Introduction:Intermuscular coherence (IMC) has the potential to become a clinical biomarker to quantify disruptions of shared neural drive to muscles in individuals with upper and lower extremity motor impairments. Here we test whether shoulder abduction, limb dominance and age affect IMC in unimpaired individuals to serve as a baseline for studies with clinical populations. Methods:Twenty-five unimpaired participants performed an established single-arm reaching task: rotating an ergometer in the horizontal plane while surface electromyography signals were recorded from the biceps, triceps and deltoids arm muscles. We compared IMC within the alpha, beta, and gamma frequency bands across three experimental factors: shoulder posture (neutral vs. abducted), arm (dominant vs. non-dominant), and age (younger {18-42 years. N = 12, 6 female} vs. older {51-74 years. N = 13, 7 female} adults). Results:We found that there was a significant effect on IMC due to shoulder posture in the alpha-band ( F = 22.4 , p = 0.0007 ), beta-band ( F = 44.6 , p = 5 × 1 0 - 5 ), and gamma-band ( F = 57.9 , p = 4 × 1 0 - 6 ). In addition, IMC was lower in the older group and significantly so in the alpha-band ( F = 6.6 , p = 0.03 ), but not in the beta- ( F = 4.5 , p = 0.07 ) and gamma-bands ( F = 0.52 , p = 0.42 ). Although the non-dominant arm tended to have higher IMC, no significant differences due to limb dominance were found. Discussion:We provide what, to our knowledge, is the first overall comparison of patterns of IMC in unimpaired individuals across arms and the adult lifespan to help future studies quantify and interpret disruptions in neuromuscular control. Beyond confirming the expected increase in IMC with shoulder abduction, we critically demonstrate that age significantly affects IMC in the alpha-band associated with propriospinal sensorimotor processes. We speculate this may be a result of spinal reorganization of spinal motor nuclei due to α -motoneurone death with healthy aging. Given the supporting evidence in this study that limb dominance does not significantly affect IMC, common drive to muscles (as quantified by IMC) is likely driven by subcortical processes that predate the neural lateralization of human upper extremity function.

Dexterous manipulation remains an aspirational goal for autonomous robotic systems, particularly when learning to lift and rotate objects against gravity with intermittent finger contacts. We use model-free reinforcement learning to compare the effect of curriculum (i.e., combinations of lift and rotation tasks) and haptic information (i.e., no-tactile versus 3D-force) on learning with a simulated three-finger robotic hand. In addition, a novel curriculum-based learning rate scheduler accelerates convergence. We demonstrate that the choice of curriculum biases the progression of learning for dexterous manipulation across objects with different weights, sizes, and shapes-underscoring the robustness of our learning approach. Unexpectedly, learning is achieved even in the absence of haptic information. This challenges conventional thinking about task "complexity" and the necessity of haptic information for dexterous manipulation for this task. This work invites the analogy of curriculum learning as a malleable developmental process from a pluripotent state driven by the nature of the learning experience.

The primary motor cortex does not uniquely or directly produce alpha motoneurone (α-MN) drive to muscles during voluntary movement. Rather, α-MN drive emerges from the synthesis and competition among excitatory and inhibitory inputs from multiple descending tracts, spinal interneurons, sensory inputs, and proprioceptive afferents. One such fundamental input is velocity-dependent stretch reflexes in lengthening muscles, which should be inhibited to enable voluntary movement. It remains an open question, however, the extent to which unmodulated stretch reflexes disrupt voluntary movement, and whether and how they are inhibited in limbs with numerous multiarticular muscles. We used a computational model of a Rhesus Macaque arm to simulate movements with feedforward α-MN commands only, and with added velocity-dependent stretch reflex feedback. We found that velocity-dependent stretch reflex caused movement-specific, typically large and variable disruptions to arm movements. These disruptions were greatly reduced when modulating velocity-dependent stretch reflex feedback (i) as per the commonly proposed (but yet to be clarified) idealized alpha-gamma (α-γ) coactivation or (ii) an alternative α-MN collateral projection to homonymous γ-MNs. We conclude that such α-MN collaterals are a physiologically tenable propriospinal circuit in the mammalian fusimotor system. These collaterals could still collaborate with α-γ coactivation, and the few skeletofusimotor fibers (β-MNs) in mammals, to create a flexible fusimotor ecosystem to enable voluntary movement. By locally and automatically regulating the highly nonlinear neuro-musculo-skeletal mechanics of the limb, these collaterals could be a critical low-level enabler of learning, adaptation, and performance via higher-level brainstem, cerebellar, and cortical mechanisms.

