Absorbance time course and anatomical registration in SI. A) Green filter image of SI cortex in vivo, used for anatomical registration of OIS images. B&C) Resulting OIS image obtained from averaging across 10 experimental trials and then summing frames taken from the time of stimulus onset to 5 seconds after stimulus offset: B) at stimulus amplitude 50 μm, C) at 400 μm. Dashed circles enclose the ROI within SI. Bottom left) Plot of the averaged absorbance. Arrows indicate time of stimulus onset (1s) and stimulus offset (11s). Absorbance values within the enclosed ROI were averaged and plotted at each amplitude as a function of time.