Decreased Cerebral Perfusion in Chronic Migraine: A Voxel-based Cerebral Blood Flow Analysis Using 3D Pseudo-continuous Arterial Spin Labeling.

BACKGROUND: A contrast agent-free approach would be preferable to the frequently used invasive approaches for evaluating cerebral perfusion in chronic migraineurs (CM). In this work, non-invasive quantitative volumetric perfusion imaging was used to evaluate alterations in cerebral perfusion in CM. METHODS: We used conventional brain structural imaging sequences and 3D pseudo-continuous arterial spin labeling (3D PCASL) to examine thirteen CM patients and fifteen normal controls (NCs). The entire brain gray matter underwent voxel-based analysis, and the cerebral blood flow (CBF) values of the altered positive areas were retrieved to look into the clinical variables' significant correlation. RESULTS: Brain regions with the decreased perfusion were located in the left postcentral gyrus, bilateral middle frontal gyrus, left middle occipital gyrus, left superior parietal lobule, left medial segment of superior frontal gyrus, and right orbital part of the inferior frontal gyrus. White matter fibers with decreased perfusion were located in bilateral superior longitudinal tracts, superior corona radiata, external capsules, anterior and posterior limbs of the internal capsule, anterior corona radiata, inferior longitudinal fasciculus, and right corticospinal tract. However, the correlation analysis showed no significant correlation between the CBF value of the above positive brain regions with clinical variables (p > 0.05). CONCLUSION: The current study provided more useful information to comprehend the pathophysiology of CM and revealed a new insight into the neural mechanism of CM from the pattern of cerebral hypoperfusion.

A fractional order-based mixture of central Wishart (FMoCW) model for reconstructing white matter fibers from diffusion MRI.

This paper introduces an algorithm for reconstructing the brain's white matter fibers (WMFs). In particular, a fractional order mixture of central Wishart (FMoCW) model is proposed to reconstruct the WMFs from diffusion MRI data. The pseudo super diffusive modality of anomalous diffusion is coupled with the mixture of central Wishart (MoCW) model to derive the proposed model. We have shown results on multiple synthetic simulations, including fibers orientations in 2 and 3 directions per voxel and experiments on real datasets of rat optic chiasm and a healthy human brain. In synthetic simulations, a varying Rician distributed noise levels, σ=0.01-0.09 is also considered. The proposed model can efficiently distinguish multiple fibers even when the angle of separation between fibers is very small. This model outperformed, giving the least angular error when compared to fractional mixture of Gaussian (MoG), MoCW and mixture of non-central Wishart (MoNCW) models.

The effects of transcranial direct current stimulation on cognition and white matter fiber integrity in stroke patients / 中华物理医学与康复杂志

Objective:To observe any effect of transcranial direct current stimulation (tDCS) on the cognition of stroke survivors and the integrity of their white matter fibers.Methods:Thirty persons with post-stroke cognitive impairment (PSCI) were randomly divided into an experimental group ( n=15) and a control group ( n=15). In addition to basic drug therapy and routine cognition training, the experimental group received 20 minutes of tDCS daily, 5 days per week for 3 weeks, while the control group received sham tDCS stimulation. Before and after the treatment, both groups′ cognitive functioning was evaluated using the mini-mental state examination (MMSE) and the Montreal cognitive assessment scale (MoCA). Their ability in the activities of daily living (ADL) was quantified using the modified Barthel index (MBI). Diffusion tensor imaging (DTI) was employed to observe any changes in the integrity of their white matter fibers. Results:The average MMSE, MOCA and MBI scores of both groups had improved significantly after the treatment, but the improvement in the experimental group was significantly greater than among the controls. The average fractional anisotroposy value of the affected inferior fronto-occipital fasciculus in both groups was positively correlated with the group′s average MMSE score and MoCA score.Conclusion:tDCS can effectively improve the cognition and functioning in the activities of daily living of stroke survivors. Its mechanism may be related to improving the integrity of the white matter fibers involved.

Anatomical and Technical Preparations of the Human Brain for White Matter Fibers Dissection with Electromagnetic Neuronavigation Assistance Technical Nuances for Application.

