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Proprioceptive Feedback and Movement Regulation
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... Proprioception is the sense of body posture and movement that is essential for a person to control their own body [8] and is also related to the sense of body ownership [9]. This sense is a complex system formed by information from various receptors. ...
... This equation was obtained based on the finding that the output of the muscle spindle encodes the length of the muscle and its temporal variation [8], and further by neglecting nonlinear factors, including the relationship between muscle length and joint angle, and assuming the relationship ...
... This result is unexpected given the neurophysiological finding that muscle spindle output encodes muscle length and its rate of change [8], and the previous study [5] that used vibration frequencies corresponding to the speed of the presented movement. Furthermore, the experiment by Gilhodes et al. [14], in which vibration stimuli were applied with a constant frequency difference that did not change over time, produced a kinesthetic illusion in the direction of muscle elongation on the side with the higher frequency. ...
The kinesthetic illusion induced by tendon vibration has the potential to be applied to virtual reality because it can provide the sensation of motion without the need to actually move the body. The psychophysical and neurophysiological properties of this phenomenon have been studied for a long time, and more recently, research has been conducted to realize the presentation of complex motion. However, there is still a lack of knowledge that quantitatively relates time-varying vibratory stimuli to the resulting kinesthesia. In response to this situation, we experimentally quantify the relationship between the time-varying frequency of the vibratory stimuli and the perceived joint angle, as a transfer function which is directly applicable to the presentation of kinesthetic illusions. To minimize temporal error, we presented vibration stimuli to one arm and a physical motion to the other arm, and asked participants to adjust the amplitude and phase of the physical motion so that the sensations of the two stimuli matched. The transfer function obtained from the experiment was nearly constant between the presented reciprocating frequencies of 0.05 Hz and 0.30 Hz, with a flat amplitude response and a phase advance of approximately 180 degrees. This transfer function represents motion in the opposite direction to that expected from existing knowledge. Possible reasons for this could be the induction of motion in the opposite direction by the tonic vibration reflex, misunderstanding by the participants, or the generation of an illusory force sensation due to the activation of the Golgi tendon organs.
... This study investigated how the elaboration of the force estimate is influenced by various sensory streams of information. As the control of the force produced by the index finger is involved in many daily activities and is encoded by an array of tactile receptors, muscle spindles, and tendon organs (Prochazka, 2011), the force reproduction task used in the present study consisted of producing index finger abduction force. Specifically, the first objective was to show that the force estimate elaborated during the TARGET phase relies, in part, on proprioceptive inputs (Experiment 1). ...
... With these stimulation patterns, all elicited neurons are simultaneously activated, contrary to what happens with neural activity during in-vivo natural touch 32 . In fact, the natural asynchronous activation is driven in a part by the probabilistic nature of action potential generation in sensory organs, such as muscle spindles 33 or touch afferents 34 , and in second part by the stochastic nature of synaptic transmission 35 . The synchronization, which generates an unnatural aggregate activity within the neural tissue, could be among the main reasons of perceived paresthesia percepts 8,27,36 . ...
Artificial communication with the brain through peripheral nerve stimulation recently showed promising results in people with sensorimotor deficits. However, these efforts fall short in delivering close-to-natural rich sensory experience, resulting in the necessity to propose novel venues for converting sensory information into neural stimulation patterns, which would possibly enable intuitive and natural sensations. To this aim, we designed and tested a biomimetic neurostimulation framework inspired by nature, able "to write" physiologically plausible information back into the residual healthy nervous system. Starting from the in-silico model of mechanoreceptors, we designed biomimetic policies of stimulation, emulating the activity of different afferent units. Then, we experimentally assessed these novel paradigms, alongside mechanical touch and commonly used, linear neuromodulations. We explored the somatosensory neuroaxis by stimulating the nerve while recording the neural responses at the dorsal root ganglion and spinal cord of decerebrated cats. Biomimetic stimulation resulted in a neural activity that travels consistently along the neuroaxis, producing the spatio-temporal neural dynamic more like the naturally evoked one. Finally, we then implemented these paradigms within the bionic device and tested it with patients. Biomimetic neurostimulations resulted in higher mobility and decreased mental effort compared to traditional approaches. The results of this neuroscience-driven technology inspired by the human body could be a model for the development of novel assistive neurotechnologies.
