Fig 4. Regression analysis of the HRF metrics, with the M and P responses pooled together for the analysis. TTP versus percentage signal change (A) shows no statistically significant correlation, with r² = 0.06408 and a slope that is not significantly different from 0 (slope = 0.453, P = .2557). The FWHM of the HRF is positively correlated with the percentage signal change (B), with r² = 0.3114 and a slope that is significantly different from 0 (slope = 1.977, P = .0070). The FWHM of the HRF is also positively correlated with the TTP (C), with r² = 0.2115 and a slope that is significantly different from zero (slope = 0.9105, P = .0313).