FIG 3. NIRS measurements of evoked CBO changes in the motor cortex on the lesion side before and after tumor resection. The ordinate indicates the concentration changes of the NIRS parameters in arbitrary units. The horizontal thick bar denotes the task period (40 seconds). Preoperative NIRS demonstrated a decrease of deoxy-Hb associated with increases of oxy-Hb and total-Hb (left), which is consistent with the physiological basis of BOLD contrast. Postoperative NIRS (2 days and 22 days after surgery) demonstrated similar increases of oxy-Hb and total-Hb, indicating the occurrence of rCBF increases in response to neuronal activation (center and right). Two days after surgery, however, deoxy-Hb increased from the baseline during the entire course of the task, whereas deoxy-Hb did not change significantly 22 days after surgery. These alterations in deoxy-Hb correlated with the changes in size of the negative BOLD signal areas in the motor cortex on the lesion side (Fig 2A).