The positive effect of venlafaxine on central motor conduction

OBJECTIVES

Using the triple stimulation technique (TST) and conventional transcranial magnetic stimulation (TMS), this study was designed to investigate the effect of venlafaxine on central motor conduction in healthy adults.

PATIENTS AND METHODS

In this crossover, self-controlled trial, eight healthy adult volunteers were randomly divided into groups A and B. In group A, the volunteers were administered 1 venlafaxine capsule once daily for 7 consecutive days, followed by a 3-day break. Next, volunteers in this group received 1 placebo capsule once daily for 7 consecutive days. Group B received the treatments in the opposite order. The index finger tapping test, grip strength test, TST and conventional TMS examination for each hand were recorded before and one week after the administration of venlafaxine or placebo.

RESULTS

Compared to the placebo stage, in the venlafaxine stage, the number of index finger taps was significantly increased for both hands, and the TST amplitude and area ratios were significantly increased. The improvement in the TST amplitude ratio was significantly and positively correlated with the improvements in performance on the index finger tapping test.

CONCLUSION

Venlafaxine positively regulates central motor conduction in healthy adults.

Effect of streptozotocin-induced diabetes on motor representations in the motor cortex and corticospinal tract in rats

Motor disorders in patients with diabetes are associated with diabetic peripheral neuropathy, which can lead to symptoms such as lower extremity weakness. However, it is unclear whether central motor system disorders can disrupt motor function in patients with diabetes. In a streptozotocin-induced rat model of type 1 diabetes, we used intracortical microstimulation to evaluate motor representations in the motor cortex, recorded antidromic motor cortex responses to spinal cord stimulation to evaluate the function of corticospinal tract (CST) axons, and used retrograde labeling to evaluate morphological alterations of CST neurons. The diabetic rats exhibited size reductions in the hindlimb area at 4 weeks and in trunk and forelimb areas after 13 weeks, with the hindlimb and trunk area reductions being the most severe. Other areas were unaffected. Additionally, we observed reduced antidromic responses in CST neurons with axons projecting to lumbar spinal segments (CST-L) but not in those with axons projecting to cervical segments (CST-C). This was consistent with the observation that retrograde-labeled CST-L neurons were decreased in number following tracer injection into the spinal cord in diabetic animals but that CST-C neurons were preserved. These results show that diabetes disrupts the CST system components controlling hindlimb and trunk movement. This disruption may contribute to lower extremity weakness in patients.

Reconstruction of white matter fibre tracts using diffusion kurtosis tensor imaging at 1.5T: Pre-surgical planning in patients with gliomas

Tractography studies for pre-surgical planning of primary brain tumors is typically done using diffusion tensor imaging (DTI), which cannot resolve crossing, kissing or highly angulated fibres. Tractography based on the estimation of the diffusion kurtosis (DK) tensor was recently demonstrated to enable tackling these limitations. However, its use in the clinical context at low 1.5T field has not yet been reported.

PURPOSE

To evaluate if the estimation of whole-brain tractography using the DK tensor is feasible for pre-surgical investigation of patients with brain tumors at 1.5T.

METHODS

Eight healthy subjects and 3 patients with brain tumors were scanned at 1.5T using a 12-channel head coil. Diffusion-weighted images were acquired with repetition/echo times of 5800/107 ms, 82 × 82 resolution, 3 × 3 × 3 mm3 voxel size, b-values of 0, 1000, 2000 s/mm2 and 64 gradient sensitising directions. Whole-brain tractography was estimated using the DK tensor and corticospinal tracts (CST) were isolated using regions-of-interest placed at the cerebral peduncles and motor gyrus. Tract size, DK metrics and CST deviation index (highest curvature point) were compared between healthy subjects and patients.

RESULTS

Tract sizes did not differ between groups. The CST deviation index was significantly higher in patients compared to healthy subjects. Fractional anisotropy was significantly lower in patients, with higher mean kurtosis asymmetry index at the highest curvature point in patients.

CONCLUSIONS

Corticospinal fibre bundles estimated using DK tensor in a 1.5T scanner presented similar properties in patients with brain gliomas as those reported in the literature using DTI-based tractography.

How accurate are prenatal tractography results? A postnatal in vivo follow-up study using diffusion tensor imaging

Prenatal detection of abnormal white matter tracts might serve as a structural marker for altered neurodevelopment. As a result of many technical and patient-related challenges, the accuracy of prenatal tractography remains unknown. We hypothesized that characteristics of prenatal tractography of the corpus callosum and corticospinal tracts derived from fetal diffusion tensor imaging (DTI) data are accurate and predictive of the integrity of these tracts postnatally. We compared callosal and corticospinal tracts of 12 subjects with paired prenatal (age: 23-35 gestational weeks) and postnatal (age: 1 day to 2 years) DTI examinations (b values of 0 s/mm² and 700 s/mm², 16 gradient encoding directions) using deterministic tractography. Evaluation for the presence of callosal segments and corticospinal tracts showed moderate degrees of accuracy (67-75%) for the four segments of the corpus callosum and moderate to high degrees of accuracy (75-92%) for the corticospinal tracts. Positive predictive values for segments of the corpus callosum ranged from 50% to 100% and for the corticospinal tracts, 89% to 100%. Negative predictive values for segments of the corpus callosum ranged from 25% to 80% and for the corticospinal tracts, 33% to 50%. The results suggest that when the tracts are not well characterized on the fetal MR, predictions about the postnatal tracts are difficult to make. However, accounting for brain maturation, prenatal visualization of the main projection and commissural tracts can be clinically used as an important predictive tool in the context of image interpretation for the assessment of fetal brain malformations.

Inhibition of the primary motor cortex and the upgoing thumb sign

Background

The upgoing thumb sign has been frequently observed in patients with minor strokes and transient ischemic attacks as an indicator of brain involvement. We assessed the effect of primary motor cortex (M1) inhibition in the development of the upgoing thumb sign.

Methods

Used repetitive Transcranial Magnetic Stimulation (rTMS, 1 Hz frequency for 15 min, 1s ISI, 900 pulses) at 60% of resting motor threshold to inhibit the right or left primary motor cortex of 10 healthy individuals. Participants were examined before and after rTMS by a neurologist who was blind to the site of motor cortex inhibition.

Results

10 neurological intact participants (5 women/5 men) were recruited for this study. 2 cases were excluded due to pre-existing possible thumb signs. After the inhibition of the primary motor cortex, in 6 subjects out of 8, we observed a thumb sign contralateral to the site of primary motor cortex inhibition. In one subject an ipsilateral thumbs sign was noted. In another case, we did not find an upgoing thumb sign.

Conclusion

The upgoing thumb sign is a subtle neurological finding that may be related to the primary motor cortex or corticospinal pathways involvements.

•

After the inhibition of the primary motor cortex, using repetitive Transcranial Magnetic Stimulation 9 (rTMS), in 7 subjects out of 8, the upgoing thumb sign was observed.

•

The upgoing thumb sign is a subtle neurological finding related to the upper motor neuron involvements.

•

The upgoing thumb sign may be seen in the primary motor cortex or corticospinal pathways lesions.

Detecting spinal pyramidal tract of amyotrophic lateral sclerosis patients with diffusion tensor tractography

The objective of this study was to determine alteration of corticospinal tract in patients with amyotrophic lateral sclerosis (ALS) using diffusion tensor tractograhy (DTT) focusing on the cervical spinal cord (C5) and transcranial magnetic stimulation (TMS). We recruited 38 ALS, 6 spinal and bulbar muscular atrophy (SBMA), 7 spastic paraplegia (SP) patients, and 8 age-matched normal controls, and then ALS were divided into two subgroups according to their clinical type: 28 ALS-limb and 10 ALS-bulbar. DTT was performed using the diffusion tensor image (DTI) track module to reconstruct two fiber tracts via C5. The fractional anisotropy (FA) values of ALS-total and ALS-limb patients were significantly reduced compared with normal controls, and SBMA patients. On the other hand, the mean diffusivity (MD) values were not significantly different among normal controls and the three disease groups. The rate of disease progression (ΔFRS-R) of ALS patients was significantly correlated with FA values and central motor conduction time (CMCT). In conclusion, the present study demonstrated a significant reduction of FA values in ALS patients, and the ΔFRS-R of ALS patients showed distinct regressions with FA values and CMCT, suggesting that this DTT analysis could be useful for detecting disease progression of ALS patients.