BACKGROUND: Klinger's fiber dissection technique is widely used for studying the anatomy of white matter. Herein, we present a technical description of Klinger's proposed fiber dissection algorithm with neuronavigation assistance which allows for a more accurate determination of the projection of association fibers. METHODS: An anatomical study was conducted on 8 hemispheres of the human brain, prepared according to the Klingler fiber dissection technique. In all the cases, a frameless electromagnetic navigation system was used. For each anatomical specimen, an individualized support device was three-dimensional -printed and placed it into the magnetic resonance imaging (MRI) gantry. MRI study of each anatomical specimen was performed using a specific protocol that enabled a subsequent three-dimensional visualization of the anatomical structures as follows: FSPGR (Fast SPoiled Gradient Recalled echo) BRAVO (BRAin VOlume Imaging), T2 CUBE, FLAIR (FLuid Attenuated Inversion Recovery) CUBE, CUBE DIR (double inversion recovery) WHITE MATTER, and CUBE DIR GRAY MATTER. RESULTS: The average time required to register an anatomical specimen in the navigation system was 7 minutes 28 seconds. In all of the 8 cases, the anatomical structures were correctly identified using neuronavigation. Moreover, the choice of MRI mode depends on the purpose of the study and the region of interest in the brain. CONCLUSIONS: Electromagnetic navigation is an accurate and useful technique. It allows the researcher the ability to virtually project the association fibers and their cortico-cortical terminations to the surface of the brain, even at the final stages of dissection when the superficial structures are removed. To obtain accurate targeting, it is important to use the appropriate neuronavigation protocol.

Effects of 3-month CPAP therapy on brain structure in obstructive sleep apnea: A diffusion tensor imaging study.

White matter (WM) fiber alterations in patients with obstructive sleep apnea (OSA) is associated with cognitive impairment, which can be alleviated by continuous positive airway pressure (CPAP). In this study, we aimed to investigate the changes in WM in patients with OSA at baseline (pre-CPAP) and 3 months after CPAP adherence treatment (post-CPAP), and to provide a basis for understanding the reversible changes after WM alteration in this disease. Magnetic resonance imaging (MRI) was performed on 20 severely untreated patients with OSA and 20 good sleepers. Tract-based spatial statistics was used to evaluate the fractional anisotropy (FA), mean diffusion coefficient, axial diffusion coefficient, and radial diffusion coefficient (RD) of WM. To assess the efficacy of treatment, 20 patients with pre-CPAP OSA underwent MRI again 3 months later. A correlation analysis was conducted to evaluate the relationship between WM injury and clinical evaluation. Compared with good sleepers, patients with OSA had decreased FA and increased RD in the anterior thalamic radiation, forceps major, inferior fronto-occipital tract, inferior longitudinal tract, and superior longitudinal tract, and decreased FA in the uncinate fasciculus, corticospinal tract, and cingulate gyrus (P < 0.05). No significant change in WM in patients with post-CPAP OSA compared with those with pre-CPAP OSA. Abnormal changes in WM in untreated patients with OSA were associated with oxygen saturation, Montreal cognitive score, and the apnea hypoventilation index. WM fiber was extensively alteration in patients with severe OSA, which is associated with cognitive impairment. Meanwhile, cognitive recovery was not accompanied by reversible changes in WM microstructure after short-term CPAP therapy.

Frontal aslant tract: Anatomy and tractography description in the Mexican population.

