FIG. 1.

The hemodynamic response for short (2 s) and long (16 s) whisker C1 stimulation. A: image montage for total blood volume (Hbt), oxyhaemoglobin (HbO₂) and deoxyhemoglobin (Hbr) for short stimulation of whisker C1. The scale bar represents the micromolar change from baseline. Stimulation occurs at time 0. Both Hbt and HbO₂ increase after stimulus onset, Hbr decreases (Hbr has been inverted so decreases appear as red regions). The Hbt increase is localized to the area surrounding barrel C1 and a branch of the middle cerebral artery lying anterior to it. The HbO₂ response is less localized than Hbt and after 3.5 s is localized to the draining veins. The Hbr decrease is also localized to the draining veins. B: image montage for Hbt, HbO₂ and Hbr for long stimulation of whisker C1. The onset responses for the long duration stimulation are similar to the short duration albeit at a slightly larger magnitude. For Hbt as the arterial response returns to baseline after 3 s a very localized region remains for the duration of the stimulation period, that overlies the whisker C1 barrel region. HbO₂ is less localised than Hbt and is biased towards the draining veins and the Hbr decrease remains localized to the draining veins. C: and D: in vivo images of the surface vasculature show the branches of the middle cerebral artery (MCA) and draining veins. E: the relationship of the barrel cortex to the surface vasculature is shown in a combined post mortem image. This post mortem image was fitted to the in vivo image so that the barrels could then be superimposed over the activation maps as a reference (these are shown in the images 4 s after stimulation onset). Scale bar = 500 μm. M, medial; L, lateral; A, anterior; P, posterior.