Correlation between age and the sciatic nerve diameter in the first 2 years of life: A high-resolution ultrasound study.

AIM: To investigate the maturation of the peripheral nervous system by analyzing the cross-sectional area of the sciatic nerve during the first 2 years of life. METHODS: The sciatic nerve was examined by high-resolution ultrasound imaging in 52 children aged 0 days to 10 years, 45 of whom were younger than 2 years. The correlation between the cross-sectional area of the nerve and the age was statistically tested. A logarithmic regression analysis was performed to develop a logarithmic growth model of the cross-sectional area. RESULTS: There is a highly significant correlation between the age and the cross-sectional area of the sciatic nerve. The growth rate can well be described by a logarithmic model. INTERPRETATION: Based on the literature on the maturation of the median nerve and nerve roots and the findings of the present study, we conclude that both the proximal and the distal parts of the nerves of the peripheral nervous system increase simultaneously. WHAT THIS PAPER ADDS: Normative values for the size of the sciatic nerve in children.

Slowing of Peripheral Nerve Conduction Velocity in Children and Adolescents With Type 1 Diabetes Is Predicted by Glucose Fluctuations.

Nerve conduction velocity (NCV) abnormalities are the forerunners of diabetic peripheral neuropathy (DPN). Therefore, this study aimed to analyze the effect of glucose profile quality on NCV in children and young adults with type 1 diabetes. Fifty-three children age 5 to 23 years with type 1 diabetes were recruited to participate in the study, which was conducted prospectively at the Children's Hospital of Eastern Switzerland from 2016 to 2022. Glycemic targets were recorded, and a cross-sectional nerve conduction study analyzing the peroneal, tibial, median motor, and median sensory nerves was performed. Data were compared with those of a control group of 50 healthy children. In the age- and height-matched diabetes subgroup aged 10-16 years, all four nerves showed significantly slower NCV, most pronounced for the peroneal nerve. Because height has a retarding effect on peroneal NCV, NCV was adjusted for height (dNCV). Peroneal dNCV correlated negatively with long-term glycated hemoglobin and highly significantly with glucose variability. Because high glucose variability clearly increases the risk of neuropathy, together with but also independently of the mean glucose level, this aspect of glycemic control should be given more attention in the care of individuals with diabetes. ARTICLE HIGHLIGHTS: There is a strong need for the better identification of early subclinical manifestations of microvascular complications, such as diabetic peripheral neuropathy, in young individuals with diabetes. To identify peripheral neuropathy and contributing factors at an asymptomatic disease stage, and to exclude height as a known modifying factor, we performed association studies of height-adjusted nerve conduction velocity. We identified high glucose variability, especially the SD of mean glucose, as an unexpectedly strong predictor of slowed nerve conduction velocity. More attention should be paid to the goal of low glucose variability in the care of individuals with diabetes.

Correlation of age and the diameter of the cervical nerve roots C5 and C6 during the first 2 years of life analyzed by high-resolution ultrasound imaging.

AIM: To analyze the increase in diameter of the nerve roots C5 and C6 in early childhood. METHODS: The nerve roots of 56 children aged 0 days to 10 years (47 younger than 2 years) were examined by high-resolution ultrasound imaging. The correlation of diameter and age was statistically tested and a logarithmic regression analysis was performed to develop a logarithmic growth model. RESULTS: The increase in nerve root diameter is greatest during the first 2 years of life and then the growth rate decreases steadily. The relationship between age and diameter follows a logarithmic curve (p < 10-8 ). INTERPRETATION: The main increase in the diameter of the nerve roots happens in the first 2 years of life. Comparing data from a previous study, our data also suggest that the maturation of the proximal part of the median nerve is comparable to the maturation of its distal segments. This suggests a synchronous maturation of the axons and myelin sheath for the whole extent of the nerve, from the radix to its very distal part. WHAT THIS PAPER ADDS: Normative values for the size of the cervical nerve roots C5 and C6; an insight into the maturation of the proximal parts of the peripheral nervous system; and the correlation between age and cervical root diameter.

