Near-infrared spectroscopy studies on cerebral blood oxygenation changes during brain activation: possible limitations of blood oxygenation level dependent functional magnetic resonance imaging

The noninvasive method of functional near-infrared spectroscopy (fNIRS) has recently been used to measure changes of optical parameters such as light absorption of brain tissue. Hemodynamics and oxygenation changes related to brain activation can be evaluated using fNIRS, with the most widely evalua ted parameters being oxygenated hemoglobin (Oxy-Hb), deoxygenated hemoglobi n (Deoxy-Hb), as well as total hemoglobin, which is the sum of Oxy-Hb and D eoxy-Hb and which reflects cerebral blood flow. The typical response is an increase in concentrations of Oxy-Hb and Total-Hb accompanied by a decrease in Deoxy-Hb; however, a variety of oxygenation and deoxygenation changes h ave been found, particularly regarding clinical studies and developmental s tudies of infants and older adults. The findings of increases of Deoxy-Hb a s well as decreases of Oxy-Hb and Total-Hb are important for understanding clinical and development changes. In addition, the findings suggest possibl e limitations or problems with blood oxygenation level dependent (BOLD)-fMR I for clinical and developmental studies, and for revealing the complexity of hemodynamics and oxygenation responses. (C) 2001 Society of Photo-Optica l Instrumentation Engineers.