Somatotopic organization of motor pathways in the internal capsule: a probabilistic diffusion tractography study

Reconstructing the somatotopic organization of the corticospinal tract remains a challenge for modern tractography methods

The corticospinal tract (CST) is a critically important white matter fiber tract in the human brain that enables control of voluntary movements of the body. The CST exhibits a somatotopic organization, which means that the motor neurons that control specific body parts are arranged in order within the CST. Diffusion magnetic resonance imaging (MRI) tractography is increasingly used to study the anatomy of the CST. However, despite many advances in tractography algorithms over the past decade, modern, state-of-the-art methods still face challenges. In this study, we compare the performance of six widely used tractography methods for reconstructing the CST and its somatotopic organization. These methods include constrained spherical deconvolution (CSD) based probabilistic (iFOD1) and deterministic (SD-Stream) methods, unscented Kalman filter (UKF) tractography methods including multi-fiber (UKF2T) and single-fiber (UKF1T) models, the generalized q-sampling imaging (GQI) based deterministic tractography method, and the TractSeg method. We investigate CST somatotopy by dividing the CST into four subdivisions per hemisphere that originate in the leg, trunk, hand, and face areas of the primary motor cortex. A quantitative and visual comparison is performed using diffusion MRI data (N = 100 subjects) from the Human Connectome Project. Quantitative evaluations include the reconstruction rate of the eight anatomical subdivisions, the percentage of streamlines in each subdivision, and the coverage of the white matter-gray matter (WM-GM) interface. CST somatotopy is further evaluated by comparing the percentage of streamlines in each subdivision to the cortical volumes for the leg, trunk, hand, and face areas. Overall, UKF2T has the highest reconstruction rate and cortical coverage. It is the only method with a significant positive correlation between the percentage of streamlines in each subdivision and the volume of the corresponding motor cortex. However, our experimental results show that all compared tractography methods are biased toward generating many trunk streamlines (ranging from 35.10% to 71.66% of total streamlines across methods). Furthermore, the coverage of the WM-GM interface in the largest motor area (face) is generally low (under 40%) for all compared tractography methods. Different tractography methods give conflicting results regarding the percentage of streamlines in each subdivision and the volume of the corresponding motor cortex, indicating that there is generally no clear relationship, and that reconstruction of CST somatotopy is still a large challenge. Overall, we conclude that while current tractography methods have made progress toward the well-known challenge of improving the reconstruction of the lateral projections of the CST, the overall problem of performing a comprehensive CST reconstruction, including clinically important projections in the lateral (hand and face areas) and medial portions (leg area), remains an important challenge for diffusion MRI tractography.

The evidence against somatotopic organization of function in the primate corticospinal tract

We review the spatial organization of corticospinal outputs from different cortical areas and how this reflects the varied functions mediated by the corticospinal tract. A long-standing question is whether the primate corticospinal tract shows somatotopical organization. Although this has been clearly demonstrated for corticofugal outputs passing through the internal capsule and cerebral peduncle, there is accumulating evidence against somatotopy in the pyramidal tract in the lower brainstem and in the spinal course of the corticospinal tract. Answering the question on somatotopy has important consequences for understanding the effects of incomplete spinal cord injury. Our recent study in the macaque monkey, using high-resolution dextran tracers, demonstrated a great deal of intermingling of fibres originating from primary motor cortex arm/hand, shoulder and leg areas. We quantified the distribution of fibres belonging to these different projections and found no significant difference in their distribution across different subsectors of the pyramidal tract or lateral corticospinal tract, arguing against somatotopy. We further demonstrated intermingling with corticospinal outputs derived from premotor and supplementary motor arm areas. We present new evidence against somatotopy for corticospinal projections from rostral and caudal cingulate motor areas and from somatosensory areas of the parietal cortex. In the pyramidal tract and lateral corticospinal tract, fibres from the cingulate motor areas overlap with each other. Fibres from the primary somatosensory cortex arm area completely overlap those from the leg area. There is also substantial overlap of both these outputs with those from posterior parietal sensorimotor areas. We argue that the extensive intermingling of corticospinal outputs from so many different cortical regions must represent an organizational principle, closely related to its mediation of many different functions and its large range of fibre diameters. The motor sequelae of incomplete spinal injury, such as central cord syndrome and 'cruciate paralysis', include much greater deficits in upper than in lower limb movement. Current teaching and text book explanations of these symptoms are still based on a supposed corticospinal somatotopy or 'lamination', with greater vulnerability of arm and hand versus leg fibres. We suggest that such explanations should now be finally abandoned. Instead, the clinical and neurobiological implications of the complex organization of the corticospinal tract need now to be taken into consideration. This leads us to consider the evidence for a greater relative influence of the corticospinal tract on upper versus lower limb movements, the former best characterized by skilled hand and digit movements.

Diffusion tensor tractography of the corticobulbar tract in a dysphagic patient with progressive supranuclear palsy: A case report

RATIONALE

This paper reports the changes over time in the corticobulbar tract (CBT) analyzed using diffusion tensor tractography (DTT) in a dysphagic patient with progressive supranuclear palsy (PSP).

PATIENT CONCERNS

A 53-year-old man initially presented with dysarthria, gait disturbance, and bradykinesia, and approximately 1-year later, downward gaze paralysis appeared. Initially, there was no dysphagia; however, approximately 2 years after visiting the hospital, symptoms of dysphagia, including difficulty swallowing pills, aspiration, and oral movement impairments appeared. The symptoms gradually progressed, and finally, mouth opening was severely damaged to the extent that it was difficult to orally feed.

INTERVENTIONS

We performed diffusion tensor imaging 3 times; at 3-month, 20-month, and 41-month from onset.

OUTCOMES

On 3-month DTT, the left CBT was well reconstructed, whereas the right CBT showed partial tearing. In the 20-month DTT, both CBTs became thinner compared to the 3-month DTT. On 41-month DTT, both CBTs became much thinner than after 3-month and 20-month DTT.

LESSONS

We observed the degree of CBT injury over time in a dysphagic patient with PSP. These results suggest that the analysis of CBT using DTT is helpful in predicting the degree of dysphagia and prognosis in patients with PSP.

Somatotopic Organization of Hyperdirect Pathway Projections From the Primary Motor Cortex in the Human Brain

Background

The subthalamic nucleus (STN) is an effective neurosurgical target to improve motor symptoms in Parkinson's Disease (PD) patients. MR-guided Focused Ultrasound (MRgFUS) subthalamotomy is being explored as a therapeutic alternative to Deep Brain Stimulation (DBS) of the STN. The hyperdirect pathway provides a direct connection between the cortex and the STN and is likely to play a key role in the therapeutic effects of MRgFUS intervention in PD patients.

Objective

This study aims to investigate the topography and somatotopy of hyperdirect pathway projections from the primary motor cortex (M1).

Methods

We used advanced multi-fiber tractography and high-resolution diffusion MRI data acquired on five subjects of the Human Connectome Project (HCP) to reconstruct hyperdirect pathway projections from M1. Two neuroanatomy experts reviewed the anatomical accuracy of the tracts. We extracted the fascicles arising from the trunk, arm, hand, face and tongue area from the reconstructed pathways. We assessed the variability among subjects based on the fractional anisotropy (FA) and mean diffusivity (MD) of the fibers. We evaluated the spatial arrangement of the different fascicles using the Dice Similarity Coefficient (DSC) of spatial overlap and the centroids of the bundles.

