Measurement of frontal lobe functional activation and related systemic effects: a near-infrared spectroscopy investigation.

Near-infrared spectroscopy (NIRS) has been used to measure changes in cerebral oxy- and deoxy- haemoglobin (delta[HbO2], delta[HHb]) in response to functional activation. It has been previously reported that during functional activation of the motor cortex heart rate increases. The aim of this study was to investigate systemic changes during functional activation of the frontal cortex. The responses to anagram presentations with varying difficulty (4-Letters and 7-Letters) over a 6 minute period were recorded. A Hamamatsu NIRO 200 NIRS system recorded delta[HbO2] and delta[HHb] using the modified Beer Lambert law (MBL) and tissue oxygenation index (TOI) employing spatial resolved spectroscopy (SRS) over the left and right frontal hemisphere. Mean blood pressure (MBP) and heart rate (HR) were measured continuously. Nine young healthy volunteers (mean age 23) were included in the analysis. Significant task related changes were observed in both the NIRS and systemic signals during the anagram solving with increases in [HbO2] and [HHb] accompanied by changes in MBP and HR. The [HbO2] and [HHb] signals measured over the frontal region were found to have a varying association with the MBP signal across different volunteers. The effect of these systemic changes on measured NIRS signals must be considered