Volitional Movements Research Articles

Continuous Lower Limb Multi‐Intent Prediction for Electromyography‐Driven Intrinsic and Extrinsic Control

Currently, electromyography (EMG)‐driven lower limb control can be divided into computational intrinsic control and interactive extrinsic control based on the participation of neural information in the controllers. However, the former method lacks detailed measurements of the expected motion, whereas the latter is prone to errors in diverse movement situations. Based on this problem, a multi‐intent prediction scheme is proposed that analyzes both rhythmic locomotion and volitional movement intent for AI‐based intrinsic and extrinsic hybrid control (AIEC). A 1D residual shrinkage convolutional network is designed to extract EMG features. The motion state is continuously predicted with an accuracy of 91.66% and the angle completion is also estimated with of 0.9540 and 0.9456 for left and right knee angles, respectively. Additionally, the comparison test further indicates that the motion state classification is significantly improved in the multitask analysis compared with the single‐task approach. This work demonstrates and verifies a novel method in EMG studies that multi‐intent recognition not only compensates for the lack of information in the analysis of single rhythmic or volitional movement, but also enhances the comprehensive performance and makes AIEC feasible, which optimizes the current EMG‐driven control for ampler intent collection and more practical robotic control.

Behavioral measurements of motor readiness in mice

Motor planning facilitates rapid and precise execution of volitional movements. Although motor planning has been classically studied in humans and monkeys, the mouse has become an increasingly popular model system to study neural mechanisms of motor planning. It remains yet untested whether mice and primates share common behavioral features of motor planning. We combined videography and a delayed response task paradigm in an autonomous behavioral system to measure motor planning in non-body-restrained mice. Motor planning resulted in both reaction time (RT) savings and increased movement accuracy, replicating classic effects in primates. We found that motor planning was reflected in task-relevant body features. Both the specific actions prepared and the degree of motor readiness could be read out online during motor planning. The online readout further revealed behavioral evidence of simultaneous preparation for multiple actions under uncertain conditions. These results validate the mouse as a model to study motor planning, demonstrate body feature movements as a powerful real-time readout of motor readiness, and offer behavioral evidence that motor planning can be a parallel process that permits rapid selection of multiple prepared actions.

Post-ischemic reorganization of sensory responses in cerebral cortex.

Sensorimotor integration is critical for generating skilled, volitional movements. While stroke tends to impact motor function, there are also often associated sensory deficits that contribute to overall behavioral deficits. Because many of the cortico-cortical projections participating in the generation of volitional movement either target or pass-through primary motor cortex (in rats, caudal forelimb area; CFA), any damage to CFA can lead to a subsequent disruption in information flow. As a result, the loss of sensory feedback is thought to contribute to motor dysfunction even when sensory areas are spared from injury. Previous research has suggested that the restoration of sensorimotor integration through reorganization or de novo neuronal connections is important for restoring function. Our goal was to determine if there was crosstalk between sensorimotor cortical areas with recovery from a primary motor cortex injury. First, we investigated if peripheral sensory stimulation would evoke responses in the rostral forelimb area (RFA), a rodent homologue to premotor cortex. We then sought to identify whether intracortical microstimulation-evoked activity in RFA would reciprocally modify the sensory response. We used seven rats with an ischemic lesion of CFA. Four weeks after injury, the rats' forepaw was mechanically stimulated under anesthesia and neural activity was recorded in the cortex. In a subset of trials, a small intracortical stimulation pulse was delivered in RFA either individually or paired with peripheral sensory stimulation. Our results point to post-ischemic connectivity between premotor and sensory cortex that may be related to functional recovery. Premotor recruitment during the sensory response was seen with a peak in spiking within RFA after the peripheral solenoid stimulation despite the damage to CFA. Furthermore, stimulation in RFA modulated and disrupted the sensory response in sensory cortex. The presence of a sensory response in RFA and the sensitivity of S1 to modulation by intracortical stimulation provides additional evidence for functional connectivity between premotor and somatosensory cortex. The strength of the modulatory effect may be related to the extent of the injury and the subsequent reshaping of cortical connections in response to network disruption.

Optimal Energy Shaping Control for a Backdrivable Hip Exoskeleton.