Results

We successfully reconstructed hyperdirect pathway projections from M1 in all five subjects. The tracts were in agreement with the expected anatomy. We identified hyperdirect pathway fascicles projecting from the trunk, arm, hand, face and tongue area in all subjects. Tract-derived measurements showed low variability among subjects, and similar distributions of FA and MD values among the fascicles projecting from different M1 areas. We found an anterolateral somatotopic arrangement of the fascicles in the corona radiata, and an average overlap of 0.63 in the internal capsule and 0.65 in the zona incerta.

Conclusion

Multi-fiber tractography combined with high-resolution diffusion MRI data enables the identification of the somatotopic organization of the hyperdirect pathway. Our preliminary results suggest that the subdivisions of the hyperdirect pathway projecting from the trunk, arm, hand, face, and tongue motor area are intermixed at the level of the zona incerta and posterior limb of the internal capsule, with a predominantly overlapping topographical organization in both regions. Subject-specific knowledge of the hyperdirect pathway somatotopy could help optimize target definition in MRgFUS intervention.

Understanding Language Reorganization With Neuroimaging: How Language Adapts to Different Focal Lesions and Insights Into Clinical Applications

When the language-dominant hemisphere is damaged by a focal lesion, the brain may reorganize the language network through functional and structural changes known as adaptive plasticity. Adaptive plasticity is documented for triggers including ischemic, tumoral, and epileptic focal lesions, with effects in clinical practice. Many questions remain regarding language plasticity. Different lesions may induce different patterns of reorganization depending on pathologic features, location in the brain, and timing of onset. Neuroimaging provides insights into language plasticity due to its non-invasiveness, ability to image the whole brain, and large-scale implementation. This review provides an overview of language plasticity on MRI with insights for patient care. First, we describe the structural and functional language network as depicted by neuroimaging. Second, we explore language reorganization triggered by stroke, brain tumors, and epileptic lesions and analyze applications in clinical diagnosis and treatment planning. By comparing different focal lesions, we investigate determinants of language plasticity including lesion location and timing of onset, longitudinal evolution of reorganization, and the relationship between structural and functional changes.

A dual larynx motor networks hypothesis

Humans are vocal modulators par excellence. This ability is supported in part by the dual representation of the laryngeal muscles in the motor cortex. Movement, however, is not the product of motor cortex alone but of a broader motor network. This network consists of brain regions that contain somatotopic maps that parallel the organization in motor cortex. We therefore present a novel hypothesis that the dual laryngeal representation is repeated throughout the broader motor network. In support of the hypothesis, we review existing literature that demonstrates the existence of network-wide somatotopy and present initial evidence for the hypothesis' plausibility. Understanding how this uniquely human phenotype in motor cortex interacts with broader brain networks is an important step toward understanding how humans evolved the ability to speak. We further suggest that this system may provide a means to study how individual components of the nervous system evolved within the context of neuronal networks. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.

The strength of corticomotoneuronal drive underlies ALS split phenotypes and reflects early upper motor neuron dysfunction

BACKGROUND

Split phenotypes, (split hand, elbow, leg, and foot), are probably unique to ALS, and are characterized by having a shared peripheral input of both affected and unaffected muscles. This implies an anatomical origin rostral to the spinal cord, primarily within the cerebral cortex. Therefore, split phenotypes are a potential marker of ALS upper motor neuron pathology. However, to date, reports documenting upper motor neuron dysfunction in split phenotypes have been limited to using transcranial magnetic stimulation and cortical threshold tracking techniques. Here, we consider several other potential methodologies that could confirm a primary upper motor neuron pathology in split phenotypes.

METHODS

We review the potential of: 1. measuring the compound excitatory post-synaptic potential recorded from a single activated motor unit, 2. cortical-muscular coherence, and 3. new advanced modalities of neuroimaging (high-resolution imaging protocols, ultra-high field MRI platforms [7T], and novel Non-Gaussian diffusion models).

CONCLUSIONS

We propose that muscles involved in split phenotypes are those functionally involved in the human motor repertoire used particularly in complex activities. Their anterior horn cells receive the strongest corticomotoneuronal input. This is also true of the weakest muscles that are the earliest to be affected in ALS. Descriptions of split hand in non-ALS cases and proposals that peripheral nerve or muscle dysfunction may be causative are contentious. Only a few carefully controlled cases of each form of split phenotype, using upper motor neuron directed methodologies, are necessary to prove our postulate.

Neural Changes Induced by a Speech Motor Treatment in Childhood Apraxia of Speech: A Case Series

We report a case series of children with childhood apraxia of speech, by describing behavioral and white matter microstructural changes following 2 different treatment approaches.Five children with childhood apraxia of speech were assigned to a motor speech treatment (PROMPT) and 5 to a language, nonspeech oral motor treatment. Speech assessment and brain MRI were performed pre- and post-treatment. The ventral (tongue/larynx) and dorsal (lips) corticobulbar tracts were reconstructed in each subject. Mean fractional anisotropy and mean diffusivity were extracted. The hand corticospinal tract was assessed as a control pathway. In both groups speech improvements paralleled changes in the left ventral corticobulbar tract fractional anisotropy. The PROMPT treated group also showed fractional anisotropy increase and mean diffusivity decrease in the left dorsal corticobulbar tract. No changes were detected in the hand tract. Our results may provide preliminary support to the possible neurobiologic effect of a multimodal speech motor treatment in childhood apraxia of speech.

Temporo-cerebellar connectivity underlies timing constraints in audition

The flexible and efficient adaptation to dynamic, rapid changes in the auditory environment likely involves generating and updating of internal models. Such models arguably exploit connections between the neocortex and the cerebellum, supporting proactive adaptation. Here, we tested whether temporo-cerebellar disconnection is associated with the processing of sound at short timescales. First, we identify lesion-specific deficits for the encoding of short timescale spectro-temporal non-speech and speech properties in patients with left posterior temporal cortex stroke. Second, using lesion-guided probabilistic tractography in healthy participants, we revealed bidirectional temporo-cerebellar connectivity with cerebellar dentate nuclei and crura I/II. These findings support the view that the encoding and modeling of rapidly modulated auditory spectro-temporal properties can rely on a temporo-cerebellar interface. We discuss these findings in view of the conjecture that proactive adaptation to a dynamic environment via internal models is a generalizable principle.

Recovery of an injured arcuate fasciculus via transcallosal fiber in a stroke patient: A case report

RATIONALE

We report on a patient whose arcuate fasciculus (AF) and corticobulbar tract (CBT) recovered following an infarct in the middle cerebral artery (MCA) territory, demonstrated on serial diffusion tensor tractography (DTT).

PATIENT CONCERNS

The patient showed moderate conduction aphasia on the Western Aphasia Battery with an aphasia quotient of 46.5‰ (spontaneous speech: 35.0‰, auditory comprehension: 36.0‰, and naming: 53.1‰) at 1 month after onset. His aphasia improved with an aphasia quotient of 49‰ (spontaneous speech: 71.0‰, auditory comprehension: 52.0‰, and naming: 59.0‰) at 10 months after onset.

DIAGNOSIS

A 44-year-old right-handed male patient presented with aphasia and quadriplegia, which occurred at the onset of an infarct in the left MCA territory.

INTERVENTION

Diffusion tensor imaging data were acquired twice (1 month and 10 months after onset).

