What is Near Infrared Hemoencephalography
Near Infrared Hemoencephalography (nirHEG) is a type of brain imaging technology that indirectly measures neuronal activity of the brain. nirHEG measures changes in relative absorption of red (660 nanometers) and infrared (850 nanometers) light passed through the skull into the brain tissue beneath the HEG sensor. The light passes through the translucent scalp, skull and brain tissue and is reflected back by blood in the tissue. The ratio of red to infrared light scattered back to the HEG sensor is used as a measure of localized blood perfusion and oxygenation.
This means that as the local oxygenation of the blood under the light source and sensor increases in response to neural activation, the signal from the HEG device changes. In this way the nirHEG device can detect local changes in the brain’s activation.
Photo showing infrared light and sensor inside of nirHEG headband.
The developer of the nirHEG neurofeedback system, Dr. Herschel Toomin found that there was a very good correlation between his device and fMRI systems, which also relies on changes in blood oxygenation to measure brain metabolism.
fMRI uses very powerful magnetic fields to detect localized changes in the magnetic properties of oxygenated blood versus de-oxygenated blood. Areas of the brain that are more active require more oxygenated blood and this demand for more energy is met by localized increases in blood flow. fMRI reveals relative differences in oxygenated blood perfusion across the brain. fMRI technology is very expensive (over $1000 per hour) compared to nirHEG ($100-$200 per hour) and permits a much higher resolution scan of the entire brain’s functioning and is most commonly used in research settings to determine which areas of the brain are involved in particular tasks. Current nirHEG systems can only detect activity in the brain’s outer layer (about 1.5 cm deep)— the cortex, and are almost exclusively used to train cortical activation through biofeedback.
In nirHEG neurofeedback, the trainee tries to increase the signal from the HEG sensor, which is equivalent to activating the cortical region of the brain under the sensor. A computer display shows the change in cortical activation over the course of time. nirHEG neurofeedback directly trains the brain itself. The trainee quickly gains greater control over the flow of blood and the density of oxygenation at the chosen scalp site. Trainees are usually instructed to concentrate and perform a task that directly relates to the region of the brain being trained— e.g., reading, doing math problems, thinking about themselves, or playing a computer game, etc. Training in the left hemisphere of the brain is enhanced by cognitive challenges; whereas training in the right hemisphere is enhanced by spatial activities. Training in the back of the head over the occipital lobes (visual cortex) is a form of relaxation and is enhanced by visualization exercises. Because it is a learning procedure, nirHEG neurofeedback is non-invasive and safe.
Graphic display showing change change in signal strength under the HEG sensor with HEG feedback.
Applications of nirHEG Neurofeedback
nirHEG is still a new neurofeedback modality and the published research on its applications and clinical efficacy is still relatively sparse. EEG neurofeedback and audiovisual entrainment (AVE) neurotherapies have been available for a lot longer and have significantly more published research supporting their use in treating various brain-based disorders and problems. But nirHEG neurofeedback is showing some real promise in the treatment of…
Attention Deficit Disorder
One thing that links these three disorders is the possibility of dysregulation of the prefrontal cortex (PFC) of the brain— the area just above your eyes and behind the forehead. The PFC is a particularly important part of the brain that is most highly evolved in humans and plays a central role in purposeful behavior—making decisions, formulating and carrying out plans and intentions, and maintaining attention and concentration in the face of competing stimuli. It coordinates the brain resources needed to carry out our intentions and evaluate our actions in terms of their success or failure in meeting objectives.
Red shows PFC area of the cortex.
The PFC also plays an important role in emotions and motivation; helping us to keep to a long-term plan by somehow holding in mind the good feelings connected with achieving that goal. As well, the PFC has the ability to inhibit other structures in the brain connected to emotions, allowing you for example to override a fear of water and drowning to learn how to swim. The PFC is especially relevant to social emotions because our ability to imagine what other people might be thinking and feeling depends on the PFC.
Numerous brain scanning studies have shown that activation in the PFC is not optimal in the brains of persons who are depressed or have attention-deficit disorder. Optimizing PFC activity may help increase focused attention and concentration, strengthen control over emotions and impulses, enhance the sense of purpose and self-possession, and increase flexible responding to the demands of a given situation. Among the symptoms of poor executive functioning in the PFC are inattention, poor planning or judgment, slow reaction time, lack of social awareness, and poor impulse and emotional control.
To date, clinical reports of nirHEG neurofeedback have most commonly focused on training the prefrontal cortex of the brain. To a large extent this is because nirHEG does not work very well over parts of the scalp that are covered in hair and, where EEG neurofeedback signals from electrodes placed on the forehead are easily contaminated by electrical noise caused by eye blinks and movement, such small muscle movements do not affect the reliability of the nirHEG signal.
Finally, although the underlying neuropathology of migraine remains unknown, there have been a number of clinical reports describing successful HEG treatment of a few hundred migraine patients to date. It is thought that nirHEG biofeedback over the PFC may strengthen inhibitory control over some part of the brain stem thought to generate migraines.
Is There Research to Support the Use of HEG Neurofeedback?
Research on the HEG device and its use in neurofeedback is still quite limited but has been going on at the University of California in Los Angeles and the Biofeedback Research Institute of Los Angeles by Drs. Herschel and Marjorie Toomin for many years. Additionally, other researchers have studied this technology for the treatment of a number of different brain disorders.
Results have suggested that HEG neurofeedback can enhance cognitive functioning and reduce symptoms associated with hypoperfusion (i.e., reduced cerebral blood flow and oxygenation) in a number of disorders.
H. Toomin (2002). Hemoencephalography (HEG): The study of regional cerebral blood flow. California Biofeedback, Summer 2002, pp.17-21.
T. Tinius (Ed.) (2004). New Developments in Blood Flow Hemoencephalography. Binghampton, NY: Haworth Medical Press.
R. Coben, L. Pudolsky (2007). Infrared imaging and neurofeedback: Initial reliability and validity. Journal of Neurotherapy, 11(3): 3-13.
Are There any Side-Effects Associated With HEG Neurofeedback?
Subjects in studies of HEG neurofeedback have not reported any significant or long lasting adverse effects. The most commonly reported side-effect is transient mild headache or fatigue following treatment sessions and lasting no longer than a day or two following. Such unpleasant side-effects appear to be the result of working too hard or too long in a training session.
How Long Does HEG Neurofeedback Take?
HEG neurofeedback sessions are typically 30-45 minutes in length and consist of some number of 10-15 minute training trials with a short rest between each trial. While many patients will experience a positive response within the first couple of sessions, successful and longer-lasting reduction of clinical symptoms, especially in chronic conditions, will commonly require 10-20 sessions of training. It is usually best to begin training with anywhere from 2-4 sessions per week for the first few weeks and then reduce the frequency of sessions as symptom improvement is solidified.
Toomin, H., Mize, W., Kwong, P., et al. (2004). Intentional Increase of Cerebral Blood Oxygenation Using Hemoencephalography (HEG): An Efficient Brain Exercise Program. Journal of Neurotherapy, Vol. 8, No. 1, pp. 5-22.
Tinius, T. (2004). New Developments in Blood Flow Hemoencephalography. Binghamto, NY: Haworth Medical Press.