Task-dependent controllers widely used in exoskeletons track predefined trajectories, which overly constrain the volitional motion of individuals with remnant voluntary mobility. Energy shaping, on the other hand, provides task-invariant assistance by altering the human body's dynamic characteristics in the closed loop. While human-exoskeleton systems are often modeled using Euler-Lagrange equations, in our previous work we modeled the system as a port-controlled-Hamiltonian system, and a task-invariant controller was designed for a knee-ankle exoskeleton using interconnection-damping assignment passivity-based control. In this paper, we extend this framework to design a controller for a backdrivable hip exoskeleton to assist multiple tasks. A set of basis functions that contains information of kinematics is selected and corresponding coefficients are optimized, which allows the controller to provide torque that fits normative human torque for different activities of daily life. Human-subject experiments with two able-bodied subjects demonstrated the controller's capability to reduce muscle effort across different tasks.

Clinical Observations of Hearing, Speech, Language and Swallowing Abilities in Locked-in Syndrome: A Case-based Study

Background: Locked-in Syndrome (LIS) is a rare neurological condition characterized by quadriplegia, mutism, and lower cranial nerve paralysis with intact eye movements and consciousness and communication through eye blink only. The irretrievable LIS condition differs from a coma, persistent vegetative state, and akinetic mutism with preserved volitional vertical eye movements and blinking involving a lack of conscious interaction with the environment. Reports and evidence on assessment and rehabilitation with LIS are scanty. Thus, this case study aims to highlight some of the challenges faced by speech-language pathologists in the assessment and management of LIS in a multidisciplinary rehabilitation center. This study also emphasizes the assessment protocol adapted to diagnose and strategies planned for intervention. 
 Case Description: A 58 years old male followed by an ischemic brain stroke diagnosed with LIS with a tracheostomy came to the department. Detailed history noted history revealed a brainstem stroke with pons involvement and a tracheostomy with percutaneous endoscopic gastrotomy and immobile vocal folds with limited epiglottic movements with impaired swallowing ability and severe aspiration. The clinical assessment was challenging and difficult to select appropriate assessment strategies for the condition. Detailed Speech, Swallow, and Language evaluations were carried out. The detailed evaluation reported the client with anarthria with tracheostomy secondary to locked-in syndrome.
 Conclusion: The present case report summarizes the need and findings of various evaluation procedures in the field of communication disorders. The role of an SLP is essential and a proper diagnostic protocol need to be considered along with spectacular observation while assessing LIS.

839 Beta-Band Power Modulation in the Human Amygdala During a Go/No-Go Reaching Task

INTRODUCTION: The role of the amygdala in motor control is a developing area of investigation. Although classically known for its involvement in emotional processing, the amygdala has also been associated with modulating motor processing. For example, increases in the gamma frequency band (30-200 Hz) have been observed during volitional movements. However, the underlying neural mechanisms of amygdaloid motor movement and inhibition are not well-understood. METHODS: Nine patients with drug resistant epilepsy underwent implantation with stereoelectroencephalographic (SEEG) depth electrodes for seizure monitoring in the amygdala (5 bilaterally, 2 left unilaterally, and 2 right unilaterally). SEEG data were sampled throughout discrete phases of a Go/No-Go task (ITI, Fixation, Go/No-Go response), which required participants to touch a target or inhibit movement based on a colored cue. A Wilcoxon signed-rank hypothesis test was used to assess significant modulations of beta-band power between the response and fixation (baseline) phases of the task. RESULTS: In the Go condition, six out of seven patients with electrodes in the right amygdala had a significant decrease in beta-band power (p < 0.0479), and four out of seven in the left amygdala (p < 0.049). During the No-Go condition, seven out of seven patients with electrodes in the right amygdala displayed statistically significant increases of beta-band power when compared to the baseline period (p < 0.0451), and four out of seven in the left amygdala (p < 0.0137). CONCLUSIONS: This study reports beta-band power modulation in the human amygdala during voluntary movement in the setting of motor execution versus inhibition. This finding adds to previous studies in other brain areas that have linked beta-band power to motor control. The presence of beta-band power modulation in No-Go conditions suggests that the beta-band potentially plays a role in amygdaloid motor inhibition.

Neuromodulation Through Spinal Cord Stimulation Restores Ability to Voluntarily Cycle After Motor Complete Paraplegia.