OUTCOMES

On one-month DTT, the discontinuation of the left AF and severe narrowing of the right CBT were observed. However, on ten-month DTT, the left AF was connected to the opposite AF by a new tract that passed through the splenium of corpus callosum, and the right CBT had become thicker.

LESSONS

We believe that our results suggest a recovery mechanism of injured AF and CBT in stroke patients.

White matter in infancy is prospectively associated with language outcomes in kindergarten

Language acquisition is of central importance to child development. Although this developmental trajectory is shaped by experience postnatally, the neural basis for language emerges prenatally. Thus, a fundamental question remains: do structural foundations for language in infancy predict long-term language abilities? Longitudinal investigation of 40 children from infancy to kindergarten reveals that white matter in infancy is prospectively associated with subsequent language abilities, specifically between: (i) left arcuate fasciculus and phonological awareness and vocabulary knowledge, (ii) left corticospinal tract and phonological awareness, and bilateral corticospinal tract with phonological memory; controlling for age, cognitive, and environmental factors. Findings link white matter in infancy with school-age language abilities, suggesting that white matter organization in infancy sets a foundation for long-term language development.

Functional Brain Anatomy

Knowledge of functional neuroanatomy is essential to design the most appropriate clinical functional MR imaging (fMR imaging) paradigms and to properly interpret fMR imaging study results. The correlation between neuroanatomy and brain function is also useful in general radiologic practice, as it improves the radiologist's ability to read routine brain examinations. Functional MR imaging is used primarily to determine the areas involved in functioning of movements, speech, and vision. Preoperative fMR imaging findings also play a key role in the neurosurgeon's decision to perform a biopsy, a subtotal resection, or a maximal resection using awake craniotomy.

Methods of Analysis: Functional MRI for Presurgical Planning

There are many technical and nontechnical steps involved in a successful clinical functional MRI (fMRI) scan. The output from scanning and analysis can only be as good as the input, so task instruction and rehearsal are the most important steps during an clinical fMRI procedure. Properly pre-processed data significantly affects statistical analysis, which has a great impact on image interpretation. Even though there is general agreement on how to process clinical fMRI data, such as algorithms for head motion detection and correction, the theory and practicalities associated with data processing remain complex and constantly evolving.

Dysphagia prognosis prediction via corticobulbar tract assessment in lateral medullary infarction: a diffusion tensor tractography study

We investigated the capacity for dysphagia prognosis prediction using diffusion tensor tractography (DTT) to assess the state of the corticobulbar tract (CBT) during the initial period following lateral medullary infarction (LMI). Twenty patients with LMI and 20 control subjects were recruited for this study. The patients were classified into two subgroups: subgroup A (16 patients with nasogastric tube required for six months or less after LMI onset) and subgroup B (4 patients with nasogastric tube required for more than six months after onset). DTT was used to reconstruct the CBTs of each patient and control subject, and the fractional anisotropy (FA) and tract volume (TV) measurements were obtained. In the affected hemisphere, the FA value of the CBT was significantly lower in subgroup B than in subgroup A and the control group (p < 0.05), with no significant difference between subgroup A and the control group. In the affected and unaffected hemispheres, the TV values of CBT in subgroups A and B were lower than those of the control group (p < 0.05), with no significant difference between subgroups A and B. In addition, among the four patients of subgroup B, reconstruction of the CBT was not possible in three patients, and the remaining patients exhibited on old lesion in the corona radiate involving descending pathway of the CBT in the affected hemisphere. We found that the injury severity of the CBT in the affected hemisphere appeared to be related to a poor dysphagia prognosis following LMI. Our results suggest that evaluation of the CBT state during the early post-LMI could be useful for dysphagia prognosis prediction.

Lower total protein and absence of neuronavigation are novel poor prognostic factors of endoscopic hematoma removal for intracerebral hemorrhage

OBJECTIVES

Endoscopic hematoma removal is widely performed for the treatment of intracerebral hemorrhage. We investigated the factors related to the prognosis of intracerebral hemorrhage after endoscopic hematoma removal.

MATERIALS AND METHODS

From 2013 to 2019, we retrospectively analyzed 75 consecutive patients with hypertensive intracerebral hemorrhage who underwent endoscopic hematoma removal. Their characteristics, including neurological symptoms, laboratory data, and radiological findings were investigated using univariate and multivariate analysis. Complications during hospitalization, Glasgow Coma Scale (GCS) score on day 7, and modified Rankin Scale (mRS) score at 6 months were considered as treatment outcomes.

RESULTS

The mean age of the patients (33 women, 42 men) was 71.8 (36-95) years. Mean GCS scores at admission and on day 7 were 10.3 ± 3.2 and 11.7 ± 3.8, respectively. The mean mRS score at 6 months was 3.8 ± 1.6, and poor outcome (mRS score ranging from 3 to 6 at 6 months) in 53 patients. Rebleeding occurred in 4 patients, and other complications in 15 patients. Multivariate analysis revealed that older age, hematoma in the basal ganglia, lower total protein level, higher glucose level, and absence of neuronavigation were associated with poor outcomes. Of the 75 patients, 9 had cerebellar hemorrhages, and they had relatively favorable outcomes compared to those with supratentorial hemorrhages.

CONCLUSION

Several factors were related to the prognosis of intracerebral hemorrhage after endoscopic hematoma removal. Lower total protein level at admission and absence of neuronavigation were novel factors related to poor outcomes of endoscopic hematoma removal for intracerebral hemorrhage.

Endoscopic hematoma removal of supratentorial intracerebral hemorrhage under local anesthesia reduces operative time compared to craniotomy

The surgical efficacy for supratentorial intracerebral hemorrhage (ICH) remains unknown. We compared the advantages of the widely practiced endoscopic hematoma removal under local anesthesia with that of craniotomy under general anesthesia for ICH. We also focused on our novel operative concept of intentional hematoma leaving technique to avoid further damage to the brain. We retrospectively analyzed 134 consecutive patients (66 endoscopies and 68 craniotomies) who were surgically treated for supratentorial ICH. The characteristics of the 134 patients were as follows: The median (interquartile range) age was 73 (61-82) years. The median Glasgow Coma Scale scores at admission, on day 7, and the median modified Rankin Scale (mRS) score at 6 months were 10 (7-13), 13 (10-14), and 4 (3-5) respectively. The statistical comparison revealed there were no differences in GCS score on day seven between the endoscopy 13 (12-14) and craniotomy group 12 (9-14). No differences were observed in mRS scores at 6 months between the endoscopy 4 (2-5) and craniotomy group 4 (3-5). However, the patients treated with our technique tended to have favorable outcomes. Multivariate analysis revealed the operative time was significantly decreased in the endoscopy group compared to the craniotomy group (p < 0.001).

Prognostic Prediction of Dysphagia by Analyzing the Corticobulbar Tract in the Early Stage of Intracerebral Hemorrhage

We investigated the predictive value of the corticobulbar tract (CBT) for dysphagia using diffusion tensor tractography in the early stage of intracerebral hemorrhage (ICH) for dysphagia. Forty-two patients with spontaneous ICH ± intraventricular hemorrhage (IVH) and 22 control subjects were recruited. The patients were classified into three groups: group A-could remove nasogastric tube (NGT) in the acute stage of ICH, group B-could remove NGT within 6 months after onset, and group C-could not remove NGT until 6 months after onset. The CBT were reconstructed, and fractional anisotropy (FA) and tract volume (TV) values were determined. The FA of the CBT in the affected hemisphere in group A was lower than in the control group (p < 0.05). The FA and TV of the CBT in the affected hemisphere in group B were lower than those in the control group (p < 0.05). In group C, the FA and TV in the affected hemisphere and unaffected hemispheres were lower than in the control group (p < 0.05). The TV of the CBT in the affected hemisphere in group B showed a moderate negative correlation with the length of time until NGT removal (r = 0.430, p < 0.05). We found that patients with CBT injuries in both hemispheres were not able to remove the NGT until 6 months after onset, whereas patients who were injured only in the affected hemisphere were able to remove NGT within 6 months of onset. The severity of injury to the CBT in the affected hemisphere appeared to be related to the length of time until NGT removal.

