Automated multimodal imaging of Caenorhabditis elegans behavior in multi-well plates.

Assays of behavior in model organisms play an important role in genetic screens, drug testing, and the elucidation of gene-behavior relationships. We have developed an automated, high-throughput imaging and analysis method for assaying behaviors of the nematode C. elegans. We use high-resolution optical imaging to longitudinally record the behaviors of 96 animals at a time in multi-well plates, and computer vision software to quantify the animals' locomotor activity, behavioral states, and egg laying events. To demonstrate the capabilities of our system we used it to examine the role of serotonin in C. elegans behavior. We found that egg-laying events are preceded by a period of reduced locomotion, and that this decline in movement requires serotonin signaling. In addition, we identified novel roles of serotonin receptors SER-1 and SER-7 in regulating the effects of serotonin on egg laying across roaming, dwelling, and quiescent locomotor states. Our system will be useful for performing genetic or chemical screens for modulators of behavior.

Nonlinear Dynamics Research of Ground Undulatory Fin Robot with Flexible Deformation and Frictional Contact.

The unique rigid-flex connection between the fin-rays and fin-surface in a bionic undulatory fin robot endows the fin-surface with both active flexibility and load-bearing capacity, enabling this robot to perform amphibious motions in underwater, terrestrial, and even marshy environments. However, investigations into dynamic modeling problems for the undulatory fin robot, considering the impact of nonlinear deformation and frictional contact on ground locomotion performance, are scarce. Given this, based on the absolute nodal coordinate formulation (ANCF), this paper presents an efficient and accurate nonlinear dynamic model for this robot to elucidate the fin's flexible deformation and motion law. This model considers material, geometric, and boundary nonlinearities, utilizing ANCF thin plate elements and reference nodes to individually describe the fin-surface and fin-rays of the undulatory fin. Then, by using the master-slave technique, a frictional contact formulation for the fin and the ground is proposed. Furthermore, we conduct in-depth research and analysis on the formation and undulatory motion of the undulatory fin, encompassing its static deformation, static contact deformation, and frictional contact motion, and successfully obtain its responses under various conditions. Research indicates that during fin-surface motion, longitudinal sliding or a tendency for sliding at the contact points results in the undulatory fin moving in a crawling gait. The proposed theoretical model correctly captures the fin's complex nonlinear deformations and frictional characteristics and reveals its ground locomotion mechanism, whose effectiveness and superiority are validated through numerical examples and experiments.

Patterns of girdle shape and their correlates in Australian limb-reduced skinks.

The evolution of limb reduction in squamates is a classic example of convergence, but the skeletal morphological patterns associated with it are underexplored. To provide insights on the biomechanical and developmental consequences of transitions to limb reduction, we use geometric morphometrics to examine the morphology of pectoral and pelvic girdles in 90 species of limb-reduced skinks and their fully limbed relatives. Clavicle shapes converge towards an acute anterior bend when forelimbs are lost but hindlimbs are retained-a morphology typical of sand-swimmers. This may either indicate functional adaptations to locomotion in fine substrates, or a developmental consequence of complete limb loss. The shape of limb-bearing elements of both girdles (coracoid and pelvis) instead closely mirrors limb reduction, becoming more simplified as undulation replaces limbed locomotion. Integration between girdles decreases in taxa lacking elements of the forelimbs but not hindlimbs, indicating differential selection on each girdle in response to distinct locomotory strategies. However, this pattern becomes less clear when considering phylogenetic history, perhaps because it is limited to one specific clade (Lerista). We show how the functional demands of locomotion can induce changes at different levels of organismal organization, including both external and internal structures.

Decoding burst swimming performance: a scaling perspective on time-to-fatigue.

Fatigue curves quantify fish swimming performance, providing information about the time ([Formula: see text]) fish can swim against a steady flow velocity (Uf) before fatiguing. Such curves represent a key tool for many applications in ecological engineering, especially for fish pass design and management. Despite years of research, though, our current ability to model fatigue curves still lacks theoretical foundations and relies primarily on fitting empirical data, as obtained from time-consuming and costly experiments. In the present article, we address this shortcoming by proposing a theoretical analysis that builds upon concepts of fish hydrodynamics to derive scaling laws linking statistical properties of [Formula: see text] to velocities Uf, pertaining to the so-called burst range. Theoretical arguments, in the present study, suggest that the proposed scaling laws may hold true for all fish species and sizes. A new experimental database obtained from over 800 trials and five small-sized Cypriniformes support theoretical predictions satisfactorily and calls for further experiments on more fish species and sizes to confirm their general validity.