Quantifying the dynamical features of discrete tasks is essential to understanding athletic performance for many sports that are not repetitive or cyclical. We compared three dynamical features of the (i) bow hand, (ii) drawing hand, and (iii) center of mass during a single bow-draw movement between professional and neophyte archers: dispersion (convex hull volume of their phase portraits), persistence (tendency to continue a trend as per Hurst exponents), and regularity (sample entropy). Although differences in the two groups are expected due to their differences in skill, our results demonstrate we can quantify these differences. The center of mass of professional athletes exhibits tighter movements compared to neophyte archers (6.3 < 11.2 convex hull volume), which are nevertheless less persistent (0.82 < 0.86 Hurst exponent) and less regular (0.035 > 0.025 sample entropy). In particular, the movements of the bow hand and center of mass differed more between groups in Hurst exponent analysis, and the drawing hand and center of mass were more different in sample entropy analysis. This suggests tighter neuromuscular control over the more fluid dynamics of the movement that exhibits more active corrections that are more individualized. Our work, therefore, provides proof of principle of how well-established dynamical analysis techniques can be used to quantify the nature and features of neuromuscular expertise for discrete movements in elite athletes.

AbstractThe primary motor cortex does not uniquely or directly produce alpha motoneurone (α-MN) drive to muscles during voluntary movement. Rather,α-MN drive emerges from the synthesis and competition among excitatory and inhibitory inputs from multiple descending tracts, spinal interneurons, sensory inputs, and proprioceptive afferents. One such fundamental input is velocity-dependent stretch reflexes in lengthening muscles, which should be inhibited to enable voluntary movement. It remains an open question, however, the extent to which unmodulated stretch reflexes disrupt voluntary movement, and whether and how they are inhibited in limbs with numerous multi-articular muscles. We used a computational model of aRhesus Macaquearm to simulate movements with feedforwardα-MN commands only, and with added velocity-dependent stretch reflex feedback. We found that velocity-dependent stretch reflex caused movement-specific, typically large and variable disruptions to arm movements. These disruptions were greatly reduced when modulating velocity-dependent stretch reflex feedback (i) as per the commonly proposed (but yet to be clarified) idealized alpha-gamma (α-γ) co-activation or (ii) an alternativeα-MN collateral projection to homonymousγ-MNs. We conclude that suchα-MN collaterals are a physiologically tenable, but previously unrecognized, propriospinal circuit in the mammalian fusimotor system. These collaterals could still collaborate withα-γco-activation, and the few skeletofusimotor fibers (β-MNs) in mammals, to create a flexible fusimotor ecosystem to enable voluntary movement. By locally and automatically regulating the highly nonlinear neuro-musculo-skeletal mechanics of the limb, these collaterals could be a critical low-level enabler of learning, adaptation, and performance via higher-level brainstem, cerebellar and cortical mechanisms.SignificanceMuscles have velocity sensors controlled byγ-MNs that produce stretch reflexes which could disrupt voluntary limb movements. Whether and how severely those unmodulated stretch reflexes disrupt voluntary movement remains unclear, especially in realistic multi-articular limbs. Our neuromechanical simulations demonstrate that unmodulated stretch reflexes greatly disrupt movements. Modulating the stretch reflex by implementing an idealized version of a long-posited (but yet unclear)α-γco-activation greatly mitigates those perturbations. However, a collateral from theα-MN to theγ-MN (which has been reported among motoneurones but not interpreted in this way) achieves similar functionality. Our results suggest this modulation of the intensity of the stretch reflex by theα-MN collateral provides an effective mechanism to locally stabilize the disruptions from stretch reflexes.

Since its invention in 1955, the Galperin symmetric triaxial seismometer has been widely used for seismic detection on Earth, and most recently on the planet Mars. In this paper, we present detailed physics of such seismometers, which has not yet been published in open literature. We extended Galperin's original work, which is based on idealized geometry and assumptions, to include more practical cases, including (1) non-idealized tilt angles of its component seismometers; (2) component seismometers that are not exactly oriented 120° apart; (3) distributed mass on the boom; and (4) the case of operations at lower frequencies.

