HEG Modes: NIRS & PIR

Yesterday, July 19, 2012, marked one year since Dr Hershel Toomim left our midst. His innovative work with HEG brain biofeedback lives on and will continue for as far as I can see.  His use of blood flow measures as a direct biofeedback source (instead of a mere confirmation measurement) has made neurofeedback accessible to many who would not or could not do the more technically difficult EEG biofeedback.  Interest grows amongst clinicians, schools and sports organizations, as well as businessmen who seek a solid way to measure attention.  In this first year since Dr. Toomim’s passing, I have implemented more than 20 HEG biofeedback training centers in the Americas.  This represents a growth of just over 30% from the year prior.  My clients are generally clinicians attending populations for headache, attention and impulse control, mood and stress control and sensory gating issues.

Invariably within my prospective client’s decision process, I will be asked about the two technologies which both provide an HEG signal for feedback; the client wanting to know which is “better”.   I don’t respond in a “better / worse” manner to my clients, and don’t intend to in this short article. Instead I will provide information from outside of the field of applied psychophysiology to shed light on the origins, research and other uses of these two technologies which were both “borrowed” from other industries for our use in benefit to the brain.

First, it’s important to share what for some is obvious, but for others, represents an encouraging new frontier in Neurofeedback (NF) and Brain Computer Interface (BCI).  This entire article is about HemoEncephaloGraphy (HEG), the term commonly used for the measurement and feedback of blood dynamics in the cortex of the brain.  This is a term coined by Dr. Toomim in his 1995 presentation to the Association for Applied Psychophysiology and Biofeedback (AAPB) conference when he reported on the initial results of his research to the plenary.  HEG represents a robust option to the more commonly known EEG biofeedback because it is not an electrical measure, so is not affected by eye and forehead muscle activity.  EEG and HEG are acronyms, and pronounced by their letters.  Recently, especially from European clients, I’ve heard HEG pronounced as if a word “hegg” but if that were the case, then we would be calling electroencephalogram an “eagg”.  The correct way is to pronounce the letters:  H.E.G.  Also important to note about terms is that HEG is a term only used and known amongst those who practice applied psychophysiology and biofeedback.  In other words, different from EEG, the term HEG does not describe the technology as much as it does the application of a blood measurement technology in a feedback loop.   This is most clearly shown by reading the patent which Dr. Toomim and Robert Marsh registered in 1999 which encompasses and application: “Apparatus and method for biofeedback of human central nervous system activity using radiation detection.”  This is important, because within HEG there are presently two distinct technologies with their own lines of psychophysiological research and terminology, and when in dialogue with these researchers, “HEG” is often a non sequitur.

As with HEG, two core technologies used to capture the brains hemodynamic are known also by their acronyms, but these are often pronounced as words:

NIRS: near infrared spectroscopy, which uses light to measure the brain’s blood oxygenation and perfusion;

PIR: passive infrared photography, which measures heat coming from the brain to infer the brain’s blood perfusion.

Again, without discussing better or worse, let’s look at the qualities of both technologies.

NIRS, is used across many industries to determine the density and composition of masses in general. It has been applied on such varied samples as stone, wood, fruits, fabrics, cold  stars and brains amongst others.  To generate its reading, NIRS emits a light in the color frequency that will be absorbed by its desired compound and measures how much light returns from the sample in order to determine the quantity of the measured compound is present in the sample. It’s simple reflectance. Send light in and measure how much light reflected back. The light that does NOT return is the measured value, because that light was absorbed by the measured substance.  In our case, this substance is oxygenated hemoglobin and it’s color range is very exact: 800nm.  When carrying carbon dioxide, the blood cells are blue in color and so do not absorb this 800nm light. As such, the readings from NIRS are very exact and have a high confidence value.  This is best illustrated by the comparisons that are regularly made between functional NIRS and functional MRI.  Outside of the biofeedback world, NIRS is making its name as a technology that can offer in-vivo cortical imaging that is on par with the MRI “outside of the tube”, and making the functional aspect of the imaging much more… functional. It is allowing researchers to take the brain imaging to the poker table, the fearful spider or pleasurable cupcake.  When working with nHEG neurofeedback, the user can know that the technology is a workhorse of the brain imaging industry.

PIR (passive infrared) technology uses a different means to generate its measure.  It does not send anything into the substance measured, but instead passively waits for any light within the infrared light (aka “heat”) spectrum to arrive at it and be registered.  The core technology, when researched online with the term “PIR” seems to be mostly applied to motion detectors and security systems.  We see PIR sensors in the corners of rooms where automatic light systems are installed (vis every Starbuck bathroom I’ve ever been in).  The novel principle which pHEG inventor, Dr. Jeff Carmen came upon was that blood carries our body’s heat. As such if pointing one of these heat sensors fixedly at the forehead, any change in the heat index was indirectly representing a change in the blood dynamic over that region.  This is fundamentally different than the more common use of PIR to “trigger a sensor”.  In the feedback use of the technology, the sensor must be able to quantify changes in temperature. The better name, thus for the technology used in pHEG is a “radio thermograph”.  Use of this technology on the brain is uncommon. When searching biological sciences literature, I did find a few studies by the respected Russian researcher named IA Shevelev from the 1990s.  In these he coined a term: thermoencephaloscopy (not yet in wikipedia).  Following his seminal work, there is a long silence in the literature until, in 2007 a new champion named A Iznak published one article so far on the subject.

In my daily practice, and also when I think over the 10 years I worked only with EEG, I am thankful to Dr. Toomim for having brought this new form to our collective toolchest.  HEG, in either form, is a robust and functional mode of neurofeedback that will only get more recognition as its effects begin to shine more in our society, through the lives of the people that it benefits.

Adrian Van Deusen is an independent researcher and practitioner of applied psychophysiology and biofeedback since 1995.  In 2003, he began studying HEG and developed a mentor-student relationship with Dr. Hershel Toomim in 2004 which endured through the end of Dr. Toomim’s life, at 95 years of age.  Adrian’s works as a researcher of HEG have included presentations at the following international conferences:  International Neuropsychological Society, Brazilian Congress of Neuropsychology, European Health Psychology Conference, Clinical Neuroscience Society,The 2nd International Meeting on Working Memory and with an accepted paper in the Spanish Journal of Psychology (Vol 15-3).