Figure 3. Capillary character of blood volume (CBV) responses, shown by the morphology of high-resolution differential maps obtained by optical imaging.

(A) Image of the cortical vasculature in the primary visual cortex of an anaesthetized macaque. (B, C) Functional maps of ocular dominance columns obtained at 540 and 810 nm, two near-isosbestic wavelengths, at which the contribution of CBV changes dominates the signals. (D) Time course of the mapping signal, showing that the appearance of oximetric maps (obtained at 605 nm, blue trace) slightly precedes that of the CBV maps (obtained at 570 nm, red trace). The larger 570 nm signal was downscaled in the figure by a factor of 4 for display purposes. Inset: Zoom into the first second of the responses. (E) Image of the cortical vasculature in the primary visual cortex of an awake macaque. (F, G) Functional maps of ocular dominance columns obtained at a strongly oximetric wavelength (605 nm) and at an isosbestic wavelength (570 nm) chosen to image CBV signals. Note that (i) the patterns of the blood-volume maps are validated by the oximetric maps, known to reflect the underlying functional architecture; and (ii) the high spatial resolution of the CBV maps strongly suggests that the functional patches can only be of capillary origin. Scale bars: 1 mm. (A–C) Modified from Frostig et al., 1990; (D–G) modified from Vanzetta et al., 2004.