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Comparative Study
. 2009 Apr;19(4):777-85.
doi: 10.1093/cercor/bhn124. Epub 2008 Jul 31.

Delineation of the middle longitudinal fascicle in humans: a quantitative, in vivo, DT-MRI study

Nikos Makris  1 , George M Papadimitriou, Jonathan R Kaiser, Scott Sorg, David N Kennedy, Deepak N Pandya
Affiliations
Comparative Study

Delineation of the middle longitudinal fascicle in humans: a quantitative, in vivo, DT-MRI study

Nikos Makris et al. Cereb Cortex. 2009 Apr.

Abstract

Experimental and imaging studies in monkeys have outlined various long association fiber bundles within the temporoparietal region. In the present study the trajectory of the middle longitudinal fascicle (MdLF) has been delineated in 4 human subjects using diffusion tensor magnetic resonance imaging segmentation and tractography. The MdLF seems to extend from the inferior parietal lobule (IPL), specifically the angular gyrus, to the temporal pole remaining within the white matter of the superior temporal gyrus (STG). Comparison of the superior longitudinal fascicle II-arcuate fascicle (SLF II-AF) with the MdLF in the same subjects revealed that MdLF is located in a medial and caudal position relative to SLF II-AF and that it extends more rostrally. Given the location of MdLF between the IPL (angular gyrus) and the STG, it is suggested that MdLF could have a role in language and attention functions.

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Figures

Figure 1.
Figure 1.
The upper panel shows 4 representative coronal sections (A–D) composed of the principal eigenvector maps (PEMS). A lateral view of the hemisphere in the center of the figure depicts the rostrocaudal level of the selected sections (A–D). These sections show the course and topography of the MdLF within the white matter of the STG (interrupted circles in A and D). The lower row shows T2-EPI sections corresponding to the DT-MRI of the upper panel to highlight the topographic anatomy and location of the MdLF shown in green on both sides. On the left side of each panel the mirror images of the coronal section on the right are depicted to show the parcellation of specific cortical regions. For this, the individual brain was segmented and parcellated using the Center for Morphometric Analysis neuroanatomic framework (Caviness et al. 1996; Filipek et al. 1994). The inset (a) on the left side of the middle row is a magnification of the STG (T1 or STG) showing the MdLF (green voxels) occupying a large portion of the white matter of STG. The colored sphere in the middle row shows the color-coding scheme adopted in the DT-MRI data analysis. Red is right-left, green is anterior–posterior and blue is superior–inferior orientations. Abbreviations: CC: corpus callosum; CGa: cingulate gyrus, anterior; CGp: cingulate gyrus, posterior; CO: central operculum; F1: superior frontal gyrus; F2: middle frontal gyrus; F3o: inferior frontal gyrus, pars opercularis; FO: frontal operculum; H1: Heschl's gyrus; INS: insula; PHa: parahippocampal gyrus, anterior; PHp: parahippocampal gyrus, posterior; PO: parietal operculum; POG: postcentral gyrus; PP: planum polare; PRG: precentral gyrus; PT: planum temporale; SGa: supramarginal gyrus, anterior; SMC: supplementary motor cortex; T1a: STG, anterior; T1p: STG, posterior; T2a: middle temporal gyrus, anterior; T2p: middle temporal gyrus, posterior; T3a: inferior temporal gyrus, anterior; T3p: inferior temporal gyrus, posterior; TFa: temporal fusiform, anterior; TFp: temporal fusiform, posterior; L: left; R: right.
Figure 2.
Figure 2.
3D renderings showing the trajectory of the stem portion of the MdLF as resulted from DT-MRI–based segmentation in the 8 hemispheres (8 hemispheres, 1R through 4L) of all the subjects analyzed in the study in a lateral view. The MdLF is shown in green projected on the background of a parasagittal T2-EPI section. Abbreviations: L: left; R: right.
Figure 3.
Figure 3.
Composite representations (A–D) of sagittal (A and B), axial (C), and coronal (D), planes of the MdLF in 4 subjects in the Talairach space. The anterior commissure corresponds to 0 mm and the posterior commissure to –24 mm. For each individual subject each MdLF has been color-coded as shown in the inset on the right of each Talairach plane. In the inset d are listed the Talairach coordinates (X = medio-lateral axis; Y = anterior–posterior axis; Z = vertical axis) of the center of mass of the 4 subjects shown in coronal plane D. These are 50.24, −13, −8.43 and −53.1, −13, −8.18 for subject 1; 54.11, −13, −8.93 and −49.46, −13, −6.04 for subject 2; 52.28, −13, −3.29, and −46.2, −13, −4.05 for subject 3; 50.47, −13, −2.02 and −47.17, −13, 0.82 for subject 4; note that in (A), (B), (C), and (D) the orientation of the tensors are coaligned with the slice-to-slice progression of the centers of mass.
Figure 4.
Figure 4.
The trajectories of the MdLF are shown on the parasagittal profile in 4 subjects (8 hemispheres, 1R through 4L) as resulted from DT-MRI–based tractography. The MdLF is shown in green contrasting on the background of a midsagittal T2-EPI section. (A and B) The tractographic results of 2 different approaches. (A) The entire segmented stem ROI was used as a seed for the tractographic delineation of MdLF. (B) A single coronal section (coronal slice −13 of Fig. 3D) was used to place the seed within the STG white matter. The Talairach coordinates of this seed are given in Figure 3D. Abbreviations: L: left; R: right.
Figure 5.
Figure 5.
The MdLF and the cortical regions it connects are shown on a parasagittal (A) and an axial profile (B) in a representative subject. MdLF resulted from DT-MRI–based tractography and the cortical regions of interest were derived using cortical parcellation (Caviness et al. 1996). MdLF fibers are shown within the cortex of the STG (T1a and T1p) in coronal sections (C) and (D). MdLF fibers within the cortex of the angular gyrus are shown in coronal (E). Abbreviations: AG: angular gyrus; T1a: STG, anterior; T1p: STG, posterior; L: left; R: right.
Figure 6.
Figure 6.
Comparison of trajectories of SLF II-AF shown in yellow and MdLF shown in green on a T2-EPI sagittal profile using DT-MRI tractography in the 4 subjects (8 hemispheres, 1R through 4L) that participated in this study. Note that MdLF is quite distinct from SLF II-AF and extends from the angular gyrus to the temporal pole within the STG. It is worth pointing out that MdLF remains medial to SLF II-AF and extends more caudally.
Figure 7.
Figure 7.
Topographic anatomy of MdLF and SLF II-AF connections based on tractographic results of an exemplar MdLF case in 3D is shown in panels A-F (see text for details). Abbreviations: AGa: angular gyrus, anterior; AGp: angular gyrus, posterior; T1a: STG, anterior; T1p: STG, posterior; L: left; R: right.
Figure 8.
Figure 8.
This figure compares the AF as described by Catani et al. (2005) (including an anterior, a posterior and a long segment) (A), with the trajectories of SLF II-AF (case 4L of Fig. 6) (B) and MdLF (C) of the present study (case 4L of Fig. 6). The SLF II-AF and MdLF are shown in (D). Note that according to the present study the MdLF is a distinct fiber pathway from the SLF II-AF.
See this image and copyright information in PMC

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