Abstract Epidural spinal cord stimulation (eSCS) of the lower thoracic spinal cord has been shown to partially restore volitional movement in patients with complete chronic spinal cord injury (cSCI). Combining eSCS with intensive locomotor training improves motor function, including standing and stepping, but many patients with cSCI suffer from long-standing muscle atrophy and loss of bone mineral density, which may prohibit safe implementation. Safe, accessible, and effective avenues for pairing neuromodulation with activity-based therapy remain unexplored. Cycling is one such option that can be utilized as an eSCS therapy given its low-risk and low-weight-bearing requirement. We investigated the feasibility and kinematics of motor-assisted and passive cycle-based therapy for cSCI patients with epidural spinal cord stimulation. Seven participants who underwent spinal cord stimulation surgery in the Epidural Stimulation After Neurologic Damage (E-STAND) trial (NCT03026816) participated in a cycling task using the motor assist MOTOmed Muvi 300. A factorial design was used such that participants were asked to cycle with and without conscious effort with and without stimulation. We used mixed effects models assessing maximum power output and time pedaling unassisted to evaluate the interaction between stimulation and conscious effort. Cycling was well-tolerated and we observed no adverse events, including in participants up to 17 years post-initial injury and up to 58 years old. All participants were found to be able to pedal without motor assist, which primarily occurred when stimulation and effort were applied together (p = 0.001). Additionally, the combination of stimulation and intention was significantly associated with higher maximum power production (p < 0.0001) and distance pedaled (p = 0.0001). No association was found between volitional movement and participant factors: age, time since injury, and spinal cord atrophy. With stimulation and conscious effort, all participants were able to achieve active cycling without motor assistance. Thus, our stationary cycling factorial study design demonstrated volitional movement restoration with eSCS in a diverse study population of cSCI participants. Further, motor-assist cycling was well-tolerated without any adverse events. Cycling has the potential to be a safe research assessment and physical therapy modality for cSCI patients utilizing eSCS who have a high risk of injury with weight bearing exercise. The cycling modality in this study was demonstrated to be a straightforward assessment of motor function and safe for all participants regardless of age or time since initial injury.

Commentary: Spinal Cord Stimulation to Improve Autonomic Regulation After Spinal Cord Injury: Can Reflex Control Be Restored.

Spinal cord electrical stimulation has recently become popular as a research tool to improve function in individuals with spinal cord injuries (SCI). Headline-worthy study after study demonstrate that this form of neuromodulation can allow individuals with paralysis to move, stand, and even walk— a previously unthinkable achievement.1–4 Subsequent work has sought to replicate these gains within the autonomic nervous system.5–7 This is a commendable undertaking; autonomic dysfunction has broad and significant clinical implications and is the source of many patients’ top health concerns.8 Studies using spinal cord stimulation to address autonomic dysfunction have largely been aimed at ameliorating orthostatic hypotension9 by supporting blood pressure.10 Blood pressure falls with upright tilt in those with SCI due to lack of sympathetic activity below the injury, despite appropriate compensatory tachycardia.11 Hence, spinal cord stimulation may be used to stimulate vascular sympathetic outflow below the lesion, preventing hypotension and obviating the need for tachycardia. This would suggest improved autonomic regulation, where the nervous system compensates to dynamic challenges to maintain homeostasis. The premise for this theory of improved autonomic regulation is modeled from responses to stimulation of the motor system wherein weak signaling pathways through the cord are amplified to achieve volitional movement. However, the motor and autonomic systems encompass vastly different regulatory mechanisms. For volitional muscle activation, central motor command elicits volleys of efferent signals down the cord proportional to perceived effort.12 After chronic paralysis, one can imagine the voluntary effort and corresponding efferent volleys are near maximal with attempted movement. However, the autonomic system is not subject to voluntary control. There is a myriad of redundancies in regulatory systems to maintain homeostasis. Indeed, autonomic responses can be either sympatho-excitatory or sympatho-inhibitory.13 Perhaps the best example of the former is the isometric exercise pressor response. At the end of sustained isometric exercise to fatigue, central command, the “feedforward mechanism involving parallel activation of motor and cardiovascular centers,”14 is maximal. In addition, group III and IV afferent feedback from the ischemic exercising muscle is maximal. As a result, directly measured neural sympathetic outflow can approach some of its highest levels.15 However, this response is not independent of autonomic sympatho-inhibitory regulation. The arterial baroreflex is sympatho-inhibitory, wherein increased stretch of barosensory vessels (the aortic arch and carotid sinus) increase afferent baroreceptor nerve firing, inhibiting sympathetic outflow to maintain pressure.16 In the context of orthostasis, reduced barosensory vessel stretch results in a “permissive” rise in sympathetic outflow. This is essentially taking the foot off the brake to promote compensatory vasoconstriction and vagal withdrawal for tachycardia. Following SCI, this spinal cord-mediated vasoconstriction is often impaired below the level of the injury.17Spinal cord stimulation in those with SCI during orthostasis may increase blood pressure through sympathetic activation, but it may not involve improved autonomic regulation by boosting weak regulatory pathways through the injured cord. In fact, spinal cord stimulation could induce unperceived pain or activation of local branched calcitonin gene-related peptide (CGRP)–related afferent fibers in the dorsal horns,18 leading to sympatho-excitation through autonomic dysreflexia.10,19 It could also cause venoconstriction, reducing venous pooling and allowing for a more effective compensatory tachycardia.20 Although preventing orthostatic intolerance is important for health in those with SCI, further work is necessary to define the exact mechanism. Inducing repeated dysreflexia would not represent an effective strategy for long-term health. Autonomic dysreflexia is associated with transient immunosuppression21 and chronic stimulation may lead to potentially dangerous hypertensive crises.To identify whether autonomic regulation can be improved, appropriate tests encompassing both sympatho-excitatory and sympatho-inhibitory pathways must be employed with and without spinal cord stimulation and comprehensive measures must be made (e.g., regional blood flows). Only in this way can we discern the ability of stimulation to truly enhance reflex autonomic regulation.