Corticospinal control from M1 and PMv areas on inhibitory cervical propriospinal neurons in humans

Inhibitory propriospinal neurons with diffuse projections onto upper limb motoneurons have been revealed in humans using peripheral nerve stimulation. This system is supposed to mediate descending inhibition to motoneurons, to prevent unwilling muscle activity. However, the corticospinal control onto inhibitory propriospinal neurons has never been investigated so far in humans. We addressed the question whether inhibitory cervical propriospinal neurons receive corticospinal inputs from primary motor (M1) and ventral premotor areas (PMv) using spatial facilitation method. We have stimulated M1 or PMv using transcranial magnetic stimulation (TMS) and/or median nerve whose afferents are known to activate inhibitory propriospinal neurons. Potential input convergence was evaluated by studying the change in monosynaptic reflexes produced in wrist extensor electromyogram (EMG) after isolated and combined stimuli in 17 healthy subjects. Then, to determine whether PMv controlled propriospinal neurons directly or through PMv-M1 interaction, we tested the connectivity between PMv and propriospinal neurons after a functional disruption of M1 produced by paired continuous theta burst stimulation (cTBS). TMS over M1 or PMv produced reflex inhibition significantly stronger on combined stimulations, compared to the algebraic sum of effects induced by isolated stimuli. The extra-inhibition induced by PMv stimulation remained even after cTBS which depressed M1 excitability. The extra-inhibition suggests the existence of input convergence between peripheral afferents and corticospinal inputs onto inhibitory propriospinal neurons. Our results support the existence of direct descending influence from M1 and PMv onto inhibitory propriospinal neurons in humans, possibly though direct corticospinal or via reticulospinal inputs.

Early corticospinal tract damage in prodromal SCA2 revealed by EEG-EMG and EMG-EMG coherence

OBJECTIVE

Clinical data suggest early involvement of the corticospinal tract (CST) in spinocerebellar ataxia type 2 (SCA2). Here we tested if early CST degeneration can be detected in prodromal SCA2 mutation carriers by electrophysiological markers of CST integrity.

METHODS

CST integrity was tested in 15 prodromal SCA2 mutation carriers, 19 SCA2 patients and 25 age-matched healthy controls, using corticomuscular (EEG-EMG) and intermuscular (EMG-EMG) coherence measures in upper and lower limb muscles.

RESULTS

Significant reductions of EEG-EMG and EMG-EMG coherences were observed in the SCA2 patients, and to a similar extent in the prodromal SCA2 mutation carriers. In prodromal SCA2, EEG-EMG and EMG-EMG coherences correlated with the predicted time to ataxia onset.

CONCLUSIONS

Findings indicate early CST neurodegeneration in SCA2. EEG-EMG and EMG-EMG coherence may serve as biomarkers of early CST neurodegeneration in prodromal SCA2 mutation carriers.

SIGNIFICANCE

Findings are important for developing preclinical disease markers in the context of currently emerging disease-modifying therapies of neurodegenerative disorders.

Persistent uncrossed corticospinal connections in patients with intractable focal epilepsy

Corticospinal connections may be bilateral at birth, but a predominantly unilateral and crossed pattern develops by the toddler years. Acquired injury can alter the normal development of laterality such that uncrossed corticospinal connections persist, particularly if the injury is early in life and involves the motor system. Whether other developmental insults, such as childhood epilepsy, affect the development of crossed laterality in the motor system is unknown, although this topic has relevance for understanding the broader impact of epilepsy on brain development. Accordingly, in a cohort of children with intractable focal epilepsy, we tested by neuronavigated transcranial magnetic stimulation (nTMS) whether childhood epilepsy is associated with persistent uncrossed corticospinal connections. Specifically, we hypothesized that in contrast to early-life neuroclastic corticospinal tract injury that induces preservation of uncrossed corticospinal connections in the contralesional hemisphere, uncrossed corticospinal connections will be preserved in the epileptic hemisphere where the corticospinal tract is intact, but overstimulated by ongoing seizures and epileptic interictal discharges. Motor cortex mapping was performed by nTMS as part of a clinical presurgical evaluation, and the analysis was limited to patients with radiographically intact motor cortices and corticospinal tracts. Given that foot motor cortex representation is often bilateral, we focused on the lateralization for the tibialis anterior muscle cortical motor representation and its relation to the seizure focus. We demonstrate preserved uncrossed corticospinal connections for the tibialis anterior region of the hemisphere affected by the epilepsy. These findings indicate a pathologically preserved immature motor lateralization in patients with epilepsy and suggest that developmental processes associated with hemispheric lateralization are affected by epilepsy.

Corticomuscular Coherence: a Novel Tool to Assess the Pyramidal Tract Dysfunction in Spinocerebellar Ataxia Type 2

Clinical signs of corticospinal tract dysfunction are a common feature of spinocerebellar ataxia type 2 (SCA2) patients. The objective of this study is to assess dysfunction of the corticospinal tract in SCA2 using corticomuscular coherence. Testing corticomuscular coherence and rating of ataxia severity and non-ataxia symptoms were performed in 19 SCA2 patients and 24 age-matched controls. Central motor conduction times (CMCT) to upper and lower right limbs were obtained for the SCA2 group using Transcraneal magnetic stimulation (TMS). SCA2 patients exhibited a significant reduction of corticomuscular coherence for lower limbs, but not for upper limbs. This difference remained significant, even when excluding those individuals with clinical signs of corticospinal tract dysfunction. Corticomuscular coherence for lower limbs correlated inversely with CMCT to tibialis anterior muscle. Corticomuscular coherence could be a valuable electrophysiological tool to assess the corticospinal tract involvement in SCA2, even in the absence of clinical signs of corticospinal tract dysfunction.

Motor cortex and spinal cord neuromodulation promote corticospinal tract axonal outgrowth and motor recovery after cervical contusion spinal cord injury

Cervical injuries are the most common form of SCI. In this study, we used a neuromodulatory approach to promote skilled movement recovery and repair of the corticospinal tract (CST) after a moderately severe C4 midline contusion in adult rats. We used bilateral epidural intermittent theta burst (iTBS) electrical stimulation of motor cortex to promote CST axonal sprouting and cathodal trans-spinal direct current stimulation (tsDCS) to enhance spinal cord activation to motor cortex stimulation after injury. We used Finite Element Method (FEM) modeling to direct tsDCS to the cervical enlargement. Combined iTBS-tsDCS was delivered for 30min daily for 10days. We compared the effect of stimulation on performance in the horizontal ladder and the Irvine Beattie and Bresnahan forepaw manipulation tasks and CST axonal sprouting in injury-only and injury+stimulation animals. The contusion eliminated the dorsal CST in all animals. tsDCS significantly enhanced motor cortex evoked responses after C4 injury. Using this combined spinal-M1 neuromodulatory approach, we found significant recovery of skilled locomotion and forepaw manipulation skills compared with injury-only controls. The spared CST axons caudal to the lesion in both animal groups derived mostly from lateral CST axons that populated the contralateral intermediate zone. Stimulation enhanced injury-dependent CST axonal outgrowth below and above the level of the injury. This dual neuromodulatory approach produced partial recovery of skilled motor behaviors that normally require integration of posture, upper limb sensory information, and intent for performance. We propose that the motor systems use these new CST projections to control movements better after injury.

Effect of prenatal exposure to ethanol on the pyramidal tract in developing rats

Prenatal exposure to ethanol induces a relative increase in the numbers of pyramidal tract axons relative to the number of corticospinal projection neurons in somatosensory/motor cortices in the adult rat. The present study examines the effects of ethanol on the numbers of axons in the developing caudal pyramidal tract, i.e., corticospinal axons. Electron microscopic analyses of the pyramidal tracts of the offspring of pregnant rat dams fed a control diet ad libitum, pair-fed a liquid control diet, or fed an ethanol-containing diet ad libitum were performed. The pups were 5-, 15-, 30- and 90-days-old. The numbers of axons in control rats fell precipitously after postnatal day (P) 15 and the frequency of myelinated axons rose dramatically between P15 and P90. Ethanol exposure had no significant effect on the numbers of pyramidal tract axons at any age. Moreover, no ethanol-induced differences in the numbers of axons in different stages of myelination, i.e., axons that were "free" of glial associations, glia-engulfed, invested by 1-2 layers of myelin, or myelinated by 3+ layers of myelin, were detected on P15. Thus, it appears that (a) pyramidal tract axons are lost or pruned during the first two postnatal weeks and (b) postnatal development of pyramidal tract axons (e.g., pruning and myelination) is not affected by ethanol. The implications are that the ethanol-induced increase in the number of axons relative to the number of somata of corticospinal neurons detected in pups and adults results from the effects of ethanol on early stages (initiation) of axogenesis.

