Figure 3.

Electrical stimulation activates a significantly larger region of the cortex. A, The spatial spread was quantified as the average radius of the 70% amplitude contour. The initial frame of activation was used, and the contour was taken from a parametrized sum of Gaussians fit to the VSDI data. B, The size of the contours is similar across whisker deflection velocities (top) and optical light intensity (bottom) but increases dramatically for increasing electrical stimulation current (middle). C, The spatial spread increased significantly more as a function of response amplitude for electrical stimuli (n = 17) than for whisker (n = 12) or optical (n = 4) stimuli.