SIMULTANEOUS RECORDING OF CEREBRAL BLOOD OXYGENATION CHANGES DURING HUMAN BRAIN ACTIVATION BY MAGNETIC-RESONANCE-IMAGING AND NEAR-INFRARED SPECTROSCOPY

Changes in cerebral blood oxygenation due to functional activation of the primary sensorimotor cortex during a unilateral finger opposition task were simultaneously mapped by deoxyhemoglobin-sensitive magnetic resonance imaging (MRI) and monitored by near-infrared spectroscopy (N IRS). Activation foci along the contralateral central sulcus displayed task-associated increases in MRI signal intensity, indicating a conco mitant decrease of the focal concentration of deoxyhemoglobin. This in terpretation was confirmed by simultaneous reductions in deoxyhemoglob in measured optically. Since observation of the latter effect required exact spatial matching of the MRI-detected activation foci and positi on of the fiber optic bundles (''optodes'') used for transmitting and receiving light, it may be concluded that optical recordings of change s in deoxyhemoglobin during functional challenge probe only a restrict ed brain tissue region. While deoxyhemoglobin responses seen by NIRS w ere smaller for ipsi- than for contralateral finger movements, task-re lated increases in oxyhemoglobin were rather similar between both cond itions and, thus, seem to be less specific. Furthermore, no consistent changes were obtained for total hemoglobin during task performance, p ossibly due to the short timing of the repetitive protocol. In general , results underline, in humans, the hitherto assumed signal physiology for functional brain mapping by oxygenation sensitive MRI and allow a ssessment of both constraints and practicability of functional studies by NIRS.