Video head impulse testing in patients with isolated (hemi)nodular infarction.

Isolated (hemi)nodular strokes as underlying cause of acute dizziness are rare, thus there are still gaps of knowledge in the clinical presentation of affected patients. Clinical and experimental evidence has suggested that lesions involving the nodulus lead to various vestibulo-ocular deficits including prolonged velocity-storage, periodic-alternating nystagmus, positional nystagmus, abolished suppression of post-rotatory nystagmus by head-tilt and impaired verticality perception. At the bedside, the angular vestibulo-ocular reflex (aVOR), as assessed by the horizontal head-impulse test (HIT), has been reported to be normal, however quantitative assessments of all six semicircular canals are lacking. The primary aim of this case series was to characterize the spectrum of clinical presentations in isolated (hemi)nodular strokes. Furthermore, based on preliminary observations, we hypothesized that the aVOR is within normal limits in isolated nodular strokes. We retrospectively included patients with isolated (hemi)nodular stroke on diffusion-weighted MR-imaging from a prospective stroke-registry. All patients received a standardized bedside neuro-otological assessment and quantitative, video-based HIT (vHIT) of all six semicircular canals. Overall ratings of vHIT (normal vs. abnormal function) were performed independently by two reviewers and disagreements were resolved. Between January 2015 and December 2021 six patients with isolated nodular (n = 1) or heminodular (n = 5) ischemic stroke were included. Clinical presentation met diagnostic criteria for acute vestibular syndrome (AVS) in 5/6 patients and for episodic vestibular syndrome (EVS) in 1/6 patients. Ocular motor abnormalities observed included the presence of spontaneous horizontal nystagmus (n = 2), positional nystagmus (5/6), head-shaking nystagmus (3/6), skew deviation (n = 1), and moderate or severe truncal ataxia (5/6). Bedside HIT was normal in all patients and no gaze-evoked or periodic alternating nystagmus was observed. aVOR-gains were within normal range in all patients and overall aVOR-function as assessed by vHIT was rated as normal in all six patients. Using quantitative, video-based testing of the horizontal and vertical aVOR, preserved integrity of the aVOR in (hemi)nodular strokes was confirmed, extending preliminary findings at the bedside. Furthermore, widespread deficits of both ocular stability, postural control and volitional eye movements were observed in our study cohort, being consistent with findings reported in previous studies.

A Method for Quantification of Stretch Reflex Excitability During Ballistic Reaching.