The Surgical White Matter Chassis: A Practical 3-Dimensional Atlas for Planning Subcortical Surgical Trajectories

BACKGROUND

The imperative role of white matter preservation in improving surgical functional outcomes is now recognized. Understanding the fundamental white matter framework is essential for translating the anatomic and functional literature into practical strategies for surgical planning and neuronavigation.

OBJECTIVE

To present a 3-dimensional (3-D) atlas of the structural and functional scaffolding of human white matter-ie, a "Surgical White Matter Chassis (SWMC)"-that can be used as an organizational tool in designing precise and individualized trajectory-based neurosurgical corridors.

METHODS

Preoperative diffusion tensor imaging magnetic resonance images were obtained prior to each of our last 100 awake subcortical resections, using a clinically available 3.0 Tesla system. Tractography was generated using a semiautomated deterministic global seeding algorithm. Tract data were conceptualized as a 3-D modular chassis based on the 3 major fiber types, organized along median and paramedian planes, with special attention to limbic and neocortical association tracts and their interconnections.

RESULTS

We discuss practical implementation of the SWMC concept, and highlight its use in planning select illustrative cases. Emphasis has been given to developing practical understanding of the arcuate fasciculus, uncinate fasciculus, and vertical rami of the superior longitudinal fasciculus, which are often-neglected fibers in surgical planning.

CONCLUSION

A working knowledge of white matter anatomy, as embodied in the SWMC, is of paramount importance to the planning of parafascicular surgical trajectories, and can serve as a basis for developing reliable safe corridors, or modules, toward the goal of "zero-footprint" transsulcal access to the subcortical space.

Projections of Brodmann Area 6 to the Pyramidal Tract in Humans: Quantifications Using High Angular Resolution Data

Primate studies indicate that the pyramidal tract (PyT) could originate from Brodmann area (BA) 6. However, in humans, the accurate origin of PyT from BA 6 is still uncertain owing to difficulties in visualizing anatomical features such as the fanning shape at the corona radiata and multiple crossings at the semioval centrum. High angular-resolution diffusion imaging (HARDI) could reliably replicate these anatomical features. We explored the origin of the human PyT from BA 6 using HARDI. With HARDI data of 30 adults from the Massachusetts General Hospital-Human Connectome Project (MGH-HCP) database and the HCP 1021 template (average of 1021 HCP diffusion data), we visualized the PyT at the 30-averaged group level and the 1021 large-sample level and validated the observations in each of the individuals. Endpoints of the fibers within each subregion were quantified. PyT fibers originating from the BA 6 were consistently visualized in all images. Specifically, the bilateral supplementary motor area (SMA) and dorsal premotor area (dPMA) were consistently found to contribute to the PyT. PyT fibers from BA 6 and those from BA 4 exhibited a twisting topology. The PyT contains fibers originating from the SMA and dPMA in BA 6. Infarction of these regions or aging would result in incomplete provision of information to the PyT and concomitant decreases in motor planning and coordination abilities.

Resting-State Functional Magnetic Resonance Imaging and Probabilistic Diffusion Tensor Imaging Demonstrate That the Greatest Functional and Structural Connectivity in the Hand Motor Homunculus Occurs in the Area of the Thumb

The primary hand motor region is classically believed to be in the "hand knob" area in the precentral gyrus (PCG). However, hand motor task-based activation is often localized outside this area. The purpose of this study is to investigate the structural and functional connectivity driven by different seed locations corresponding to the little, index, and thumb in the PCG using probabilistic diffusion tractography (PDT) and resting-state functional magnetic resonance imaging (rfMRI). Twelve healthy subjects had three regions of interest (ROIs) placed in the left PCG: lateral to the hand knob (thumb area), within the hand knob (index finger area), and medial to the hand knob (little finger area). Connectivity maps were generated using PDT and rfMRI. Individual and group level analyses were performed. Results show that the greatest hand motor connectivity between both hemispheres was obtained using the ROI positioned just lateral to the hand knob in the PCG (the thumb area). The number of connected voxels in the PCG between the two hemispheres was greatest in the lateral-most ROI (the thumb area): 279 compared with 13 for the medial-most ROI and 9 for the central hand knob ROI. Similarly, the highest white matter connectivity between the two hemispheres resulted from the ROI placed in the lateral portion of PCG (p < 0.003). The maximal functional and structural connectivity of the hand motor area between hemispheres occurs in the thumb area, located laterally at the "hand knob." Thus, this location appears maximal for rfMRI and PDT seeding of the motor area.

The Relationship Between Leukoaraiosis Involving Contralateral Corticobulbar Tract and Dysphagia in Patients with Acute Unilateral Corona Radiata Infarction with Corticobulbar Tract Involvement

This study investigated the impact of leukoaraiosis (LA) involving the contralateral corticobulbar tract (CBT) on dysphagia in patients with unilateral corona radiata (CR) infarction with CBT involvement. Patients admitted to the Department of Neurology (September 2011-August 2014) were evaluated; those with a first episode of acute unilateral CR infarction involving the CBT and with LA were included. The 'Case' group comprised patients with LA involving the contralateral CBT; the 'Control' group comprised patients with LA not involving the contralateral CBT. The primary outcome was the feeding method at discharge; secondary outcomes were the feeding method at admission and results of the bedside swallowing test, videofluoroscopic swallowing study (VFSS), videofluoroscopic dysphagia scale, penetration-aspiration scale, American Speech-Language-Hearing Association National Outcome Measurement System Swallowing Scale (ASHA NOMS), oral transit time, and pharyngeal transit time. Infarct size was measured using brain magnetic resonance imaging; LA severity was rated using the Fazekas scale. Eighty-one patients were included (mean age 64.6 ± 11.5 years; 64% male; Case group: 20, 5 underwent VFSS; Control group: 67, 11 underwent VFSS). The Case group was older and had higher total Fazekas scale score than the Control group. The feeding method at discharge and ASHA NOMS score were significantly worse in the Case group than in the Control group. Multivariate analysis revealed that LA involving the contralateral CBT independently predicted the feeding method at discharge and ASHA NOMS score. In conclusion, LA involving the contralateral CBT is associated with dysphagia in patients with unilateral CR infarction involving the CBT.

Tractography Verified by Intraoperative Magnetic Resonance Imaging and Subcortical Stimulation During Tumor Resection Near the Corticospinal Tract

BACKGROUND

Tractography is a popular tool for visualizing the corticospinal tract (CST). However, results may be influenced by numerous variables, eg, the selection of seeding regions of interests (ROIs) or the chosen tracking algorithm.

OBJECTIVE

To compare different variable sets by correlating tractography results with intraoperative subcortical stimulation of the CST, correcting intraoperative brain shift by the use of intraoperative MRI.