In animals, both body and neural control have co-evolved to be adaptable to the environment. While a newborn foal learns quickly how to use its legs, traditional robotic approaches require careful engineering and calibration for stable walking robots. Bio-inspired robotics aims to bridge this gap.

Described here is a concept for a variable-altitude aerobot mission to Venus developed as part of the 2020 NASA Planetary Science Summer School in collaboration with NASA Jet Propulsion Laboratory. The Venus Air and Land Expedition: a Novel Trailblazer for in situ Exploration (VALENTInE) is a long-duration New Frontiers–class mission to Venus in alignment with the goals recommended by the 2013 Planetary Science Decadal Survey. VALENTInE would have five science objectives: (1) determine the driving force of atmospheric superrotation, (2) determine the source of D/H and noble gas inventory, (3) determine the properties that govern how light is reflected within the lower cloud later, (4) determine whether the tesserae are felsic, and (5) determine whether there is evidence of a recent dynamo preserved in the rock record. The proposed mission concept has a total duration of 15 Earth days and would float at an altitude of 55 km, along with five dips to a lower altitude of 45 km to study Venus’s lower atmosphere. The instrument payload allows for measurements of the atmosphere, surface, and interior of Venus and includes six instruments: an atmospheric weather suite, a mass spectrometer, a multispectral imager, a near-infrared spectrometer, light detection and ranging, and a magnetometer. Principle challenges included a limitation caused by battery lifetime and low technology readiness levels for aerobots that can survive the harsh conditions of Venus’s atmosphere. This preliminary mission was designed to fit within an assumed New Frontiers 5 (based on inflated New Frontiers 4) cost cap.

INTRODUCTION:Physical human-robot interaction offers a compelling platform for assessing recovery from neurological injury; however, robots currently used for assessment have typically been designed for the requirements of rehabilitation, not assessment. In this work, we present the design, control, and experimental validation of the SE-AssessWrist, which extends the capabilities of prior robotic devices to include complete wrist range of motion assessment in addition to stiffness evaluation. METHODS:The SE-AssessWrist uses a Bowden cable-based transmission in conjunction with series elastic actuation to increase device range of motion while not sacrificing torque output. Experimental validation of robot-aided wrist range of motion and stiffness assessment was carried out with five able-bodied individuals. RESULTS:The SE-AssessWrist achieves the desired maximum wrist range of motion, while having sufficient position and zero force control performance for wrist biomechanical assessment. Measurements of two-degree-of-freedom wrist range of motion and stiffness envelopes revealed that the axis of greatest range of motion and least stiffness were oblique to the conventional anatomical axes, and approximately parallel to each other. CONCLUSIONS:Such an assessment could be beneficial in the clinic, where standard clinical measures of recovery after neurological injury are subjective, labor intensive, and graded on an ordinal scale.

ABSTRACT As long-period ground motion holds the key to understanding the interior of the Earth’s Moon, reducing long-period noise sources will be an essential area of focus in the design of future lunar seismometers. For the proposed Lunar Geophysical Network (LGN), the International Lunar Network (ILN) Science Definition Team specifies that an LGN enabling seismometer will need to be more sensitive than any previous seismometer at frequencies below 1 Hz. In an effort toward lowering the seismometer noise floor for lunar geophysical missions, we evaluate the 1/f Brownian noise and the temperature sensitivity of a seismometer. Temperature sensitivity of a seismometer is related to an important component of the seismometer output noise that is proportional to the temperature noise in the environment. The implications of the ILN requirement are presented in the context of the state-of-the-art InSight Seismic Experiment for Interior Structure (SEIS) Very Broad Band (VBB) planetary seismometer. Brownian noise due to internal friction was estimated for future lunar operation after accounting for the rebalance of the product of mass and distance to the center of gravity of the pendulum for the SEIS-VBB sensor. We find that Brownian noise could be a limiting factor in meeting the ILN requirement for lunar seismometers. Further, we have developed a formalism to understand the temperature sensitivity of a seismometer, relating it quantitatively to the local gravity, the thermoelastic coefficient of the spring, change in center of gravity, and the coefficient of thermal expansion of the mechanical structures. We found that in general the temperature sensitivity of a seismometer is proportional to the local gravity, and so the temperature sensitivity can be reduced when operating on a planetary body with lower gravity. Our Brownian noise and temperature sensitivity models will be useful in the design of the next generation of planetary seismometers.

