Evidence of a middle longitudinal fasciculus in the human brain from fiber dissection

Abstract

A rostrocaudal pathway connecting the temporal and parietal lobes was described in monkeys using autoradiography and was named the middle longitudinal fasciculus (MdLF). Recently, the use of diffusion tensor tractography has allowed it to be depicted in human volunteers. In the present study, a technique of fiber dissection was used in 18 cadaveric human brains to investigate the presence of this fasciculus and to detail its anatomical relationships. On the basis of our findings, fiber dissection provides evidence for a long horizontal bundle medial to the arcuate fasciculus and extending to the superior temporal gyrus. Its fibers occupy the lateral-most layer of the upper portion of the stratum sagittale and partially cover the inferior fronto-occipital fasciculus, which is situated deeper and slightly inferiorly. Whereas MdLF fibers continue on a relatively superficial level to reach the superior temporal gyrus, the inferior fronto-occipital fasciculus penetrates the deep temporal white matter and crosses the insular lobe. Although diffusion tensor imaging suggests that the MdLF terminates in the angular gyrus, this was not confirmed by the present study. These long association fibers continue onward posteriorly into upper portions of the occipital lobe. Further studies are needed to understand the role of the MdLF in brain function.

Structural and functional integration between dorsal and ventral language streams as revealed by blunt dissection and direct electrical stimulation

“…[Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] De Witt Hamer et al, 2011;Kinoshita et al, 2015;Maldonado et al, 2013;Makris et al, 2013]. Many recent studies have demonstrated that long-and short-range WM connections constitute the fundamental structural background of brain processing by providing a multimodal functional integration among different and distributed neural populations [Hosseini and Kesler, 2013;Skudlarski et al, 2008].…”

Transport for language south of the Sylvian fissure: The routes and history of the main tracts and stations in the ventral language network

“…As a potential explanation to these contradictory findings, a recent large-scale tractography study delineated two bundles within the MdLF: both bundles were found to originate within the STG, with one branch terminating in the angular gyrus and the other in the SPL (Makris et al, 2013). Thus at the posterior end of the temporal lobe, the MdLF passes through the sagittal stratum and then curves upwards through the corona radiata to terminate in both the AG and SPL (Makris et Makris et al, 2013;Maldonado et al, 2013;Menjot de Champfleur et al, 2013;Wang et al, 2013).…”

How Klingler’s dissection permits exploration of brain structural connectivity? An electron microscopy study of human white matter

“…Fiber dissection has been extensively used to support diffusion tractography and intraoperative electrostimulation data, to demonstrate the existence of fiber bundles that are difficult to track (Kinoshita et al 2012;Maldonado et al 2013), to illustrate surgical applications (De Benedictis et al 2012;Martino et al 2013a), or to study cortical terminations that are difficult to assess with diffusion tractography (Martino et al 2013b;Sarubbo et al 2013). Nevertheless, dissection based on Klingler's method sometimes appears as a historical technique in the Neuroscience community and several limitations regarding its use as a validation tool for tractography have been raised.…”

“…It was neglected for a long time and received renewed attention following the development of MR tractography. Since then, published dissection studies have used such a freezing-defrosting step (Ture et al 2000;Peuskens et al 2004;Peltier et al 2006;Fernandez-Miranda et al 2008;Martino et al 2010;Kinoshita et al 2012;Maldonado et al 2013;Sarubbo et al 2013), although no study has explored the consequences of this preparation on white matter microstructure. One of the major concerns about using Klingler's method is indeed that it is unclear how freezing and defrosting may help accurately separate fibers along their main direction, and separate tracts from the surrounding white matter.…”