Background: The aim of the study was to describe the origin, course, and termination of frontal aslant tract (FAT) in the Mexican population of neurosurgical referral centers. Methods: From January 2018 to May 2019, we analyzed 50 magnetic resonance imaging (MRI) studies in diffusion tensor imaging sequences of patients of the National Institute of Neurology and Neurosurgery "Manuel Velasco Suárez." Five brains were fixed by the Klingler method and dissected in the neurosurgery laboratory of the Hospital Civil de Guadalajara to identify the origin, trajectory, and ending of the FAT. Results: FAT was identified in 100% of the MRI and brain dissections. The origin of the FAT was observed in 63% from the supplementary premotor area, 24% from the supplementary motor area, and 13% in both areas. Its ending was observed in the pars opercularis in 81%, pars triangularis in 9%, and in both pars opercularis and ventral premotor area in 10% in the magnetic resonance images, with a left side predominance. In the hemispheres dissections, the origin of FAT was identified in 60% from the supplementary premotor area, 20% from the supplementary motor area, and 20% in both areas. Its ending was observed in the pars opercularis in 80% and the pars triangularis in 20%. It was not identified as an individual fascicle connected with the contralateral FAT. Conclusion: In the Mexican population, FAT has a left predominance; it is originated more frequently in the supplementary premotor area, passes dorsal to the superior longitudinal fascicle II and the superior periinsular sulcus, and ends more commonly in the pars opercularis.

Segregated circuits for phonemic and semantic fluency: A novel patient-tailored disconnection study.

Phonemic and semantic fluency are neuropsychological tests widely used to assess patients' language and executive abilities and are highly sensitive tests in detecting language deficits in glioma patients. However, the networks that are involved in these tasks could be distinct and suggesting either a frontal (phonemic) or temporal (semantic) involvement. 42 right-handed patients (26 male, mean age = 52.5 years, SD=±13.3) were included in this retrospective study. Patients underwent awake (54.8%) or asleep (45.2%) surgery for low-grade (16.7%) or high-grade-glioma (83.3%) in the frontal (64.3%) or temporal lobe (35.7%) of the left (50%) or right (50%) hemisphere. Pre-operative tractography was reconstructed for each patient, with segmentation of the inferior fronto-occipital fasciculus (IFOF), arcuate fasciculus (AF), uncinate fasciculus (UF), inferior longitudinal fasciculus (ILF), third branch of the superior longitudinal fasciculus (SLF-III), frontal aslant tract (FAT), and cortico-spinal tract (CST). Post-operative percentage of damage and disconnection of each tract, based on the patients' surgical cavities, were correlated with verbal fluencies scores at one week and one month after surgery. Analyses of differences between fluency scores at these timepoints (before surgery, one week and one month after surgery) were performed; lesion-symptom mapping was used to identify the correlation between cortical areas and post-operative scores. Immediately after surgery, a transient impairment of verbal fluency was observed, that improved within a month. Left hemisphere lesions were related to a worse verbal fluency performance, being a damage to the left superior frontal or temporal gyri associated with phonemic or semantic fluency deficit, respectively. At a subcortical level, disconnection analyses revealed that fluency scores were associated to the involvement of the left FAT and the left frontal part of the IFOF for phonemic fluency, and the association was still present one month after surgery. For semantic fluency, the correlation between post-surgery performance emerged for the left AF, UF, ILF and the temporal part of the IFOF, but disappeared at the follow-up. This approach based on the patients' pre-operative tractography, allowed to trace for the first time a dissociation between white matter pathways integrity and verbal fluency after surgery for glioma resection. Our results confirm the involvement of a frontal anterior pathway for phonemic fluency and a ventral temporal pathway for semantic fluency. Finally, our longitudinal results suggest that the frontal executive pathway requires a longer interval to recover compared to the semantic one.

Heritable anisotropy associated with cognitive impairments among patients with schizophrenia and their non-psychotic relatives in multiplex families.

BACKGROUND: To test the functional implications of impaired white matter (WM) connectivity among patients with schizophrenia and their relatives, we examined the heritability of fractional anisotropy (FA) measured on diffusion tensor imaging data acquired in Pittsburgh and Philadelphia, and its association with cognitive performance in a unique sample of 175 multigenerational non-psychotic relatives of 23 multiplex schizophrenia families and 240 unrelated controls (total = 438). METHODS: We examined polygenic inheritance (h2r) of FA in 24 WM tracts bilaterally, and also pleiotropy to test whether heritability of FA in multiple WM tracts is secondary to genetic correlation among tracts using the Sequential Oligogenic Linkage Analysis Routines. Partial correlation tests examined the correlation of FA with performance on eight cognitive domains on the Penn Computerized Neurocognitive Battery, controlling for age, sex, site and mother's education, followed by multiple comparison corrections. RESULTS: Significant total additive genetic heritability of FA was observed in all three-categories of WM tracts (association, commissural and projection fibers), in total 33/48 tracts. There were significant genetic correlations in 40% of tracts. Diagnostic group main effects were observed only in tracts with significantly heritable FA. Correlation of FA with neurocognitive impairments was observed mainly in heritable tracts. CONCLUSIONS: Our data show significant heritability of all three-types of tracts among relatives of schizophrenia. Significant heritability of FA of multiple tracts was not entirely due to genetic correlations among the tracts. Diagnostic group main effect and correlation with neurocognitive performance were mainly restricted to tracts with heritable FA suggesting shared genetic effects on these traits.

