Figure 2. Comparison of the spatio-temporal characteristics of sensory-evoked changes in oxidative metabolism and blood flow.

Left Panel: Activity maps obtained in rat whisker barrel cortex upon stimulation of two distinct whiskers (C2, top; D2, bottom, see insets for the corresponding somatotopy) from flavoprotein autofluorescence (AF) (left) and laser speckle imaging (LSI) (right). The color code depicts the percentage of signal increase from baseline. The horizontal and vertical lines facilitate the comparison across sub-panels, showing that the spatial pattern of the blood flow response was considerably less focal than that of the changes in oxidative metabolism, although their peaks of the activation roughly co-localized. Right Panel: Time course of AF and LSI responses. (A) AF (blue) and LSI (red) depict time courses from a single trial (2 s stimulation of vibrissa C2, average over area of >50% peak activation). Data points are represented by markers. Solid lines are fitted gamma curves. The shaded rectangle shows the stimulation. (B) Signal-averaged time course (20 trials). Note the excellent agreement between the single trial (A) and the average data (B). (C) Grand average (50% of the peak activation of C2 and D2 stimulations) fitted gamma curves (thick lines) ±1 standard deviation (thin lines) of the AF (blue) and LSI (red) responses. (D) Mean time course of the size of the activated area for AF (blue) and LSI (red). Shown are the areas with >25% (solid), >50% (dashed), and >75% (dotted) of the peak response. Note that the active area determined from AF is considerably smaller than that obtained from LSI. In addition, onset of the latter signal is delayed relative to the former, supporting the concept that the oxidative metabolism response is faster and more localized to neuronal activation than the blood flow response (with permission from: Weber et al., 2004).