Hemoencephalography

Hemoencephalography (HEG) is a relatively new neurofeedback technique within the field of neurotherapy. Neurofeedback, a specific form of biofeedback, is based on the idea that human beings can consciously alter their brain function through training sessions in which they attempt to change the signal generated by their brain and measured via some neurological feedback mechanism. By so doing, participants increase cerebral blood flow to a specified region of the brain, consequently increasing brain activity and performance on tasks involving that region of the brain. Hemoencephalography (HEG) is a relatively new neurofeedback technique within the field of neurotherapy. Neurofeedback, a specific form of biofeedback, is based on the idea that human beings can consciously alter their brain function through training sessions in which they attempt to change the signal generated by their brain and measured via some neurological feedback mechanism. By so doing, participants increase cerebral blood flow to a specified region of the brain, consequently increasing brain activity and performance on tasks involving that region of the brain. Both approaches to hemoencephalography, near infrared and passive infrared, are indirect measures of neural activity based on neurovascular coupling. Neurovascular coupling is the mechanism by which cerebral blood flow is matched to metabolic activity. When a region of the cortex is used in a specific cognitive task, neuronal activity in that region increases, consequently increasing local metabolic rate. To keep up with the nutritional and waste removal demands of a higher metabolic rate, cerebral blood flow to the cortical area in use must increase proportionally. Along with the increase in flow, hemoglobin molecules in the blood, which are responsible for the transport and transference of oxygen to tissue throughout the body, must increase the amount of oxygen they deliver to the activated region of the cortex, resulting in a greater local blood oxygenation level. This is also referred to as the haemodynamic response. Developed by Dr. Hershel Toomim, near infrared hemoencephalography measures changes in the local oxygenation level of the blood. Similar to functional magnetic resonance imaging, which uses changes in the magnetic properties of blood resulting from oxygenation to form an image of brain activity, NIR utilizes the changes in blood translucence resulting from oxygenation to generate a signal that can be consciously manipulated in neurofeedback sessions. At the most basic level, NIR hemoencephalography shines alternating red (660 nm) and near infra-red (850 nm) light on a specified area of the brain, usually through the forehead. While the skull is largely translucent to these wavelengths of light, blood is not. The red light is used as a probe, while the infrared light provides a relatively stable baseline for comparison. Photoelectric cells in a spectrophotometer device worn on the forehead measure the amount of each wavelength of light reflected by cerebral blood flow in the activated cortical tissue and send the data to a computer, which then calculates the ratio of red to infrared light and translates it into a visual signal of corresponding to oxygenation level on a graphical interface the patient can see. The key nutrient monitored by NIR is oxygen. In NIR, as the ratio of oxygenated hemoglobin (HbO2) to deoxygenated hemoglobin (Hb) increases, the blood becomes less and less translucent and scatters more of the red light, instead of absorbing it. In contrast, the amount of infrared light scattered by the blood is largely impermeable to changes in the oxygenation level of hemoglobin. Developed by Dr. Jeffrey Carmen, a privately practicing psychologist in New York, passive infrared HEG is a marriage of the classic hemoencephalography principles employed by Toomim and a technique known as thermoscopy. PIR uses a sensor similar to the NIR sensor to detect light from a narrow band of the infrared spectrum that corresponds to the amount of heat being generated by an active brain region, as well as the local blood oxygenation level. The heat detected by PIR is proportional to the amount of sugar being burned to maintain the increased metabolic rate necessary to fuel elevated neuronal activity. PIR has a poorer resolution than NIR and this treatment typically focuses on more global increases in cerebral blood flow. The first true instance of neurofeedback occurred in 1963, when University of Chicago professor Joseph Kamiya trained a volunteer to recognize and alter alpha brain wave activity. Just five years later, Barry Sterman conducted a revolutionary study on cats at the behest of NASA that proved that cats trained to consciously alter their sensorimotor rhythm were resistant to doses of hydrazine that typically induce seizures. This finding was applied to humans in 1971 when Sterman trained an epileptic to control her seizures through a combination of sensorimotor rhythm and EEG neurotherapy to the extent that she obtained a driver's license after only three months of treatment. Around the same time Hershel Toomim was founding Toomim Biofeedback Laboratories and Biocomp Research Institute on the basis of a device known as the Alpha Pacer that measured brain waves. After decades of work with various biofeedback mechanisms, Toomim accidentally stumbled upon conscious control of cerebral blood flow in 1994. He developed a device specific to this measure that he called a Near Infrared Spectrophotometry Hemencephalography system, coining the term 'hemoencephalography', in 1997. A clinician user of NIR HEG, Jeffrey Carmen, adapted Toomim's system for migraines in 2002 by integrating peripheral thermal biofeedback into the design. Since then, both techniques have been applied to numerous disorders of frontal and prefrontal lobe function. Sherrill, R. (2004). Prior to training with the HEG device, patients are given a standardized pre test, most often the Test of Variables of Attention (TOVA), to assess baseline cognitive functioning. Patient progress will be tracked using the same measure at the beginning and end of every neurotherapy session. Single photon emission computed tomography (SPECT) assessments may also be conducted pre and post treatment, depending on the patient's disorder. Training sessions are typically 45 minutes to an hour in length, with intermittent breaks. At the outset, all sessions are performed at a certified neurotherapy provider's clinic (though some at-home options are now available) and begin 2-3 times weekly in frequency. Depending on the patient, training may last from a couple of months to a couple of years. High variability in red light activity (large range from low to high output) is typically characteristic of people with problems of the prefrontal cortex. Low variability is associated with more normal functioning. The ratio of red/infrared light refraction is displayed as a visual signal on a computer monitor and may also be translated into an auditory signal in which higher pitch corresponds to greater oxygenation. During a HEG training session patients attempt to increase the signal generated by the HEG sensor. Progress is measured by reduced variability.