Automatic gait evoking in healthy adults through Vojta's peripheric somatosensory stimulation: a double-blind randomized controlled trial.

BACKGROUND: To study the effects of different interventions on automatic gait processing in contrast with voluntary gait processing in healthy subjects. METHODS: A double-blind randomised controlled trial was designed (120 able-body persons between 18 and 65 years old entered and completed the study), with pre-intervention and post-intervention assessments using the 6-Minute Walk Test (6MWT). The participants were randomly distributed into four groups. Prior to intervention, all participants performed voluntary gait on the ground (VoG) in a calibrated circuit following the 6MWT. The presence of automatic gait (AG) was explored post-intervention without a voluntary demand in the same circuit following the 6MWT. Each group received a different intervention for 30 min: Vojta stimulation, MOTOMED® at no less than 60 revolutions/minute, treadmill walking at 3 km/h, and resting in a chair (control). The main assessment, conducted by a blinded rater, was the difference in distance covered (in meters) during the 6MWT between pre- and post-intervention. Surface electromyography (sEMG) average root mean square (RMS) signals in the right tibialis anterior, right soleus, right rectus femoris, and right biceps femoris were also considered outcome measures. RESULTS: The Vojta group was the only one that initiated AG after the intervention (476.4 m ± 57.1 in VoG versus 9.0 m ± 8.9 in AG, p < 0.001) with comparable kinematics and EMG parameters during voluntary gait, except for ankle dorsal flexion. Within the Vojta group, high variability in kinematics, sEMG activity, and distance covered was observed. CONCLUSIONS: AG isolation is approachable through Vojta at only one session measurable with the 6MWT without any voluntary gait demand. No automatic gait effects were observed post-intervention in the other groups. TRIAL REGISTRATION: NCT04689841 (ClinicalTrials.gov).

Repeatability of whole herd lameness scoring: an analysis of a New Zealand dataset.

AIMS: To assess whether a whole-herd lameness score on a New Zealand dairy farm in spring could predict lameness prevalence on the same farm in summer (and vice versa) and whether a single-herd lameness score could be used to determine whether herd lameness prevalence was < 5% in both spring and summer. METHODS: Prevalence data (proportion of the herd with lameness score ≥ 2 and with score 3; 0-3 scale) from a study where 120 dairy farms across New Zealand were scored in spring and in the following summer were analysed using limits-of-agreement analysis. In addition, farms were categorised as having either acceptable welfare (lameness prevalence < 5% in both spring and summer) or not (lameness prevalence ≥ 5% in either spring or summer or both). The accuracy and specificity of a single, whole-herd lameness score at identifying herds with acceptable welfare were then calculated. RESULTS: The limits-of-agreement analysis suggests that 95% of the time, the prevalence of lameness in summer would be expected to be between 0.23 and 4.3 times that of the prevalence in spring. The specificity and accuracy of identifying a farm as acceptable on both occasions from a single observation were, respectively, 74% and 92% in spring, and 59% and 87% in summer. CONCLUSIONS: A single, one-off, whole-herd lameness score does not accurately predict future lameness prevalence. Similarly, acceptable status (lameness prevalence < 5%) in one season is not sufficiently specific to be used to predict welfare status in subsequent seasons. CLINICAL RELEVANCE: Whole-herd lameness scoring should be used principally as a means of detecting lame cows for treatment. A single whole-herd lameness score by an independent assessor should not be used to determine a herd's welfare status.

Muscle-Tendon Unit Properties in Mice Bred for High Levels of Voluntary Running: Novel Physiologies, Coadaptation, Trade-Offs, and Multiple Solutions in the Evolution of Endurance Running.