... As pointed out above, effort perception only arises when a voluntary motor command is produced, that is when an efference copy is generated and, by association, when the fusimotor system activates intrafusal fibres through alpha-gamma coactivation. During voluntary isometric contractions, the firing rate of spindle afferents increases compared to the relaxed state (Prochazka, 1996;Wilson et al., 1997). This increase suggests that gamma drives are conveyed through muscle spindles to reach afferent fibres, providing feedback to the brain regarding the amount of fusimotor commands received by intrafusal fibres. ...
figure legend The perception of effort is intimately tied to the neural signals related to motor command magnitude. The efference copy has long been recognized as the primary signal that the brain processes to generate a sense of effort. However, recent evidence suggests that reafferent muscle spindle signals may also play a crucial role in effort perception, particularly through interactions with the efference copy. During voluntary contractions, alpha‐motoneurons (innervating force‐producing extrafusal fibres) and gamma‐motoneurons (innervating intrafusal fibres) are coactivated. The fusimotor commands transmitted by gamma‐motoneurons to intrafusal fibres are conveyed through muscle spindles to reach afferent fibres. Reafferent spindle signals thus provide feedback to the brain regarding the amount of fusimotor commands received by intrafusal fibres. While the precise mechanisms underlying the interactions between the efference copy and reafferent muscle spindle signals remain speculative, we propose that future research should focus on identifying these mechanisms to further our understanding of the generation of effort perception. image
In this issue, “25 Years Ago” revisits the article “Posture Control of a Cockroach-Like Robot” by Gabriel Nelson and Roger Quinn, in
IEEE Control Systems Magazine
, vol. 19, no. 2, pp. 9–14. Below is an excerpt from the article.
Artificial communication with the brain through peripheral nerve stimulation shows promising results in individuals with sensorimotor deficits. However, these efforts lack an intuitive and natural sensory experience. In this study, we design and test a biomimetic neurostimulation framework inspired by nature, capable of “writing” physiologically plausible information back into the peripheral nervous system. Starting froman in-silico model ofmechanoreceptors, we develop biomimetic stimulation policies. We then experimentally assess them alongside mechanical touch and common linear neuromodulations. Neural responses resulting from biomimetic neuromodulation are consistently transmitted towards dorsal root ganglion and spinal cord of cats, and their spatio-temporal neural dynamics resemble those naturally induced. We implement these paradigms within the bionic device and test it with patients (ClinicalTrials.gov identifier NCT03350061). He we report that biomimetic neurostimulation improves mobility (primary outcome) and reduces mental effort (secondary outcome) compared to traditional approaches. The outcomes of this neuroscience-driven technology, inspired by the human body,
may serve as a model for advancing assistive neurotechnologies.
In individuals with sensory-motor impairments, missing limb functions can be restored using neuroprosthetic devices that directly interface with the nervous system. However, restoring the natural tactile experience through electrical neural stimulation requires complex encoding strategies. Indeed, they are presently limited in effectively conveying or restoring tactile sensations by bandwidth constraints. Neuromorphic technology, which mimics the natural behavior of neurons and synapses, holds promise for replicating the encoding of natural touch, potentially informing neurostimulation design. In this perspective, we propose that incorporating neuromorphic technologies into neuroprostheses could be an effective approach for developing more natural human-machine interfaces, potentially leading to advancements in device performance, acceptability, and embeddability. We also highlight ongoing challenges and the required actions to facilitate the future integration of these advanced technologies.
Exoskeletons intended for partial assistance of walking should be able to follow the gait pattern of their users, via online adaptive control strategies rather than imposing predefined kinetic or kinematic profiles. NeuroMuscular Controllers (NMCs) are adaptive strategies inspired by the neuromuscular modeling methods that seek to mimic and replicate the behavior of the human nervous system and skeletal muscles during gait. This study presents a novel design of a NMC, applied for the first time to partial assistance hip exoskeletons. Rather than the two-phase (stance/swing) division used in previous designs for the modulation of reflexes, a 5-state finite state machines is designed for gait phase synchronisation. The common virtual muscle model is also modified by assuming a stiff tendon, allowing for a more analytical computation approach for the muscle state resolution. As a first validation, the performance of the controller was tested with 9 healthy subjects walking at different speeds and slopes on a treadmill. The generated torque profiles show similarity to biological torques and optimal assistance profiles in the literature. Power output profiles of the exoskeleton indicate good synchronization with the users' intended movements, reflected in predominantly positive work by the assistance. The results also highlight the adaptability of the controller to different users and walking conditions, without the need for extensive parameter tuning.