Optically pumped magnetometers disclose magnetic field components of the muscular action potential.

AIM: Aiming at analysing the signal conduction in muscular fibres, the spatio-temporal dynamics of the magnetic field generated by the propagating muscle action potential (MAP) is studied. METHOD: In this prospective, proof of principle study, the magnetic activity of the intrinsic foot muscle after electric stimulation of the tibial nerve was measured using optically pumped magnetometers (OPMs). A classical biophysical electric dipole model of the propagating MAP was implemented to model the source of the data. In order to account for radial currents of the muscular tubules system, a magnetic dipole oriented along the direction of the muscle was added. RESULTS: The signal profile generated by the activity of the intrinsic foot muscles was measured by four OPM devices. Three OPM sensors captured the spatio-temporal magnetic field pattern of the longitudinal intrinsic foot muscles. Changes of the activation pattern reflected the propagating muscular action potential along the muscle. A combined electric and magnetic dipole model could explain the recorded magnetic activity. INTERPRETATION: OPM devices allow for a new, non-invasive way to study MAP patterns. Since magnetic fields are less altered by the tissue surrounding the dipole source compared to electric activity, a precise analysis of the spatial characteristics and temporal dynamics of the MAP is possible. The classic electric dipole model explains major but not all aspects of the magnetic field. The field has longitudinal components generated by intrinsic structures of the muscle fibre. By understanding these magnetic components, new methods could be developed to analyse the muscular signal transduction pathway in greater detail. The approach has the potential to become a promising diagnostic tool in peripheral neurological motor impairments.

Investigation of the temporal and spatial dynamics of muscular action potentials through optically pumped magnetometers.

AIM: This study aims to simultaneously record the magnetic and electric components of the propagating muscular action potential. METHOD: A single-subject study of the monosynaptic stretch reflex of the musculus rectus femoris was performed; the magnetic field generated by the muscular activity was recorded in all three spatial directions by five optically pumped magnetometers. In addition, the electric field was recorded by four invasive fine-wire needle electrodes. The magnetic and electric fields were compared by modelling the muscular anatomy of the rectus femoris muscle and by simulating the corresponding magnetic field vectors. RESULTS: The magnetomyography (MMG) signal can reliably be recorded following the stimulation of the monosynaptic stretch reflex. The MMG signal shows several phases of activity inside the muscle, the first of which is the propagating muscular action potential. As predicted by the finite wire model, the magnetic field vectors of the propagating muscular action potential are generated by the current flowing along the muscle fiber. Based on the magnetic field vectors, it was possible to reconstruct the pinnation angle of the muscle fibers. The later magnetic field components are linked to the activation of the contractile apparatus. Interpretation MMG allows to analyze the muscle physiology from the propagating muscular action potential to the initiation of the contractile apparatus. At the same time, this methods reveals information about muscle fiber direction and extend. With the development of high-resolution magnetic cameras, that are based on OPM technology, it will be possible to image the function and structure of the biomagnetic field of any skeletal muscle with high precision. This method could be used both, in clinical medicine and also in sports science.

Etiology of Carpal Tunnel Syndrome in a Large Cohort of Children.

(1) Background: Carpal tunnel syndrome (CTS), a compressive mononeuropathy of the median nerve at the wrist, is rare in childhood and occurs most frequently due to secondary causes. (2) Methods: Medical history, electrodiagnostic findings, and imaging data of patients with CTS from two pediatric neuromuscular centers were analyzed retrospectively. The etiology of CTS was investigated and compared with the literature. (3) Results: We report on a cohort of 38 CTS patients (n = 22 females, n = 29 bilateral, mean age at diagnosis 9.8 years). Electrodiagnostic studies of all patients revealed slowing of the antidromic sensory or orthodromic mixed nerve conduction velocities across the carpal tunnel or lack of the sensory nerve action potential and/or prolonged distal motor latencies. Median nerve ultrasound was diagnostic for CTS and confirmed tumorous and vascular malformations. Etiology was secondary in most patients (n = 29; 76%), and mucopolysaccharidosis was the most frequent underlying condition (n = 14; 37%). Idiopathic CTS was rare in this pediatric cohort (n = 9; 24%). (4) Conclusion: Since CTS in childhood is predominantly caused by an underlying disorder, a thorough evaluation and search for a causative condition is recommended in this age group.