AbstractMuscle-tendon unit (MTU) morphology and physiology are likely major determinants of locomotor performance and therefore Darwinian fitness. However, the relationships between underlying traits, performance, and fitness are complicated by phenomena such as coadaptation, multiple solutions, and trade-offs. Here, we leverage a long-running artificial selection experiment in which mice have been bred for high levels of voluntary running to explore MTU adaptation, as well as the role of coadaptation, multiple solutions, and trade-offs, in the evolution of endurance running. We compared the morphological and contractile properties of the triceps surae complex, a major locomotor MTU, in four replicate selected lines to those of the triceps surae complex in four replicate control lines. All selected lines have lighter and shorter muscles, longer tendons, and faster muscle twitch times than all control lines. Absolute and normalized maximum shortening velocities and contractile endurance vary across selected lines. Selected lines have similar or lower absolute velocities and higher endurance than control lines. However, normalized shortening velocities are both higher and lower in selected lines than in control lines. These findings potentially show an interesting coadaptation between muscle and tendon morphology and muscle physiology, highlight multiple solutions for increasing endurance running performance, demonstrate that a trade-off between muscle speed and endurance can arise in response to selection, and suggest that a novel physiology may sometimes allow this trade-off to be circumvented.

Propulsive efficiency of spatiotemporally asymmetric oscillating appendages at intermediate Reynolds numbers.

Many organisms use flexible appendages for locomotion, feeding, and other functional behaviors. The efficacy of these behaviors is determined in large part by the fluid dynamics of the appendage interacting with its environment. For oscillating appendages at low Reynolds numbers, viscosity dominates over inertia, and appendage motion must be spatially asymmetric to generate net flow. At high Reynolds numbers, viscous forces are negligible and appendage motion is often also temporally asymmetric, with a fast power stroke and a slow recovery stroke; such temporal asymmetry does not affect the produced flow at low Reynolds numbers. At intermediate Reynolds numbers, both viscous and inertial forces play non-trivial roles---correspondingly, both spatial and temporal asymmetry can strongly affect overall propulsion. Here we perform experiments on three robotic paddles with different material flexibilities and geometries, allowing us to explore the effects of motion asymmetry (both spatial and temporal) on force production. We show how a flexible paddle's time-varying shape throughout the beat cycle can reorient the direction of the produced force, generating both thrust and lift. We also evaluate the propulsive performance of the paddle by introducing a new quantity, which we term "integrated efficiency". This new definition of propulsive efficiency can be used to directly evaluate an appendage's performance independently from full-body swimming dynamics. Use of the integrated efficiency allows for accurate performance assessment, generalization, and comparison of oscillating appendages in both robotic devices and behaving organisms. Finally, we show that a curved flexible paddle generates thrust more efficiently than a straight paddle, and produces spatially asymmetric motion---thereby improving performance---without the need for complex actuation and controls, opening new avenues for bioinspired technology development.

Age- and size-related changes in hind limb muscles in two baboon species (Papio anubis and P. papio).

Body size has an impact on all biological functions and analyzing how body size impacts functional traits such as locomotion is critical. Body size does not only vary across species but also during ontogeny. Indeed, juvenile animals are often at a competitive disadvantage due to their smaller absolute size. Consequently, understanding size- and age-related changes in the locomotor system is critical for our understanding of adult phenotypes. Here, we address this question by exploring growth of the hind limb muscles in two species of closely related baboons that differ in their ecology, the olive baboon, Papio Anubis, the Guinea baboon, and Papio papio. To do so, we dissected 40 P. anubis and 10 P. papio and measured the mass and physiological cross-sectional area (PCSA) of the hind limb muscles. Our results showed no sexual differences in size- or age-related growth patterns, but did show differences between species. Whereas the scaling of muscle mass and PCSA was largely isometric in P. anubis, allometric scaling was more common in P. papio. Despite these differences between species, the knee extensors and external rotators at the knee scaled with positive allometry in both species highlighting their important role during adult locomotion. Although life-history data for P. papio are scarce, we suggest that differences between species may be associated with differences in adult body size and age of locomotor independence between species.

Magnetically Actuated Soft Microrobot with Environmental Adaptative Multimodal Locomotion Towards Targeted Delivery.

