Motoneuron Pool Research Articles

Single-session effects of acute intermittent hypoxia on breathing function after human spinal cord injury

After spinal cord injury (SCI) respiratory complications are a leading cause of morbidity and mortality. Acute intermittent hypoxia (AIH) triggers spinal respiratory motor plasticity in rodent models, and repetitive AIH may have the potential to restore breathing capacity in those with SCI. As an initial approach to provide proof of principle for such effects, we tested single-session AIH effects on breathing function in adults with chronic SCI. 17 adults (13 males; 34.1 ± 14.5 years old; 13 motor complete SCI; >6 months post injury) completed two randomly ordered sessions, AIH versus sham. AIH consisted of 15, 1-min episodes (hypoxia: 10.3% O2; sham: 21% O2) interspersed with room air breathing (1.5 min, 21% oxygen); no attempt was made to regulate arterial CO2 levels. Blood oxygen saturation (SpO2), maximal inspiratory and expiratory pressures (MIP; MEP), forced vital capacity (FVC), and mouth occlusion pressure within 0.1 s (P0.1) were assessed. Outcomes were compared using nonparametric Wilcoxon's tests, or a 2 × 2 ANOVA. Baseline SpO2 was 97.2 ± 1.3% and was unchanged during sham experiments. During hypoxic episodes, SpO2 decreased to 84.7 ± 0.9%, and returned to baseline levels during normoxic intervals. Outcomes were unchanged from baseline post-sham. Greater increases in MIP were evident post AIH vs. sham (median values; +10.8 cmH2O vs. -2.6 cmH2O respectively, 95% confidence interval (−18.7) – (−4.3), p = .006) with a moderate Cohen's effect size (0.68). P0.1, MEP and FVC did not change post-AIH. A single AIH session increased maximal inspiratory pressure generation, but not other breathing functions in adults with SCI. Reasons may include greater spared innervation to inspiratory versus expiratory muscles or differences in the capacity for AIH-induced plasticity in inspiratory motor neuron pools. Based on our findings, the therapeutic potential of AIH on breathing capacity in people with SCI warrants further investigation.

Phrenic and Hypoglossal motor unit pathology in a Spinocerebellar ataxia type 7 mouse model

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant neurodegenerative disorder caused by a deleterious CAG repeat expansion in the coding region of the ataxin-7 gene on chromosome 3. Patients with infantile SCA-7 have the largest repeat expansion (>200 repeats) and the most severe disease characterized by progressive loss of coordination, dysarthria, dysphagia and retinal degeneration. Death in these infants results from severe hypotonia, aspiration pneumonia and respiratory failure. To understand the mechanism behind aspiration and respiratory failure in SCA7, we comprehensively examined hypoglossal (XII) and phrenic neuropathology of a mouse model of infantile SCA7: the SCA7-266Q mice. Previously, we showed that SCA7-266Q mice exhibit progressive respiratory dysfunction along with irregular breathing and prolonged apneic events by 9-11 weeks of age. In this study, we performed post-mortem histological analysis of the XII and phrenic motor neurons and nerves in SCA-7 and WT control mice at 9 weeks of age. Specifically, we studied the presence of glial cells and the degree of neurodegeneration within these motor nuclei. We also performed g-ratio analysis on semi-thin sections of the XII and phrenic nerves. Finally, using electron microscopy, we examined the mitochondrial and myelin pathology in XII and phrenic nerves. The phrenic motor neurons exhibit enhanced neurodegeneration, exacerbated astrogliosis and microglial recruitment in the motor neuron pool. In addition, the XII and phrenic nerves of SCA7-266Q mice have increased g-ratio compared to WT controls which signifies thinning of myelin sheaths and is consistent with demyelination. Furthermore, EM images of the XII and phrenic nerves demonstrate an increase in size of mitochondria in SCA7-266Q mice compared to their WT controls. Finally, preliminary qPCR data exhibited an anomaly in the expression of the neuromuscular junction markers in the diaphragm of the SCA7-266Q mice. Clinically, these findings underscore the importance of respiratory neuropathology that is responsible for the dysphagia, aspiration pneumonia and respiratory failure seen in infantile SCA7.