Stretch reflexes are crucial for performing accurate movements and providing rapid corrections for unpredictable perturbations. Stretch reflexes are modulated by supraspinal structures via corticofugal pathways. Neural activity in these structures is difficult to observe directly, but the characterization of reflex excitability during volitional movement can be used to study how these structures modulate reflexes and how neurological injuries impact this control, such as in spasticity after stroke. We have developed a novel protocol to quantify stretch reflex excitability during ballistic reaching. This novel method was implemented using a custom haptic device (NACT-3D) capable of applying high-velocity (270 °/s) joint perturbations in the plane of the arm while participants performed 3D reaching tasks in a large workspace. We assessed the protocol on four participants with chronic hemiparetic stroke and two control participants. Participants reached ballistically from a near to a far target, with elbow extension perturbations applied in random catch trials. Perturbations were applied before movement, during the early phase of movement, or near peak movement velocity. Preliminary results show that stretch reflexes were elicited in the stroke group in the biceps muscle during reaching, as measured by electromyographic (EMG) activity both before (pre-motion phase) and during (early motion phase) movement. Reflexive EMG was also seen in the anterior deltoid and pectoralis major in the pre-motion phase. In the control group, no reflexive EMG was seen, as expected. This newly developed methodology allows the study of stretch reflex modulation in new ways by combining multijoint movements with haptic environments and high-velocity perturbations.

Chapter 2 - Upper and lower motor neuron neurophysiology and motor control

This chapter considers the principles that underlie neurophysiological studies of upper motor neuron or lower motor neuron lesions, based on an understanding of the normal structure and function of the motor system. Human motor neurophysiology consists of an evaluation of the active components of the motor system that are relevant to volitional movements. Relatively primitive motor skills include locomotion, much dependent on the spinal cord central pattern generator, reaching, involving proximal and distal muscles activation, and grasping. Humans are well prepared to perform complex movements like writing. The role of motor cortex is critical for the motor activity, very dependent on the continuous sensory feedback, and this is essential for adapting the force and speed control, which contributes to motor learning. Most corticospinal neurons in the brain project to brainstem and spinal cord, many with polysynaptic inhibitory rather than excitatory connections. The monosynaptic connections observed in humans and primates constitute a specialized pathway implicated in fractional finger movements. Spinal cord has a complex physiology, and local reflexes and sensory feedback are essential to control adapted muscular contraction during movement. The cerebellum has a major role in motor coordination, but also consistent roles in sensory activities, speech, and language, in motor and spatial memory, and in psychological activity. The motor unit is the final effector of the motor drive. The complex interplay between the lower motor neuron, its axon, motor end-plates, and muscle fibers allows a relevant plasticity in the movement output.

Convulsive behaviors of spontaneous recurrent seizures in a mouse model of extended hippocampal kindling.

Growing studies indicate that vigilance states and circadian rhythms can influence seizure occurrence in patients with epilepsy and rodent models of epilepsy. Electrical kindling, referred to brief, repeated stimulations of a limbic structure, is a commonly used model of temporal lobe epilepsy. Kindling via the classic protocol lasting a few weeks does not generally induce spontaneous recurrent seizures (SRS), but extended kindling that applies over the course of a few months has shown to induce SRS in several animal species. Kindling-induced SRS in monkeys and cats were observed mainly during resting wakefulness or sleep, but the behavioral activities associated with SRS in rodent models of extended kindling remain unknown. We aimed to add information in this area using a mouse model of extended hippocampal kindling. Middle-aged C57 black mice experienced ≥80 hippocampal stimulations (delivered twice daily) and then underwent continuous 24 h electroencephalography (EEG)-video monitoring for SRS detection. SRS were recognized by EEG discharges and associated motor seizures. The five stages of the modified Racine scale for mice were used to score motor seizure severities. Seizure-preceding behaviors were assessed in a 3 min period prior to seizure onset and categorized as active and inactive. Three main observations emerged from the present analysis. (1) SRS were found to predominantly manifest as generalized (stage 3-5) motor seizures in association with tail erection or Straub tail. (2) SRS occurrences were not significantly altered by the light on/off cycle. (3) Generalized (stage 3-5) motor seizures were mainly preceded by inactive behaviors such as immobility, standing still, or apparent sleep without evident volitional movement. Considering deeper subcortical structures implicated in genesis of tail erection in other seizure models, we postulate that genesis of generalized motor seizures in extended kindled mice may involve deeper subcortical structures. Our present data together with previous findings from post-status epilepticus models support the notion that ambient cage behaviors are strong influencing factors of SRS occurrence in rodent models of temporal lobe epilepsy.

