Fig. 5.

TD-DCS measures on a rat during two periods of normocapnia (blue and green lines) and hypercapnia (red line). (a) TPSF measured during normocapnia (blue and green) and hypercapnia. The curves are overlapping, suggesting negligible changes in tissue scattering and absorption with hypercapnia (red). The shaded areas span the range of the 37 gates 48 ps wide shifted 12 ps each. The gray shaded area indicates the gate at the border between the early (light blue) and late (pink) gates. (b) Slope of the field autocorrelation functions for the 37 gates as a function of the path length during normocapnia (blue and green symbols) and hypercapnia (red symbols). The open circles correspond to the 13 early gates; the closed circles correspond to the 24 late gates. The decay rate is much higher for late gates, and assuming a constant scattering coefficient across tissue layers, by using Eq. (2), we find the BF is three times higher in the brain than in the scalp and skull. When comparing the normocapnia and hypercapnia periods, the decay rate for early gates does not change significantly; instead, the decay rate for late gates increases with hypercapnia.