Change in cross-sectional area of the median nerve with age in neonates, infants and children analyzed by high-resolution ultrasound imaging.

AIM: To analyze age dependencies in the cross-sectional area (CSA) of the median nerve during early childhood. METHOD: A total of 43 participants (32 of whom were children younger than 2 years) were included in this cross-sectional study to analyze the age dependency of the CSA of the median nerve at three locations (wrist, forearm and upper arm) using high-resolution ultrasound images. RESULTS: A strong and highly significant correlation was found between age and CSA (p < 0.001). When plotted, the relationship followed a logarithmic curve (p < 0.001) with a growth rate that decreases with age. Based on the regression analysis, a temporally similar increase in CSA for all three locations was found. The nerve reaches 70% of its final CSA by 2 years of age at all three locations. INTERPRETATION: Similar to the nerve conduction speed, the increase in CSA is greatest during the first 2 years of life. Then, the rate gradually and synchronously slows at the proximal and distal locations. Measurement of the CSA in the clinical setting might offer a new method to assess the maturation of the nervous system in infants with minimal interference.

The Phenotypic Spectrum of PRRT2-Associated Paroxysmal Neurologic Disorders in Childhood.

Pathogenic variants in PRRT2, encoding the proline-rich transmembrane protein 2, have been associated with an evolving spectrum of paroxysmal neurologic disorders. Based on a cohort of children with PRRT2-related infantile epilepsy, this study aimed at delineating the broad clinical spectrum of PRRT2-associated phenotypes in these children and their relatives. Only a few recent larger cohort studies are on record and findings from single reports were not confirmed so far. We collected detailed genetic and phenotypic data of 40 previously unreported patients from 36 families. All patients had benign infantile epilepsy and harbored pathogenic variants in PRRT2 (core cohort). Clinical data of 62 family members were included, comprising a cohort of 102 individuals (extended cohort) with PRRT2-associated neurological disease. Additional phenotypes in the cohort of patients with benign sporadic and familial infantile epilepsy consist of movement disorders with paroxysmal kinesigenic dyskinesia in six patients, infantile-onset movement disorders in 2 of 40 individuals, and episodic ataxia after mild head trauma in one girl with bi-allelic variants in PRRT2. The same girl displayed a focal cortical dysplasia upon brain imaging. Familial hemiplegic migraine and migraine with aura were reported in nine families. A single individual developed epilepsy with continuous spikes and waves during sleep. In addition to known variants, we report the novel variant c.843G>T, p.(Trp281Cys) that co-segregated with benign infantile epilepsy and migraine in one family. Our study highlights the variability of clinical presentations of patients harboring pathogenic PRRT2 variants and expands the associated phenotypic spectrum.

Automated axon length quantification for populations of labelled neurons.

Virus-based methods for labelling populations of cortical neurons, when combined with cell-type specific recombinant promoters and techniques allowing temporal control of gene expression, provide neuroscience with new opportunities to examine the connectivity between brain regions and how this connectivity is modified by experience or disease. However, to take full advantage of these technical advances, it is necessary to develop new methods for quantification of the axonal projections revealed. Here we describe a method for quantitative analysis of axonal projection patterns emanating from populations of labelled cells, using transmitted light bright field microscopy. A single high resolution image of an area to be analysed is first acquired using mosaic extended focus image microscopy. This image is then analysed by specifically developed image processing algorithms that identify and track axon segments present. For quantitative analysis, measurement grids consisting of a user-defined number of individual elements are placed over an area of interest, with the computer-based method then returning the summed length of the axon segments in each element. Axon density plots can thus be generated. We present an example from rat brain showing, over a whole coronal section, axon densities emanating from a population of layer 2/3 somatosensory neurons.

