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Combined DTI Tractography and Functional MRI Study of the Language Connectome in Healthy Volunteers: Extensive Mapping of White Matter Fascicles and Cortical Activations.

Vassal F, Schneider F, Boutet C, Jean B, Sontheimer A, Lemaire JJ - PLoS ONE (2016)

Bottom Line: Eight putative WM fascicles for language were probed using a deterministic DTI-FT technique: the arcuate fascicle (AF), superior longitudinal fascicle (SLF), uncinate fascicle (UF), temporo-occipital fascicle, inferior fronto-occipital fascicle (IFOF), middle longitudinal fascicle (MdLF), frontal aslant fascicle and operculopremotor fascicle.WM fascicle terminations were also observed beyond fMRI-confirmed language areas and reached numerous cortical areas involved in different functional brain networks.These findings suggest that the reported WM fascicles are not exclusively involved in language and might be related to other cognitive functions such as visual recognition, spatial attention, executive functions, memory, and processing of emotional and behavioral aspects.

View Article: PubMed Central - PubMed

Affiliation: IGCNC (Image-Guided Clinical Neuroscience and Connectomics), EA 7282, Unité de Formation et de Recherche Médecine, Université d'Auvergne, Clermont-Ferrand, France.

ABSTRACT
Despite a better understanding of brain language organization into large-scale cortical networks, the underlying white matter (WM) connectivity is still not mastered. Here we combined diffusion tensor imaging (DTI) fiber tracking (FT) and language functional magnetic resonance imaging (fMRI) in twenty healthy subjects to gain new insights into the macroscopic structural connectivity of language. Eight putative WM fascicles for language were probed using a deterministic DTI-FT technique: the arcuate fascicle (AF), superior longitudinal fascicle (SLF), uncinate fascicle (UF), temporo-occipital fascicle, inferior fronto-occipital fascicle (IFOF), middle longitudinal fascicle (MdLF), frontal aslant fascicle and operculopremotor fascicle. Specific measurements (i.e. volume, length, fractional anisotropy) and precise cortical terminations were derived for each WM fascicle within both hemispheres. Connections between these WM fascicles and fMRI activations were studied to determine which WM fascicles are related to language. WM fascicle volumes showed asymmetries: leftward for the AF, temporoparietal segment of SLF and UF, and rightward for the frontoparietal segment of the SLF. The lateralization of the AF, IFOF and MdLF extended to differences in patterns of anatomical connections, which may relate to specific hemispheric abilities. The leftward asymmetry of the AF was correlated to the leftward asymmetry of fMRI activations, suggesting that the lateralization of the AF is a structural substrate of hemispheric language dominance. We found consistent connections between fMRI activations and terminations of the eight WM fascicles, providing a detailed description of the language connectome. WM fascicle terminations were also observed beyond fMRI-confirmed language areas and reached numerous cortical areas involved in different functional brain networks. These findings suggest that the reported WM fascicles are not exclusively involved in language and might be related to other cognitive functions such as visual recognition, spatial attention, executive functions, memory, and processing of emotional and behavioral aspects.

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Overall display of the white matter fascicles.Display of the eight white matter fascicles systematically reconstructed within the left (left column) and right (right column) hemispheres (20 healthy subjects). Color code: green = arcuate fascicle; turquoise = frontoparietal segment of the superior longitudinal fascicle; light blue = temporoparietal segment of the superior longitudinal fascicle; red = uncinate fascicle; orange = temporo-occipital fascicle; yellow = inferior fronto-occipital fascicle; purple = middle longitudinal fascicle; blue = frontal aslant fascicle; pink = operculopremotor fascicle.
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pone.0152614.g004: Overall display of the white matter fascicles.Display of the eight white matter fascicles systematically reconstructed within the left (left column) and right (right column) hemispheres (20 healthy subjects). Color code: green = arcuate fascicle; turquoise = frontoparietal segment of the superior longitudinal fascicle; light blue = temporoparietal segment of the superior longitudinal fascicle; red = uncinate fascicle; orange = temporo-occipital fascicle; yellow = inferior fronto-occipital fascicle; purple = middle longitudinal fascicle; blue = frontal aslant fascicle; pink = operculopremotor fascicle.

Mentions: We successfully reconstructed the eight WM fascicles bilaterally in all 20 healthy subjects, thus giving a total of 320 WM fascicles (Fig 4). The cortical terminations of each WM fascicle within the left and right hemispheres are reported in Table 3 along with their percent occurrences. Broadly, we observed an asymmetrical representation of WM fascicles, with different connection patterns (i.e. whole cortical territories reached by the fiber terminations) within the left and right hemispheres (intra-subject variability) as well as between subjects. The most frequent connection patterns are reported in Table 4. Three WM fascicles showed standout asymmetries: (1) AF showed predominant direct connections between Broca’s and Wernicke’s areas in the left hemisphere (100% of subjects) but not in the right (only 40%); (2) IFOF showed prominent connections with the SPL in the right hemisphere (45% of subjects) but not in the left (0%); (3) MdLF showed prominent connections with the SPL in the right hemisphere (55% of subjects) but not in the left (only 15%), and connections with the AG were more prevalent in the left hemisphere (95%) than the right (65%). The whole-brain connectivity of the eight WM fascicles is further discussed in S1 Text.


