Figure 1. Selectivity of blood vessel dilation to sensory stimuli in species with and without cortical orientation maps.

a, Schematic of cat visual cortex showing the columnar organization of neurons by orientation preference and a pial surface artery with multiple branches penetrating the parenchyma. Different colors of neuronal cell bodies represent their different preferred stimulus orientations. b, Time courses and polar plots (averages of six (upper panel) and eight (lower panel) trials) of the changes in dilation of two layer 2/3 arterioles in cat visual cortex to visual stimulation. Error bands represent s.e.m. and gray bars represent the periods of visual stimulation. In this and subsequent figures, stimuli were gratings that drifted in eight different directions of motion and polar plots are normalized to the maximum response. c, Time course and polar plot of responses from a surface artery in cat (average of four trials). d, Population distribution and median orientation selectivity index (OSI) for parenchymal (n = 79 vessels in 18 cats) and surface (n = 24 vessels in 9 cats) vessels. e, Schematic of rat visual cortex where neurons with different orientation preferences are intermingled. f–g, Time courses and polar plots of responses from two parenchymal arterioles (averages of seven (upper panel) and eight (lower panel) trials) and a surface artery (average of five trials) in rat visual cortex. h, Population distribution and median OSI for parenchymal (n = 16 vessels in 6 rats) and surface (n = 21 vessels in 7 rats) vessels.