Contributions of bilateral white matter to chronic aphasia symptoms as assessed by diffusion tensor MRI

Abstract

Language reorganisation following stroke has been studied widely. However, while studies of brain activation and grey matter examined both hemispheres, studies of white matter changes have mostly focused on the left hemisphere. Here we examined the relationship between bilateral hemispheric white matter and aphasia symptoms. 15 chronic stroke patients with aphasia and 18 healthy adults were studied using Diffusion Weighted Imaging data. By applying histogram analysis, Tract-Based Spatial Statistics, tractography and lesion-tract overlap methods, it was found that damage to the left hemisphere in general, and to the arcuate fasciculus in particular, correlated with impairments on word repetition, object naming, sentence comprehension and homophone and rhyme judgement. However, no such relationship was found in the right hemisphere. It is suggested that while some language function in aphasia can be explained by damage to the left arcuate fasciculus, it cannot be explained by looking at the contra-lesional tract.

Keywords: Arcuate fasciculus; Diffusion Tensor Imaging; Language; Stroke.

Fig. 1

An overlay of all patients’ lesions in coronal (A), sagittal (B) and axial (C) planes. Colours represent number of patients with a lesion to a specific voxel. Warmer areas indicate areas of greater lesion overlap. Colour range runs from 1 (the lowest value in the image) to 11 (the highest value in the image). MNI coordinates of the centroid of the cluster with the largest lesion overlap: x = −29, y = −2 and z = 23.

Fig. 2

An example of a seed (yellow) and target (red) Regions of Interest used for tracking the Arcuate Fasciculus (A); and a probabilistic left hemispheric Arcuate Fasciculus map based on 17 healthy participants, seen from coronal (B), sagittal (C) and axial (D) views (colour scale represents probabilities from 0 to 1).

Fig. 3

Mean Fractional Anisotropy (FA) values and tract volume (corrected for intracranial volume) of the right and left hemispheric Arcuate Fasciculus, in patients and controls. Bars represent ±1 standard error.

Fig. 4

Correlations between Lesion-Tract Overlap (LTO) and behaviour. Y axis represents raw scores (A–C) or percentage correct (D, E).