Optimal Factors of Diffusion Tensor Imaging Predicting Corticospinal Tract Injury in Patients with Brain Tumors

Objective

To identify the optimal factors in diffusion tensor imaging for predicting corticospinal tract (CST) injury caused by brain tumors.

Materials and Methods

This prospective study included 33 patients with motor weakness and 64 patients with normal motor function. The movement of the CST, minimum distance between the CST and the tumor, and relative fractional anisotropy (rFA) of the CST on diffusion tensor imaging, were compared between patients with motor weakness and normal function. Logistic regression analysis was used to obtain the optimal factor predicting motor weakness.

Results

In patients with motor weakness, the displacement (8.44 ± 6.64 mm) of the CST (p = 0.009), minimum distance (3.98 ± 7.49 mm) between the CST and tumor (p < 0.001), and rFA (0.83 ± 0.11) of the CST (p < 0.001) were significantly different from those of the normal group (4.64 ± 6.65 mm, 14.87 ± 12.04 mm, and 0.98 ± 0.05, respectively) (p = 0.009, p < 0.001, and p < 0.001). The frequencies of patients with the CST passing through the tumor (6%, p = 0.002), CST close to the tumor (23%, p < 0.001), CST close to a malignant tumor (high grade glioma, metastasis, or lymphoma) (19%, p < 0.001), and CST passing through infiltrating edema (19%, p < 0.001) in the motor weakness group, were significantly different from those of the patients with normal motor function (0, 8, 1, and 10%, respectively). Logistic regression analysis showed that decreased rFA and CST close to a malignant tumor were effective variables related to motor weakness.

Conclusion

Decreased fractional anisotropy, combined with closeness of a malignant tumor to the CST, is the optimal factor in predicting CST injury caused by a brain tumor.

Preclinical and Clinical Evidence on Ipsilateral Corticospinal Projections: Implication for Motor Recovery

Motor impairment is the most common complication after stroke, and recovery of motor function has been shown to be dependent on the extent of lesion in the ipsilesional corticospinal tract (iCST) and activity within ipsilesional primary and secondary motor cortices. However, work from neuroimaging research has suggested a role of the contralesional hemisphere in promoting recovery after stroke potentially through the ipsilateral uncrossed CST fibers descending to ipsilateral spinal segments. These ipsilateral fibers, sometimes referred to as "latent" projections, are thought to contribute to motor recovery independent of the crossed CST. The aim of this paper is to evaluate using cumulative evidence from animal models and human patients on whether an uncrossed CST component is present in mammals and conserved through primates and humans, and whether iCST fibers have a functional role in hemiparetic/hemiplegic human conditions. This review highlights that an ipsilateral uncrossed CST exists in human during development, but the evidence on a functionally relevant iCST component in adult humans is still elusive. In addition, this review argues that whereas activity within the ipsilesional cortex is essential for enhancing motor recovery after stroke, the role of iCST projections specifically is still controversial. Finally, conclusions from current literature emphasize the importance of activity in the ipsilesional cortex and the integrity of crossed CST fibers as major determinants of motor recovery after brain injury.

MR imaging for accurate prediction of outcome after perinatal arterial ischemic stroke: Sooner not necessarily better

BACKGROUND

Involvement of the corticospinal tracts after perinatal arterial ischemic stroke (PAIS) is strongly correlated with adverse motor outcome.

METHODS

Two full-term infants with PAIS, with two early MRI scans available, are reported.

RESULTS

Diffusion weighted imaging (DWI)-MRI, performed within 24 h following onset of seizures and repeated 48 h later, clearly showed restricted diffusion within the middle cerebral artery territory on both MRIs, but clear patterns of signal intensity changes in the descending corticospinal tracts on the second MRI only.

CONCLUSION

Since involvement of the corticospinal tracts is essential for prediction of motor outcome, we may need to reconsider optimal timing of MR imaging for prediction of neurodevelopmental outcome after PAIS.

Corticobulbar motor evoked potentials from tongue muscles used as a control in cervical spinal surgery

Objective

Motor evoked potentials (MEPs) changes might be caused to the non-surgically induced factors during cervical spinal surgery. Therefore, control MEPs recorded cranially to the exit of the C5 root are highly recommendable in cervical spinal surgery. We studied whether corticobulbar MEPs (C-MEPs) from tongue muscle could be used as a control MEPs in cervical spinal surgery.

Methods

Twenty-five consecutive cervical spinal surgeries were analyzed. Stimulation of motor area for tongue was done by subcutaneous electrodes placed at C3/C4 (10-20 EEG System), and recording was done from both sides of tongue.

Results

C-MEPs were recorded successfully 24 out of the 25 (96%) tested patients. Forty-six out of fifty MEPs (92%) from tongue muscles were monitorable from the baseline. In two patients, we could obtain only unilateral C-MEPs. Mean MEPs latencies obtained from the left and right side of the tongue were 11.5 ± 1 ms and 11.5 ± 0.8 ms, respectively.

Conclusions

Monitoring C-MEPs from tongue muscles might be useful control in cervical spinal surgery. They were easily elicited and relatively free from phenomenon of peripheral stimulation of the hypoglossal nerves.

Significance

This is first study to identify the usefulness of C-MEPs as a control of cervical spinal surgery.

Diagnostic Challenge of Diffusion Tensor Imaging in a Patient With Hemiplegia After Traumatic Brain Injury

A 51-year-old man showed hemiplegia on his right side after a traumatic brain injury (TBI). On initial brain computed tomography (CT) scan, an acute subdural hemorrhage in the right cerebral convexity and severe degrees of midline shifting and subfalcine herniation to the left side were evident. On follow-up brain magnetic resonance imaging (MRI), there were multiple microhemorrhages in the left parietal and occipital subcortical regions. To explain the occurrence of right hemiplegia after brain damage which dominantly on the right side of brain, we used diffusion tensor imaging (DTI) to reconstruct the corticospinal tract (CST), which showed nearly complete injury on the left CST. We also performed motor-evoked potentials, and stimulation of left motor cortex evoked no response on both sides of upper extremity. We report a case of patient with hemiplegia after TBI and elucidation of the case by DTI rather than CT and MRI.

Localization of the corticospinal tract within the porcine spinal cord: Implications for experimental modeling of traumatic spinal cord injury

Spinal cord injury (SCI) researchers have predominately utilized rodents for SCI modeling and experimentation. Unfortunately, a large number of novel therapies developed in rodent models have failed to demonstrate efficacy in human clinical trials which suggests that improved animal models are an important translational tool. Recently, porcine models of SCI have been identified as a valuable intermediary model for preclinical evaluation of promising therapies to aid clinical translation. However, the localization of the major spinal tracts in pigs has not yet been described. Given that significant differences exist in the location of the corticospinal tract (CST) between rodents and humans, determining its location in pigs will provide important information related to the translational potential of the porcine pre-clinical model of SCI. Thus, the goal of this study is to investigate the localization of the CST within the porcine spinal cord. Mature female domestic pigs (n=4, 60kg) received microinjections of fluorescent dextran tracers (Alexa Fluor, 10,000MW) into the primary motor cortex, using image-guided navigation (StealthStation^®), to label the CST. At 5 weeks post-tracer injection animals were euthanized, the entire neuroaxis harvested and processed for histological examination. Serial sections of the brain and spinal cord were prepared and imaged using confocal microscopy to observe the location of the CST in pigs. Results demonstrate that the CST of pigs is located in the lateral white matter, signifying greater similarity to human anatomical structure compared to that of rodents. We conclude that the corticospinal tract in pigs demonstrates anatomical similarity to human, suggesting that the porcine model has importance as a translational intermediary pre-clinical model.

Unravelling the effect of experimental pain on the corticomotor system using transcranial magnetic stimulation and electroencephalography

The interaction between pain and the motor system is well-known, with past studies showing that pain can alter corticomotor excitability and have deleterious effects on motor learning. The aim of this study was to better understand the cortical mechanisms underlying the interaction between pain and the motor system. Experimental pain was induced on 19 young and healthy participants using capsaicin cream, applied on the middle volar part of the left forearm. The effect of pain on brain activity and on the corticomotor system was assessed with electroencephalography (EEG) and transcranial magnetic stimulation (TMS), respectively. Compared to baseline, resting state brain activity significantly increased after capsaicin application in the central cuneus (theta frequency), left dorsolateral prefrontal cortex (alpha frequency), and left cuneus and right insula (beta frequency). A pain-evoked increase in the right primary motor cortex (M1) activity was also observed (beta frequency), but only among participants who showed a reduction in corticospinal output (as depicted by TMS recruitment curves). These participants further showed greater beta M1-cuneus connectivity than the other participants. These findings indicate that pain-evoked increases in M1 beta power are intimately tied to changes in the corticospinal system, and provide evidence that beta M1-cuneus connectivity is related to the corticomotor alterations induced by pain. The differential pattern of response observed in our participants suggest that the effect of pain on the motor system is variable from on individual to another; an observation that could have important clinical implications for rehabilitation professionals working with pain patients.