Optically Pumped Magnetometers for Magneto-Myography to Study the Innervation of the Hand.

The central nervous system exerts control over the activation of muscles via a dense network of nerve fibers targeting each individual muscle. There are numerous clinical situations where a detailed assessment of the nerve-innervation pattern is required for diagnosis and treatment. Especially, deep muscles are hard to examine and are as yet only accessible by uncomfortable and painful needle EMG techniques. Just recently, a new and flexible method and device became available to measure the small magnetic fields generated by the contraction of the muscles: optically pumped magnetometers (OPMs). OPMs are small devices that measure the zero-field level crossing resonance of spin-polarized rubidium atoms. The resonance is dependent on the local magnetic field strength, and therefore, these devices are able to measure small magnetic fields in the range of a few hundred femtoteslas. In this paper, we demonstrate as a proof of principle that OPMs can be used to measure the low magnetic fields generated by small hand muscles after electric stimulation of the ulnar or median nerve. We show that using this technique, we are able to record differential innervation pattern of small palmar hand muscles and are capable of distinguishing between areas innervated by the median or ulnar nerve. We expect that the new approach will have an important impact on the diagnosis of nerve entrapment syndromes, spinal cord lesions, and neuromuscular diseases.

Transmitted light brightfield mosaic microscopy for three-dimensional tracing of single neuron morphology.

A fundamental challenge in neuroscience is the determination of the three-dimensional (3D) morphology of neurons in the cortex. Here we describe a semiautomated method to trace single biocytin-filled neurons using a transmitted light brightfield microscope. The method includes 3D tracing of dendritic trees and axonal arbors from image stacks of serial 100-microm-thick tangential brain sections. Key functionalities include mosaic scanning and optical sectioning, high-resolution image restoration, and fast, parallel computing for neuron tracing. The mosaic technique compensates for the limited field of view at high magnification, allowing the acquisition of high-resolution image stacks on a scale of millimeters. The image restoration by deconvolution is based on experimentally verified assumptions about the optical system. Restoration yields a significant improvement of signal-to-noise ratio and resolution of neuronal structures in the image stack. Application of local threshold and thinning filters result in a 3D graph representation of dendrites and axons in a section. The reconstructed branches are then manually edited and aligned. Branches from adjacent sections are spliced, resulting in a complete 3D reconstruction of a neuron. A comparison with 3D reconstructions from manually traced neurons shows that the semiautomated system is a fast and reliable alternative to the manual tracing systems currently available.

A Non-Magnetic Rotating Disk Stimulator for the Study of Neuromagnetic Correlates of Sensorimotor Interaction.

Fine motor skills in humans require close interaction between the motor and the sensory systems. It is still not fully understood, how sensory feedback modulates motor commands. This is due to the fact, that there is no approach for investigating the sensorimotor cortical-interaction in sufficient detail. The fast and precise communication between the sensory and motor-systems requires measurements of cortical activity with high temporal and spatial resolution. Magnetoencephalography (MEG) is capable of both. Previously, we showed that sensory responses, can be observed by repetitive tactile stimulation. Further, motor cortex responses can be generated by periodical increase and decrease of muscle tone. Utilizing both observations we have designed an MEG and magnetic resonance imaging (MRI) compatible stimulator allowing for the study of brain activity related to sensorimotor integration. The stimulator consists of a rotating disk with an elevation such that subject senses with his finger the speed of the disk. With the force applied by the finger onto the disk, the subject can control its speed. During the experiment the subject is asked to keep the speed of the disk constant while the driving torque is systematically manipulated. This closed-loop design is especially useful to analyze the fast and continuous information flow between the two systems. In a single case pilot study using MEG, we could show that a detailed analysis of the sensorimotor-network is possible. In contrast to existing paradigms this setup allows separate time-locked analysis of the sensory- and motor-component independently and therefore the calculation of latency parameters for both systems. In the future this method will help to understand the interaction between the two systems in much greater detail.