Reply to a Reply

Ogas and Gaddam's reply to my review of their book Journey of the Mind covers a lot of ground. Little of it, alas, deals with the issues I raised. It is largely an expansion of Steven Grossberg's resonance theory which, of course, played a prominent role in the book. I have no problems with Grossberg's model. It is an interesting, influential, quantitative approach to human cognitive functioning that uses neural nets to capture the operations of “modules.” But it's not going to result in an understanding of the origins of minds. Also, as noted in my review, it's seriously lacking in key features such as embodiment, movement, affect, development, aging, and socialization.It is not the complete theory of the human mind that Ogas and Gaddam appear to believe it is. For one, it does not enable theorists “to discard conjectured mental entities . . . such as . . . conscious cells.” The sentient cell is a central feature of my cellular basis of consciousness theory. It is also a fundamental element in a variety of approaches to cell biology and, as argued in a variety of recent publications, a necessary feature of the first unicellular species. Without sentience the original prokaryotes would have been Darwinian dead ends. Without valenced perceptions and directed, volitional movement they could not have survived the tumultuous environment they emerged into.But the book has “Journey” in the title, and my problem was with the nature of the trip they took us on. The early sections are, as noted, “muddled” when it comes to the functions of species that lack nervous systems. The material on cell biology is wrong in many places. The “emergentist's dilemma” is not even acknowledged. They claim that species without nervous systems cannot have an existential consciousness but provide no reason why this should be true. Did things change when neurons evolved? Of course. But things changed many times over geological time: eukaryotic species, multicellularity, photosynthesis, oxygen production, warm-blooded metabolism, legs, and so on.I appreciate that Ogas and Gaddam “wrote Journey of the Mind to present accessible versions of URT's key ideas to a popular audience.” But they didn't do that until the second half. And when they made this move to Grossberg's theory, the sole focus was on human cognitive functions, not the earlier evolutionary mechanisms that preceded the emergence of Homo sapient minds.

Functional and neuromuscular changes induced via a low-cost, muscle-computer interface for telerehabilitation: A feasibility study in chronic stroke.

Stroke is a leading cause of adult disability in the United States. High doses of repeated task-specific practice have shown promising results in restoring upper limb function in chronic stroke. However, it is currently challenging to provide such doses in clinical practice. At-home telerehabilitation supervised by a clinician is a potential solution to provide higher-dose interventions. However, telerehabilitation systems developed for repeated task-specific practice typically require a minimum level of active movement. Therefore, severely impaired people necessitate alternative therapeutic approaches. Measurement and feedback of electrical muscle activity via electromyography (EMG) have been previously implemented in the presence of minimal or no volitional movement to improve motor performance in people with stroke. Specifically, muscle neurofeedback training to reduce unintended co-contractions of the impaired hand may be a targeted intervention to improve motor control in severely impaired populations. Here, we present the preliminary results of a low-cost, portable EMG biofeedback system (Tele-REINVENT) for supervised and unsupervised upper limb telerehabilitation after stroke. We aimed to explore the feasibility of providing higher doses of repeated task-specific practice during at-home training. Therefore, we recruited 5 participants (age = 44-73 years) with chronic, severe impairment due to stroke (Fugl-Meyer = 19-40/66). They completed a 6-week home-based training program that reinforced activity of the wrist extensor muscles while avoiding coactivation of flexor muscles via computer games. We used EMG signals to quantify the contribution of two antagonistic muscles and provide biofeedback of individuated activity, defined as a ratio of extensor and flexor activity during movement attempt. Our data suggest that 30 1-h sessions over 6 weeks of at-home training with our Tele-REINVENT system is feasible and may improve individuated muscle activity as well as scores on standard clinical assessments (e.g., Fugl-Meyer Assessment, Action Research Arm Test, active wrist range of motion) for some individuals. Furthermore, tests of neuromuscular control suggest modest changes in the synchronization of electroencephalography (EEG) and EMG signals within the beta band (12-30 Hz). Finally, all participants showed high adherence to the training protocol and reported enjoying using the system. These preliminary results suggest that using low-cost technology for home-based telerehabilitation after severe chronic stroke is feasible and may be effective in improving motor control via feedback of individuated muscle activity.