The development of environmentally adaptive solutions for magnetically actuated microrobots to enable targeted delivery in complex and confined fluid environments presents a significant challenge. Inspired by the natural locomotion of crucian carp, a barbell-shaped soft microrobot (MBS2M) is proposed. A mechano-electromagnetic hybrid actuation system is developed to generate oscillating magnetic fields to manipulate the microrobot. The MBS2M can seamlessly transition between three fundamental locomotion modes: fast navigation (FN), high-precision navigation (HPN), and fixed-point rotation (FPR). Moreover, the MBS2M can move in reverse without turning. The multimodal locomotion endows the MBS2M's adaptability in diverse environments. It can smoothly pass through confined channels, climb over obstacles, overcome gravity for vertical motion, track complex pathways, traverse viscous environments, overcome low fluid resistance, and navigate complex spaces mimicking in vivo environments. Additionally, the MBS2M is capable of drug loading and release in response to ultrasound excitation. In an ex vivo porcine liver vein, the microrobot demonstrated targeted navigation under ultrasound guidance, showcasing its potential for specialized in vivo tasks.

Validation of intrinsic capacity and healthy sleep pattern in middle-aged and older adults: a longitudinal Chinese study assessing healthy ageing.

OBJECTIVES: Intrinsic capacity (IC), a multidimensional construct encompassing mental and physical capacities, has been established in the aging framework by the World Health Organization. However, the detailed relationship between IC and Chinese sleep patterns (nighttime sleep and post-lunch naps) remains inadequately elucidated. METHODS: Participants in this study were individuals aged ≥45 years residing in China, included in the China Health and Retirement Longitudinal Study (CHARLS). We analyzed 4 years of CHARLS data from the first wave (May 2011-March 2012) to the second wave (July 2015-January 2016). Data from these waves were utilized for longitudinal analysis. Self-reported data included nighttime sleep and nap duration, along with other baseline characteristics. The IC evaluation involved physical examinations and blood tests. Initially, linear regression was used to assess the relationship between total sleep duration, nighttime sleep duration, nap duration, and IC change between the two waves that were determined by marginal effects (ME) and their corresponding 95% confidence intervals (CIs). Regression splines were employed to explore potential nonlinear associations. Subgroup and sensitivity analyses were conducted to investigate the heterogeneity of IC change under specific conditions and the robustness of our results. Mediation analysis was performed to identify potential factors mediating the relationship between sleep patterns and IC change. RESULTS: Both excessive (>10 h) (total, ME: -1.12; 95% CI: -1.61, -0.64; nighttime, ME: -1.44; 95% CI: -2.29, -0.59) and insufficient (<6 h) sleep duration (total, ME: -0.43; 95% CI: -0.68, -0.18; nighttime, ME: -0.50; 95% CI: -0.73, -0.27) negatively impacted IC change. Moderate naps (≤60 min) mitigated the decline in IC change (ME: 0.28; 95% CI: 0.07, 0.49). IC values decreased at the slowest rate when nap time constituted one-seventh of total sleep time. The onset of dyslipidemia partially mediated the association between naps (≤60 min) and IC change (P = 0.02). CONCLUSIONS: These findings suggest that maintaining a healthy sleep pattern of 6-8 h of nighttime or total sleep, along with a post-lunch nap of ≤60 min, helps preserve optimal IC or delay its decline. This is particularly beneficial for cognitive, psychological, and locomotion performance among middle-aged and older adults.

Enhanced phasic calf muscle activation with swing resistance enhances propulsion of the paretic leg in people post-stroke.