The art of combining neuroanatomy and microsurgical skills in modern neurosurgery.

Neurosurgical training outside the operating room has become a priority for all neurosurgeons around the world. The exponential increase in the number of publications on training in neurosurgery reflects changes in the environment that future neurosurgeons are expected to work in. In modern practice, patients and medicolegal experts demand objective measures of competence and proficiency in the growing list of techniques available to treat complex neurosurgical conditions. It is important to ensure the myriad of training models available lead to tangible improvements in the operating room. While neuroanatomy textbooks and atlases are continually revised to teach the aspiring surgeon anatomy with a three-dimensional perspective, developing technical skills are integral to the pursuit of excellence in neurosurgery. Parapharsing William Osler, one of the fathers of neurosurgical training, without anatomical knowledge we are lost, but without the experience and skills from practice our journey is yet to begin. It is important to constantly aspire beyond competence to mastery, as we aim to deliver good outcomes for patients in an era of declining case volumes. In this article, we discuss, based on the literature, the most commonly used training models and how they are integrated into the treatment of some surgical brain conditions.

Direct evidence of the relationship between brain metastatic adenocarcinoma and white matter fibers: A fiber dissection and diffusion tensor imaging tractography study.

It is commonly known that brain metastases usually have clear boundaries in magnetic resonance imaging. However, little is known regarding the trajectory of white matter fibers around the tumors, especially using the fiber dissection technique. Here, we focused on the anatomical interaction between white matter fibers and the tumor, using the fiber dissection in a postmortem brain with metastatic tumor and compared the findings with those of diffusion tensor imaging (DTI) tractography. One postmortem human brain hemisphere with metastatic adenocarcinoma in the Broca's area was dissected using fiber dissection following the Klingler's method. In order to compare the in vitro and in vivo results, additional brains from 15 patients with metastatic adenocarcinomas, the volumes of which were comparable to that of the adenocarcinoma in the brain used for fiber dissection, were analyzed using DTI tractographic reconstruction. Morphological findings of white matter bundles running around the tumor were compared between the two techniques. In the fiber dissection technique, the superior longitudinal fascicle, arcuate fascicle, and frontal aslant tract could be dissected, and the white matter bundles were curved and retracted to avoid the tumor. In all the cases analyzed, white matter fibers or streamlines surrounding the tumor avoided the lesion. Using the fiber dissection technique, this is the first direct evidence to elucidate the anatomy of white matter fibers affected by a metastatic brain. This suggests that brain metastatic adenocarcinoma is an intra-axial neoplasm with extra-axial white matter structures.

Comparison Between Transcortical and Interhemispheric Approaches to the Atrium of Lateral Ventricle Using Combined White Matter Fiber Dissections and Magnetic Resonance Tractography.

OBJECTIVE: The objective of this study was to compare transcortical and posterior interhemispheric approaches to the atrium using a combined approach of white matter fiber dissections and magnetic resonance (MR) tractography. METHODS: Ten cerebral hemispheres were examined and dissected from the lateral-to-medial surface and from the medial-to-lateral surface, with special attention to the white matter tracts related to the atrium. MR tractography was used to show the relationship of three-dimensional white matter fibers with the atrium of the lateral ventricle and to compare with cadaveric dissection results. RESULTS: The atrium was related laterally to the superior longitudinal fasciculus II and III, middle longitudinal fasciculus, arcuate fasciculus, vertical occipital fasciculus, and sagittal stratum. Medially, it is related to the superior longitudinal fasciculus I, cingulum, sledge runner, and forceps major. CONCLUSIONS: A combined approach of cadaveric white matter fiber dissections and MR tractography were used to describe the main white matter tracts related to the posterior interhemispheric approach and the transcortical approach, providing an in-depth understanding of the three-dimensional anatomy of white matter fibers and the atrium. In the present study, among approaches examined, the posterior interhemispheric parasplenial transprecuneus approach placed fewer eloquent tracts at risk; however, traversing the sledge runner and the forceps major is unavoidable by this approach.