METHODS

Seeding ROIs were created by means of motor cortex segmentation, functional MRI (fMRI), and navigated transcranial magnetic stimulation (nTMS). Based on these ROIs, tractography was run for each patient using a deterministic and a probabilistic algorithm. Tractographies were processed on pre- and postoperatively acquired data.

RESULTS

Using a linear mixed effects statistical model, best correlation between subcortical stimulation intensity and the distance between tractography and stimulation sites was achieved by using the segmented motor cortex as seeding ROI and applying the probabilistic algorithm on preoperatively acquired imaging sequences. Tractographies based on fMRI or nTMS results differed very little, but with enlargement of positive nTMS sites the stimulation-distance correlation of nTMS-based tractography improved.

CONCLUSION

Our results underline that the use of tractography demands for careful interpretation of its virtual results by considering all influencing variables.

Dysarthria in pallidal Deep Brain Stimulation in dystonia depends on the posterior location of active electrode contacts: a pilot study

BACKGROUND

Pallidal Deep Brain Stimulation (GPi-DBS) is an efficient treatment for primary dystonia. We investigated stimulation-induced dysarthria, which is the most frequent side-effect of GPi-DBS.

METHODS

Speech was recorded while reading a standard text, and performing rapid syllable repetitions ON and OFF DBS in ten dystonia patients (6 men; 3 cervical, 4 segmental, 3 generalized, unselected for DBS-related speech impairments). Speech and articulation rate, pauses, and syllable repetition rates were extracted via acoustic analysis. Locations of active stimulation contacts and volumes of tissue activated (VTA) were calculated.

RESULTS

The number of pauses increased significantly ON vs. OFF stimulation (Wilcoxon test, p < 0.05). More posteriorly localized active contacts were associated with slower syllable repetition (Pearson correlation, p < 0.05). VTA size did not correlate with any measure of dysarthria.

CONCLUSION

Using quantitative acoustic signal analysis, this study demonstrates that GPi-DBS alters motor aspects of speech. Both inadvertent stimulation of parts of the internal capsule, or interference with GPi function and outflow are possible causes. Understanding causes of GPi-DBS-induced speech changes can improve DBS programming.

Recovery of an injured corticobulbar tract in a patient with stroke: A case report

RATIONALE

The corticobulbar tract (CBT) is known to be involved in the motor function of the non-oculomotor cranial nuclei and controls the muscles of the face, head, and neck. Several studies have reported injury of the CBT in patients with brain injury, however, little is known about recovery of the injured CBT.

PATIENT CONCERNS

A 59-year-old right-handed male underwent decompressive craniectomy for management of brain swelling and intracerebral hemorrhage following an infarction in the left middle cerebral artery territory. Initially, the patient had showed severe dysphagia and had to be fed using a Levin tube. Five weeks after the onset of stroke, the patient was transferred to the rehabilitation department and underwent comprehensive rehabilitative therapy. Cranioplasty was performed eight weeks after the onset. The patient was completely recovered from dysphagia and the Levine tube was removed nine weeks after the onset.

INTERVENTIONS

Diffusion tensor imaging was performed twice; at five weeks and nine weeks from the onset.

OUTCOME

On five-week diffusion tensor tractography (DTT), the right CBT was discontinued at the subcortical white matter and showed severe narrowing and the left CBT was not reconstructed. By contrast, on nine-week DTT, the right CBT was extended to the cerebral cortex and thickened while the left CBT remained not reconstructed in DTT.

LESSONS

This case demonstrates the association of the recovery of injured CBT with the recovery of dysphagia using DTT.

Localization of orofacial representation in the corona radiata, internal capsule and cerebral peduncle in Macaca mulatta

Subcortical white matter injury is often accompanied by orofacial motor dysfunction, but little is known about the structural substrates accounting for these common neurological deficits. We studied the trajectory of the corticobulbar projection from the orofacial region of the primary (M1), ventrolateral (LPMCv), supplementary (M2), rostral cingulate (M3) and caudal cingulate (M4) motor regions through the corona radiata (CR), internal capsule (IC) and crus cerebri of the cerebral peduncle (ccCP). In the CR each pathway was segregated. Medial motor area fibers (M2/M3/M4) arched over the caudate and lateral motor area fibers (M1/LPMCv) curved over the putamen. At superior IC levels, the pathways were widespread, involving the anterior limb, genu and posterior limb with the M3 projection located anteriorly, followed posteriorly by projections from M2, LPMCv, M4 and M1, respectively. Inferiorly, all pathways maintained this orientation but shifted posteriorly, with adjacent fiber bundles overlapping minimally. In the ccCP, M3 fibers were located medially and M1 fibers centromedially, with M2, LPMCv, and M4 pathways overlapping in between. Finally, at inferior ccCP levels, all pathways overlapped. Following CR and superior IC lesions, the dispersed pathway distribution may correlate with acute orofacial dysfunction with spared pathways contributing to orofacial motor recovery. In contrast, the gradually commixed nature of pathway representation inferiorly may enhance fiber vulnerability and correlate with severe, prolonged deficits following lower subcortical and midbrain injury. Additionally, in humans these findings may assist in interpreting orofacial movements evoked during deep brain stimulation, and neuroimaging tractography efforts to localize descending orofacial motor pathways.

Capsular stroke modeling based on somatotopic mapping of motor fibers

Recently, several capsular stroke models have been reported with different targets of destruction. This study was performed to establish an accurate internal capsule (IC) target for capsular stroke modeling in rats. We injected adeno-associated virus serotype 5 (AAV)-CaMKII-EYFP into forelimb motor cortex and AAV-CaMKII-mCherry into hindlimb motor cortex (n = 9) to anterogradely trace the pyramidal fibers and map their somatotopic distribution in the IC. On the basis of the neural tracing results, we created photothrombotic infarct lesions in rat forelimb and hindlimb motor fiber (FMF and HMF) areas of the IC (n = 29) and assessed motor behavior using a forelimb-use asymmetry test, a foot-fault test, and a single-pellet reaching test. We found that the FMFs and HMFs were primarily distributed in the inferior portion of the posterior limb of the IC, with the FMFs located largely ventral to the HMFs but with an area of partial overlap. Photothrombotic lesions in the FMF area resulted in persistent motor deficits. In contrast, lesions in the HMF area did not result in persistent motor deficits. These results indicate that identification of the somatotopic distribution of pyramidal fibers is critical for accurate targeting in animal capsular stroke models: only infarcts in the FMF area resulted in long-lasting motor deficits.

Oropharyngeal dysphagia in secondary normal pressure hydrocephalus due to corticobulbar tract compression: cases series and review of literature

The association and mechanism involved in swallowing disturbance and normal pressure hydrocephalus (NPH) needs to be established. We report a case report where a patient who showed progressive swallowing dysfunction was diagnosed with secondary NPH. Tractography analysis showed corticobulbar tract compression by ventricular dilation. Drainage operation led to the recovery of tract volume with an improvement of swallowing function. We also report ten case series in which secondary NPH was associated with a swallowing disturbance. In these cases, dysphagia also showed improvement after shunt operation. We review the literature regarding the corticobulbar tract and its association with swallowing disturbance and the possible underlying pathophysiological mechanism in secondary NPH. This report highlights that swallowing disturbance may manifest in those with secondary NPH due to corticobulbar tract involvement. Our findings suggest that involvement of the corticobulbar tract may be a possible cause of dysphagia in secondary NPH that may be reversible after shunt operation.