Electrical neuromodulation of the cervical spinal cord facilitates forelimb skilled function recovery in spinal cord injured rats

Enabling motor control by epidural electrical stimulation of the spinal cord is a promising therapeutic technique for the recovery of motor function after a spinal cord injury (SCI). Although epidural electrical stimulation has resulted in improvement in hindlimb motor function, it is unknown whether it has any therapeutic benefit for improving forelimb fine motor function after a cervical SCI. We tested whether trains of pulses delivered at spinal cord segments C6 and C8 would facilitate the recovery of forelimb fine motor control after a cervical SCI in rats. Rats were trained to reach and grasp sugar pellets. Immediately after a dorsal funiculus crush at C4, the rats showed significant deficits in forelimb fine motor control. The rats were tested to reach and grasp with and without cervical epidural stimulation for 10weeks post-injury. To determine the best stimulation parameters to activate the cervical spinal networks involved in forelimb motor function, monopolar and bipolar currents were delivered at varying frequencies (20, 40, and 60Hz) concomitant with the reaching and grasping task. We found that cervical epidural stimulation increased reaching and grasping success rates compared to the no stimulation condition. Bipolar stimulation (C6- C8+ and C6+ C8-) produced the largest spinal motor-evoked potentials (sMEPs) and resulted in higher reaching and grasping success rates compared with monopolar stimulation (C6- Ref+ and C8- Ref+). Forelimb performance was similar when tested at stimulation frequencies of 20, 40, and 60Hz. We also found that the EMG activity in most forelimb muscles as well as the co-activation between flexor and extensor muscles increased post-injury. With epidural stimulation, however, this trend was reversed indicating that cervical epidural spinal cord stimulation has therapeutic potential for rehabilitation after a cervical SCI.

Functional Reconstruction of Motor and Language Pathways Based on Navigated Transcranial Magnetic Stimulation and DTI Fiber Tracking for the Preoperative Planning of Low Grade Glioma Surgery: A New Tool for Preservation and Restoration of Eloquent Networks

BACKGROUND

Surgery of low-grade gliomas (LGGs) in eloquent areas still presents a challenge. New technologies have been introduced to enable the performance of "functional", customized preoperative planning aimed at maximal resection, while reducing the risk of postoperative deficits. We describe our experience in the surgery of LGGs in eloquent areas using preoperative planning based on navigated transcranial magnetic stimulation (nTMS) and diffusion tensor imaging (DTI) tractography.

METHODS

Sixteen patients underwent preoperative planning, using nTMS and nTMS-based DTI tractography. Motor and language functions were mapped. Preoperative data allowed for tailoring of the surgical strategy. The impact of these modalities on surgical planning was evaluated. Influence on functional outcome was analyzed in comparison with results in a historical control group.

RESULTS

In 12 patients (75 %), nTMS added useful information on functional anatomy and surgical risks. Surgical strategy was modified in 9 of 16 cases (56 %). The nTMS "functional approach" provided a good outcome at discharge, with a decrease in postoperative motor and/or language deficits, as compared with controls (6 vs. 44 %; p = 0.03).

CONCLUSIONS

The functional preoperative mapping of speech and motor pathways based on nTMS and DTI tractography provided useful information, allowing us to plan the best surgical strategy for radical resection; this resulted in improved postoperative neurological results.

Unravelling motor networks in patients with chronic disorders of consciousness: A promising minimally invasive approach

Behavioral responsiveness and awareness levels correlate with the degree of functional connectivity within cortical-thalamocortical networks, whose breakdown accounts for chronic disorders of consciousness (DOC). Our study was aimed at assessing the role of the primary motor area (M1) and premotor-M1 circuitry dysfunction in motor output deterioration in minimally conscious state (MCS) and unresponsive wakefulness syndrome (UWS) patients. As a control group, we included a healthy subject (HC) sample in the study. We evaluated the effects of different types of transcranial magnetic stimuli over M1 by recording post-stimulus time histogram (PSTH), which includes a series of peaks of unit firing activity that match with D and I-waves, characterizing the descending corticospinal volleys evoked by transcranial magnetic stimuli. As compared to HC, DOC patients showed a dysfunction of intra-M1 and premotor-M1 circuits, which correlated with the Coma Recovery Scale-Revised scorings. Nonetheless, one UWS patient showed a partially preserved premotor-M1 circuitry, paralleled by a severe intra-M1 circuitry dysfunction. Our data suggest that motor unresponsiveness in some DOC patients may be due to a pure motor output failure, as in the functional locked-in syndrome (fLIS), rather than to a premotor-motor connectivity impairment, which instead characterizes MCS and UWS.

Extent of altered white matter in unilateral and bilateral periventricular white matter lesions in children with unilateral cerebral palsy

AIMS

To investigate the extent of white matter damage in children with unilateral cerebral palsy (UCP) caused by periventricular white matter lesions comparing between unilateral and bilateral lesions; and to investigate a relationship between white matter microstructure and hand function.

METHODS AND PROCEDURES

Diffusion MRI images from 46 children with UCP and 18 children with typical development (CTD) were included. Subjects were grouped by side of hemiparesis and unilateral or bilateral lesions. A voxel-wise white matter analysis was performed to identify regions where fractional anisotropy (FA) was significantly different between UCP groups and CTD; and where FA correlated with either dominant or impaired hand function (using Jebsen Taylor Hand Function Test).

OUTCOMES AND RESULTS

Children with unilateral lesions had reduced FA in the corticospinal tract of the affected hemisphere. Children with bilateral lesions had widespread reduced FA extending into all lobes. In children with left hemiparesis, impaired hand function correlated with FA in the contralateral corticospinal tract. Dominant hand function correlated with FA in the posterior thalamic radiations as well as multiple other regions in both left and right hemiparesis groups.

CONCLUSIONS AND IMPLICATIONS

Periventricular white matter lesions consist of focal and diffuse components. Focal lesions may cause direct motor fibre insult resulting in motor impairment. Diffuse white matter injury is heterogeneous, and may contribute to more global dysfunction.

Brain-machine interfaces for rehabilitation of poststroke hemiplegia

Noninvasive brain-machine interfaces (BMIs) are typically associated with neuroprosthetic applications or communication aids developed to assist in daily life after loss of motor function, eg, in severe paralysis. However, BMI technology has recently been found to be a powerful tool to promote neural plasticity facilitating motor recovery after brain damage, eg, due to stroke or trauma. In such BMI paradigms, motor cortical output and input are simultaneously activated, for instance by translating motor cortical activity associated with the attempt to move the paralyzed fingers into actual exoskeleton-driven finger movements, resulting in contingent visual and somatosensory feedback. Here, we describe the rationale and basic principles underlying such BMI motor rehabilitation paradigms and review recent studies that provide new insights into BMI-related neural plasticity and reorganization. Current challenges in clinical implementation and the broader use of BMI technology in stroke neurorehabilitation are discussed.

Rodent spinal cord injury models for studies of axon regeneration

For over a century, axon regeneration has been considered the Holy Grail for spinal cord injury (SCI) repair. Although there are other factors that could contribute to improving function, restoring the long motor and sensory tracts that are interrupted by SCI has the greatest potential for actually reversing paralysis, restoring the brain's control of autonomic functions mediated by sympathetic and parasympathetic circuits of the spinal cord and restoring sensation. Accordingly and in keeping with the overall theme of this special issue, this review focuses narrowly on rodent SCI models for studies of axon regeneration.

Transcranial Magnetic Stimulation and Diffusion Tensor Tractography for Evaluating Ambulation after Stroke

BACKGROUND AND PURPOSE

We aimed to investigate the usefulness of combining transcranial magnetic stimulation (TMS) and diffusion tensor tractography (DTT) to evaluate corticospinal tract (CST) integrity and subsequently predict ambulatory function after middle cerebral artery (MCA) stroke.