Reduced propulsion of the paretic leg contributes to impaired walking in people post-stroke. The goal of this study was to determine whether phasic electrical stimulation to the paretic gastrocnemius muscle combined with resistance applied to the non-paretic leg during swing phase while walking would enhance muscle activation of the paretic gastrocnemius and propulsive force of the paretic leg. Fifteen individuals who had a stroke visited the lab once to complete two experimental sessions (i.e., cross-over design; session order randomized). Each session consisted of 1) treadmill walking with either "motor stimulation and swing resistance" or "swing resistance only" (10-min walking: 1-min baseline, 7-min adaptation to intervention, & 2-min post-adaptation) and 2) instrumented treadmill walking before and after treadmill walking. Results: Participants showed enhanced muscle activation of the paretic gastrocnemius (P=0.03) and improved anteroposterior ground reaction force of the paretic leg (P=0.01) immediately after the treadmill walking with "motor stimulation and swing resistance", whereas no improvements after the walking with "swing resistance only". Those enhanced gastrocnemius muscle activation (P=0.02) and improved ground reaction force (P=0.03) were retained until the late post-adaptation period and 10 min after treadmill walking, respectively. Conclusion: Walking with "motor stimulation and swing resistance" may enhance forced use of the paretic leg and improve propulsive force of the paretic leg. Applying phasic electrical stimulation to the paretic gastrocnemius muscle and swing resistance to the non-paretic leg during walking can be used as a novel intervention strategy to improve motor control of the paretic leg and walking in people post-stroke.

Cell-type-specific origins of locomotor rhythmicity at different speeds in larval zebrafish.

Different speeds of locomotion require heterogeneous spinal populations, but a common mode of rhythm generation is presumed to exist. Here, we explore the cellular versus synaptic origins of spinal rhythmicity at different speeds by performing electrophysiological recordings from premotor excitatory interneurons in larval zebrafish. Chx10-labeled V2a neurons are divided into at least two morphological subtypes proposed to play distinct roles in timing and intensity control. Consistent with distinct rhythm generating and output patterning functions within the spinal V2a population, we find that descending subtypes are recruited exclusively at slow or fast speeds and exhibit intrinsic cellular properties suitable for rhythmogenesis at those speeds, while bifurcating subtypes are recruited more reliably at all speeds and lack appropriate rhythmogenic cellular properties. Unexpectedly, however, phasic firing patterns during locomotion in rhythmogenic and non-rhythmogenic V2a neurons alike are best explained by distinct modes of synaptic inhibition linked to cell type and speed. At fast speeds reciprocal inhibition in descending V2a neurons supports phasic firing, while recurrent inhibition in bifurcating V2a neurons helps pattern motor output. In contrast, at slow speeds recurrent inhibition in descending V2a neurons supports phasic firing, while bifurcating V2a neurons rely on reciprocal inhibition alone to pattern output. Our findings suggest cell-type-specific, not common, modes of rhythmogenesis generate and coordinate different speeds of locomotion.

Fine-grained descending control of steering in walking Drosophila.

Locomotion involves rhythmic limb movement patterns that originate in circuits outside the brain. Purposeful locomotion requires descending commands from the brain, but we do not understand how these commands are structured. Here, we investigate this issue, focusing on the control of steering in walking Drosophila. First, we describe different limb "gestures" associated with different steering maneuvers. Next, we identify a set of descending neurons whose activity predicts steering. Focusing on two descending cell types downstream of distinct brain networks, we show that they evoke specific limb gestures: one lengthens strides on the outside of a turn, while the other attenuates strides on the inside of a turn. Our results suggest that a single descending neuron can have opposite effects during different locomotor rhythm phases, and we identify networks positioned to implement this phase-specific gating. Together, our results show how purposeful locomotion emerges from specific, coordinated modulations of low-level patterns.

Changes in intra- and interlimb reflexes from forelimb cutaneous afferents after staggered thoracic lateral hemisections during locomotion in cats.

