Frontal activation during a verbal-fluency task as measured by near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is an optical method which allows non-invasive in vivo measurements of concentration changes of oxygenated hemoglobin (O(2)Hb) and deoxygenated hemoglobin (HHb) in brain tissue. The present study investigated the blood oxygenation changes that were associated with the execution of the Verbal-Fluency Test (VFT) in left and right prefrontal brain areas of 14 healthy subjects by means of NIRS. During the VFT, subjects were required to pronounce as many nouns as possible beginning with the letters "A," "F," and "S." Compared to a baseline resting condition, we found a significant increase of O2Hb (left hemisphere: baseline, 1.2+/-1.1microm; VFT(letterS), 3.56+/-2.02microm; right hemisphere: baseline, 1.26+/-1.08microm; VFT(letterS), 3.67+/-2.03microm) and a significant decrease of HHb (left hemisphere: baseline, -0.21+/-0.59microm; VFT(letterS), -0.67+/-0.60microm; right hemisphere: baseline, -0.29+/-0.53microm; VFT(letterS), -0.68+/-0.44microm) during the execution of the VFT over both hemispheres. No lateralization effects were observed. The results confirm that NIRS is suitable for the measurement of blood oxygenation changes in frontal brain areas that are associated with cognitive tasks.