Functional clustering of whole brain white matter fibers.

BACKGROUND: Large numbers of fibers produced by fiber tractography are often grouped into bundles with anatomical interpretations. Traditional clustering methods usually generate bundles with spatial anatomic coherences only. To associate bundles with function, some studies incorporate functional connectivity of grey matter to guide clustering on the premise that fibers provide the basis of information transmission for cortex. However, functional properties along fiber tracts were ignored by these methods. Considering several recent studies showing that BOLD (Blood-Oxygen-Level Dependent) signals of white matter contain functional information of axonal fibers, this work is motivated to demonstrate that whole brain white matter fibers can be clustered with integration of functional and structural information they contain. NEW METHODS: We proposed a novel algorithm based on Gaussian mixture model and expectation maximization to achieve optimal bundling with both structural and functional coherences. The functional coherence between two fibers is defined as the average correlation in BOLD signal between corresponding points. Whole brain fibers under resting state and sensory stimulation conditions were used to demonstrate the effectiveness of the proposed technique. RESULTS: Our in vivo experiments show the robustness of proposed algorithm and influences of weights between structure and function, and repeatability of reconstructed major bundles across individuals. COMPARISON WITH EXISTING METHODS: In contrast to traditional methods, the proposed clustering method can achieve structurally more compact bundles, which are specifically related to evoking function. CONCLUSION: The proposed concept and framework can be used to identify functional pathways and their structural features under specific function loading.

Building connectomes using diffusion MRI: why, how and but.

Why has diffusion MRI become a principal modality for mapping connectomes in vivo? How do different image acquisition parameters, fiber tracking algorithms and other methodological choices affect connectome estimation? What are the main factors that dictate the success and failure of connectome reconstruction? These are some of the key questions that we aim to address in this review. We provide an overview of the key methods that can be used to estimate the nodes and edges of macroscale connectomes, and we discuss open problems and inherent limitations. We argue that diffusion MRI-based connectome mapping methods are still in their infancy and caution against blind application of deep white matter tractography due to the challenges inherent to connectome reconstruction. We review a number of studies that provide evidence of useful microstructural and network properties that can be extracted in various independent and biologically relevant contexts. Finally, we highlight some of the key deficiencies of current macroscale connectome mapping methodologies and motivate future developments.

Impaired long contact white matter fibers integrity is related to depression in Parkinson's disease.

AIMS: Depression is one of the most common nonmotor symptoms in Parkinson's disease (PD). But the pathogenesis is still unclear. Studies have shown that depression in PD is closely related to the white matter abnormalities, but the number of studies is still very small and lack of whole brain white matter lesions study. METHODS: In this study, we investigated whole brain white matter integrity in 31 depressed PD patients and 37 nondepressed PD patients by diffusion tensor imaging. RESULTS: There was no difference in age, gender, age of onset, disease duration, Hoehn-Yahr scale, Unified Parkinson's Disease Rating Scale scores-III, and Mini-Mental State Examination scores between the two groups. The only difference was the Hamilton Depression Rating Scale. Depressed PD patients showed reduced fractional anisotropy values in the left anterior corona radiata, left posterior thalamic radiation, left cingulum, left superior longitudinal fasciculus, left sagittal stratum (including inferior longitudinal fasciculus and inferior fronto-occipital fasciculus), and left uncinate fasciculus. In patients with depression, the Hamilton Depression Rating Scale (HDRS) was negatively correlated with the FA value in the left cingulum (r = -0.712, P = .032) and left superior longitudinal fasciculus (r = -0.699, P = .025). CONCLUSIONS: This study suggested depression in PD was related to impaired white matter integrity especially the long contact fibers in the left hemisphere. These findings may be helpful for further understanding the potential mechanisms underlying depression in PD.

