Automatic parcellation of human cortical gyri and sulci using standard anatomical nomenclature

Abstract

Precise localization of sulco-gyral structures of the human cerebral cortex is important for the interpretation of morpho-functional data, but requires anatomical expertise and is time consuming because of the brain's geometric complexity. Software developed to automatically identify sulco-gyral structures has improved substantially as a result of techniques providing topologically correct reconstructions permitting inflated views of the human brain. Here we describe a complete parcellation of the cortical surface using standard internationally accepted nomenclature and criteria. This parcellation is available in the FreeSurfer package. First, a computer-assisted hand parcellation classified each vertex as sulcal or gyral, and these were then subparcellated into 74 labels per hemisphere. Twelve datasets were used to develop rules and algorithms (reported here) that produced labels consistent with anatomical rules as well as automated computational parcellation. The final parcellation was used to build an atlas for automatically labeling the whole cerebral cortex. This atlas was used to label an additional 12 datasets, which were found to have good concordance with manual labels. This paper presents a precisely defined method for automatically labeling the cortical surface in standard terminology.

Figure 1. Inflated view of the manual parcellation of one hemisphere of the Training set

Numerical indices refer to the anatomical regions defined in Table 1: superior (Sup), anterior (Ant), lateral (Lat), posterior (Post), medial (Med), and inferior views are provided. Both gyral and sulcal cortices are visible on this representation. The lateral fossa is displayed on a separate lateral view (Lat. fossa) oriented to better show: the insula (17: central S. and long insular G., 18: short insular G) limited by the circular sulcus of the insula (47: ant, 48: inf, 49: sup), and the superior aspect of the superior temporal gyrus (35: planum polare, 33: transverse temporal G., 74: transverse temporal S, 36: planum polare). The inflated lateral views of all 12 subjects are shown in supplementary figures 3A and 3B; the inflated medial views in supplementary figures 4A and 4B.

Figure 2. pial view of the manual parcellation of one hemisphere of the Training set

Numerical indices refer to the anatomical regions defined in Table 1: superior (Sup), anterior (Ant), lateral (Lat), posterior (Post), medial (Med), and inferior views are provided. Notice that the sulcal cortex is mostly invisible on this representation of the cortical surface. The pial lateral views of all 12 subjects are shown in supplementary figures 5A and 5B; the pial medial views in supplementary figures 6A and 6B.

Figure 3. CI values for each of the 74 labels across the 12 subjects

A CI after boundary correction (CI_C) was computed for right and left hemisphere across the 12 subjects for each of the 74 anatomical labels. Results are presented in increasing values of CI.

Figure 4. Plot of the area and CIc

The average area was plotted against the average concordance index after boundary correction (CIc) for each of the 74 parcellation units in the right (rh) and left (lh) hemispheres.