning technique. In fact, amplitude training is at least an indirect measure of synchrony. A good way to think about synchrony training relative to traditional NFB is like you would think of an afterburner added to a jet engine or a fuel injector added to a combustion engine. You take an already steep learning curve and make it even steeper. If that is true then clinical implications for synchrony are substantial, and MindFitness applications even greater.

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