Hemoencephalography

Hemoencephalography (HEG) is a type of functional near-infrared imaging (fNIR) of the level of neuronal activity in the brain. One method of doing this takes advantage of the translucent nature of the cranium and differences in absorption rates of various wavelengths of light for oxygenated vs. unoxygenated blood. Two different lights placed on the scalp are shone into the brain and the relative differences between the amount of each light that is reflected back out through the scalp provide a relative measure of changes in blood oxygen level. Another method simply involves placing an infrared sensor on the scalp to detect the amount of heat radiation at that spot. Although each method detects changes in level of cerebral activity, one as it as reflected in oxygen level, the other as reflected by thermal level, and although each method is used for similar biofeedback purposes, e.g. treatment of migraine headaches, the pattern of results are somewhat different at times.

While HEG can theoretically be used as a sort of cheap functional magnetic resonance imaging (fMRI), very little research has been done as of yet examining its efficacy in this role—(fNIR), under the direction of Britton Chance, has been designed and used for this purpose. Instead, most research has focused on its use for biofeedback.