Neural correlates of language variability in preschool-aged boys with autism spectrum disorder

Children with autism vary widely in their language abilities, yet the neural correlates of this language variability remain unclear, especially early in development. Diffusion tensor imaging (DTI) was used to examine diffusivity measures along the length of 18 major fiber tracts in 104 preschool-aged boys with autism spectrum disorder (ASD). The boys were assigned to subgroups according to their level of language development (Low: no/low language, Middle: small vocabulary, High: large vocabulary and grammar), based on their raw scores on the expressive language (EL) and receptive language (RL) sections of the Mullen Scales of Early Learning (MSEL). Results indicate that the subgroups differed in fractional anisotropy (FA), mean diffusivity (MD), and radial diffusivity (RD) along the inferior longitudinal fasciculus (ILF) in both hemispheres. Moreover, FA correlated significantly with Mullen EL and RL raw scores, but not ADOS severity score, along the left and right ILF. Subgroups also differed in MD (but not FA) along the left superior longitudinal fasiculus and left corticospinal tract, but these differences were not correlated with language scores. These findings suggest that white matter microstructure in the left and right ILF varies in relation to lexical development in young males with ASD. The findings also support the use of raw scores on language-relevant standardized tests for assessing early language-brain relationships. Autism Res 2017. © 2017 International Society for Autism Research, Wiley Periodicals, Inc. Autism Res 2017, 10: 1107-1119. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

Functional MRI vs. navigated TMS to optimize M1 seed volume delineation for DTI tractography. A prospective study in patients with brain tumours adjacent to the corticospinal tract

BACKGROUND

DTI-based tractography is an increasingly important tool for planning brain surgery in patients suffering from brain tumours. However, there is an ongoing debate which tracking approaches yield the most valid results. Especially the use of functional localizer data such as navigated transcranial magnetic stimulation (nTMS) or functional magnetic resonance imaging (fMRI) seem to improve fibre tracking data in conditions where anatomical landmarks are less informative due to tumour-induced distortions of the gyral anatomy. We here compared which of the two localizer techniques yields more plausible results with respect to mapping different functional portions of the corticospinal tract (CST) in brain tumour patients.

METHODS

The CSTs of 18 patients with intracranial tumours in the vicinity of the primary motor area (M1) were investigated by means of deterministic DTI. The core zone of the tumour-adjacent hand, foot and/or tongue M1 representation served as cortical regions of interest (ROIs). M1 core zones were defined by both the nTMS hot-spots and the fMRI local activation maxima. In addition, for all patients, a subcortical ROI at the level of the inferior anterior pons was implemented into the tracking algorithm in order to improve the anatomical specificity of CST reconstructions. As intra-individual control, we additionally tracked the CST of the hand motor region of the unaffected, i.e., non-lesional hemisphere, again comparing fMRI and nTMS M1 seeds. The plausibility of the fMRI-ROI- vs. nTMS-ROI-based fibre trajectories was assessed by a-priori defined anatomical criteria. Moreover, the anatomical relationship of different fibre courses was compared regarding their distribution in the anterior-posterior direction as well as their location within the posterior limb of the internal capsule (PLIC).

RESULTS

Overall, higher plausibility rates were observed for the use of nTMS- as compared to fMRI-defined cortical ROIs (p < 0.05) in tumour vicinity. On the non-lesional hemisphere, however, equally good plausibility rates (100%) were observed for both localizer techniques. fMRI-originated fibres generally followed a more posterior course relative to the nTMS-based tracts (p < 0.01) in both the lesional and non-lesional hemisphere.

CONCLUSION

NTMS achieved better tracking results than fMRI in conditions when the cortical tract origin (M1) was located in close vicinity to a brain tumour, probably influencing neurovascular coupling. Hence, especially in situations with altered BOLD signal physiology, nTMS seems to be the method of choice in order to identify seed regions for CST mapping in patients.

Bulbar dysfunction in normal pressure hydrocephalus: a prospective study

OBJECTIVE Normal pressure hydrocephalus (NPH) is clinically characterized by gait disturbance, cognitive impairment, and urinary incontinence, as well as enlargement of the ventricles. To the best of the authors' knowledge, there have been no previous publications regarding the correlation between bulbar dysfunction and NPH. The primary objective of this study was to compare preoperative and postoperative prevalence of bulbar dysfunction in patients with NPH. Secondary objectives included assessing the results of surgery for swallowing, speech, gait, cognition, and urination, and evaluating the correlation between bulbar dysfunction and triad symptoms. METHODS Fifty-three patients with NPH who underwent shunt placement surgery at Siriraj Hospital were included in the study. Patients were evaluated for gait, cognition, urination, swallowing, and speech before and 6 months after shunt placement. Triad symptoms were assessed using standard methods. Bulbar dysfunctions were assessed using the Swallowing Problem Questionnaire, Thai Articulation Test, Resonation Screening Test (RST), and Thai Nasality Test. The Thai Speech Assessment Program and nasometer were used for objective speech measurement. RESULTS Preoperatively, 86% (43/50) of patients had swallowing problems and 75% (37/49) had speech problems, as measured by the RST. Postoperatively, there was significant improvement in swallowing (p < 0.001), speech problems by RST (p = 0.008), and voice volume (p = 0.009), but no significant change in the nasometer test. All triad symptoms were improved. There were significant correlations between swallowing impairment and gait disturbance (r = 0.358, p = 0.009), and RST and cognitive impairment (r = -0.502, p < 0.001). CONCLUSIONS This is the first study of bulbar dysfunction in patients with NPH. The results showed that the prevalence of bulbar dysfunction is very high. The correlation between bulbar dysfunction and the classic NPH triad has been documented and published. These bulbar symptoms also significantly improved after surgery. As such, bulbar dysfunction should be regarded as a core symptom that should be considered along with the classic triad in the clinical diagnosis and management of NPH.

Symmetrical Location Characteristics of Corticospinal Tract Associated With Hand Movement in the Human Brain: A Probabilistic Diffusion Tensor Tractography

The purpose of this study is to elucidate the symmetrical characteristics of corticospinal tract (CST) related with hand movement in bilateral hemispheres using probabilistic fiber tracking method. Seventeen subjects were participated in this study. Fiber tracking was performed with 2 regions of interest, hand activated functional magnetic resonance imaging (fMRI) results and pontomedullary junction in each cerebral hemisphere. Each subject's extracted fiber tract was normalized with a brain template. To measure the symmetrical distributions of the CST related with hand movement, the laterality and anteriority indices were defined in upper corona radiata (CR), lower CR, and posterior limb of internal capsule. The measured laterality and anteriority indices between the hemispheres in each different brain location showed no significant differences with P < 0.05. There were significant differences in the measured indices among 3 different brain locations in each cerebral hemisphere with P < 0.001. Our results clearly showed that the hand CST had symmetric structures in bilateral hemispheres. The probabilistic fiber tracking with fMRI approach demonstrated that the hand CST can be successfully extracted regardless of crossing fiber problem. Our analytical approaches and results seem to be helpful for providing the database of CST somatotopy to neurologists and clinical researches.

Deficits in tongue motor control are linked to microstructural brain damage in multiple sclerosis: a pilot study

Background

Deterioration of fine motor control of the tongue is common in Multiple Sclerosis (MS) and has a major impact on quality of life. However, the underlying neuronal substrate is largely unknown. Here, we aimed to explore the association of tongue motor dysfunction in MS patients with overall clinical disability and structural brain damage.