METHODS

Forty-three patients with first MCA stroke underwent TMS and DTT to evaluate CST integrity. Patients were classified into four groups according to the presence of motor-evoked potentials (MEPs) obtained from the tibialis anterior muscle and CST integrity. Motor impairment and functional status were assessed using the Fugl-Meyer Assessment, Functional Ambulation Category, and Korean modified Barthel Index, both at the time of admission and after 4 weeks of rehabilitation.

RESULTS

Patients with the presence of both measurable MEPs and a preserved CST showed better motor recovery and ambulatory function than other groups at the 4-week follow-up. Intact CSTs were not visualized in patients without detectable MEPs. Among the patients displaying MEPs, those with preserved CSTs showed better recovery of paretic lower extremities.

CONCLUSIONS

Combined assessment using TMS and DTT to evaluate CST integrity confers advantages in predicting motor and ambulation recovery in patients with MCA stroke.

Juvenile amyotrophic lateral sclerosis: Classical wine glass sign on magnetic resonance imaging

Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig disease, is a chronic degenerative neurologic disease and is characterized by the selective involvement of the motor system. Usually, patients present with upper motor neuron (UMN) and lower motor neuron compromise. Degeneration of the UMN in the cerebral cortex is one of the main pathologic changes in ALS. These changes usually affect corticospinal tracts leading to degeneration of the fibers which show characteristic hyperintensities along the tracts leading to the “wine glass sign.” Patients with ALS usually present in the sixth decade of life; presentation in pediatric age in the form of juvenile ALS being rare.

Abnormal corticospinal tract function and motor cortex excitability in non-ataxic SCA2 mutation carriers: A TMS study

OBJECTIVE

To evaluate if the corticospinal tract is affected in the prodromal stage of spinocerebellar ataxia type 2 (SCA2), prior to development of the cerebellar syndrome.

METHODS

A cross-sectional study was conducted in 37 non-ataxic SCA2 mutation carriers and in age- and sex-matched healthy controls. All subjects underwent clinical assessment and transcranial magnetic stimulation to determine corticospinal tract integrity to the right abductor pollicis brevis and tibialis anterior muscles.

RESULTS

Non-ataxic SCA2 mutation carriers showed significantly higher resting and active motor thresholds for both muscles, and prolonged cortical silent periods and central motor conduction times (CMCT), compared to controls. CMCT to the tibialis anterior correlated directly with CAG repeat size, and inversely with predicted time to ataxia onset.

CONCLUSION

Findings provide novel electrophysiological evidence for affection of the corticospinal tract and motor cortex in prodromal SCA2. Slowed conduction in the corticospinal tract to the lower limbs reflects polyglutamine neurotoxicity, and predicts time to ataxia onset.

SIGNIFICANCE

Identification of corticospinal tract damage and decreases motor cortical excitability in the prodromal stage of SCA2 allows early disease monitoring. This will become important as soon as effective neuroprotective treatment will be available.

The association of motor imagery and kinesthetic illusion prolongs the effect of transcranial direct current stimulation on corticospinal tract excitability

Background

A kinesthetic illusion induced by a visual stimulus (KI) can produce vivid kinesthetic perception. During KI, corticospinal tract excitability increases and results in the activation of cerebral networks. Transcranial direct current stimulation (tDCS) is emerging as an alternative potential therapeutic modality for a variety of neurological and psychiatric conditions, such that identifying factors that enhance the magnitude and duration of tDCS effects is currently a topic of great scientific interest. This study aimed to establish whether the combination of tDCS with KI and sensory-motor imagery (MI) induces larger and longer-lasting effects on the excitability of corticomotor pathways in healthy Japanese subjects.

Methods

A total of 21 healthy male volunteers participated in this study. Four interventions were investigated in the first experiment: (1) anodal tDCS alone (tDCSa), (2) anodal tDCS with visually evoked kinesthetic illusion (tDCSa + KI), (3) anodal tDCS with motor imagery (tDCSa + MI), and (4) anodal tDCS with kinesthetic illusion and motor imagery (tDCSa + KIMI). In the second experiment, we added a sham tDCS intervention with kinesthetic illusion and motor imagery (sham + KIMI) as a control for the tDCSa + KIMI condition. Direct currents were applied to the right primary motor cortex. Corticospinal excitability was examined using transcranial magnetic stimulation of the area associated with the left first dorsal interosseous.

Results

In the first experiment, corticomotor excitability was sustained for at least 30 min following tDCSa + KIMI (p < 0.01). The effect of tDCSa + KIMI on corticomotor excitability was greater and longer-lasting than that achieved in all other conditions. In the second experiment, significant effects were not achieved following sham + KIMI.

Conclusions

Our results suggest that tDCSa + KIMI has a greater therapeutic potential than tDCS alone for inducing higher excitability of the corticospinal tract. The observed effects may be related to sustained potentiation of resultant cerebral activity during combined KI, MI, and tDCSa.

Comparison of Diffusion Tensor Tractography and Motor Evoked Potentials for the Estimation of Clinical Status in Subacute Stroke

Objective

To compare diffusion tensor tractography (DTT) and motor evoked potentials (MEPs) for estimation of clinical status in patients in the subacute stage of stroke.

Methods

Patients with hemiplegia due to stroke who were evaluated using both DTT and MEPs between May 2012 and April 2015 were recruited. Clinical assessments investigated upper extremity motor and functional status. Motor status was evaluated using Medical Research Council grading and the Fugl-Meyer Assessment of upper limb and hand (FMA-U and FMA-H). Functional status was measured using the Modified Barthel Index (MBI). Patients were classified into subgroups according to DTT findings, MEP presence, fractional anisotropy (FA) value, FA ratio (rFA), and central motor conduction time (CMCT). Correlations of clinical assessments with DTT parameters and MEPs were estimated.

Results

Fifty-five patients with hemiplegia were recruited. In motor assessments (FMA-U), MEPs had the highest sensitivity and negative predictive value (NPV) as well as the second highest specificity and positive predictive value (PPV). CMCT showed the highest specificity and PPV. Regarding functional status (MBI), FA showed the highest sensitivity and NPV, whereas CMCT had the highest specificity and PPV. Correlation analysis showed that the resting motor threshold (RMT) ratio was strongly associated with motor status of the upper limb, and MEP parameters were not associated with MBI.

Conclusion

DTT and MEPs could be suitable complementary modalities for analyzing the motor and functional status of patients in the subacute stage of stroke. The RMT ratio was strongly correlated with motor status.

Changes of the corticospinal tract in the unaffected hemisphere in stroke patients: A diffusion tensor imaging study

We investigated changes of the corticospinal tract (CST) in the unaffected hemisphere according to severity of the CST injury, using diffusion tensor imaging (DTI). According to the severity of the CST injury in the affected hemisphere, the stroke patients showed different aspects of fiber volume increment of the CST in the unaffected hemisphere; the fiber volume was increased in the early phase in patients with mild injury of CST and later phase in patients with severe injury of CST.

Long-term consequences of conditional genetic deletion of PTEN in the sensorimotor cortex of neonatal mice

Targeted deletion of the phosphatase and tensin homolog on chromosome ten (PTEN) gene in the sensorimotor cortex of neonatal mice enables robust regeneration of corticospinal tract (CST) axons following spinal cord injury as adults. Here, we assess the consequences of long-term conditional genetic PTEN deletion on cortical structure and neuronal morphology and screen for neuropathology. Mice with a LoxP-flanked exon 5 of the PTEN gene (PTENf/f mice) received AAV-Cre injections into the sensorimotor cortex at postnatal day 1 (P1) and were allowed to survive for up to 18months. As adults, mice were assessed for exploratory activity (open field), and motor coordination using the Rotarod®. Some mice received injections of Fluorogold into the spinal cord to retrogradely label the cells of origin of the CST. Brains were prepared for neurohistology and immunostained for PTEN and phospho-S6, which is a downstream marker of mammalian target of rapamycin (mTOR) activation. Immunostaining revealed a focal area of PTEN deletion affecting neurons in all cortical layers, although in some cases PTEN expression was maintained in many small-medium sized neurons in layers III-IV. Neurons lacking PTEN were robustly stained for pS6. Cortical thickness was significantly increased and cortical lamination was disrupted in the area of PTEN deletion. PTEN-negative layer V neurons that give rise to the CST, identified by retrograde labeling, were larger than neurons with maintained PTEN expression, and the relative area occupied by neuropil vs. cell bodies was increased. There was no evidence of tumor formation or other neuropathology. Mice with PTEN deletion exhibited open field activity comparable to controls and there was a trend for impaired Rotarod performance (not statistically significant). Our findings indicate that early postnatal genetic deletion of PTEN that is sufficient to enable axon regeneration by adult neurons causes neuronal hypertrophy but no other detectable neuropathology.