In quadrupeds, such as cats, cutaneous afferents from the forepaw dorsum signal external perturbations and send inputs to spinal circuits to co-ordinate the activity in muscles of all four limbs. How these cutaneous reflex pathways from forelimb afferents are reorganized after an incomplete spinal cord injury is not clear. Using a staggered thoracic lateral hemisections paradigm, we investigated changes in intralimb and interlimb reflex pathways by electrically stimulating the left and right superficial radial nerves in seven adult cats and recording reflex responses in five forelimb and ten hindlimb muscles. After the first (right T5-T6) and second (left T10-T11) hemisections, forelimb-hindlimb co-ordination was altered and weakened. After the second hemisection, cats required balance assistance to perform quadrupedal locomotion. Short-, mid- and long-latency homonymous and crossed reflex responses in forelimb muscles and their phase modulation remained largely unaffected after staggered hemisections. The occurrence of homolateral and diagonal mid- and long-latency responses in hindlimb muscles evoked with left and right superficial radial nerve stimulation was significantly reduced at the first time point after the first hemisection, but partially recovered at the second time point with left superficial radial nerve stimulation. These responses were lost or reduced after the second hemisection. When present, all reflex responses, including homolateral and diagonal, maintained their phase-dependent modulation. Therefore, our results show a considerable loss in cutaneous reflex transmission from cervical to lumbar levels after incomplete spinal cord injury, albeit with preservation of phase modulation, probably affecting functional responses to external perturbations. KEY POINTS: Cutaneous afferent inputs co-ordinate muscle activity in the four limbs during locomotion when the forepaw dorsum contacts an obstacle. Thoracic spinal cord injury disrupts communication between spinal locomotor centres located at cervical and lumbar levels, impairing balance and limb co-ordination. We investigated cutaneous reflexes from forelimb afferents during quadrupedal locomotion by electrically stimulating the superficial radial nerve bilaterally, before and after staggered lateral thoracic hemisections in cats. We showed a loss/reduction of mid- and long-latency homolateral and diagonal reflex responses in hindlimb muscles early after the first hemisection that partially recovered with left superficial radial nerve stimulation, before being reduced after the second hemisection. Targeting cutaneous reflex pathways from forelimb afferents projecting to the four limbs could help develop therapeutic approaches aimed at restoring transmission in ascending and descending spinal pathways.

Origami-Inspired Vacuum-Actuated Foldable Actuator Enabled Biomimetic Worm-like Soft Crawling Robot.

The development of a soft crawling robot (SCR) capable of quick folding and recovery has important application value in the field of biomimetic engineering. This article proposes an origami-inspired vacuum-actuated foldable soft crawling robot (OVFSCR), which is composed of entirely soft foldable mirrored origami actuators with a Kresling crease pattern, and possesses capabilities of realizing multimodal locomotion incorporating crawling, climbing, and turning movements. The OVFSCR is characterized by producing periodically foldable and restorable body deformation, and its asymmetric structural design of low front and high rear hexahedral feet creates a friction difference between the two feet and contact surface to enable unidirectional movement. Combining an actuation control sequence with an asymmetrical structural design, the body deformation and feet in contact with ground can be coordinated to realize quick continuous forward crawling locomotion. Furthermore, an efficient dynamic model is developed to characterize the OVFSCR's motion capability. The robot demonstrates multifunctional characteristics, including crawling on a flat surface at an average speed of 11.9 mm/s, climbing a slope of 3°, carrying a certain payload, navigating inside straight and curved round tubes, removing obstacles, and traversing different media. It is revealed that the OVFSCR can imitate contractile deformation and crawling mode exhibited by soft biological worms. Our study contributes to paving avenues for practical applications in adaptive navigation, exploration, and inspection of soft robots in some uncharted territory.

Concurrent Oncolysis and Neurolesion Repair by Dual Gene-Engineered hNSCs in an Experimental Model of Intraspinal Cord Glioblastoma.

Intramedullary spinal cord glioblastoma (ISCG) is lethal due to lack of effective treatment. We previously established a rat C6-ISCG model and the antitumor effect of F3.CD-TK, an hNSC line expressing CD and TK, via producing cytocidal 5FU and GCV-TP. However, the neurotherapeutic potential of this hNSC approach has remained uninvestigated. Here for the first time, cultured F3.CD-TK cells were found to have a markedly higher oncolytic effect, which was GJIC-dependent, and BDNF expression but less VEGF secretion than F3.CD. In Rowett athymic rats, F3.CD-TK (1.5 × 106 cells/10 µL × 2), injected near C6-ISCG (G55 seeding 7 days earlier: 10 K/each) and followed by q.d. (×5/each repeat; i.p.) of 5FC (500 mg/kg/5 mL/day) and GCV (25 mg/kg/1 mL/day), robustly mitigated cardiorespiratory, locomotor, and sensory deficits to improve neurofunction and overall survival compared to animals receiving either F3.CD or F3.CD-TK+F3.CD debris formula. The F3.CD-TK regimen exerted greater tumor penetration and neural inflammation/immune modulation, reshaped C6-ISCG topology to increase the tumor's surface area/volume ratio to spare/repair host axons (e.g., vGlut1+ neurites), and had higher post-prodrug donor self-clearance. The multimodal data and mechanistic leads from this proof-of-principle study suggest that the overall stronger anti-ISCG benefit of our hNSC-based GDEPT is derived from its concurrent oncolytic and neurotherapeutic effects.

