Stanford Fiber Tractography Lab - Major White Matter Tracts
Arcuate Fasciculus
The arcuate fasciculus (AF) is probably the most well-known association tract. It is so named because it forms an “arc” like trajectory, as it connects the lateral temporal gyri with the ventro-lateral frontal gyri. Early tractography studies of the AF described it as a 3-part tract consisting of a deep “arcuate” portion and a two-part superficial portion. More recent descriptions however describe it as a two-part system consisting solely of dorsal (upper) and ventral (lower) temporo-frontal components. The AF is strongly leftward-lateralized in both volume and connectivity. Interestingly, the AFs leftward-lateralization is thought to be evolutionary: Humans have complex and well-developed ability to communicate phonologically, and the AF is thought to be the primary neural substrate of mapping sound to meaning. It connects Wernicke’s area (Brodmann area 22) to Broca’s area (Brodmann area 44 and 45). Tractography performed in primates has revealed a lack of AF leftward-lateralization, which is thought to correspond to their less-developed phonological communicative abilities.
Selected References:
1.) Fernández-Miranda, J. C., Wang, Y., Pathak, S., Stefaneau, L., Verstynen, T., & Yeh, F. C. (2015). Asymmetry, connectivity, and segmentation of the arcuate fascicle in the human brain. Brain Structure and Function, 220(3), 1665-1680.
2.) Rilling, J. K., Glasser, M. F., Preuss, T. M., Ma, X., Zhao, T., Hu, X., & Behrens, T. E. (2008). The evolution of the arcuate fasciculus revealed with comparative DTI. Nature neuroscience, 11(4), 426.
3.) Rilling, J., Glasser, M. F., Jbabdi, S., Andersson, J., & Preuss, T. M. (2012). Continuity, divergence, and the evolution of brain language pathways. Frontiers in evolutionary neuroscience, 3, 11.
4.) Fernández-Miranda, J. C., Rhoton Jr, A. L., Álvarez-Linera, J., Kakizawa, Y., Choi, C., & de Oliveira, E. P. (2008). Three‐dimensional microsurgical and tractographic anatomy of the white matter of the human brain. Neurosurgery, 62(suppl_3), SHC989-SHC1028.
5.) Catani, M., & Jones, D. K. (2005). Perisylvian language networks of the human brain. Annals of neurology, 57(1), 8-16.
Superior Longitudinal Fasciculus
The superior longitudinal fasciculus (SLF) lies atop the AF and is even considered to be part of the same system as the AF by some. It is a purely parieto-frontal tract, traversing the dorsal (upper) white matter in the cerebral hemisphere. Due to early tractography methods being unable to differentiate close-proximity white matter systems at high levels of detail, it is easy to see why the SLF is often confused as part of the AF system. Nevertheless, the SLF and AF are distinctly different tracts, as evidenced by the SLFs rightward connective and volumetric lateralization. The modern tractographic description of the SLF is of a two-part system, the SLF II (dorsal) and SLF III (ventral). Older descriptions of the SLF were of a four-part system. It was later revealed that the SLF I was in fact part of the cingulum. SLF IV is otherwise known as the AF, which is a distinct and separate fiber tract. The SLF is thought to sub-serve visuo-spatial attention and language functionality.
Selected References:
1.) Wang, X., Pathak, S., Stefaneanu, L., Yeh, F. C., Li, S., & Fernandez-Miranda, J. C. (2016). Subcomponents and connectivity of the superior longitudinal fasciculus in the human brain. Brain Structure and Function, 221(4), 2075-2092.
2.) De Schotten, M. T., Dell'Acqua, F., Forkel, S. J., Simmons, A., Vergani, F., Murphy, D. G., & Catani, M. (2011). A lateralized brain network for visuospatial attention. Nature neuroscience, 14(10), 1245.
3.) Fernández-Miranda, J. C., Rhoton Jr, A. L., Álvarez-Linera, J., Kakizawa, Y., Choi, C., & de Oliveira, E. P. (2008). Three‐dimensional microsurgical and tractographic anatomy of the white matter of the human brain. Neurosurgery, 62(suppl_3), SHC989-SHC1028.