Methods

We employed a force transducer based quantitative-motor system (Q-Motor) to objectively assess tongue function in 33 patients with MS. The variability of tongue force output (TFV) and the mean applied tongue force (TF) were measured during an isometric tongue protrusion task. Twenty-three age and gender matched healthy volunteers served as controls. Correlation analyses of motor performance in MS patients with individual disease burden as expressed by the Expanded Disability Status Scale (EDSS) and with microstructural brain damage as measured by the fractional anisotropy (FA) on Diffusion Tensor Imaging were performed.

Results

MS patients showed significantly increased TFV and decreased TF compared to controls (p < 0.02). TFV but not TF was correlated with the EDSS (p < 0.04). TFV was inversely correlated with FA in the bilateral posterior limb of the internal capsule expanding to the brain stem (p < 0.001), a region critical to tongue function. TF showed a weaker, positive and unilateral correlation with FA in the same region (p < 0.001).

Conclusions

Changes in TFV were more robust and correlated better with disease phenotype and FA changes than TF. TFV might serve as an objective and non-invasive outcome measure to augment the quantitative assessment of motor dysfunction in MS.

Anatomy and lateralization of the human corticobulbar tracts: an fMRI-guided tractography study

The left hemisphere lateralization bias for language functions, such as syntactic processing and semantic retrieval, is well known. Although several theories and clinical data indicate a link between speech motor execution and language, the functional and structural brain lateralization for these functions has never been examined concomitantly in the same individuals. Here, we used functional MRI during rapid silent syllable repetition (/lalala/, /papapa/ and /pataka/, known as oral diadochokinesis or DDK) to map the cortical representation of the articulators in 17 healthy adults. In these same participants, functional lateralization for language production was assessed using the well-established verb generation task. We then used DDK-related fMRI activation clusters to guide tractography of the corticobulbar tract from diffusion-weighted MRI. Functional MRI revealed a wide inter-individual variability of hemispheric asymmetry patterns (left and right dominant, as well as bilateral) for DDK in the motor cortex, despite predominantly left hemisphere dominance for language-related activity in Broca's area. Tractography revealed no evidence for structural asymmetry (based on fractional anisotropy) within the corticobulbar tract. To our knowledge, this study is the first to reveal that motor brain activation for syllable repetition is unrelated to functional asymmetry for language production in adult humans. In addition, we found no evidence that the human corticobulbar tract is an asymmetric white matter pathway. We suggest that the predominance of dysarthria following left hemisphere infarct is probably a consequence of disrupted feedback or input from left hemisphere language and speech planning regions, rather than structural asymmetry of the corticobulbar tract itself.

Topographic organization of motor fibre tracts in the human brain: findings in multiple locations using magnetic resonance diffusion tensor tractography

OBJECTIVES

To identify the hand and foot fibre tracts of the corticospinal tract (CST), and to evaluate the relative locations, angles, and distances of two fibre tracts using diffusion tensor tractography (DTT).

METHODS

Twelve healthy subjects were enrolled. The regions of interests (ROIs) were drawn in the functional magnetic resonance imaging (fMRI) activation areas and pons in each subject for fibre tracking. We evaluated fibre tract distributions using distances and angles between two fibre tracts starting from the location of a hand fibre tract in multiple brain regions.

RESULTS

The measured angles and distances were 96.43-150°/2.69-9.93 mm (upper CR), 91.86-180°/1.63-7.42 mm (lower CR), 54.47-75°/0.75-4.45 mm (PLIC), and 3.65-90°/0.11-2.36 mm (pons), respectively. The distributions between CR and other sections, such as PLIC and pons, were statistically significant (p < 0.05). There were no significant differences between the upper and lower CR\ or between the PLIC and pons.

CONCLUSIONS

This study showed that the somatotopic arrangement of the hand fibre tract was located at the anterolateral portion in CR and at the anteromedial portion in PLIC and pons, based on the foot fibre. Our methods and results seem to be helpful in motor control neurological research.

KEY POINTS

• We evaluated somatotopic arrangement of CST at multiple anatomical locations. • Somatotopic arrangements and fibre tract distributions were evaluated based on hand fibre location. • Relative angles, locations, and distances between two fibres vary according to their anatomical locations.

Identification of the Corticobulbar Tracts of the Tongue and Face Using Deterministic and Probabilistic DTI Fiber Tracking in Patients with Brain Tumor

BACKGROUND AND PURPOSE

The corticobulbar tract of the face and tongue, a critical white matter tract connecting the primary motor cortex and the pons, is rarely detected by deterministic DTI fiber tractography. Detection becomes even more difficult in the presence of a tumor. The purpose of this study was to compare identification of the corticobulbar tract by using deterministic and probabilistic tractography in patients with brain tumor.

MATERIALS AND METHODS

Fifty patients with brain tumor who underwent DTI were studied. Deterministic tractography was performed by using the fiber assignment by continuous tractography algorithm. Probabilistic tractography was performed by using a Monte Carlo simulation method. ROIs were drawn of the face and tongue motor homunculi and the pons in both hemispheres.

RESULTS

In all subjects, fiber assignment by continuous tractography was ineffectual in visualizing the entire course of the corticobulbar tract between the face and tongue motor cortices and the pons on either side. However, probabilistic tractography successfully visualized the corticobulbar tract from the face and tongue motor cortices in all patients on both sides. No significant difference (P < .08) was found between both sides in terms of the number of voxels or degree of connectivity. The fractional anisotropy of both the face and tongue was significantly lower on the tumor side (P < .03). When stratified by tumor type, primary-versus-metastatic tumors, no differences were observed between tracts in terms of the fractional anisotropy and connectivity values (P > .5).

CONCLUSIONS

Probabilistic tractography successfully reconstructs the face- and tongue-associated corticobulbar tracts from the lateral primary motor cortex to the pons in both hemispheres.

Injury of the corticobulbar tract in patients with dysarthria following cerebral infarct: diffusion tensor tractography study

OBJECTIVES

Little is known about injury of the corticobulbar tract (CBT) in stroke patients. We attempted to investigate injury of the CBT in patients with dysarthria following cerebral infarct, using diffusion tensor tractography (DTT).

METHODS

Eight patients with dysarthria following a corona radiata infarct and 12 control subjects were recruited for this study. Diffusion tensor imaging was performed at 14.3 days after onset and reconstruction of the CBT was performed using the probabilistic tractography method. Fractional anisotropy, mean diffusivity, and tract volume of the CBT were measured.

RESULTS

Reconstructed CBTs in the affected hemisphere of the patient group were thinner than those of the unaffected hemisphere of the patient group and the control group. Regarding the DTT parameters of the CBTs, fractional anisotropy and tract volume were significantly lower in the affected hemisphere of the patient group than in the unaffected hemisphere of the patient group and the control group (p < 0.05). However, we did not observe any difference in the mean diffusivity value (p > 0.05).

CONCLUSIONS

We demonstrated injury of the CBT in patients with dysarthria following cerebral infarct in the corona radiata using DTT. This result indicates the importance of CBT evaluation for dysarthria in patients with cerebral infarct. Therefore, we suggest that evaluations of the CBT using DTT would be useful for patients with dysarthria following cerebral infarct.

