Absorbance trends surrounding the ROI across five experiments. A) Plots of absorbance and standard deviation averaged across all experiments (n = 5). Plotted absorbances were measured at radial distances between 1 and 1.5 mm away from the center of the ROI (defined earlier). B) Plot of the maximal change in absorbance (solid line) as a function of stimulus amplitude. The linear trend, obtained from averaged absorbance measured within the ROI (dashed line from figure 3) has been simultaneously plotted on the axes to demonstrate the significant differences between the two regions.