Gravity-induced loss of consciousness (G-LOC), which is presumably caused by a reduction of cerebral blood flow resulting in a decreased oxygen supply to the brain, is a major threat to pilots of high-performance fighter aircraft. The application of cerebral near-infrared spectroscopy (NIRS) to monitor gravity-induced cerebral oxygenation debt has generated concern over potential sources of extracranial contamination. The recently developed NIR spatially-resolved spectroscopy (SRS-NIRS) has been confirmed to provide frontal cortical tissue hemoglobin saturation (Tissue Oxygenation Index, TOI). In this study, we monitored the TOI and the standard NIRS measured chromophore concentration changes of oxygenated hemoglobin (O₂Hb) and deoxygenated hemoglobin (HHb) in 141 healthy male pilots during various levels of +Gz (head-to-foot inertial forces) exposure to identify the differences between subjects who lose consciousness and those who do not during high Gz exposure. Subjects were exposed to 7 centrifuge profiles, with Gz levels from 4 Gz to 8 Gz and an onset rate from 0.1 to 6.0 Gz / sec. The SRS-NIRS revealed an approximate15% decrease in the TOI in G-LOC. The present study also demonstrated the TOI to be a useful variable to evaluate the effect of the anti-G protection system. However, there was no significant difference found between conditions with and without G-LOC in subjects with terminated G exposure. Further studies which elucidate the mechanism(s) behind the wide variety of individual differences may be needed for a method of G-LOC prediction to be effectively realized.