Figure 2.

Generation of the candidate hemodynamic response function (HRF) models. (Top) In the proposed method, the shifted P_ETCO2 waveform was convolved with different HRFs to identify the best approximation of the observed BOLD signal. (Bottom) Three parameters (${\alpha }_1$, ${\beta }_1$, and ${\beta }_2$) were varied in the proposed model, producing 26 candidate HRFs. The response delay (time to peak) is predominantly charged by $\alpha$ (bottom left); The shape variant of the HRF is predominantly charged by ${\beta }_1$ (the maximum; bottom middle) and ${\beta }_2$ (the undershoot; bottom right).