Inferior Fronto-Occipital Fasciculus
The inferior fronto-occipital fasciculus (IFOF) is one of the lesser-understood major association tracts in the brain. As its name suggests it is a longitudinal tract originating from the ventro-lateral frontal areas, travelling to the parieto-occipital cortices in the posterior hemispheres. At its anterior and posterior ends, it fans-out from its respective origins before narrowing into a compact “stem” portion as it passes through the ventral external capsule. Due to its length, which spans the entire antero-posterior distance of the cerebral hemisphere, and its close relationship with several other white matter tracts (the uncinate fasciculus, inferior longitudinal fasciculus, claustrum and optic radiations), it is relatively difficult to study using traditional post-mortem dissection techniques. Tractography has provided novel insights into its structure and connectivity, though results remain controversial. Some authors have proposed its connection to the temporal lobe in addition to occipital and parietal connectivity. Stimulation of white matter corresponding to the path of the IFOF during awake neurosurgery elicits semantic deficits, thus semantic functionality is thought to be the IFOFs main role. Interestingly, this tract is absent in simians, which are known to lack semantic capacity, lending credence to the IFOFs postulated role in humans.
Selected References:
1.) Panesar, S. S., Yeh, F. C., Deibert, C. P., Fernandes-Cabral, D., Rowthu, V., Celtikci, P., ... & Fernández-Miranda, J. C. (2017). A diffusion spectrum imaging-based tractographic study into the anatomical subdivision and cortical connectivity of the ventral external capsule: uncinate and inferior fronto-occipital fascicles. Neuroradiology, 59(10), 971-987.
2.) Hau, J., Sarubbo, S., Perchey, G., Crivello, F., Zago, L., Mellet, E., ... & Petit, L. (2016). Cortical terminations of the inferior fronto-occipital and uncinate fasciculi: anatomical stem-based virtual dissection. Frontiers in neuroanatomy, 10, 58.
3.) Fernández-Miranda, J. C., Rhoton Jr, A. L., Álvarez-Linera, J., Kakizawa, Y., Choi, C., & de Oliveira, E. P. (2008). Three‐dimensional microsurgical and tractographic anatomy of the white matter of the human brain. Neurosurgery, 62(suppl_3), SHC989-SHC1028.
4.) Martino, J., Brogna, C., Robles, S. G., Vergani, F., & Duffau, H. (2010). Anatomic dissection of the inferior fronto-occipital fasciculus revisited in the lights of brain stimulation data. cortex, 46(5), 691-699.
Uncinate Fasciculus
The uncinate fasciculus (UF) is a short, hook-shaped tract originating in the orbito-frontal cortex ventral and lateral to the IFOF. It initially travels backwards with the IFOF into the ventral external capsule (temporal stem), however here the UF hooks away, downwards and anteriorly to terminate within the temporo-polar regions. Classical descriptions of the UF describe a tract connected to the amygdala, thus implicating it as a limbic rather than association tract. Its amygdalar connectivity has been recently disputed by tractographic data, however. Other proposed roles of the UF are in self-awareness and memory.
Selected References
1.) Panesar, S. S., Yeh, F. C., Deibert, C. P., Fernandes-Cabral, D., Rowthu, V., Celtikci, P., ... & Fernández-Miranda, J. C. (2017). A diffusion spectrum imaging-based tractographic study into the anatomical subdivision and cortical connectivity of the ventral external capsule: uncinate and inferior fronto-occipital fascicles. Neuroradiology, 59(10), 971-987.
2.) Hau, J., Sarubbo, S., Perchey, G., Crivello, F., Zago, L., Mellet, E., ... & Petit, L. (2016). Cortical terminations of the inferior fronto-occipital and uncinate fasciculi: anatomical stem-based virtual dissection. Frontiers in neuroanatomy, 10, 58.
3.) Von Der Heide, R. J., Skipper, L. M., Klobusicky, E., & Olson, I. R. (2013). Dissecting the uncinate fasciculus: disorders, controversies and a hypothesis. Brain, 136(6), 1692-1707.
4.) Fernández-Miranda, J. C., Rhoton Jr, A. L., Álvarez-Linera, J., Kakizawa, Y., Choi, C., & de Oliveira, E. P. (2008). Three‐dimensional microsurgical and tractographic anatomy of the white matter of the human brain. Neurosurgery, 62(suppl_3), SHC989-SHC1028.
Middle Longitudinal Fasciculus
Little is known about the middle longitudinal fasiculus (MdLF). It is one of the more recently described brain fascicles and it originates from the posterior aspects of the dorso-lateral temporal lobe, approximately deep to the termination of the Sylvian fissure. It travels upwards, obliquely and deep to the AF, terminating in the rostral parietal and caudal occipital gyri. Due to its connectivity profile, it is thought to sub-serve auditory-attention. Note, the MdLF may be confused with another white matter tract: the medial longitudinal fasciculus (MLF), which is a brainstem tract sub-serving bilateral eye movements.