Diffusion tensor imaging suggests extrapontine extension of pediatric diffuse intrinsic pontine gliomas

PURPOSE

To apply DTI to detect early extrapontine extension of pediatric diffuse intrinsic pontine glioma along the corticospinal tracts.

METHODS

In children with diffuse intrinsic pontine glioma, low-grade brainstem glioma, and age-matched controls, DTI metrics were measured in the posterior limb of the internal capsule and posterior centrum semiovale. Histological examination was available in one patient.

RESULTS

6 diffuse intrinsic pontine glioma, 8 low-grade brainstem glioma, and two groups of 25 controls were included. In diffuse intrinsic pontine glioma compared to controls, fractional anisotropy was lower in the bilateral posterior limb of the internal capsule, axial diffusivity was lower in the bilateral posterior centrum semiovale and posterior limb of the internal capsule, while radial diffusivity was higher in the bilateral posterior limb of the internal capsule. No significant differences were found between low-grade brainstem glioma and controls. In diffuse intrinsic pontine glioma compared to low-grade brainstem glioma, axial diffusivity was lower in the bilateral posterior limb of the internal capsule. Histological examination in one child showed tumor cells in the posterior limb of the internal capsule.

CONCLUSION

Reduction in fractional anisotropy and axial diffusivity and increase in radial diffusivity in diffuse intrinsic pontine glioma may reflect tumor extension along the corticospinal tracts as shown by histology. DTI may detect early extrapontine tumor extension in diffuse intrinsic pontine glioma before it becomes apparent on conventional MRI sequences.

Corticospinal tract modeling for neurosurgical planning by tracking through regions of peritumoral edema and crossing fibers using two-tensor unscented Kalman filter tractography

PURPOSE

The aim of this study was to present a tractography algorithm using a two-tensor unscented Kalman filter (UKF) to improve the modeling of the corticospinal tract (CST) by tracking through regions of peritumoral edema and crossing fibers.

METHODS

Ten patients with brain tumors in the vicinity of motor cortex and evidence of significant peritumoral edema were retrospectively selected for the study. All patients underwent 3-T magnetic resonance imaging (MRI) including functional MRI (fMRI) and a diffusion-weighted data set with 31 directions. Fiber tracking was performed using both single-tensor streamline and two-tensor UKF tractography methods. A two-region-of-interest approach was used to delineate the CST. Results from the two tractography methods were compared visually and quantitatively. fMRI was applied to identify the functional fiber tracts.

RESULTS

Single-tensor streamline tractography underestimated the extent of tracts running through the edematous areas and could only track the medial projections of the CST. In contrast, two-tensor UKF tractography tracked fanning projections of the CST despite peritumoral edema and crossing fibers. Based on visual inspection, the two-tensor UKF tractography delineated tracts that were closer to motor fMRI activations, and it was apparently more sensitive than single-tensor streamline tractography to define the tracts directed to the motor sites. The volume of the CST was significantly larger on two-tensor UKF than on single-tensor streamline tractography ([Formula: see text]).

CONCLUSION

Two-tensor UKF tractography tracks a larger volume CST than single-tensor streamline tractography in the setting of peritumoral edema and crossing fibers in brain tumor patients.

Microstructural asymmetry of the corticospinal tracts predicts right-left differences in circle drawing skill in right-handed adolescents

Most humans show a strong preference to use their right hand, but strong preference for the right hand does not necessarily imply a strong right–left asymmetry in manual proficiency (i.e., dexterity). Here we tested the hypothesis that intra-individual asymmetry of manual proficiency would be reflected in microstructural differences between the right and left corticospinal tract (CST) in a cohort of 52 right-handed typically-developing adolescents (11–16 years). Participants were asked to fluently draw superimposed circles with their right dominant and left non-dominant hand. Temporal regularity of circle drawing movements was assessed for each hand using a digitizing tablet. Although all participants were right-handed, there was substantial inter-individual variation regarding the relative right-hand advantage for fluent circle drawing. All subjects underwent whole-brain diffusion tensor imaging at 3 Tesla. The right and left CST were defined as regions-of-interest and mean fractional anisotropy (FA) and diffusivity values were calculated for right and left CST. On average, mean FA values were higher in the left CST relative to right CST. The degree of right–left FA asymmetry showed a linear relationship with right–left asymmetry in fluent circle drawing after correction for age and gender. The higher the mean FA values were in the left dominant CST relative to the right non-dominant CST, the stronger was the relative right-hand advantage for regular circle drawing. These findings show that right–left differences in manual proficiency are highly variable in right-handed adolescents and that this variation is associated with a right-left microstructural asymmetry of the CST.

Combined motor cortex and spinal cord neuromodulation promotes corticospinal system functional and structural plasticity and motor function after injury

An important strategy for promoting voluntary movements after motor system injury is to harness activity-dependent corticospinal tract (CST) plasticity. We combine forelimb motor cortex (M1) activation with co-activation of its cervical spinal targets in rats to promote CST sprouting and skilled limb movement after pyramidal tract lesion (PTX). We used a two-step experimental design in which we first established the optimal combined stimulation protocol in intact rats and then used the optimal protocol in injured animals to promote CST repair and motor recovery. M1 was activated epidurally using an electrical analog of intermittent theta burst stimulation (iTBS). The cervical spinal cord was co-activated by trans-spinal direct current stimulation (tsDCS) that was targeted to the cervical enlargement, simulated from finite element method. In intact rats, forelimb motor evoked potentials (MEPs) were strongly facilitated during iTBS and for 10 min after cessation of stimulation. Cathodal, not anodal, tsDCS alone facilitated MEPs and also produced a facilitatory aftereffect that peaked at 10 min. Combined iTBS and cathodal tsDCS (c-tsDCS) produced further MEP enhancement during stimulation, but without further aftereffect enhancement. Correlations between forelimb M1 local field potentials and forelimb electromyogram (EMG) during locomotion increased after electrical iTBS alone and further increased with combined stimulation (iTBS+c-tsDCS). This optimized combined stimulation was then used to promote function after PTX because it enhanced functional connections between M1 and spinal circuits and greater M1 engagement in muscle contraction than either stimulation alone. Daily application of combined M1 iTBS on the intact side and c-tsDCS after PTX (10 days, 27 min/day) significantly restored skilled movements during horizontal ladder walking. Stimulation produced a 5.4-fold increase in spared ipsilateral CST terminations. Combined neuromodulation achieves optimal motor recovery and substantial CST outgrowth with only 27 min of daily stimulation compared with 6h, as in our prior study, making it a potential therapy for humans with spinal cord injury.

Ipsilesional motor-evoked potential absence in pediatric hemiparesis impacts tracking accuracy of the less affected hand

This study analyzed the relationship between electrophysiological responses to transcranial magnetic stimulation (TMS), finger tracking accuracy, and volume of neural substrate in children with congenital hemiparesis. Nineteen participants demonstrating an ipsilesional motor-evoked potential (MEP) were compared with eleven participants showing an absent ipsilesional MEP response. Comparisons of finger tracking accuracy from the affected and less affected hands and ipsilesional/contralesional (I/C) volume ratio for the primary motor cortex (M1) and posterior limb of internal capsule (PLIC) were done using two-sample t-tests. Participants showing an ipsilesional MEP response demonstrated superior tracking performance from the less affected hand (p=0.016) and significantly higher I/C volume ratios for M1 (p=0.028) and PLIC (p=0.005) compared to participants without an ipsilesional MEP response. Group differences in finger tracking accuracy from the affected hand were not significant. These results highlight differentiating factors amongst children with congenital hemiparesis showing contrasting MEP responses: less affected hand performance and preserved M1 and PLIC volume. Along with MEP status, these factors pose important clinical implications in pediatric stroke rehabilitation. These findings may also reflect competitive developmental processes associated with the preservation of affected hand function at the expense of some function in the less affected hand.

Surgical Treatment of Cavernous Malformations Involving the Posterior Limb of the Internal Capsule: Utility and Predictive Value of Preoperative Diffusion Tensor Imaging

OBJECTIVE

The surgical treatment of cavernous malformations involving the posterior limb of the internal capsule (PLIC-CMs) is challenging. The aim of this study was to determine the utility and predictive value of preoperative diffusion tensor imaging (DTI) in the surgical treatment of PLIC-CMs.

