Human brain white matter atlas: identification and assignment of common anatomical structures in superficial white matter

Abstract

Structural delineation and assignment are the fundamental steps in understanding the anatomy of the human brain. The white matter has been structurally defined in the past only at its core regions (deep white matter). However, the most peripheral white matter areas, which are interleaved between the cortex and the deep white matter, have lacked clear anatomical definitions and parcellations. We used axonal fiber alignment information from diffusion tensor imaging (DTI) to delineate the peripheral white matter, and investigated its relationship with the cortex and the deep white matter. Using DTI data from 81 healthy subjects, we identified nine common, blade-like anatomical regions, which were further parcellated into 21 subregions based on the cortical anatomy. Four short association fiber tracts connecting adjacent gyri (U-fibers) were also identified reproducibly among the healthy population. We anticipate that this atlas will be useful resource for atlas-based white matter anatomical studies.

Figure 1

The ICBM-DTI-81 atlas, hand-segmented DWM structures, and SWM. (A): The ICBM-152 atlas used as a target image to register the DTI data from 81 normal subjects. (B): The ICBMDTI-81 atlas, which was created by linearly averaging the normative DTI data. The hand-segmented WM parcellation map (WMPM) is superimposed. (C): Probabilistic WM map. (D): A 3D view of the WMPM representing the anatomy of the DWM. (E) and (F): 3D views of the SWM, defined by 0.6 white matter probability. Figures_[S21] A-D and the WMPM are from our previous publication (Mori et al., 2008b) and are presented in this figure to help visualize the relationship with the SWM.

Figure 2

Nine blade-like structures (blades) defined by different level of the white matter probability in the SWM; A: 60%, B: 70%, C: 80%, and D: 90%. The blades are: superior frontal blade (SF, purple); middle frontal blade (MF, light green); inferior frontal blade (IF, deep green); pre-central blade (PrC, yellow); post-central blade (PoC, blue); superior parietal blade (SP, brown); parieto-temporal blade (PT, red); temporal blade (Tmp, ochre); and occipital blade (OC, light blue).

Figure 3

Results of nine blade identifications in five individual brains. The color assignment is the same as Figure 2.

Figure 4

Comparison of the blade and cortical structures. (A) – (C): Nine blade-like structures (blades) viewed from 3 different angles. (D) – (F): The probabilistic cortical parcellation results obtained from 40 subjects (LPBA40), labeled by the name of gyri. Abbreviations are: SFG, superior frontal girus; MFG, middle frontal girus; IFG, inferior frontal girus; PrCG, pre-central girus; PoCG, post-central girus; SPG; superior parietal girus; SMG, supramarginal girus; AG, angular girus; STG; superior temporal girus; MTG, middle temporal girus; ITG, inferior temporal girus; SOG, superior occipital girus; MOG, middle occipital girus; IFG, inferior occipital girus. The names of the gyri are color-coded based on the color assignment of the blades.

Figure 5

Inter-blade connectivity studies with tractography. (A): Overall fiber structures in the SWM. In most of the blade-like structures, the fiber orientation is aligned along the radial orientation and intra-blade fibers could not be located. (B): Results of inter-blade tract reconstruction. The four short association fibers identified in this study are: frontal short association fiber (yellow); fronto-central short association fibers (green); central short association fibers (red); and parietal short association fibers (blue) . The one long association fiber, the parieto-temporal long association fiber, is shown in purple. (C): Detailed views of the four short association fibers in the left side; the arrow indicates the orientation of the front of the brain.

Figure 6

Locations of the four short association fibers in the ICBM-DTI-81 atlas (ICBM-152 coordinates). The yellow (1), green (2), red (3), and blue (4) arrows indicate the locations of the frontal, fronto-central, central, and parietal association fibers, respectively. The Y and Z slice locations are defined by the distance (mm) from the anterior commissure.

Figure 7

Identification of the four short association fibers in individual brains. Results from five normal individuals, not included in the ICBM-DTI-81, are shown. The color assignment is the same as Fig. 5.