Changes in white matter integrity follow excitatory rTMS treatment of post-stroke aphasia

Abstract

Purpose: In this study, we examine whether an excitatory repetitive transcranial magnetic stimulation (rTMS) protocol called intermittent theta burst stimulation (iTBS) applied to the affected left hemisphere leads to changes in white matter fractional anisotropy (FA).

Methods: Diffusion tensor imaging (DTI) data were collected in 8 aphasic stroke patients before and after 10 daily iTBS treatments. Alignment of structural and DTI data and derivation of diffusion index maps were performed using Analysis of Functional NeuroImages software followed by Tract-Based Spatial Statistics using FMRIB Software Library. Paired t-tests were performed to compare pre- to post-rTMS changes in FA.

Results: There were significant (p < 0.001) left-hemispheric FA increases near the inferior and superior frontal gyri and anterior corpus callosum. FA also increased in the right midbrain and bilaterally near temporal, parietal and posterior cingulate regions. FA decreased bilaterally near the fusiform gyrus and in left cerebellum.

Conclusions: Overall, left-hemispheric regions that showed increased FA corresponded to areas previously shown to have increases in fMRI language activation after iTBS. The increased white matter integrity near the stimulation sites may reflect improvements in cortical function mediated by excitatory rTMS through its ability to facilitate synaptic connections.

Fig. 1

Timeline of the study procedures. All subjects underwent language testing and MRI scanning within one week prior to and one week after the excitatory repetitive transcranial magnetic stimulation (rTMS) treatment (intermittent theta burst stimulation (iTBS)).

Fig. 2

Tract-Based Spatial Statistics (TBSS) analysis of the pre- to post-rTMS changes in fractional anisotropy (FA). Clusters in blue represent decreases, while those in red/yellow represent increases in FA (only changes significant at uncorrected p<0.001 are shown). The numbers (1–14) correspond to the clusters described in Table 2. The green skeleton represents the center of white matter tracts common to the group with FA ≥ 0.2 and is superimposed on the standard MNI152 T1-weighted anatomical image. The white arrows indicate areas with breaks in the green skeleton that represent damaged white matter not included in TBSS analysis. The axial slices are displayed in in radiological convention (left on the picture is right in the brain) and range in MNI coordinates from z = -39 (top left) to z = +44 (bottom right).