Effects of Hemoencephalographic (HEG) Training at Three Prefrontal Locations Upon EEG Ratios at Cz
Background. Light in the wavelength region of 650 to 1000 nanometers is able to penetrate living human tissue, including bone. Medical research has exploited this optical window into the body to develop non-invasive monitoring of brain functioning. In 1994 Herschel Toomim discovered that he could both measure and teach persons to control the amount of oxygenated blood flowing in the prefrontal regions with such an optical device. He has labeled the biofeedback of brain blood flow hemoencephalography (HEG). Methods. A fifteen-year-old male with a history of mild articulation problems and poor spelling was administered twenty sessions of combined HEG/EEG biofeedback, with a referential recording at Cz. Feedback in each session was conducted in three trials with the HEG optodes placed over the left eye, at midline, and over the right eye for ten minutes each. The order of placement was counterbalanced across trials. Changes in HEG levels within each trial were computed and plotted across sessions, as was the theta/beta ratio for each trial. Results. The subject clearly learned improved voluntary control over brain blood flow. The slope of increases of HEG within each trial improved across sessions at all three forehead locations. There were three indications from this case that HEG training to improve attention might be most efficacious at the midline location: (a) the theta/beta ratio at Cz decreased slightly over sessions only in response to HEG training at midline, (b) bursts of beta lasting ten seconds or more occurred more often, and (c) occasionally a marked increase in HEG within a trial was associated with a corresponding increase in power in beta. This occurred only with HEG at midline. Conclusion. HEG biofeedback is a promising treatment modal-ity, especially for improving the functioning of executive control systems mediated by the prefrontal regions of the cerebral cortex.