Selected References:
1.) Wang, Y., Fernández-Miranda, J. C., Verstynen, T., Pathak, S., Schneider, W., & Yeh, F. C. (2012). Rethinking the role of the middle longitudinal fascicle in language and auditory pathways. Cerebral cortex, 23(10), 2347-2356.
2.) de Champfleur, N. M., Maldonado, I. L., Moritz-Gasser, S., Machi, P., Le Bars, E., Bonafé, A., & Duffau, H. (2013). Middle longitudinal fasciculus delineation within language pathways: a diffusion tensor imaging study in human. European journal of radiology, 82(1), 151-157.
3.) Makris, N., Preti, M. G., Wassermann, D., Rathi, Y., Papadimitriou, G. M., Yergatian, C., ... & Kubicki, M. (2013). Human middle longitudinal fascicle: segregation and behavioral-clinical implications of two distinct fiber connections linking temporal pole and superior temporal gyrus with the angular gyrus or superior parietal lobule using multi-tensor tractography. Brain imaging and behavior, 7(3), 335-352.
4.) De Witt Hamer, P. C., Moritz‐Gasser, S., Gatignol, P., & Duffau, H. (2011). Is the human left middle longitudinal fascicle essential for language? A brain electrostimulation study. Human brain mapping, 32(6), 962-973.
Inferior Longitudinal Fasciculus
The inferior longitudinal fasciculus (ILF) was first described in the 19th and early 20th centuries. In the 1980’s however, its existence was called into question by studies using radioisotope tracers in primates. The introduction of tractography has re-opened the debate, with most modern studies agreeing on its existence. Nevertheless, its structure and composition remains a subject of controversy. It originates from the antero-lateral temporal gyri and travels backwards, joining the white matter of the sagittal stratum (containing the inferior fronto-occipital fasciculus, optic radiations and tapetum) as it travels posteriorly. It terminates in both medial and lateral areas of the occipital lobe. Due to its connectivity to the lateral temporal and occipital regions, it is implicated in semantic functionality and facial recognition. Interestingly, prior to the availability of MRI imaging, researchers postulated its role in facial recognition by correlating the inability to recognize faces (prosopagnosia) with stroke-related damage to the ventral temporal white matter areas.
Selected References
1.) Panesar, S. S., Yeh, F. C., Jacquesson, T., Hula, W., & Fernandez-Miranda, J. C. (2018). A Quantitative Tractography Study into the Connectivity, Segmentation and Laterality of the Human Inferior Longitudinal Fasciculus. Frontiers in Neuroanatomy, 12.
2.) Latini, F., Mårtensson, J., Larsson, E. M., Fredrikson, M., Åhs, F., Hjortberg, M., ... & Ryttlefors, M. (2017). Segmentation of the inferior longitudinal fasciculus in the human brain: a white matter dissection and diffusion tensor tractography study. Brain research, 1675, 102-115.
3.) Tusa, R. J., & Ungerleider, L. G. (1985). The inferior longitudinal fasciculus: a reexamination in humans and monkeys. Annals of neurology, 18(5), 583-591.
4.) Catani, M., Jones, D. K., Donato, R., & Ffytche, D. H. (2003). Occipito‐temporal connections in the human brain. Brain, 126(9), 2093-2107.
5.) Fernández-Miranda, J. C., Rhoton Jr, A. L., Álvarez-Linera, J., Kakizawa, Y., Choi, C., & de Oliveira, E. P. (2008). Three‐dimensional microsurgical and tractographic anatomy of the white matter of the human brain. Neurosurgery, 62(suppl_3), SHC989-SHC1028.
The Frontal Aslant Tract
The frontal aslant tract (FAT) is recently described fronto-frontal tract. It travels from the superior frontal gyrus dorsally, to the ventro-lateral frontal gyri via an oblique trajectory. Its dorso-medial connectivity is to motor and supplementary motor areas. Its ventro-lateral connectivity is to areas associated with speech initiation ventrally. Little is known about its functionality, though its connectivity patterns implicate it in motor-speech initiation, coordination and timing of motor function, amongst other roles.
Selected References:
1.) Kinoshita, M., de Champfleur, N. M., Deverdun, J., Moritz-Gasser, S., Herbet, G., & Duffau, H. (2015). Role of fronto-striatal tract and frontal aslant tract in movement and speech: an axonal mapping study. Brain Structure and Function, 220(6), 3399-3412.