Broadband seismometers and gravitational wave detectors make use of mechanical resonators with a high quality factor to reduce Brownian noise. At low frequency, Brownian noise is ultimately dominated by internal friction in the suspension, which has a 1/f noise compared with the white noise arising from viscous dissipation. Internal friction is typically modeled as a frequency-dependent loss and can be challenging to measure reliably through experiment. In this work, we present the physics and experimental implementation of electrostatic frequency reduction (EFR) in a mechanical oscillator-a method to measure dissipation as a function of frequency. By applying a high voltage to two parallel capacitor plates, with the center plate being a suspended mass, an electrostatic force is created that acts as a negative stiffness mechanism to reduce the system's resonance frequency. Through EFR, the loss angle can be measured as a function of frequency by measuring amplitude decay response curves for a range of applied voltages. We present experimental measurements of the loss angle for three metal helical extension springs in the nominal frequency range 0.7-2.9 Hz at 0.2 Hz intervals, demonstrating the possibility for fine adjustment of the resonance frequency for loss angle measurements. A quality factor proportional to the resonance frequency squared was measured, an indication that internal friction and other non-viscous dissipation elements, such as electrostatic damping, were the prominent loss mechanisms in our experiments. Finally, we consider the implications of Brownian noise arising from internal friction on a low 1/f noise seismometer.

A broadband seismometer has been identified as an important scientific instrument that can be deployed on the surface of Earth’s Moon in the near future. To achieve the goals of the International Lunar Network, this next generation of seismometers is required to achieve at least 2 × 10−10 ms−2 Hz−1/2 at 1 mHz, which are several orders of magnitude more sensitive at the same frequency than the ones deployed during the Apollo program; their goal is to capture the lunar seismic noise floor, observe the lunar normal modes, and record distant teleseisms from all over the Moon. The Electrostatic Frequency Reduction (EFR) technique has been employed in a seismometer design in our laboratory and can enhance the Moonquake measurement sensitivity covering a longer period down to 1 mHz. EFR has advantages over the traditional frequency reduction techniques since it can be autonomously tuned and lowers the resonance frequency without modifying the mechanical design of a capacitive readout seismometer, an approach desirable for spaceflight-qualified instrumentation. A drawback is that we have also found that the EFR as well as other frequency reduction techniques amplify the temperature sensitivity of a seismometer beyond the limit of a conventional temperature control system. Here, we describe quantitatively and analytically the temperature dependence of a spring suspended mass model of a seismometer and provide practical solutions to minimize the thermal effects on a lunar seismometer using the EFR technique. By choosing the materials for the seismometer housing and the spring suspension that could balance the shear modulus and thermal expansion coefficients, one could mitigate the thermal sensitivity of the seismometer using the EFR technique. These modifications allow us to approach the stringent requirements for instrument self-noise necessary for the science objective.

The wrist is an essential component in performing the activities of daily living (ADLs) associated with a high quality of life. After a neurological disorder, motor function of the hand and wrist can be affected, reducing quality of life. Many experiments have illustrated that more wrist flexion/extension is required than radial/ulnar deviation when performing ADLs; however, how this result translates to efficiency in performing ADLs has not been investigated. Motivated by clinical assessment during neurorehabilitation, in this paper we investigate with able-bodied participants how performing tasks representative of the Jebsen-Taylor Hand Function Test are impacted when a splint constrains the user to a single rotational degree of freedom of the wrist. Twenty participants enrolled in the study, performing five tasks under five conditions, including constraint to pure flexion/extension and radial/ulnar deviation. The importance of wrist movement direction in performing ADLs efficiently found in this study could shape clinical wrist rehabilitation paradigms and wrist rehabilitation robot designs.