The human egomotion network

All volitional movement in a three-dimensional space requires multisensory integration, in particular of visual and vestibular signals. Where and how the human brain processes and integrates self-motion signals remains enigmatic. Here, we applied visual and vestibular self-motion stimulation using fast and precise whole-brain neuroimaging to delineate and characterize the entire cortical and subcortical egomotion network in a substantial cohort (n=131). Our results identify a core egomotion network consisting of areas in the cingulate sulcus (CSv, PcM/pCi), the cerebellum (uvula), and the temporo-parietal cortex including area VPS and an unnamed region in the supramarginal gyrus. Based on its cerebral connectivity pattern and anatomical localization, we propose that this region represents the human homologue of macaque area 7a. Whole-brain connectivity and gradient analyses imply an essential role of the connections between the cingulate sulcus and the cerebellar uvula in egomotion perception. This could be via feedback loops involved updating visuo-spatial and vestibular information. The unique functional connectivity patterns of PcM/pCi hint at central role in multisensory integration essential for the perception of self-referential spatial awareness. All cortical egomotion hubs showed modular functional connectivity with other visual, vestibular, somatosensory and higher order motor areas, underlining their mutual function in general sensorimotor integration.

Reflexive and volitional saccadic eye movements and their changes in age and progressive supranuclear palsy

Background and objectivesSaccades, rapid movements of the eyes towards a visual or remembered target, are useful in understanding the healthy brain and the pathology of neurological conditions such as progressive supranuclear palsy (PSP). We set out to investigate the parameters of horizontal reflexive and volitional saccades, both visually guided and memory-guided, over a 1 min epoch in healthy individuals and PSP patients. MethodsAn experimental paradigm tested reflexive, volitional visually guided, and volitional memory-guided saccades in young healthy controls (n = 14; 20–31 years), PSP patients (n = 11; 46–75 years) and older age-matched healthy controls (n = 6; 56–71 years). The accuracy and velocity of saccades was recorded using an EyeBrain T2® video eye tracker and analyses performed using the MyEyeAnalysis® software. Two-way analysis of variance (ANOVA) was used to identify significant effects (p < 0.01) between young and older controls to investigate the effects of ageing upon saccades, and between PSP patients and age-matched controls to study the effects of PSP upon saccades. ResultsIn both healthy individuals and PSP patients, volitional saccades are slower and less accurate than reflexive saccades. In PSP patients, accuracy is lower across all saccade types compared to age-matched controls, but velocity is lower only for reflexive saccades. Crucially, there is no change in accuracy or velocity of consecutive saccades over short (one-minute) timescales in controls or PSP patients. ConclusionsVelocity and accuracy of saccades in PSP does not decrease over one-minute timescales, contrary to that previously observed in Parkinson's Disease (PD), suggesting a potential clinical biomarker for the distinction of PSP from PD.

Emergence of Distinct Neural Subspaces in Motor Cortical Dynamics during Volitional Adjustments of Ongoing Locomotion.

The ability to modulate ongoing walking gait with precise, voluntary adjustments is what allows animals to navigate complex terrains. However, how the nervous system generates the signals to precisely control the limbs while simultaneously maintaining locomotion is poorly understood. One potential strategy is to distribute the neural activity related to these two functions into distinct cortical activity coactivation subspaces so that both may be conducted simultaneously without disruptive interference. To investigate this hypothesis, we recorded the activity of primary motor cortex in male nonhuman primates during obstacle avoidance on a treadmill. We found that the same neural population was active during both basic unobstructed locomotion and volitional obstacle avoidance movements. We identified the neural modes spanning the subspace of the low-dimensional dynamics in primary motor cortex and found a subspace that consistently maintains the same cyclic activity throughout obstacle stepping, despite large changes in the movement itself. All of the variance corresponding to this large change in movement during the obstacle avoidance was confined to its own distinct subspace. Furthermore, neural decoders built for ongoing locomotion did not generalize to decoding obstacle avoidance during locomotion. Our findings suggest that separate underlying subspaces emerge during complex locomotion that coordinates ongoing locomotor-related neural dynamics with volitional gait adjustments. These findings may have important implications for the development of brain-machine interfaces.SIGNIFICANCE STATEMENT Locomotion and precise, goal-directed movements are two distinct movement modalities with known differing requirements of motor cortical input. Previous studies have characterized the cortical activity during obstacle avoidance while walking in rodents and felines, but, to date, no such studies have been completed in primates. Additionally, in any animal model, it is unknown how these two movements are represented in primary motor cortex (M1) low-dimensional dynamics when both activities are performed at the same time, such as during obstacle avoidance. We developed a novel obstacle avoidance paradigm in freely moving nonhuman primates and discovered that the rhythmic locomotion-related dynamics and the voluntary, gait-adjustment movement separate into distinct subspaces in M1 cortical activity. Our analysis of decoding generalization may also have important implications for the development of brain-machine interfaces.