Specific Features of the Motor Potentials of the Leg Muscles Induced by Magnetic Stimulation under the Conditions of a Five-Day \u201cDry\u201d Immersion in Healthy Volunteers

The aim of this study was to analyze the mechanisms of the development of hypogravitational hyperreflexia in the motoneuron pool of gravity-dependent muscles such as the gastrocnemius and soleus muscles of the leg under the conditions of five-day “dry” immersion in healthy volunteers using the method of transcranial and trans-spinal magnetic stimulation. The essence of the method lies in the stimulation of the areas of interest (motor areas of the cerebral cortex and lumbosacral thickening) with an electromagnetic stimulus. The study involved 10 subjects at the age of 29.9 ± 6.9 years, with no history of movement disorders or neurological diseases. The excitability of the motor neuron pool in both muscles was judged by the values of the thresholds and amplitudes of the motor response caused by transcranial and trans-spinal magnetic stimulations. A general pattern manifested in a significant decrease in thresholds and an increase in the amplitudes of motor responses caused by trans-spinal magnetic stimulation in both muscles gas been discovered. Specifically, the threshold of spinal evoked motor responses in both muscles decreased by 20%, and the amplitude increased by 150% after the end of immersion. The data obtained during the experiment confirm the spinal nature of the origin of hypogravitational hyperreflexia.

Rodent Experimental Model of Konzo: Characterization of Motor Impairment and Neurodegeneration after Cassava Neurotoxicity in the Rat

Konzo is a motor neuron neurodegenerative disease caused by bitter cassava toxicity that presents as a non-progressive spastic paraparesis. The ability of bitter cassava to produce behavioural and structural changes in adult rat nervous system was examined. Twenty five rats were used for this study, and pruned to 20 after consistent baseline performance was achieved (n=20; control=5, cassava chow=15). The rats were switched to a cassava diet for another 5 weeks (n=15). After the cassava consumption period, 5 rats underwent rehabilitation training three times a week and their performance tested once in a week for 5 weeks. Quantitative and qualitative assessments using a reaching movement scale and reach-to-grasp success rate were respectively carried out. Animals subjected to cassava toxicity performed significantly worse than the controls when determining the success rate in a reach-to-grasp experiment (baseline=69.8%, cassava diet=21.4%, post-cassava diet =48.9%). The various movement of the rat was analysed using ANOVA and there was significant difference (p < 0.05) in the performance. The rats couldn’t pronate, grasp, withdraw or open the digits properly when fed with cassava diet. Histology showed neuropathological damages on the motor cortex, less neurons in the motor neuron pool of the spinal cord and disruption of pyramidal layer of the hippocampus when rats were given bitter cassava. Immunofluorescence stain shows motor neurons and numerous choline acetyltransferase (ChAT+) processes and some C-boutons. There are behavioural evidence and neuropathological changes in the motor cortex and ventral horn of the spinal cord that may underlie movement impairments in rats fed with bitter cassava.

Constructing an adult orofacial premotor atlas in Allen mouse CCF.

Premotor circuits in the brainstem project to pools of orofacial motoneurons to execute essential motor action such as licking, chewing, breathing, and in rodent, whisking. Previous transsynaptic tracing studies only mapped orofacial premotor circuits in neonatal mice, but the adult circuits remain unknown as a consequence of technical difficulties. Here, we developed a three-step monosynaptic transsynaptic tracing strategy to identify premotor neurons controlling vibrissa, tongue protrusion, and jaw-closing muscles in the adult mouse. We registered these different groups of premotor neurons onto the Allen mouse brain common coordinate framework (CCF) and consequently generated a combined 3D orofacial premotor atlas, revealing unique spatial organizations of distinct premotor circuits. We further uncovered premotor neurons that simultaneously innervate multiple motor nuclei and, consequently, are likely to coordinate different muscles involved in the same orofacial motor actions. Our method for tracing adult premotor circuits and registering to Allen CCF is generally applicable and should facilitate the investigations of motor controls of diverse behaviors.

Pholcodine-induced Stevens-Johnson syndrome in a patient with COVID-19

Reaction time is accelerated if a loud (startling) sound accompanies the cue—the “StartReact” effect. Animal studies revealed a reticulospinal substrate for the startle reflex; StartReact may similarly involve the reticulospinal...

Crosstalk opposing view: Independent fusimotor control of muscle spindles in humans: there is little to gain.

Crosstalk opposing view: Independent fusimotor control of muscle spindles in humans: there is little to gain.