Introduction: The NRC Decadal Survey for Planetary Science identified the Lunar Geophysical Network (LGN) as a high-yield New-Frontiers-class mission concept that will place a long-lived and globally distributed network of geophysical instruments on the surface of the Moon to understand the nature and evolution of the lunar interior from the crust to the core. This will enable examining the initial stages of planetary differentiation frozen in time some 3-3.5 billion years ago. LGN’s objectives are designed to discover the interior structure and composition of the Moon, which was not possible with the Apollo network [1-3]. Although a large set of seismic data has already been collected during the Apollo missions, key questions remains about the sizes and states of the lunar crust, mantle, and core. It was found during Apollo that the Moon is seismically rather quiet compared to the Earth, and that the seismometers deployed were not sensitive enough to resolve the background noise of the Moon. As a result, valuable scientific information was not recorded, even though, the Apollo seismometers are very sensitive, even by today’s standards [1-2, 4]. The LGN will require a very sensitive broadband (0.01-1Hz) seismometer ~10 times more sensitive than the state of the art. The development of a sensitive seismometer that can operate in a cryogenic environment is also in line with NASA’s broader mission goal, to understand the evolutionary history and make-up of ocean worlds. Precise seismic measurements on the crustal thickness of icy moons [5] and the depth of their oceans will help in the evaluation of their ability to harbor and sustain life. [5]. Sensitive seismometers are critical for detecting faint motions deep within a planet which can be used to reconstruct its interior and shed light on processes such as plate tectonics and ocean waves [6]. We are currently pursuing a task under the umbrella of the NASA Maturation of Instruments for Solar System Exploration (MatISSE) program to develop a LGN mission enabling prototype Planetary Broad Band Seismometer (PBBS). The aim of the PBBS is to not only meet, but exceed the requirements necessary for the LGN. To accomplish this task, the PBBS makes use of a new technology to reduce its natural frequency through electrical means, as opposed to the traditional mechanical frequency reduction. Figure 1: An image of a partially assembled PBBS prototype for illustrating the main components related to this work. PBBS Description: The principle of operation of the PBBS is based on the electrostatic frequency reduction (EFR) technique, which was first discussed by Griggs et. al [7]. An applied voltage applies an electrostatic force on the test mass which opposes the spring force, effectively reducing the spring rate. The displacement of the test mass relative to the ground is recorded by capacitive sensing plates (see Figure 1). Ground Motion Testing: We operated the PBBS without force feedback to evaluate its acceleration noise. We discovered that despite using low coefficient of thermal expansion (CTE) materials for construction, the PBBS is highly sensitive to temperature (see Figures 2 and 3), and that this sensitivity increases with the frequency reduction.

In an attempt to promote greater functional recovery after spinal cord injury, researchers have begun exploring combinatorial treatments, such as robotic rehabilitation combined with stem cell transplantation. Since these treatment methods are in their nascent stages, rodent models have been proposed for initial investigations. Robots have been built for locomotion rehabilitation and planar forelimb reach and grasp assessment with rodents; however, a robotic platform suitable for three-dimensional movement rehabilitation of the rodent forelimb has not yet been developed. In this paper, a novel three degree of freedom robotic manipulator for automated forelimb rehabilitation combined with stem cell transplantation after cervical spinal cord injury with rats is proposed. The robot interfaces with a rat in an end-effector manner, measuring and interacting with the forelimb in the 3D Cartesian space. In this work, we trained two rats through behavioral shaping to actively interact with the device during two robot control modes. This work provides preliminary investigations into the feasibility of 3D forelimb rehabilitation with rats, which could be translated as a paradigm for combinatorial treatments after spinal cord injury in a controlled manner.

Currently, wrist passive stiffness and active range of motion, two clinically relevant properties, are assessed using devices designed for rehabilitation. As a result, these devices do not have sufficient torque output and range of motion for complete wrist biomechanical assessment. To address these limitations, we are developing an actuation module specifically for assessing wrist biomechanical properties. Our device employs a serial kinematic exoskeletal architecture to directly interact with and measure wrist flexion/extension and radial/ulnar deviation. A Bowden cable-based actuation scheme, locating the motors off-board, was adopted for increased device range of motion and torque output compared with previous wrist exoskeletons. Additionally, the device was designed to incorporate a rotational elastic element at each joint, creating series elastic actuators, for accurate torque control and direct torque measurement. In this work, we present the design and demonstration of a 1-DOF module of the device, which can interact with a user’s wrist in flexion/extension, providing an important first step towards the control, evaluation, and application of the 2-DOF device.

Spinal cord injury patients undergoing clinical treatment using robots to deliver rehabilitation have seen mixed functional gains. As a result, researchers have begun exploring combinatorial treatment options in an attempt to promote greater functional recovery. Since these treatment methods are in their nascent stages and would be difficult to apply in the variable injury types found in the human population, rodent models have been proposed for initial investigations. In an attempt at elucidating the impacts of rehabilitation, robotic devices have recently been created for rodents. These devices have primarily focused on rehabilitation in hind limb functional recovery at the thoracic level; however, the majority of human spinal cord injury patients exhibit injury at the cervical level, adversely affecting hand function and severely impairing total mobility and independence.