(A) Left: The 473-nm laser beam visualized in fluorescent medium. Right: Schematic illustration of the OG beam centered on a diving arteriole. The full width at half maximum (FWHM = 230 μm) of the beam is superimposed on a mean intensity projection (MIP) of a 2-photon image stack of FITC-labeled vasculature through the top 116 μm. Individual images were acquired every 3 μm. Red arrows indicate the direction of flow in the arteriole. (B) Simulated spatial profile of the OG beam in cortical tissue. Top: Color-coded photon density. Bottom: Photon density as a function of depth (z-axis) and as a function of the radial distance (r) at three different depths (75, 225, and 425 μm). (C) Left: An example vascular MIP throughout the top 180 μm. Right: the measurement plane 180 μm deep including intravascular FITC (green) and SR101-labeled astrocytes (red). The white line indicates the scanning trajectory used for diameter measurements in (D). (D) Diameter change time-courses of the diving arteriole in (C) in response to the sensory and OG stimuli (sensory: black, average of 10 stimulus trials; OG: red, single trial). (E) Each thin gray line shows an average response within one subject. Across-subject average is overlaid in thick black. Error bars indicate SE across subjects. The mean peak dilation, peak constriction, and the ratio of peak dilation to peak constriction are shown in the inset. Error bars indicate SE across subjects. (F) Averaged dilation time-courses grouped by depth. An expanded view of the initial 4 s after the stimulus onset is shown. The depth in μm is indicated on the left. Error bars indicate SE across subjects. (G) Dilation onset (black) and time-to-peak (red) as a function of depth. Conventions are as in Figure 1C. (H) As in (G) for constriction onset (see text).