Human Fetal Brain Connectome: Structural Network Development from Middle Fetal Stage to Birth.

Complicated molecular and cellular processes take place in a spatiotemporally heterogeneous and precisely regulated pattern in the human fetal brain, yielding not only dramatic morphological and microstructural changes, but also macroscale connectomic transitions. As the underlying substrate of the fetal brain structural network, both dynamic neuronal migration pathways and rapid developing fetal white matter (WM) fibers could fundamentally reshape early fetal brain connectome. Quantifying structural connectome development can not only shed light on the brain reconfiguration in this critical yet rarely studied developmental period, but also reveal alterations of the connectome under neuropathological conditions. However, transition of the structural connectome from the mid-fetal stage to birth is not yet known. The contribution of different types of neural fibers to the structural network in the mid-fetal brain is not known, either. In this study, diffusion tensor magnetic resonance imaging (DT-MRI or DTI) of 10 fetal brain specimens at the age of 20 postmenstrual weeks (PMW), 12 in vivo brains at 35 PMW, and 12 in vivo brains at term (40 PMW) were acquired. The structural connectome of each brain was established with evenly parcellated cortical regions as network nodes and traced fiber pathways based on DTI tractography as network edges. Two groups of fibers were categorized based on the fiber terminal locations in the cerebral wall in the 20 PMW fetal brains. We found that fetal brain networks become stronger and more efficient during 20-40 PMW. Furthermore, network strength and global efficiency increase more rapidly during 20-35 PMW than during 35-40 PMW. Visualization of the whole brain fiber distribution by the lengths suggested that the network reconfiguration in this developmental period could be associated with a significant increase of major long association WM fibers. In addition, non-WM neural fibers could be a major contributor to the structural network configuration at 20 PMW and small-world network organization could exist as early as 20 PMW. These findings offer a preliminary record of the fetal brain structural connectome maturation from the middle fetal stage to birth and reveal the critical role of non-WM neural fibers in structural network configuration in the middle fetal stage.

An automated string-based approach to extracting and characterizing White Matter fiber-bundles.

In this paper, we propose an automated approach to extracting White Matter (WM) fiber-bundles through clustering and model characterization. The key novelties of our approach are: a new string-based formalism, allowing an alternative representation of WM fibers, a new string dissimilarity metric, a WM fiber clustering technique, and a new model-based characterization algorithm. Thanks to these novelties, the complex problem of WM fiber-bundle extraction and characterization reduces to a much simpler and well-known string extraction and analysis problem. Interestingly, while several past approaches extract fiber-bundles by grouping available fibers on the basis of provided atlases (and, therefore, cannot capture possibly existing fiber-bundles nor represented in the atlases), our approach first clusters available fibers once and for all, and then tries to associate obtained clusters with models provided directly and dynamically by users. This more dynamic and interactive way of proceeding can help the detection of fiber-bundles autonomously proposed by our approach and not present in the initial models provided by experts.

Whole brain fiber-based comparison (FBC)-A tool for diffusion tensor imaging-based cohort studies.

We present a novel method for fiber-based comparison of diffusion tensor imaging (DTI) scans of groups of subjects. The method entails initial preprocessing and fiber reconstruction by tractography of each brain in its native coordinate system. Several diffusion parameters are sampled along each fiber and used in subsequent comparisons. A spatial correspondence between subjects is established based on geometric similarity between fibers in a template set (several choices for template are explored), and fibers in all other subjects. Diffusion parameters between groups are compared statistically for each template fiber. Results are presented at single fiber resolution. As an initial exploratory step in neurological population studies this method points to the locations affected by the pathology of interest, without requiring a hypothesis. It does not make any grouping assumptions on the fibers and no manual intervention is needed. The framework was applied here to 18 healthy subjects and 23 amyotrophic lateral sclerosis (ALS) patients. The results are compatible with previous findings and with the tract based spatial statistics (TBSS) method. Hum Brain Mapp 37:477-490, 2016. © 2015 Wiley Periodicals, Inc.

