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Fig 3. The mean percentage changes of BOLD signals as a function of time for the 6 subjects included in this study. Only 4 curves (room air, 3%, 5%, 7%) are shown for better visualization clarity. A, The signal intensity (SI) response shows the ON-OFF fBOLD pattern in response to the visual stimulation, superimposed on hBOLD changes from hypercapnia. Note the gradual decrease of fBOLD amplitude from early to late hypercapnia that is particularly prominent at high concentrations of CO2 inhalation. Furthermore, steady-state fBOLD signals are seen to decrease with increasing CO2 concentration. Posthypercapnic fBOLD amplitude returns to a level similar to the prehypercapnic phase. Min indicates minutes. B, The hBOLD signal intensity changes positively correlate with the inhaled CO2 concentrations. In addition, the time duration to reach steady-state hBOLD level seems to increase with higher hypercapnic perturbations.