METHODS

Patients with PLIC-CMs who were surgically treated between September 2012 and June 2015 were reviewed. All patients underwent preoperative DTI. Three major fiber tracts were selected for evaluation: 1) corticospinal tract (CST); 2) arcuate fasciculus (AF); and 3) optic radiation (OR). The utility of preoperative DTI for surgical approach selection and intraoperative navigation was documented. An involvement grading system of the major fibers was applied to determine the predictive value of preoperative DTI. A last modified Rankin Scale (mRS) score of 0-2 was considered a good outcome, and a last mRS >2 was considered a poor outcome.

RESULTS

Thirteen patients with 13 PLIC-CMs were reviewed in this study. All the lesions were radically resected via the corridor formed by CST, AF, and OR. None of the patents suffered from mRS >3, and 7 patients (53.8%) got good outcomes at the last clinic visit. The difference between the preoperative mRS scores and last mRS scores was not significant (P = 0.673). The involvement grade of the fiber tracts was significantly associated with the surgical outcome (P = 0.011).

CONCLUSIONS

Preoperative DTI may be a promising tool to determine the surgical approach and predict the surgical outcomes in patients with PLIC-CMs.

Axonal dysfunction in internal capsule is closely associated with early motor deficits after intracerebral hemorrhage in mice

Previously we showed that expansion of intracerebral hemorrhage (ICH) into the internal capsule greatly aggravated neurological symptoms in mice. Here we examined ICH-associated events in the internal capsule with relation to neurological dysfunction. Corticospinal axons labeled by biotinylated dextran amine exhibited fragmented appearance after ICH induced by local injection of collagenase into the internal capsule. Fragmentation of axonal structures was confirmed by neurofilament-H immunostaining, which was evident from 6h after induction of ICH. We also observed accumulation of amyloid precursor protein, which indicated compromised axonal transport, from 3h after induction of ICH. The early defect in axonal transport was accompanied by a robust decline in motor performance. Local application of an axonal transport inhibitor colchicine to the internal capsule induced a prompt decline in motor performance, suggesting that compromised axonal transport is closely associated with early neurological dysfunction in ICH. Arrest of axonal transport and fragmentation of axonal structures were also induced by local injection of thrombin, but not by thrombin receptor activator peptide-6, a protease-activated receptor-1 agonist. These results suggest that receptor-independent actions of thrombin mediate disruption of structure and function of axons by hemorrhage expansion into the internal capsule, which leads to severe neurological dysfunction.

Isolated Painless Foot Drop due to Cerebral Infarction Mimicking Lumbar Radiculopathy: A Case Report

Although they usually originate from peripheral problems, foot drop is caused by lesions affecting the neural pathway related to dorsiflexor muscles, whether of central or peripheral origin. We present a patient with sudden isolated foot drop caused by a small infarct in the primary motor cortex mimicking a peripheral origin. This report indicates that patients presenting isolated foot drop should be managed carefully and the possibility of both central and peripheral causes should be considered. To our knowledge, this is the first report of sudden isolated foot drop caused by a cortical infarction mimicking lumbar radiculopathy.

Stathmin is enriched in the developing corticospinal tract

Understanding the intra- and extracellular proteins involved in the development of the corticospinal tract (CST) may offer insights into how the pathway could be regenerated following traumatic spinal cord injury. Currently, however, little is known about the proteome of the developing corticospinal system. The present study, therefore, has used quantitative proteomics and bioinformatics to detail the protein profile of the rat CST during its formation in the spinal cord. This analysis identified increased expression of 65 proteins during the early ingrowth of corticospinal axons into the spinal cord, and 36 proteins at the period of heightened CST growth. A majority of these proteins were involved in cellular assembly and organization, with annotations being most highly associated with cytoskeletal organization, microtubule dynamics, neurite outgrowth, and the formation, polymerization and quantity of microtubules. In addition, 22 proteins were more highly expressed within the developing CST in comparison to other developing white matter tracts of the spinal cord of age-matched animals. Of these differentially expressed proteins, only one, stathmin 1 (a protein known to be involved in microtubule dynamics), was both highly enriched in the developing CST and relatively sparse in other developing descending and ascending spinal tracts. Immunohistochemical analyses of the developing rat spinal cord and fetal human brain stem confirmed the enriched pattern of stathmin expression along the developing CST, and in vitro growth assays of rat corticospinal neurons showed a reduced length of neurite processes in response to pharmacological perturbation of stathmin activity. Combined, these findings suggest that stathmin activity may modulate axonal growth during development of the corticospinal projection, and reinforces the notion that microtubule dynamics could play an important role in the generation and regeneration of the CST.

Cerebral vasospasm and corticospinal tract injury induced by a modified rat model of subarachnoid hemorrhage

OBJECTIVE

Double-hemorrhage rat models of subarachnoid hemorrhages (SAH) are most effective at simulating delayed cerebral vasospasms (CVS). The present study modified the models to minimize additional trauma and investigated injury of the corticospinal tract (CST) using diffusion tensor imaging (DTI).

METHODS

On the first day, 0.3ml of autologous arterial blood was collected by puncturing the caudal artery and injected into the cisterna magna via percutaneous puncture; and the operation was repeated on the third day. The diameters of the basilar artery (BA), middle cerebral artery (MCA), and anterior cerebral artery (ACA) were measured by magnetic resonance angiography on days 3, 5, 7, 9, and 11 post-SAH. Meanwhile, on days 3, 7, 11, 15 and 19, DTI was performed to evaluate the injury of the CST at cerebral peduncle (CP) and pyramidal tract (Py) by measuring fractional anisotropy (FA) value.

RESULTS

Blood was deposited mainly in the basal cistern. Diameters of BA, MCA, and ACA were significantly reduced. FA value of the CP was lower in the SAH group than in the control group; but FA value of Py wasn't different between the two groups.

CONCLUSION

This is a minimally-invasive and high performance rat model of SAH. Additionally, the occurrence of CVS is firm and the axons in CP are injured.

Prediction of Motor Recovery Using Diffusion Tensor Tractography in Supratentorial Stroke Patients With Severe Motor Involvement

OBJECTIVE

To investigate whether early stage diffusion tensor tractography (DTT) values predict motor function at 3 months after onset in supratentorial stroke patients with severe motor involvement.

METHODS

A retrospective study design was used to analyze medical records and neuroimaging data of 49 supratentorial stroke patients with severe motor involvement. Diffusion tensor imaging was assessed within 3 weeks after stroke in all patients. Three-dimensional tractography of the ipsilateral corticospinal tract (CST) was performed using the fiber assignment of the continuous tracking algorithm. The two-step DTT analysis was used. The first step was classification according to ipsilateral CST visualization. The second step was a quantitative analysis of the visible-CST group parameters. Motor function was assessed at 2 weeks and at 3 months after stroke. Comparative and correlation analyses were performed between DTT-derived measures and motor assessment scores.

RESULTS

Motor function of the upper extremity at 3 months after stroke was significantly higher in the visible-CST group than that in the nonvisible-CST group (p<0.05). Early stage fractional anisotropy was of DTT correlated significantly with upper extremity motor function at 3 months after stroke in the visible-CST group (p<0.05).

CONCLUSION

These results demonstrate that early DTT-derived measures predict motor recovery in the upper extremity at 3 months after onset in supratentorial stroke patients with severe motor involvement.

Longitudinal three-dimensional-T2WI-SPACE study on wallerian degeneration in cat corticospinal tract and underlying pathology changes

PURPOSE

To investigate the feasibility of T2W-SPACE technique in early detection of WD, the signal evolutions of degenerated corticospinal tract (CST) on T2W-SPACE, and their underlying pathological changes.

MATERIALS AND METHODS

The WD model of the CST was established in 23 cats through excision of cortical origins of the tract. Eight cats were scanned with the T2W-SPACE technique at 8 sequential time points, i.e. 0 (before modeling), 2, 4, 6, 8, 10, 20 and 30 days after modeling, and then they were pathologically examined. The remaining 15 cats (3 per group) also underwent pathological examination at 2, 4, 6, 10 and 20 days after modeling, respectively. The ratios of T2 signal intensity (rT2s) between the affected and unaffected sides of CST were analyzed.

RESULTS

During the first 4 days, SPACE could not detect any significant changes of the affected CST, although axonal degeneration was pathologically observed at the second day. From 6 to 10 days, the rT2s decreased monotonously, which is corresponded to histological findings of myelin degeneration and phagocyte proliferation. From 10 to 20 days, rT2s kept relatively stable at a low level and started to recover after that; the pathological changes of this period was characterized by marked phagocytizing activities.

