To determine the possible role in language processing of two recently identified temporal intralobar white matter fascicles, namely temporal vertical tract (TVT) and temporal longitudinal tract (TLT), in individuals with primary progressive aphasia (PPA).

Tractography has recently revealed the existence of two tracts in the human brain: the TLT connecting posterior and anterior temporal regions and TVT connecting the most posterior region of the superior temporal gyrus to the middle temporal gyrus. The function of these tracts is completely unknown.

We used diffusion tensor imaging tractography and spherical deconvolution tractography to dissect the TVT and TLT, respectively, in 98 PPA patients and 43 matched controls (HCs). We compared diffusion measures of these fascicles between HCs and PPA and then correlated them with language performances in PPA.

We found that performance in single word comprehension significantly correlated with fractional anisotropy (r=0.325, p<0.01) and with mean diffusivity (r=-0.635, p<0.01) of the left TLT. We also found significant correlations between reading exceptional words and both fractional anisotropy (r=0.303; p<0.01) and mean diffusivity (r=-0.373; p=0.001) of the left TVT.

Our results demonstrate the involvement of TVT and TLT in two different aspect of language, namely single word comprehension and reading, respectively. These results lead to considering the inclusion of TVT and TLT in connectional models of language.