Nonlinear anisotropic diffusion filtering of three-dimensional image data from two-photon microscopy.

Two-photon microscopy in combination with novel fluorescent labeling techniques enables imaging of three-dimensional neuronal morphologies in intact brain tissue. In principle it is now possible to automatically reconstruct the dendritic branching patterns of neurons from 3-D fluorescence image stacks. In practice however, the signal-to-noise ratio can be low, in particular in the case of thin dendrites or axons imaged relatively deep in the tissue. Here we present a nonlinear anisotropic diffusion filter that enhances the signal-to-noise ratio while preserving the original dimensions of the structural elements. The key idea is to use structural information in the raw data-the local moments of inertia-to locally control the strength and direction of diffusion filtering. A cylindrical dendrite, for example, is effectively smoothed only parallel to its longitudinal axis, not perpendicular to it. This is demonstrated for artificial data as well as for in vivo two-photon microscopic data from pyramidal neurons of rat neocortex. In both cases noise is averaged out along the dendrites, leading to bridging of apparent gaps, while dendritic diameters are not affected. The filter is a valuable general tool for smoothing cellular processes and is well suited for preparing data for subsequent image segmentation and neuron reconstruction.

Hydraulic driven fast and precise nonmagnetic tactile stimulator for neurophysiological and MEG measurements.

Electric stimulation of the peripheral nerves is well established as a diagnostic and research tool to analyze the somatosensory system. However, electric stimulation has some disadvantages. Electric stimulation of the median nerve triggers action potentials in all fiber populations of the nerve. Electric stimulation further creates artifacts and courses discomfort which is usually not well tolerated in the awake child. Therefore, the development of a more specific stimulation has constantly been a goal in recent years. There have been several approaches in the past to deliver somatic stimulation. However, all of them failed short in some aspects. In this study, a new type of somatosensory stimulator device was developed and compared against the gold standard of electric stimulation. The stimulation is achieved by repetitive tactile stimulation of the index finger using a blunt needle. In contrast to all previous approaches, we use a hydraulic system to move the needle up and downward. Given that water is very well suited to conduct pressure pulses it is possible to place the tactile stimulator device holding the needle close to the subject and the hydraulic driving system outside a critical area. Using a phantom, we showed that our stimulator is capable of delivering a stimulus precise on the submillisecond time scale. In addition, we test our stimulator on a healthy adult and compare the results against the electric stimulation. We can show the feasibility of measuring the electric responses of the peripheral nerve and while using MEG also the response of the primary somatosensory cortex. The tactile stimulation showed a more spatial focuses activation of the primary somatosensory cortex when compared against the electric stimulation. The proposed high-precision tactile stimulator will make it possible to analyze the somatosensory system noninvasively in children in the future.

Experience-induced plasticity of thalamocortical axons in both juveniles and adults.

We examined the effect of sensory deprivation on thalamocortical (TC) projections to the rat primary somatosensory cortex at different postnatal ages ranging from P0 to P96. Rats had their whiskers clipped off with one or two vibrissae spared. TC axons innervating barrel cortex were specifically labeled by injecting virus expressing fluorescent proteins into the corresponding primary (VPM) and/or secondary (POm) thalamic nuclei. The density of VPM axons in deprived columns was ≈34% lower relative to spared columns with a concomitant decrease in bouton density, suggesting a deprivation-induced retraction of VPM axons. Axonal changes were reversible upon regrowth of the clipped whiskers and independent of age at deprivation, indicating the absence of a critical period for anatomical plasticity. The POm projection was not obviously altered by sensory deprivation. We suggest that retraction and regrowth of TC axons substantially contribute to long-term deprivation-dependent functional plasticity.