A novel homozygous MCOLN1 double mutant allele leading to TRP channel domain ablation underlies Mucolipidosis IV in an Italian Child

Mucolipidosis type IV (MLIV) is a very rare disorder of late endosome/lysosome transport, characterized by neurodevelopmental abnormalities and progressive visual impairment owing to corneal clouding and retinal dystrophy. Greater than 70 % of MLIV patients are of Ashkenazi Jewish ancestry. Here we report a novel MCOLN1double mutant allele [c.395_397delCTG;c.468_474dupTTGGACC] which introduces a premature stop codon [p.Ala132del; p.Asn159LeufsX27] leading to almost complete abrogation of the region coding mucolipin-1, a member of the transient receptor potential (TRP) cation channel family. The genomic lesion was identified in homozygous state, in a non-Jewish Italian MLIV patient, who also presented abnormal serum gastrin levels. Conventional and advanced MRI sequences, including diffusion tensor imaging and tractography, were used for the assessment of white matter involvement in the patient.

Anatomical location and somatotopic organization of the corticospinal tract in the corona radiata of the normal human brain: a diffusion tensor tractography study

The anatomical location and somatotopic organization of the corticospinal tract (CST) in the corona radiata (CR) of the normal human brain have not been studied using diffusion tensor tractography so far. In this study, the anatomical location and somatotopic organization of the CST in the CR were evaluated by determining the highest probabilistic locations and distances between the upper and lower extremities in the slices of upper and lower CR in the brain. In the mediolateral direction, the average of the highest probabilistic locations for the upper and lower extremities were 40.27 and 37.16% at the upper CR level and 38.19 and 37.14% at the lower CR level, respectively. In the anteroposterior direction, the average of the highest probabilistic locations for the upper and lower extremities were 62.52 and 75.65% at the upper CR level and 60.19 and 68.12% at the lower CR level, respectively. The average distances between upper and lower extremities for the mediolateral direction were 2.41 mm at the upper CR level and 1.21 mm at the lower CR level. The average distances between upper and lower extremities for the anteroposterior direction were 5.23 mm at the upper CR level and 4.47 mm at the lower CR level, respectively. Our findings suggest that the anatomical location and somatotopic organization for the upper extremity are located anterolaterally to the lower extremity in the CR of a normal human brain and distances between the upper and lower extremities become decreased as the CST descends from the upper to the lower CR level.

The anatomical location of the corticobulbar tract at the corona radiata in the human brain: diffusion tensor tractography study

Many studies have reported on the anatomical location of the corticobulbar tract (CBT). However, no study has reported on the anatomical location of the corona radiata (CR). Using diffusion tensor tractography, we investigated the anatomical location of the CBT at the CR in normal subjects. Forty healthy normal subjects were enrolled in this study. Diffusion tensor images were acquired at 1.5-T, and the CBT was reconstructed using FMRIB software. The highest probabilistic location of the CBT was defined as the location on an axial slice in the upper and lower CRs. The CBT was located at an average of 49.13% and 49.91% in the antero-posterior direction between the most anterior point and the most posterior point of the lateral ventricle at the upper and lower CR, respectively. Regarding medio-lateral direction, between the midline and the most lateral point of the brain, the CBT was located at an average of 36.58% and 32.73% at the upper and lower CR, respectively. According to our findings, the CBT was located almost halfway between the most anterior point and the most posterior point of the lateral ventricle at the CR, and almost one third between the midline and the most lateral point of the brain at the CR.

Improved nTMS- and DTI-derived CST tractography through anatomical ROI seeding on anterior pontine level compared to internal capsule

Imaging of the course of the corticospinal tract (CST) by diffusion tensor imaging (DTI) is useful for function-preserving tumour surgery. The integration of functional localizer data into tracking algorithms offers to establish a direct structure–function relationship in DTI data. However, alterations of MRI signals in and adjacent to brain tumours often lead to spurious tracking results. We here compared the impact of subcortical seed regions placed at different positions and the influences of the somatotopic location of the cortical seed and clinical co-factors on fibre tracking plausibility in brain tumour patients.

The CST of 32 patients with intracranial tumours was investigated by means of deterministic DTI and neuronavigated transcranial magnetic stimulation (nTMS). The cortical seeds were defined by the nTMS hot spots of the primary motor area (M1) of the hand, the foot and the tongue representation. The CST originating from the contralesional M1 hand area was mapped as intra-individual reference. As subcortical region of interests (ROI), we used the posterior limb of the internal capsule (PLIC) and/or the anterior inferior pontine region (aiP). The plausibility of the fibre trajectories was assessed by a-priori defined anatomical criteria. The following potential co-factors were analysed: Karnofsky Performance Scale (KPS), resting motor threshold (RMT), T1-CE tumour volume, T2 oedema volume, presence of oedema within the PLIC, the fractional anisotropy threshold (FAT) to elicit a minimum amount of fibres and the minimal fibre length.

The results showed a higher proportion of plausible fibre tracts for the aiP-ROI compared to the PLIC-ROI. Low FAT values and the presence of peritumoural oedema within the PLIC led to less plausible fibre tracking results. Most plausible results were obtained when the FAT ranged above a cut-off of 0.105. In addition, there was a strong effect of somatotopic location of the seed ROI; best plausibility was obtained for the contralateral hand CST (100%), followed by the ipsilesional hand CST (>95%), the ipsilesional foot (>85%) and tongue (>75%) CST. In summary, we found that the aiP-ROI yielded better tracking results compared to the IC-ROI when using deterministic CST tractography in brain tumour patients, especially when the M1 hand area was tracked. In case of FAT values lower than 0.10, the result of the respective CST tractography should be interpreted with caution with respect to spurious tracking results. Moreover, the presence of oedema within the internal capsule should be considered a negative predictor for plausible CST tracking.

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Somatotopic CST tractography was done in 32 patients with eloquent brain tumours.

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Seeding ROIs were defined by navigated TMS of the M1 hot spot (hand, foot, tongue).

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Using the anterior pons as a second ROI yielded more plausible tracts than the PLIC.

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Low FAT and oedema of the internal capsule were negative predictors.

Reduced integrity of sensorimotor projections traversing the posterior limb of the internal capsule in children with congenital hemiparesis

There is reduced integrity of corticospinal projections that traverse the posterior limb of the internal capsule (PLIC) in children with unilateral cerebral palsy (CP). It remains unclear whether there are changes in integrity of other projections traversing the PLIC. Forty children with congenital hemiparesis and 15 typically developing children underwent structural and diffusion-weighted MRI. All children with congenital hemiparesis showed lesions to the periventricular white matter. Structural images were parcellated into 34 cortical regions per hemisphere and posterior limb of the internal capsule was identified. PLIC connections to each cortical region were extracted using probabilistic tractography. Differences between hemispheres for each cortical projection (asymmetry index (AI)) and tract microstructure (fractional anisotropy (FA), mean diffusivity (MD)) were assessed. The results showed that 17 children (42.5%) with congenital hemiparesis showed bilateral lesions on structural MRI. Projections to the primary motor cortex (precentral gyrus and paracentral lobule) showed greater asymmetry in unilateral CP group compared to typically developing children and indicate reduced projections on the hemisphere contralateral to the impaired limb (i.e., contralateral hemisphere). Reduced FA and increased MD were also observed for connections with the primary motor cortex, primary sensory cortex (postcentral gyrus) and precuneus on the contralateral hemisphere in children with congenital hemiparesis. Similar changes were observed between children with unilateral and bilateral lesions on structural MRI. Notably, microstructural changes were associated with deficits in both sensory and motor function. The findings further unravel the underlying neuroanatomical correlates of sensorimotor deficits in children with congenital hemiparesis.