The role of enhanced plantar-surface sensory feedback on lower limb EMG during planned gait termination

Purpose/aim of the study: Generation of smooth movement relies on the central nervous system (CNS) having information from the visual, vestibular and somatosensory systems to effectively execute motor behaviour. Recently, cutaneous afferent inputs have been linked to lower leg motorneuron pools, resulting in a growing interest of adding texture to the plantar foot sole interface as a novel method to facilitate cutaneous feedback. The aim of this study was to characterize the changes in magnitude and temporal organization of muscle activity, and to investigate motor output changes from enhanced tactile feedback during perturbed gait termination. Materials and methods: Thirty young adults experienced an unpredictable platform perturbation when completing planned gait termination. The study manipulated two experimental variables: 1) direction of platform tilt (anterior, posterior, medial, lateral), and 2) foot sensory facilitation (non-facilitated, facilitated). Upper and lower leg EMG onset, cessation time and integrated EMG (iEMG) were measured in addition to common gait parameters (walking velocity, step length, step width). Results: Gait termination over a textured surface resulted in significantly earlier upper leg EMG onset times and modified iEMG of rectus femoris, vastus medialis and biceps femoris muscles. Conclusions: Results of this study suggest that the addition of cutaneous feedback under the plantar-surface of the foot increases the ability to generate an earlier muscle response, consequently improving response ability to an unexpected perturbation. Secondly, enhanced tactile feedback appears to inform the CNS of the magnitude of the threat to the balance control system, providing additional insight into how the CNS uses enhanced tactile feedback during a gait termination task.

Non-uniform Effects of Nociceptive Stimulation to Motoneurones during Experimental Muscle Pain

Nociceptive stimulation is predicted to uniformly inhibit motoneurone pools of painful muscles and those producing painful movements. Although reduced motoneurone discharge rate during pain provides some evidence, recent data show evidence of increased excitability of some motoneurones. These observations suggest non-uniform effects of nociception on motoneurone excitability. More direct measures are required, but this is difficult to assess as few measures enable in vivo evaluation of motoneurone excitability in humans. We investigated changes in motoneurone excitability during experimental pain using two methods in separate experiments: (i) estimation of the time-course of motoneurone afterhyperpolarization (AHP) from interval death rate analysis of interspike intervals of single motor unit discharge; and (ii) probability of early motoneurone discharge to a descending volley excited using transcranial magnetic stimulation (TMS). Tibialis anterior motor units were recorded with fine-wire electrodes before, during and after painful infusion of 5% hypertonic saline into the muscle. Activation of 17 units (16 participants) could be used for AHP analysis. Data show shortened (n = 11) and lengthened (n = 6) AHP time-course. Increased (n = 6) and decreased (n = 6) probability of early motoneurone discharge were observed in the TMS experiment. These convergent observations suggest non-uniform effects of nociceptive stimulation on motoneurone pools. This does not support the hypothesis that nociceptive input induces uniform inhibition of painful muscle. Instead, interpretation of results implies redistribution of activity between motor units, with possible benefit for unloading painful tissues. This finding supports an interpretation that differs from the generally accepted view in pain physiology regarding adaptation to motor function in pain.

In-silico development and assessment of a Kalman filter motor decoder for prosthetic hand control

Up to 50% of amputees abandon their prostheses, partly due to rapid degradation of the control systems, which require frequent recalibration. The goal of this study was to develop a Kalman filter-based approach to decoding motoneuron activity to identify movement kinematics and thereby provide stable, long-term, accurate, real-time decoding. The Kalman filter-based decoder was examined via biologically varied datasets generated from a high-fidelity computational model of the spinal motoneuron pool. The estimated movement kinematics controlled a simulated MuJoCo prosthetic hand. This clear-box approach showed successful estimation of hand movements under eight varied physiological conditions with no retraining. The mean correlation coefficient of 0.98 and mean normalized root mean square error of 0.06 over these eight datasets provide proof of concept that this decoder would improve long-term integrity of performance while performing new, untrained movements. Additionally, the decoder operated in real-time (~0.3 ms). Further results include robust performance of the Kalman filter when re-trained to more severe post-amputation limitations in the type and number of motoneurons remaining. An additional analysis shows that the decoder achieves better accuracy when using the firing of individual motoneurons as input, compared to using aggregate pool firing. Moreover, the decoder demonstrated robustness to noise affecting both the trained decoder parameters and the decoded motoneuron activity. These results demonstrate the utility of a proof of concept Kalman filter decoder that can support prosthetics’ control systems to maintain accurate and stable real-time movement performance.

Variations in Muscle Activity and Exerted Torque During Temporary Blood Flow Restriction in Healthy Individuals.

