In Reply

Abstract

In Reply: We thank Dr Bartsch and colleagues for their commentary. The authors raise several interesting points, such as the reduction of false-negative trackings using probabilistic tractography with crossing fibers modeling, and the high risk of reading impairment if the left inferior parietal lobe is damaged. We appreciate their favorable assessment of our article and agree with their correction. Specifically, the most lateral component of the temporoparietal fiber intersection area (TPFIA) is not the horizontal portion, but the vertical portion of the superior longitudinal fasciculus (SLF).1 However, the vertical portion of the SLF should be differentiated from the vertical occipital fasciculus (VOF) (Figure). Classical anatomical studies describe the VOF or Wernicke perpendicular fasciculus as a connection between the superior occipital gyrus and the posterior parietal lobe superiorly, and the fusiform gyrus at the temporal base inferiorly.2 Recent diffusion tensor imaging studies describe the VOF as a tract located within the occipital lobe, specifically connecting the occipitotemporal sulcus to the lateral portion of the occipital parietal junction.3 The tract described in our article is not connected to the occipital lobe, because it is located at the temporoparietal junction. As we had previously described, this tract connects the posterior portion of the inferior parietal lobe (ie, angular gyrus) with the middle temporal gyrus,4 and corresponds to the connection described by Catani and colleagues as the vertical portion of the SLF.5FIGURE: A, fiber dissection of the tracts that pass through the temporoparietal fiber intersection area (TPFIA) in a left hemisphere. The vertical portion of the superior longitudinal fasciculus (SLF) has been tilted superiorly to expose the arcuate fasciculus. The vertical portion of the SLF is located at the temporoparietal junction and connects the posterior portion of the inferior parietal lobe (ie, angular gyrus) with the middle temporal gyrus. B, the vertical portion of the SLF was removed. The vertical occipital fasciculus (VOF) was dissected, and small pieces of paper were placed underneath this tract to demonstrate that it was completely separated from the deeper structures. It is evidenced that the VOF is located posterior to the TPFIA, specifically within the occipital lobe. The VOF connects the superior occipital gyrus with the temporo-occipital junction. C, schematic representation of the same tracts presented in A and B. 1 = vertical portion of the SLF; 2 = arcuate fasciculus; 3 = VOF. CS, central sulcus; PCG, precentral gyrus; MTG, middle temporal gyrus; SMG, supramarginal gyrus; STG, superior temporal gyrus.It is important to emphasize that the SLF is the most complex connection in the human brain, and that the available descriptions of this tract provide basic anatomic information. Further anatomical and functional studies are needed because the detailed understanding of this bundle remains to be ascertained. Disclosures Dr Martino receives specific funding from the 11/18 API grant entitled “Estudio de la conectividad conectividad cerebral mediante disección de fibras estructural.” “Fundación Marqués de Valdecilla,” IFIMAV, Santander, Cantabria, Spain. October, 8, 2010. The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.