Comparison of SI cortical responses evoked by low- and high-amplitude 25 Hz flutter stimuli. A: View of the somatosensory cortex with the lateral end of the central sulcus (CS) at the top. Stimulus location is shown on the hand figurine. B: Optical response of the SI to the low-amplitude (50 μm peak-to-peak) flutter. Shown is the light absorbance image ([poststimulus image – prestimulus image]/prestimulus image) averaged across 20 stimulus trials, and in each trial across 3 poststimulus images taken during the 5–7 sec interval of continuous stimulation. Increased light absorbance is indicated by darker shading. C: Optical response of SI to the high-amplitude (400 μm) flutter. D & E: Magnified 3-D surface maps of OIS magnitude in the responding cortical region. F & G: Orientation of segmentation in the M-L dimension (F) and the A-P dimension (G). H, I, L & M: Spatiointensive histograms generated via segmentation of areas indicated in F & G for two different stimulus conditions. J, K, N & O: Periodograms showing the spatial frequency composition of the spatiointensive histograms. Note change in the power spectra with the change in stimulus amplitude in data sampled in the A-P orientation, but not in the M-L orientation.