Zhongming Liu1, Cristina Rios1, Lin Yang1, Nanyin Zhang2,3, Wei Chen2,3, Bin He1
1Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA; 2Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA; 3Department of Radiology, University of Minnesota Medical School, Minneapolis, MN, USA
The BOLD nonlinearity may reflect a nonlinear neural response to stimuli and/or a nonlinear vascular response to neural activity. To pinpoint the origin of the BOLD nonlinearity, we investigated the nonlinear effects of neural and vascular responses to sustained visual stimuli with variable temporal frequency ranging from 1/6 to 25 Hz. Using scalp EEG, we found the neural response nonlinearity existed only at very short ISI (<200 ms). Using fMRI, we observed the BOLD nonlinearity for ISI between 0.25 and 4 sec. Such nonlinearity has an exclusively vascular origin and is attributed to the vascular refractory effect instead of the vascular saturation effect.