Prefrontal hypooxygenation during language processing assessed with near-infrared spectroscopy.

Near-infrared spectroscopy (NIRS) is a noninvasive optical method which allows in vivo measurements of relative concentrations of oxygenated (O2Hb) and desoxygenated hemoglobin (HHb). It has been successfully applied to assess the blood oxygenation changes during cerebral ischemia in man. An interesting application of NIRS is the investigation of regional cerebral blood oxygenation during physiological brain functions. In the present study, left and right anterior prefrontal brain areas of 10 healthy subjects were investigated with 2-channel NIRS during language processing (reading aloud). Nonverbal visual perception (picture observation) was performed as a control condition. Compared to the respective baseline conditions, a significant HHb increase and an O2Hb decrease as a trend were found during language processing but not during the nonverbal perceptual task, and no hemispheric differences were found. The metabolic activation patterns differed significantly between the tasks indicating the changes due to the language-related efforts but not to visual perception. Based on previous findings of metabolic brain imaging studies the results are best explained as a complementary phenomenon consisting in relative anterior prefrontal hypoperfusion due to a blood volume redistribution which favors language-related temporal areas.