Recent studies suggest that transitory blood flow restriction (BFR) may improve the outcomes of training from anatomical (hypertrophy) and neural control perspectives. Whilst the chronic consequences of BFR on local metabolism and tissue adaptation have been extensively investigated, its acute effects on motor control are not yet fully understood. In this study, we compared the neuromechanical effects of continuous BFR against non-restricted circulation (atmospheric pressure—AP), during isometric elbow flexions. BFR was achieved applying external pressure either between systolic and diastolic (lower pressure—LP) or 1.3 times the systolic pressure (higher pressure—HP). Three levels of torque (15, 30, and 50% of the maximal voluntary contraction—MVC) were combined with the three levels of pressure for a total of 9 (randomized) test cases. Each condition was repeated 3 times. The protocol was administered to 12 healthy young adults. Neuromechanical measurements (torque and high-density electromyography—HDEMG) and reported discomfort were used to investigate the response of the central nervous system to BFR. The investigated variables were: root mean square (RMS), and area under the curve in the frequency domain—for the torque, and average RMS, median frequency and average muscle fibres conduction velocity—for the EMG. The discomfort caused by BFR was exacerbated by the level of torque and accumulated over time. The torque RMS value did not change across conditions and repetitions. Its spectral content, however, revealed a decrease in power at the tremor band (alpha-band, 5–15 Hz) which was enhanced by the level of pressure and the repetition number. The EMG amplitude showed no differences whilst the median frequency and the conduction velocity decreased over time and across trials, but only for the highest levels of torque and pressure. Taken together, our results show strong yet transitory effects of BFR that are compatible with a motor neuron pool inhibition caused by increased activity of type III and IV afferences, and a decreased activity of spindle afferents. We speculate that a compensation of the central drive may be necessary to maintain the mechanical output unchanged, despite disturbances in the afferent volley to the motor neuron pool.

Force Steadiness: From Motor Units to Voluntary Actions.

Voluntary actions are controlled by the synaptic inputs that are shared by pools of spinal motor neurons. The slow common oscillations in the discharge times of motor units due to these synaptic inputs are strongly correlated with the fluctuations in force during submaximal isometric contractions (force steadiness) and moderately associated with performance scores on some tests of motor function. However, there are key gaps in knowledge that limit the interpretation of differences in force steadiness.

Quantifying mitochondrial volume density in phrenic motor neurons

BackgroundPrevious assessments of mitochondrial volume density within motor neurons used electron microscopy (EM) to image mitochondria. However, adequate identification and sampling of motor neurons within a particular motor neuron pool is largely precluded using EM. Here, we present an alternative method for determining mitochondrial volume density in identified motor neurons within the phrenic motor neuron (PhMN) pool, with greatly increased sampling. New methodThis novel method for assessing mitochondrial volume density in PhMNs uses a combination of intrapleural injection of Alexa 488-conjugated cholera toxin B (CTB) to retrogradely label PhMNs, followed by intrathecal application of MitoTracker Red to label mitochondria. This technique was validated by comparison to 3D EM determination of mitochondrial volume density as a “gold standard”. ResultsA mean mitochondrial volume density of ∼11 % was observed across PhMNs using the new MitoTracker Red method. This compared favourably with mitochondrial volume density (∼11 %) measurements using EM. Comparison with existing methodThe range, mean and variance of mitochondrial volume density estimates in PhMNs were not different between EM and fluorescent imaging techniques. ConclusionsFluorescent imaging may be used to estimate mitochondrial volume density in a large sample of motor neurons, with results similar to EM, although EM did distinguish finer mitochondrion morphology compared to MitoTracker fluorescence. Compared to EM methods, the assessment of a larger sample size and unambiguous identification of motor neurons belonging to a specific motor neuron pool represent major advantages over previous methods.

Concurrent Prediction of Finger Forces Based on Source Separation and Classification of Neuron Discharge Information.