Stimulation Mapping of Myelinated Tracts in Awake Patients.

For a long time, although the functional anatomy of human cortex has extensively been studied, subcortical white matter tracts have received little consideration. Recent advances in tractography have opened the door to a non-invasive investigation of the subcortical fibers in vivo. However, this method cannot study directly the function of the bundles. Interestingly, for the first time in the history of cognitive neurosciences, direct axonal electrostimulation (DES) mapping of the neural pathways offers the unique opportunity to investigate the function of the connectomal anatomy. Indeed, this technique is able to perform real-time anatomo-functional correlations in awake patients who undergo brain surgery, especially at the level of the subcortical fibers. Here, the aim is to review original data issued from DES of myelinated tracts in adults, with regard to the functional connectivity mediating the sensorimotor, visuo-spatial, language, cognitive and emotional functions, as well as the interactions between these different sub-networks, leading ultimately to explore consciousness. Therefore, axonal stimulation is a valuable tool in the field of connectomics, that is, the map of neural connections, in order to switch from the traditional localizationist view of brain processing to a networking model in which cerebral functions are underpinned by the dynamic interactions of large-scale distributed and parallel sub-circuits. Such connectomal account should integrate the anatomic constraint represented by the subcortical fascicles. Indeed, post-lesional neuroplasticity is possible only on the condition that the white matter fibers are preserved, to allow communication and temporal synchronization among delocalized inter-connected networks.

Microsurgical anatomy of the inferior limiting insular sulcus and the temporal stem.

OBJECT: The purpose of this study was to describe the location of each white matter pathway in the area between the inferior limiting insular sulcus (ILS) and temporal horn that may be crossed in approaches through the temporal stem to the medial temporal lobe. METHODS: The fiber tracts in 14 adult cadaveric cerebral hemispheres were examined using the Klingler technique. The fiber dissections were completed in a stepwise manner, identifying each white matter pathway in different planes and describing its position in relation to the anterior end of the ILS. RESULTS: The short-association fibers from the extreme capsule, which continue toward the operculae, are the most superficial subcortical layer deep to the ILS. The external capsule fibers are found deeper at an intermediate layer and are formed by the uncinate fasciculus, inferior frontooccipital fasciculus, and claustrocortical fibers in a sequential anteroposterior disposition. The anterior commissure forms the next deeper layer, and the optic radiations in the sublenticular part of the internal capsule represent the deepest layer. The uncinate fasciculus is found deep to the anterior third of the ILS, whereas the inferior frontooccipital fasciculus and optic radiations are found superficial and deep, respectively, at the posterior two-thirds of this length. CONCLUSIONS: The authors' findings suggest that in the transsylvian approach, a 6-mm incision beginning just posterior to the limen insula through the ILS will cross the uncinate fasciculus but not the inferior frontooccipital fasciculus or optic radiations, but that longer incisions carry a risk to language and visual functions.

Fiberfox: facilitating the creation of realistic white matter software phantoms.

PURPOSE: Phantom-based validation of diffusion-weighted image processing techniques is an important key to innovation in the field and is widely used. Openly available and user friendly tools for the flexible generation of tailor-made datasets for the specific tasks at hand can greatly facilitate the work of researchers around the world. METHODS: We present an open-source framework, Fiberfox, that enables (1) the intuitive definition of arbitrary artificial white matter fiber tracts, (2) signal generation from those fibers by means of the most recent multi-compartment modeling techniques, and (3) simulation of the actual MR acquisition that allows for the introduction of realistic MRI-related effects into the final image. RESULTS: We show that real acquisitions can be closely approximated by simulating the acquisition of the well-known FiberCup phantom. We further demonstrate the advantages of our framework by evaluating the effects of imaging artifacts and acquisition settings on the outcome of 12 tractography algorithms. CONCLUSION: Our findings suggest that experiments on a realistic software phantom might change the conclusions drawn from earlier hardware phantom experiments. Fiberfox may find application in validating and further developing methods such as tractography, super-resolution, diffusion modeling or artifact correction.