2.) Kemerdere, R., de Champfleur, N. M., Deverdun, J., Cochereau, J., Moritz-Gasser, S., Herbet, G., & Duffau, H. (2016). Role of the left frontal aslant tract in stuttering: a brain stimulation and tractographic study. Journal of neurology, 263(1), 157-167.
3.) de Schotten, M. T., Dell’Acqua, F., Valabregue, R., & Catani, M. (2012). Monkey to human comparative anatomy of the frontal lobe association tracts. Cortex, 48(1), 82-96.
4.) Catani, M., Dell’Acqua, F., Vergani, F., Malik, F., Hodge, H., Roy, P., ... & De Schotten, M. T. (2012). Short frontal lobe connections of the human brain. cortex, 48(2), 273-291.
The Cingulum
The cingulum is an elusive tract, traversing antero-posteriorly immediately adjacent to the midline in each hemisphere. Its course corresponds roughly with the cingulate gyrus, occupying the medial portion of each hemisphere on top of the corpus callosum. It is composed of both long and very short fiber populations. Due to this reason, most tractography algorithms experience difficulty when attempting to track the cingulum bundle. Generally, the bundle originates from below the rostrum of the corpus callosum, and follows its outer contour, travelling anteriorly and dorsally with the genu, posteriorly over the body and wrapping underneath the splenium. The cingulum then branches laterally in a portion known as the isthmus, before terminating in the hippocampal gyri of each medial temporal lobe. Due to its connectivity with various limbic nuclei and the hippocampus it is considered both an association and limbic tract. Its exact functions remain to be elucidated, however.
Selected References
1.) Concha, L., Gross, D. W., & Beaulieu, C. (2005). Diffusion tensor tractography of the limbic system. American Journal of Neuroradiology, 26(9), 2267-2274.
2.) Gong, G., Jiang, T., Zhu, C., Zang, Y., Wang, F., Xie, S., ... & Guo, X. (2005). Asymmetry analysis of cingulum based on scale‐invariant parameterization by diffusion tensor imaging. Human brain mapping, 24(2), 92-98.
3.) Wakana, S., Caprihan, A., Panzenboeck, M. M., Fallon, J. H., Perry, M., Gollub, R. L., ... & Blitz, A. (2007). Reproducibility of quantitative tractography methods applied to cerebral white matter. Neuroimage, 36(3), 630-644.
The Fornix
The fornix is a limbic white matter tract located deep in the brain. Two “pillars” originate from the mamillary bodies as separate tracts, in each hemisphere. The pillars travel up and posteriorly, joining in the midline to form the “body” of the fornix. The body travels on the undersurface of the septum pellucidum before dividing again posteriorly. These divisions, known as fimbriae curve around the postero-superior surfaces of each thalamus then travel into the temporal lobes before terminating in the hippocampi. Due to its hippocampal connectivity, the fornix is implicated in memory functionality.
Selected References
1.) Concha, L., Gross, D. W., & Beaulieu, C. (2005). Diffusion tensor tractography of the limbic system. American Journal of Neuroradiology, 26(9), 2267-2274.
2.) Catani, M., Howard, R. J., Pajevic, S., & Jones, D. K. (2002). Virtual in vivo interactive dissection of white matter fasciculi in the human brain. Neuroimage, 17(1), 77-94.
3.) Catani, M., Dell’Acqua, F., & De Schotten, M. T. (2013). A revised limbic system model for memory, emotion and behaviour. Neuroscience & Biobehavioral Reviews, 37(8), 1724-1737.
Corticospinal Tracts
The corticospinal tracts are probably the best known of all white matter tracts. They are projection rather than association fibers. They originate from the motor cortex of the pre-central gyrus, which gives off tracts in a pattern corresponding to the well-known “motor homunculus.” This fan-like projection of fibers converges and travels ventrally (downwards) via posterior limb of the internal capsule. The fibers originating at the more lateral regions of the pre-frontal motor cortex “twist” around to travel on the medial aspect of the descending corticospinal tract, giving it a characteristic appearance that can be replicated by tractography. From the internal capsule, the corticospinal fibers continue ventrally into the brainstem via cerebral peduncle. They pass downwards through the pons and at the anterior aspect of the medulla they decussate (cross over the midline) in structures known as the pyramids. The result of decussation is that each motor cortex controls the limbs on the opposite side of the body. Corticospinal fibers originating from the motor cortex travelling latero-medially meet the perpendicularly travelling fibers of the arcuate and superior longitudinal fasciculi as they travel antero-posteriorly. The area where these meetings occur is known as the centrum semiovale. Older tractography algorithms using diffusion tensor imaging (DTI) may have trouble tracking crossing fibers due to this interaction.