A reliable neural-machine interface is essential for humans to intuitively interact with advanced robotic hands in an unconstrained environment. Existing neural decoding approaches utilize either discrete hand gesture-based pattern recognition or continuous force decoding with one finger at a time. We developed a neural decoding technique that allowed continuous and concurrent prediction of forces of different fingers based on spinal motoneuron firing information. High-density skin-surface electromyogram (HD-EMG) signals of finger extensor muscle were recorded, while human participants produced isometric flexion forces in a dexterous manner (i.e. produced varying forces using either a single finger or multiple fingers concurrently). Motoneuron firing information was extracted from the EMG signals using a blind source separation technique, and each identified neuron was further classified to be associated with a given finger. The forces of individual fingers were then predicted concurrently by utilizing the corresponding motoneuron pool firing frequency of individual fingers. Compared with conventional approaches, our technique led to better prediction performances, i.e. a higher correlation ([Formula: see text] versus [Formula: see text]), a lower prediction error ([Formula: see text]% MVC versus [Formula: see text]% MVC), and a higher accuracy in finger state (rest/active) prediction ([Formula: see text]% versus [Formula: see text]%). Our decoding method demonstrated the possibility of classifying motoneurons for different fingers, which significantly alleviated the cross-talk issue of EMG recordings from neighboring hand muscles, and allowed the decoding of finger forces individually and concurrently. The outcomes offered a robust neural-machine interface that could allow users to intuitively control robotic hands in a dexterous manner.

Towards human motor augmentation by voluntary decoupling beta activity in the neural drive to muscle and force production

Objective. Effective human motor augmentation should rely on biological signals that can be volitionally modulated without compromising natural motor control. Approach. We provided human subjects with real-time information on the power of two separate spectral bands of the spiking activity of motor neurons innervating the tibialis anterior muscle: the low-frequency band (<7 Hz), which is directly translated into natural force control, and the beta band (13–30 Hz), which is outside the dynamics of the neuromuscular system. Main Results. Subjects could gain control over the powers in these two bands to navigate a cursor towards specific targets in a 2D space (experiment 1) and to up- and down-modulate beta activity while keeping steady force contractions (experiment 2). Significance. Results indicate that beta projections to the spinal motor neuron pool can be voluntarily controlled partially decoupled from natural muscle contractions and, therefore, they could be valid control signals for implementing effective human motor augmentation platforms.

Impact of β-range-induced oscillatory activity on human input–output relationship of the corticospinal pathway

ABSTRACT Objective: The aim of the study was to show that short-lasting (90 s) transcranial alternating current stimulation (tACS) at 20 Hz delivered over the left primary motor cortex (M1) is able to change the shape of recruitment curve of the corticospinal pathway. Methods: The corticospinal pathway was studied during tACS by means of the relationship between the intensity of transcranial magnetic stimulation (TMS) delivered over the left M1 and corresponding motor evoked potentials (MEPs) recorded from the right first dorsal interosseus muscle (FDI), in nine healthy subjects. In order to extract characteristics of the input–output relationship that have particular physiological relevance, data were fitted to the Boltzmann sigmoidal function by the Levenberg–Marquardt nonlinear, least mean squares algorithm. Results: The β-rhythm tACS influenced the shape and parameters of the input–output relation, so that the initial segment of the conditioned curve (from threshold to 30% of maximum muscle size) diverged, while the subsequent segment converged to overlap the unconditioned control curve. Discussion: β-rhythm tACS conditions only a definite subset of corticospinal elements influencing less than 30% of the entire motoneuronal pool. The fact that β-rhythm tACS mainly affects the most excitable motoneurons could explain the observed antikinetic effect of the tACS at β-rhythm applied in the motor regions.

Rostrocaudal Distribution of the C-Fos-Immunopositive Spinal Network Defined by Muscle Activity during Locomotion.

The optimization of multisystem neurorehabilitation protocols including electrical spinal cord stimulation and multi-directional tasks training require understanding of underlying circuits mechanisms and distribution of the neuronal network over the spinal cord. In this study we compared the locomotor activity during forward and backward stepping in eighteen adult decerebrated cats. Interneuronal spinal networks responsible for forward and backward stepping were visualized using the C-Fos technique. A bi-modal rostrocaudal distribution of C-Fos-immunopositive neurons over the lumbosacral spinal cord (peaks in the L4/L5 and L6/S1 segments) was revealed. These patterns were compared with motoneuronal pools using Vanderhorst and Holstege scheme; the location of the first peak was correspondent to the motoneurons of the hip flexors and knee extensors, an inter-peak drop was presumably attributed to the motoneurons controlling the adductor muscles. Both were better expressed in cats stepping forward and in parallel, electromyographic (EMG) activity of the hip flexor and knee extensors was higher, while EMG activity of the adductor was lower, during this locomotor mode. On the basis of the present data, which showed greater activity of the adductor muscles and the attributed interneuronal spinal network during backward stepping and according with data about greater demands on postural control systems during backward locomotion, we suppose that the locomotor networks for movements in opposite directions are at least partially different.