The Executive Council of the International Society of Biomechanics has initiated and overseen the commemorations of the Society’s 50th Anniversary in 2023. This included multiple series of lectures at the ninth World Congress of Biomechanics in 2022 and XXIXth Congress of the International Society of Biomechanics in 2023, all linked to special issues of International Society of Biomechanics’ affiliated journals. This special issue of the Journal of Applied Biomechanics is dedicated to the biomechanics of the neuromusculoskeletal system. The reader is encouraged to explore this special issue which comprises 6 papers exploring the current state-of the-art, and future directions and roles for neuromusculoskeletal biomechanics. This editorial presents a very brief history of the science of the neuromusculoskeletal system’s 4 main components: the central nervous system, musculotendon units, the musculoskeletal system, and joints, and how they biomechanically integrate to enable an understanding of the generation and control of human movement. This also entails a quick exploration of contemporary neuromusculoskeletal biomechanics and its future with new fields of application.
Discharges of single muscle spindle primary afferents were recorded in normal cats during rapid, imposed limb movements which stretched the receptor-bearing muscles. The spindles discharged in bursts during the stretch, each burst preceding by about 10 msec an EMG burst in the receptor-bearing muscle. In stretches of very short duration, which only allowed sufficient time for one spindle burst, only one EMG burst was observed. This suggests that both the short latency and the longer latency EMG responses to rapid muscle stretching depend, at least in part, on the prior occurrence of bursts of spindle discharge.
Movement is arguably the most fundamental and important function of the nervous system. Purposive movement requires the coordination of actions within many areas of the cerebral cortex, cerebellum, basal ganglia, spinal cord, and peripheral nerves and sensory receptors, which together must control a highly complex biomechanical apparatus made up of the skeleton and muscles. Beginning at the level of biomechanics and spinal reflexes and proceeding upward to brain structures in the cerebellum, brainstem and cerebral cortex, the chapters in this book highlight the important issues in movement control. Commentaries provide a balanced treatment of the articles that have been written by experts in a variety of areas concerned with movement, including behaviour, physiology, robotics, and mathematics.
This monograph represents the current status of neuro ethological research on the diurnal behavior of the stick in sect, Carausius morosus. The growing profusion of inter related studies, many of which are published only in German, makes an overview of this field increasingly difficult. Many stick insect results contribute to general problems like con trol of catalepsy, control of walking, program-dependent reactions and control of joint position. For this reason I decided to compile and synthesize the results that are pre sently available even though the analyses are far from con cluded. In addition to both published and unpublished results of the group in Kaiserslautern (Bassler, Cruse, Ebner, Graham, Pfluger, Storrer, as well as doctoral and masters students), I have drawn upon the literature which had ap peared as of summer 1981. This includes above all the work of Godden and of Wendler and his colleagues in Cologne. A summary of the anatomical and physiological background, necessary for an understanding of these investigations, is provided in an appendix (Chap. 6). Methodological details must be obtained from the original publications. Figures for which no source is given are from my own studies. I intend to update this monograph on an annual basis. Requests for these supplements should be directed to me in Kaiserslautern. I would like to express my appreciation to all members of the group in Kaiserslautern for their constructive discussions, their unflagging cooperation, and their permission to include hitherto unpublished results.
The co-ordination of the flight movements of Schistocerca gregaria Forskål was examined in order to determine the extent of central patterning and reflex control. Electrical recordings from wing sensory nerves showed many units which responded to wing movements of various kinds. During flight the sensory discharge was timed to certain phases of the wing-beat cycle. Surgical removal of the sources of timed input did not abolish patterned output, which resembled that during flight, but the frequency of cycling was considerably reduced. Either electrical stimulation of the nerve cord or continuous wind on the head could elicit the pattern. A multiplicity of oscillators in the flight control system was demonstrated. It is suggested that the basic co-ordination of flight is an inherent function of the central nervous system but that peripheral feedback loops influence the frequency of operation and details of pattern.
Static and dynamic fusimotor neurones are most easily distinguished by their — sensitivity-reducing vs -increasing — action on the dynamic Ia response to large stretch, during stimulation at high rates (e.g. 100/s). However, occasionally high-rate static γ-action (as recognized by relying on a number of independent criteria; Emonet-Dénand et al., 1977) may also cause a modest increase of the dynamic index. Yet this measure, being a one point estimate of dynamic response, is slightly arbitrary, and rigorous analysis of Ia responses to sinusoidal stretch of widely ranging amplitude has so far revealed a uniform sensitivity-reducing action of static γ-axons. This was true for sine frequencies up to 20 Hz and for high stimulation rates (Goodwin et al., 1975; Hulliger et al., 1977). However, qualitative observations suggested that this reduction of sensitivity might sometimes be restricted to such high stimulation rates, whereas low-rate (20–30/s) γs-action could, paradoxically, enhance Ia sensitivity to sinusoids (Emonet-Dénand et al., 1972).