Figure 2.

Spatial registration and analysis methods. The 3D spatial locations of all sampled sites in the MFP region were estimated with a custom-built stereoscopic x-ray imaging system. The 3D locations were registered (A, left) to a high-resolution (500 μm) anatomical MRI. Anatomical variability before (gray cortical ribbon; left, inset) and after neurophysiological recordings (blue cortical ribbon, left inset) can result in subpixel registration error. To improve the overall accuracy of the registration, nonlinear registration using FMRIB's FNIRT registration tool was performed (A, right), and the resulting transform was applied to the estimated positions of the recording sites (A, inset represents the overall spatial movement of sites projected in a 2D slice). The spatial position of each recording site was projected to the closest orthogonal node of a high-resolution mid-layer mesh of the cortical surface (B, left). Sites that moved a distance >1250 μm from their original 3D position to the 2D surface manifold were excluded (B, right, gray dots) from further analysis. The area for analysis was selected by choosing the approximate center of the fMRI MFP activation in each monkey and including all nodes on the cortical mesh within a maximal geodesic radius (7 mm). The radius was chosen to be approximately the greatest distance that would not encroach into face-selective activations at posterior (PL) or anterior (AL) locations.