Figure 1.

Measurement of fine-scale correlation structure. A, V1 vertex mesh and indices. The cortical patch corresponding to striate cortex (area V1) is centered about the calcarine sulcus on the medial aspect of the occipital lobe. V1 was identified by position in surface topology. The two primary axes of striate cortex (AP and SI) are indicated and correspond to the eccentricity and polar angle dimensions of retinotopic organization, respectively. In standard template space, V1 comprises 3091 surface vertices, as outlined on the surface mesh. V1 vertices were indexed as outlined in A (lower right). The selected arrangement was to facilitate visual display of the pattern matrices and has no effects upon the quantitative results of the analyses. B, SI and AP arrangement of vertices. The two panels illustrate the indexing of vertices within area V1 by mapping different shades of color to index values. These color scales demonstrate how the vertices were numbered along 6 discrete bands along the SI dimension (corresponding to polar angle). Within each band, vertices were then numbered along the AP dimension (corresponding to eccentricity). C, Cortical surface distance matrix. The distance along the cortical surface may be calculated for any pair of points within striate cortex. The distances between all possible pairings of vertices are shown as a matrix. The structure seen within the matrix is a consequence of the numbered ordering of the vertices shown in A and B. This structure may be more easily understood by examining the matrices that express distance between points only along the SI or AP directions. D, Calculating the neural pattern matrix. Within the set of indexed V1 vertices, the Pearson's (R) correlation of the resting-state fMRI data between each pair of vertices was obtained. Each pairwise correlation provided one cell of a resulting pattern matrix. The pattern matrix was derived for each subject for both within-hemisphere correlation structure and between-hemisphere correlation structure.