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Integrating functional and diffusion magnetic resonance imaging for analysis of structure-function relationship in the human language network.

Morgan VL, Mishra A, Newton AT, Gore JC, Ding Z - PLoS ONE (2009)

Bottom Line: The results showed that different language pathways exhibited different structural and functional connectivity, indicating varying levels of inter-dependence in processing across regions.However, fractional anisotropy was found not to be correlated with functional connectivity along paths connecting either BA and SMA or BA and WA.These findings suggest that structure-function relations in the human language circuits may involve a number of confounding factors that need to be addressed.

View Article: PubMed Central - PubMed

Affiliation: Vanderbilt University Institute of Imaging Science, Nashville, TN, USA. victoria.morgan@vanderbilt.edu

ABSTRACT

Background: The capabilities of magnetic resonance imaging (MRI) to measure structural and functional connectivity in the human brain have motivated growing interest in characterizing the relationship between these measures in the distributed neural networks of the brain. In this study, we attempted an integration of structural and functional analyses of the human language circuits, including Wernicke's (WA), Broca's (BA) and supplementary motor area (SMA), using a combination of blood oxygen level dependent (BOLD) and diffusion tensor MRI.

Methodology/principal findings: Functional connectivity was measured by low frequency inter-regional correlations of BOLD MRI signals acquired in a resting steady-state, and structural connectivity was measured by using adaptive fiber tracking with diffusion tensor MRI data. The results showed that different language pathways exhibited different structural and functional connectivity, indicating varying levels of inter-dependence in processing across regions. Along the path between BA and SMA, the fibers tracked generally formed a single bundle and the mean radius of the bundle was positively correlated with functional connectivity. However, fractional anisotropy was found not to be correlated with functional connectivity along paths connecting either BA and SMA or BA and WA.

Conclusions/significance: These findings suggest that structure-function relations in the human language circuits may involve a number of confounding factors that need to be addressed. Nevertheless, the insights gained from this work offers a useful guidance for continued studies that may provide a non-invasive means to evaluate brain network integrity in vivo for use in diagnosing and determining disease progression and recovery.

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Diagram of DTI tracking procedure.Centroids of BA and WA are shown as gray spheres connected by a dashed black line. The seed plane used for origin of path 2 (BA to WA) normal to the line joining the centroids is shown in green. Examples of tracts connecting regions of interest are illustrated in red.
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pone-0006660-g002: Diagram of DTI tracking procedure.Centroids of BA and WA are shown as gray spheres connected by a dashed black line. The seed plane used for origin of path 2 (BA to WA) normal to the line joining the centroids is shown in green. Examples of tracts connecting regions of interest are illustrated in red.

Mentions: To initiate the adaptive fiber tracking, two circular seed planes were first defined such that they were respectively midway at and perpendicular to the line joining the centroids of BA and SMA of path 1, and that connecting the centroids of BA and WA of path 2 (Figure 2). The seed planes were sufficiently large to intersect all possible fiber pathways connecting two target regions of interest (ROI). A total number of 8000 iterations of fiber tracking were launched from 2000 uniformly sampled seed points in each of the planes (4 per voxel). Fiber tracking proceeded in both directions from the seed planes according to Equations 1–3 above, and was terminated when it reached a point with FA<0.1, or when it reached an ROI. Fibers that connected both target ROIs were stored for further analysis. We note that the purpose of using a small FA value as a termination criterion for the tracking process was to prevent it from entering the regions containing cerebral-spinal fluid, but still permitting it to traverse white matter and gray matter regions.


Integrating functional and diffusion magnetic resonance imaging for analysis of structure-function relationship in the human language network.

Morgan VL, Mishra A, Newton AT, Gore JC, Ding Z - PLoS ONE (2009)

Diagram of DTI tracking procedure.Centroids of BA and WA are shown as gray spheres connected by a dashed black line. The seed plane used for origin of path 2 (BA to WA) normal to the line joining the centroids is shown in green. Examples of tracts connecting regions of interest are illustrated in red.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2721978&req=5

pone-0006660-g002: Diagram of DTI tracking procedure.Centroids of BA and WA are shown as gray spheres connected by a dashed black line. The seed plane used for origin of path 2 (BA to WA) normal to the line joining the centroids is shown in green. Examples of tracts connecting regions of interest are illustrated in red.
Mentions: To initiate the adaptive fiber tracking, two circular seed planes were first defined such that they were respectively midway at and perpendicular to the line joining the centroids of BA and SMA of path 1, and that connecting the centroids of BA and WA of path 2 (Figure 2). The seed planes were sufficiently large to intersect all possible fiber pathways connecting two target regions of interest (ROI). A total number of 8000 iterations of fiber tracking were launched from 2000 uniformly sampled seed points in each of the planes (4 per voxel). Fiber tracking proceeded in both directions from the seed planes according to Equations 1–3 above, and was terminated when it reached a point with FA<0.1, or when it reached an ROI. Fibers that connected both target ROIs were stored for further analysis. We note that the purpose of using a small FA value as a termination criterion for the tracking process was to prevent it from entering the regions containing cerebral-spinal fluid, but still permitting it to traverse white matter and gray matter regions.

Bottom Line: The results showed that different language pathways exhibited different structural and functional connectivity, indicating varying levels of inter-dependence in processing across regions.However, fractional anisotropy was found not to be correlated with functional connectivity along paths connecting either BA and SMA or BA and WA.These findings suggest that structure-function relations in the human language circuits may involve a number of confounding factors that need to be addressed.

View Article: PubMed Central - PubMed

Affiliation: Vanderbilt University Institute of Imaging Science, Nashville, TN, USA. victoria.morgan@vanderbilt.edu

ABSTRACT

Background: The capabilities of magnetic resonance imaging (MRI) to measure structural and functional connectivity in the human brain have motivated growing interest in characterizing the relationship between these measures in the distributed neural networks of the brain. In this study, we attempted an integration of structural and functional analyses of the human language circuits, including Wernicke's (WA), Broca's (BA) and supplementary motor area (SMA), using a combination of blood oxygen level dependent (BOLD) and diffusion tensor MRI.

Methodology/principal findings: Functional connectivity was measured by low frequency inter-regional correlations of BOLD MRI signals acquired in a resting steady-state, and structural connectivity was measured by using adaptive fiber tracking with diffusion tensor MRI data. The results showed that different language pathways exhibited different structural and functional connectivity, indicating varying levels of inter-dependence in processing across regions. Along the path between BA and SMA, the fibers tracked generally formed a single bundle and the mean radius of the bundle was positively correlated with functional connectivity. However, fractional anisotropy was found not to be correlated with functional connectivity along paths connecting either BA and SMA or BA and WA.

Conclusions/significance: These findings suggest that structure-function relations in the human language circuits may involve a number of confounding factors that need to be addressed. Nevertheless, the insights gained from this work offers a useful guidance for continued studies that may provide a non-invasive means to evaluate brain network integrity in vivo for use in diagnosing and determining disease progression and recovery.

Show MeSH
Related in: MedlinePlus