Volitional Head Movement Deficits and Alterations in Gait Speed Following Mild Traumatic Brain Injury.

Unconstrained head motion is necessary to scan for visual cues during navigation, for minimizing threats, and to allow regulation of balance. Following mild traumatic brain injury (mTBI) people may experience alterations in head movement kinematics, which may be pronounced during gait tasks. Gait speed may also be impacted by the need to turn the head while walking in these individuals. The aim of this study was to examine head kinematics during dynamic gait tasks and the interaction between kinematics and gait speed in people with persistent symptoms after mTBI. A clinical assessment laboratory. A cross-sectional, matched-cohort study. Forty-five individuals with a history of mTBI and 46 age-matched control individuals. All participants were tested at a single time point and completed the Functional Gait Assessment (FGA) while wearing a suite of body-mounted inertial measurement units (IMUs). Data collected from the IMUs were gait speed, and peak head rotation speed and amplitude in the yaw and pitch planes during the FGA-1, -3, and -4 tasks. Participants with mTBI demonstrated significantly slower head rotations in the yaw ( P = .0008) and pitch ( P = .002) planes. They also demonstrated significantly reduced amplitude of yaw plane head rotations ( P < .0001), but not pitch plane head rotations ( P = .84). Participants with mTBI had significantly slower gait speed during normal gait (FGA-1) ( P < .001) and experienced a significantly greater percent decrease in gait speed than healthy controls when walking with yaw plane head rotations (FGA-3) ( P = .02), but not pitch plane head rotations (FGA-4) ( P = .11). Participants with mTBI demonstrated smaller amplitudes and slower speeds of yaw plane head rotations and slower speeds of pitch plane head rotations during gait. Additionally, people with mTBI walked slower during normal gait and demonstrated a greater reduction in gait speed while walking with yaw plane head rotations compared with healthy controls.

A Review of Functional Restoration From Spinal Cord Stimulation in Patients With Spinal Cord Injury.

Traumatic spinal cord injury often leads to loss of sensory, motor, and autonomic function below the level of injury. Recent advancements in spinal cord electrical stimulation (SCS) for spinal cord injury have provided potential avenues for restoration of neurologic function in affected patients. This review aims to assess the efficacy of spinal cord stimulation, both epidural (eSCS) and transcutaneous (tSCS), on the return of function in individuals with chronic spinal cord injury. The current literature on human clinical eSCS and tSCS for spinal cord injury was reviewed. Seventy-one relevant studies were included for review, specifically examining changes in volitional movement, changes in muscle activity or spasticity, or return of cardiovascular pulmonary, or genitourinary autonomic function. The total participant sample comprised of 327 patients with spinal cord injury, each evaluated using different stimulation protocols, some for sensorimotor function and others for various autonomic functions. One hundred eight of 127 patients saw improvement in sensorimotor function, 51 of 70 patients saw improvement in autonomic genitourinary function, 32 of 32 patients saw improvement in autonomic pulmonary function, and 32 of 36 patients saw improvement in autonomic cardiovascular function. Although this review highlights SCS as a promising therapeutic neuromodulatory technique to improve rehabilitation in patients with SCI, further mechanistic studies and stimulus parameter optimization are necessary before clinical translation.

Expectation of volitional arm movement has prolonged effects on the grip force exerted on a pinched object.

Humans closely coordinate the grip force exerted on a hand-held object with changes in the load arising from the object's dynamics. Recent work suggests the grip force is responsive to the predictability of the load forces as well. The well-known grip-force-load-force coupling is intermittent when the load arising from volitional movements fluctuates predictably, whereas grip force increases when loads are unpredictable. Here, we studied the influence of expected but uncertain volitional movements on the digit forces during a static grasp. Young, healthy participants used a pinch grasp to hold an instrumented object and track visual targets by moving the object. We quantified the mean grip force, the temporal decline in grip force (slacking), and the coupling between the pressing digit forces that yield the grip force during static prehension with no expectation of movement, and during the static phase of a choice reaction time task, when the participant expected to move the object after a variable duration. Simply expecting to move the object led to sustained (for at least 5s) higher magnitude and lower slacking in the grip force, and weaker coupling between the pressing digit forces. These effects were modulated by the direction of the expected movement and the object's mass. The changes helped to maintain the safety margin for the current grasp and likely facilitated the transition from static to dynamic object manipulation. Influence of expected actions on the current grasp may have implications for manual dexterity and its well-known loss with age.