Selected References
1.) Holodny, A. I., Gor, D. M., Watts, R., Gutin, P. H., & Ulug, A. M. (2005). Diffusion-tensor MR tractography of somatotopic organization of corticospinal tracts in the internal capsule: initial anatomic results in contradistinction to prior reports. Radiology, 234(3), 649-653.
2.) Wakana, S., Caprihan, A., Panzenboeck, M. M., Fallon, J. H., Perry, M., Gollub, R. L., ... & Blitz, A. (2007). Reproducibility of quantitative tractography methods applied to cerebral white matter. Neuroimage, 36(3), 630-644.
3.) Kunimatsu, A., Aoki, S., Masutani, Y., Abe, O., Hayashi, N., Mori, H., ... & Ohtomo, K. (2004). The optimal trackability threshold of fractional anisotropy for diffusion tensor tractography of the corticospinal tract. Magnetic Resonance in Medical Sciences, 3(1), 11-17.
4.) Qazi, A. A., Radmanesh, A., O'donnell, L., Kindlmann, G., Peled, S., Whalen, S., ... & Golby, A. J. (2009). Resolving crossings in the corticospinal tract by two-tensor streamline tractography: method and clinical assessment using fMRI. Neuroimage, 47, T98-T106.
5.) Okada, T., Mikuni, N., Miki, Y., Kikuta, K. I., Urayama, S. I., Hanakawa, T., ... & Hashimoto, N. (2006). Corticospinal tract localization: integration of diffusion-tensor tractography at 3-T MR imaging with intraoperative white matter stimulation mapping—preliminary results. Radiology, 240(3), 849-857.
Optic Radiations
The optic radiations are the most posterior component of the visual pathways. They originate from the lateral geniculate nucleus (LGN), which lies on the undersurface of the thalamus. These fibers fan out from the LGN, first travelling medially and anteriorly within the medial temporal lobe, medial to the anterior horn of the lateral ventricle. They then turn obliquely, almost 180° as they pass over the ceiling of the lateral ventricle, whilst fanning out. This turning is known as Meyer’s loop. The fibers then continue posteriorly after turning, now lateral to the lateral wall of the third ventricle. They are separated from the actual lateral ventricular wall by another thin sheet of white matter known as the tapetum. The optic radiations with the sagittal stratum, deep to the inferior fronto-occipital fasciculus, to terminations above and below the calcarine sulcus (primary visual cortices). If a portion of the optic radiations is damaged due to a stroke or other insult, it usually results in partial loss of visual field corresponding to the damaged area. Meyer’s loop is a very important surgical landmark, especially for temporal lobe surgery. Surgeons must be aware of the anterior extent of Meyer’s loop and its distance from the temporal pole to avoid unintentional damage and subsequent post-surgical visual deficits.
Selected references
1.) Yoshino, M., Abhinav, K., Yeh, F. C., Panesar, S., Fernandes, D., Pathak, S., ... & Fernandez-Miranda, J. C. (2016). Visualization of cranial nerves using high-definition fiber tractography. Neurosurgery, 79(1), 146-165.
2.) Sincoff, E. H., Tan, Y., & Abdulrauf, S. I. (2004). White matter fiber dissection of the optic radiations of the temporal lobe and implications for surgical approaches to the temporal horn. Journal of neurosurgery, 101(5), 739-746.
3.) Kier, E. L., Staib, L. H., Davis, L. M., & Bronen, R. A. (2004). MR imaging of the temporal stem: anatomic dissection tractography of the uncinate fasciculus, inferior occipitofrontal fasciculus, and Meyer’s loop of the optic radiation. American Journal of Neuroradiology, 25(5), 677-691.
4.) Sherbondy, A. J., Dougherty, R. F., Napel, S., & Wandell, B. A. (2008). Identifying the human optic radiation using diffusion imaging and fiber tractography. Journal of vision, 8(10), 12-12.
5.) Clatworthy, P. L., Williams, G. B., Acosta-Cabronero, J., Jones, S. P., Harding, S. G., Johansen-Berg, H., & Baron, J. C. (2010). Probabilistic tractography of the optic radiations—an automated method and anatomical validation. Neuroimage, 49(3), 2001-2012.