Combined DTI Tractography and Functional MRI Study of the Language Connectome in Healthy Volunteers: Extensive Mapping of White Matter Fascicles and Cortical Activations.

Vassal F, Schneider F, Boutet C, Jean B, Sontheimer A, Lemaire JJ - PLoS ONE (2016)

Overall display of the white matter fascicles.Display of the eight white matter fascicles systematically reconstructed within the left (left column) and right (right column) hemispheres (20 healthy subjects). Color code: green = arcuate fascicle; turquoise = frontoparietal segment of the superior longitudinal fascicle; light blue = temporoparietal segment of the superior longitudinal fascicle; red = uncinate fascicle; orange = temporo-occipital fascicle; yellow = inferior fronto-occipital fascicle; purple = middle longitudinal fascicle; blue = frontal aslant fascicle; pink = operculopremotor fascicle.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4814138&req=5

pone.0152614.g004: Overall display of the white matter fascicles.Display of the eight white matter fascicles systematically reconstructed within the left (left column) and right (right column) hemispheres (20 healthy subjects). Color code: green = arcuate fascicle; turquoise = frontoparietal segment of the superior longitudinal fascicle; light blue = temporoparietal segment of the superior longitudinal fascicle; red = uncinate fascicle; orange = temporo-occipital fascicle; yellow = inferior fronto-occipital fascicle; purple = middle longitudinal fascicle; blue = frontal aslant fascicle; pink = operculopremotor fascicle.
Mentions: We successfully reconstructed the eight WM fascicles bilaterally in all 20 healthy subjects, thus giving a total of 320 WM fascicles (Fig 4). The cortical terminations of each WM fascicle within the left and right hemispheres are reported in Table 3 along with their percent occurrences. Broadly, we observed an asymmetrical representation of WM fascicles, with different connection patterns (i.e. whole cortical territories reached by the fiber terminations) within the left and right hemispheres (intra-subject variability) as well as between subjects. The most frequent connection patterns are reported in Table 4. Three WM fascicles showed standout asymmetries: (1) AF showed predominant direct connections between Broca’s and Wernicke’s areas in the left hemisphere (100% of subjects) but not in the right (only 40%); (2) IFOF showed prominent connections with the SPL in the right hemisphere (45% of subjects) but not in the left (0%); (3) MdLF showed prominent connections with the SPL in the right hemisphere (55% of subjects) but not in the left (only 15%), and connections with the AG were more prevalent in the left hemisphere (95%) than the right (65%). The whole-brain connectivity of the eight WM fascicles is further discussed in S1 Text.

Bottom Line: Eight putative WM fascicles for language were probed using a deterministic DTI-FT technique: the arcuate fascicle (AF), superior longitudinal fascicle (SLF), uncinate fascicle (UF), temporo-occipital fascicle, inferior fronto-occipital fascicle (IFOF), middle longitudinal fascicle (MdLF), frontal aslant fascicle and operculopremotor fascicle.WM fascicle terminations were also observed beyond fMRI-confirmed language areas and reached numerous cortical areas involved in different functional brain networks.These findings suggest that the reported WM fascicles are not exclusively involved in language and might be related to other cognitive functions such as visual recognition, spatial attention, executive functions, memory, and processing of emotional and behavioral aspects.

View Article: PubMed Central - PubMed

Affiliation: IGCNC (Image-Guided Clinical Neuroscience and Connectomics), EA 7282, Unité de Formation et de Recherche Médecine, Université d'Auvergne, Clermont-Ferrand, France.

ABSTRACT
Despite a better understanding of brain language organization into large-scale cortical networks, the underlying white matter (WM) connectivity is still not mastered. Here we combined diffusion tensor imaging (DTI) fiber tracking (FT) and language functional magnetic resonance imaging (fMRI) in twenty healthy subjects to gain new insights into the macroscopic structural connectivity of language. Eight putative WM fascicles for language were probed using a deterministic DTI-FT technique: the arcuate fascicle (AF), superior longitudinal fascicle (SLF), uncinate fascicle (UF), temporo-occipital fascicle, inferior fronto-occipital fascicle (IFOF), middle longitudinal fascicle (MdLF), frontal aslant fascicle and operculopremotor fascicle. Specific measurements (i.e. volume, length, fractional anisotropy) and precise cortical terminations were derived for each WM fascicle within both hemispheres. Connections between these WM fascicles and fMRI activations were studied to determine which WM fascicles are related to language. WM fascicle volumes showed asymmetries: leftward for the AF, temporoparietal segment of SLF and UF, and rightward for the frontoparietal segment of the SLF. The lateralization of the AF, IFOF and MdLF extended to differences in patterns of anatomical connections, which may relate to specific hemispheric abilities. The leftward asymmetry of the AF was correlated to the leftward asymmetry of fMRI activations, suggesting that the lateralization of the AF is a structural substrate of hemispheric language dominance. We found consistent connections between fMRI activations and terminations of the eight WM fascicles, providing a detailed description of the language connectome. WM fascicle terminations were also observed beyond fMRI-confirmed language areas and reached numerous cortical areas involved in different functional brain networks. These findings suggest that the reported WM fascicles are not exclusively involved in language and might be related to other cognitive functions such as visual recognition, spatial attention, executive functions, memory, and processing of emotional and behavioral aspects.

Show MeSH