The connectivity of the superior longitudinal fasciculus: a tractography DTI study

Abstract 

Purpose

The left superior longitudinal fasciculus (SLF) has been felt to link receptive with expressive language areas. The latter is located in the pars opercularis (Broca's area) of the left inferior frontal gyrus. We report the findings with tractography of the SLF in a group of normal volunteers.

Methods and materials

The data and subsidiary results of 12 normal right-handed volunteers who participated in an institutional review board-approved diffusion tensor imaging study were evaluated. The SLF fibers were obtained bilaterally placing a region of interest at the triangular-shaped region lateral to each of the corticospinal tracts, in a coronal plane along the rostral aspect of the corpus callosum. A sagittal fractional anisotropy image was used to determine the rostral endpoint of the SLF fibers in the white matter pertaining to specific gyri or pars of the frontal lobe. The SLF projection to Broca's area was ranked qualitatively as none, minimal, most or all. Findings are presented in descriptive statistics.

Results

The SLF projection to Broca's areas was absent in seven subjects (58.3%) and minimal in five (41.6%). SLF's rostral end points were found uniquely or mainly in the precentral gyrus in 100% of cases.

Conclusion

The SLF was found connecting the posterior language areas to the precentral gyrus and only marginally in some cases to the canonical Broca's area. This finding is consistent with reports describing lack of correlation between lateralization of the SLF and language areas. The understanding of language circuitry is beginning to emerge with the use of tractography.

Keywords: DTI, Tractography, Superior longitudinal fasciculus, Arcuate, Fasciculus, Conduction aphasia, Language, MRI, Brain, Broca, Wernicke, Language organization