CONCLUSION

SPACE technique can detect Wallerian degeneration at an early stage, and the signal evolution is consistent with the pathological processes.

Structural hallmarks of amyotrophic lateral sclerosis progression revealed by probabilistic fiber tractography

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive limb and/or bulbar muscular weakness and atrophy. Although ALS-related alterations of motor and extra-motor neuronal networks have repeatedly been reported, their temporal dynamics during disease progression are not well understood. Recently, we reported a decline of motor system activity and a concurrent increase of hippocampal novelty-evoked modulations across 3 months of ALS progression. To address whether these functional changes are associated with structural ones, the current study employed probabilistic fiber tractography on diffusion tensor imaging (DTI) data using a longitudinal design. Therein, motor network integrity was assessed by DTI-based tracking of the intracranial corticospinal tract, while connectivity estimates of occipito-temporal tracts (between visual and entorhinal, perirhinal or parahippocampal cortices) served to assess structural changes that could be related to the increased novelty-evoked hippocampal activity across time described previously. Complementing these previous functional observations, the current data revealed an ALS-related decrease in corticospinal tract structural connectivity compared to controls, while in contrast, visuo-perirhinal connectivity was relatively increased in the patient group. Importantly, beyond these between-group differences, a rise in the patients' occipito-temporal tract strengths occurred across a 3-month interval, while at the same time no changes in corticospinal tract connectivity were observed. In line with previously identified functional alterations, the dynamics of these structural changes suggest that the affection of motor- and memory-related networks in ALS emerges at distinct disease stages: while motor network degeneration starts primarily during early (supposedly pre-symptomatic) phases, the hippocampal/medial temporal lobe dysfunctions arise at later stages of the disease.

Detection of hand and leg motor tract injury using novel diffusion tensor MRI tractography in children with central motor dysfunction

PURPOSE

To examine whether an objective segmenation of corticospinal tract (CST) associated with hand and leg movements can be used to detect central motor weakness in the corresponding extremities in a pediatric population.

MATERIAL AND METHODS

This retrospective study included diffusion tensor imaging (DTI) of 25 children with central paresis affecting at least one limb (age: 9.0±4.2years, 15 boys, 5/13/7 children with left/right/both hemispheric lesions including ischemia, cyst, and gliosis), as well as 42 pediatric control subjects with no motor dysfunction (age: 9.0±5.5years, 21 boys, 31 healthy/11 non-lesional epilepsy children). Leg- and hand-related CST pathways were segmented using DTI-maximum a posteriori (DTI-MAP) classification. The resulting CST volumes were then divided by total supratentorial white matter volume, resulting in a marker called "normalized streamline volume ratio (NSVR)" to quantify the degree of axonal loss in separate CST pathways associated with leg and hand motor functions. A receiver operating characteristic curve was applied to measure the accuracy of this marker to identify extremities with motor weakness.

RESULTS

NSVR values of hand/leg CST selectively achieved the following values of accuracy/sensitivity/specificity: 0.84/0.84/0.57, 0.82/0.81/0.55, 0.78/0.75/0.55, 0.79/0.81/0.54 at a cut-off of 0.03/0.03/0.03/0.02 for right hand CST, left hand CST, right leg CST, and left leg CST, respectively. Motor weakness of hand and leg was most likely present at the cut-off values of hand and leg NSVR (i.e., 0.029/0.028/0.025/0.020 for left-hand/right-hand/left-leg/right-leg). The control group showed a moderate age-related increase in absolute CST volumes and a biphasic age-related variation of the normalized CST volumes, which were lacking in the paretic children.

CONCLUSIONS

This study demonstrates that DTI-MAP classification may provide a new imaging tool to quantify axonal loss in children with central motor dysfunction. Using this technique, we found that early-life brain lesions affect the maturational trajectory of the primary motor pathway which may be used as an effective marker to facilitate evidence-based treatment of paretic children.

Novel diffusion tensor imaging technique reveals developmental streamline volume changes in the corticospinal tract associated with leg motor control

BACKGROUND

Diffusion tensor imaging (DTI) has expanded our knowledge of corticospinal tract (CST) anatomy and development. However, previous developmental DTI studies assessed the CST as a whole, overlooking potential differences in development of its components related to control of the upper and lower extremities. The present cross-sectional study investigated age-related changes, side and gender differences in streamline volume of the leg- and hand-related segments of the CST in children.

SUBJECTS AND METHODS

DTI data of 31 children (1-14 years; mean age: 6±4 years; 17 girls) with normal conventional MRI were analyzed. Leg- and hand-related CST streamline volumes were quantified separately, using a recently validated novel tractography approach. CST streamline volumes on both sides were compared between genders and correlated with age.

RESULTS

Higher absolute streamline volumes were found in the left leg-related CST compared to the right (p=0.001) without a gender effect (p=0.4), whereas no differences were found in the absolute hand-related CST volumes (p>0.4). CST leg-related streamline volumes, normalized to hemispheric white matter volumes, declined with age in the right hemisphere only (R=-.51; p=0.004). Absolute leg-related CST streamline volumes showed similar, but slightly weaker correlations. Hand-related absolute or normalized CST streamline volumes showed no age-related variations on either side.

CONCLUSION

These results suggest differential development of CST segments controlling hand vs. leg movements. Asymmetric volume changes in the lower limb motor pathway may be secondary to gradually strengthening left hemispheric dominance and is consistent with previous data suggesting that footedness is a better predictor of hemispheric lateralization than handedness.

Plasticity of motor network and function in the absence of corticospinal projection

Despite the obvious clinical interest, our understanding of how developmental mechanisms are redeployed during degeneration and regeneration after brain and spinal cord injuries remains quite rudimentary. In animal models of spinal cord injury, although spontaneous regeneration of descending axons is limited, compensation by intact corticospinal axons, descending tracts from the brainstem, and local intrinsic spinal networks all contribute to the recovery of motor function. Here, we investigated spontaneous motor compensation and plasticity that occur in the absence of corticospinal tract, using Celsr3|Emx1 mice in which the corticospinal tract is completely and specifically absent as a consequence of Celsr3 inactivation in the cortex. Mutant mice had no paresis, but displayed hyperactivity in open-field, and a reduction in skilled movements in food pellet manipulation tests. The number of spinal motoneurons was reduced and their terminal arbors at neuromuscular junctions were atrophic, which was reflected in electromyography deficits. Rubrospinal projections, calretinin-positive propriospinal projections, afferent innervation of motoneurons by calretinin-positive segmental interneurons, and terminal ramifications of monoaminergic projections were significantly increased. Contrary to control animals, mutants also developed a severe and persistent disability of forelimb use following the section of the rubrospinal tract at the C4 spinal level. These observations demonstrate for the first time that the congenital absence of the corticospinal tract induces spontaneous plasticity, both at the level of the motor spinal cord and in descending monoaminergic and rubrospinal projections. Such compensatory mechanisms could be recruited in case of brain or spinal cord lesion or degeneration.

Impact of treatment duration and lesion size on effectiveness of chondroitinase treatment post-SCI

The effects of 2weeks of intralesional chondroitinase abc (ch'abc) treatment on anatomical plasticity and behavioral recovery are examined in adult cats and compared to results achieved with 4weeks of treatment following tightly controlled lateral hemisection injuries. Analyses also were completed using 35 cats with a range of hemisection magnitudes to assess relationships between treatment duration, lesion size and functional recovery. Results indicate that both 2 and 4weeks of treatment significantly increased the number of rubrospinal tract (RuST) neurons with axons below the lesion, but neither affected the number of corticospinal tract neurons. Similarly, both treatment periods also accelerated recovery of select motor tasks, which carries considerable importance with respect to human health care and rehabilitation. Four weeks of treatment promoted recovery beyond that seen with 2weeks in its significant impact on accuracy of movement critical for placement of the ipsilateral hindlimb onto small support surfaces during the most challenging locomotor tasks. Analyses, which extended to a larger group of cats with a range of lesion magnitudes, indicate that 4weeks of ch'abc treatment promoted earlier recovery as well as significantly greater targeting accuracy even in cats with larger lesions. Together, these results support the potential for ch'abc to promote anatomical and behavioral recovery and suggest that intraspinal treatment with ch'abc continues to enhance motor recovery and performance beyond the subacute injury period and diminishes the impact of lesion size.