An Atoh1 CRE Knock-In Mouse Labels Motor Neurons Involved in Fine Motor Control.

Motor neurons (MNs) innervating the digit muscles of the intrinsic hand (IH) and intrinsic foot (IF) control fine motor movements. The ability to reproducibly label specifically IH and IF MNs in mice would be a beneficial tool for studies focused on fine motor control. To this end, we find that a CRE knock-in mouse line of Atoh1, a developmentally expressed basic helix-loop-helix (bHLH) transcription factor, reliably expresses CRE-dependent reporter genes in ∼60% of the IH and IF MNs. We determine that CRE-dependent expression in IH and IF MNs is ectopic because an Atoh1 mouse line driving FLPo recombinase does not label these MNs although other Atoh1-lineage neurons in the intermediate spinal cord are reliably identified. Furthermore, the CRE-dependent reporter expression is enriched in the IH and IF MN pools with much sparser labeling of other limb-innervating MN pools such as the tibialis anterior (TA), gastrocnemius (GS), quadricep (Q), and adductor (Ad). Lastly, we find that ectopic reporter expression begins postnatally and labels a mixture of α and γ-MNs. Altogether, the Atoh1 CRE knock-in mouse strain might be a useful tool to explore the function and connectivity of MNs involved in fine motor control when combined with other genetic or viral strategies that can restrict labeling specifically to the IH and IF MNs. Accordingly, we provide an example of sparse labeling of IH and IF MNs using an intersectional genetic approach.

ОСОБЕННОСТИ РАСПРЕДЕЛЕНИЯ КАЛЬРЕТИНИН-ИММУНОПОЗИТИВНЫХ НЕЙРОНОВ В ПОЯСНИЧНОМ ОТДЕЛЕ СПИННОГО МОЗГА КОШКИ ( FELIS CATUS )

The variety of neural networks of the central nervous system is determined by the heterogeneity of the neuron populations. Calcium-binding proteins can be used as markers of neurons of different morphotypes. One of the most common calcium-binding proteins in nervous system is calretinin. In the present work, using an indirect immunohistochemical method, calretinin-immunopositive neuronal populations of the lumbar segments of the cat spinal cord were marked. In the study we identified 19 morphotypes of neurons with strict segmental and laminar localization; an attempt was made to compare the proposed function of the neuron type with the available literature data. Among the identified morphotypes, three are localized in lamina I and correspond to neurons involved in the transmission of painful and temperature information. In lamina II, cells of the one morphotype were found, on which pain afferents converge. Three types of project neurons transmitting information from peripheral mechano- and nociceptors to supraspinal structures are presented in laminae III-IV. Laminae V-VI are characterized by functionally different neurons of five morphotypes: interneurons of the Clarke’s nuclei and a similar zone of the caudal lumbar segments, to which proprioceptive information converges; neurons on the lateral border between the white and gray matter, responding to painful and tactile signals; and two types of randomly distributed interneurons, projection or propriospinal neurons that receive heterogeneous afferent signals from muscle spindles. In laminae VII-VIII, two types of sympathetic preganglionic neurons (in the intermediolateral and intercalated nuclei), Renshaw's interneurons, and three types of differently sized multipolar cells were identified, the function of which is difficult to determine. No immunopositive neurons were found in lamina IX, represented by motoneuron pools. Around the central canal in lamina X, rare neurons are localized, the function for which, due to the small number of their morphological features, is not defined.

Spinal motor mapping by epidural stimulation of lumbosacral posterior roots in humans.

SummaryEpidural electrical stimulation of the spinal cord is an emergent strategy for the neurological recovery of lower-extremity motor function. Motoneuron pools are thought to be recruited by stimulation of posterior roots. Here, we linked electromyographic data of epidurally evoked lower-extremity responses of 34 individuals with upper motoneuron disorders to a population model of the spinal cord constructed using anatomical parameters of thousands of individuals. We identified a relationship between segmental stimulation sites and activated spinal cord segments, which made spinal motor mapping from epidural space possible despite the complex anatomical interface imposed by the posterior roots. Our statistical approach provided evidence for low-threshold sites of posterior roots and effects of monopolar and bipolar stimulation previously predicted by computer modeling and allowed us to test the impact of different upper motoneuron disorders on the evoked responses. Finally, we revealed a statistical association between intraoperative and postoperative mapping of the spinal cord.