A New Measure for Quantifying Four-Limb Coordination of Human Gait Based on Mobility Sensors.

Coordinated movement of four limbs is a hallmark of healthy locomotion. No measures exist to quantify four-limb coordination. This study aimed to investigate temporal four-limb coordination and proposed a new metric for quantifying the inter-limb phase of rhythmic locomotion-related movements. Kinetic data of arm and leg movements generated during walking (self-selected speed) from healthy adults were used to extract the phases (φ) between all possible limb pairings. The φ series were used to calculate each pair's Phase Coordination Index (PCI). The PCI quantifies the accuracy and consistency of generating anti-phased rhythmic movements (lower PCI values mean better coordination). We also calculated the Quadruple-PCI (Q-PCI) by combining all φ values of all limb pairs. We found a significant correlation between the PCI values of all limb pairings and the Q-PCI (pairs involving arms: Pearson's R > 0.79, p < 0.001; leg-leg: Pearson's R = 0.3, p < 0.01). The PCI values that involve arms (median values between 6.5% and 8.3%) were significantly higher than the leg-leg PCI (median values between 3.8% and 4.1%), and the Q-PCI (median values between 8.3% and 9.7%) was significantly higher than all other PCI values. We also found a negative correlation between the arm swing amplitude and the PCI values (Spearman's Rho of different limb pairings ranging from -0.25 to -0.5, p < 0.05), suggesting that higher arm swing amplitude leads to better coordination. Four-limb coordination analysis is a novel method for comprehensive assessment of gait coordination, which is often compromised among persons with disabilities.

Operation of spinal sensorimotor circuits controlling phase durations during tied-belt and split-belt locomotion after a lateral thoracic hemisection.

Locomotion is controlled by spinal circuits that interact with supraspinal drives and sensory feedback from the limbs. These sensorimotor interactions are disrupted following spinal cord injury. The thoracic lateral hemisection represents an experimental model of an incomplete spinal cord injury, where connections between the brain and spinal cord are abolished on one side of the cord. To investigate the effects of such an injury on the operation of the spinal locomotor network, we used our computational model of cat locomotion recently published in eLife (Rybak et al., 2024) to investigate and predict changes in cycle and phase durations following a thoracic lateral hemisection during treadmill locomotion in tied-belt (equal left-right speeds) and split-belt (unequal left-right speeds) conditions. In our simulations, the "hemisection" was always applied to the right side. Based on our model, we hypothesized that following hemisection, the contralesional ("intact", left) side of the spinal network is mostly controlled by supraspinal drives, whereas the ipsilesional ("hemisected", right) side is mostly controlled by somatosensory feedback. We then compared the simulated results with those obtained during experiments in adult cats before and after a mid-thoracic lateral hemisection on the right side in the same locomotor conditions. Our experimental results confirmed many effects of hemisection on cat locomotion predicted by our simulations. We show that having the ipsilesional hindlimb step on the slow belt, but not the fast belt, during split-belt locomotion substantially reduces the effects of lateral hemisection. The model provides explanations for changes in temporal characteristics of hindlimb locomotion following hemisection based on altered interactions between spinal circuits, supraspinal drives, and somatosensory feedback.

Olfactory Projections to Locomotor Control Centers in the Sea Lamprey.

Although olfaction is well known to guide animal behavior, the neural circuits underlying the motor responses elicited by olfactory inputs are poorly understood. In the sea lamprey, anatomical evidence shows that olfactory inputs project to the posterior tuberculum (PT), a structure containing dopaminergic (DA) neurons homologous to the mammalian ventral tegmental area and the substantia nigra pars compacta. Olfactory inputs travel directly from the medial olfactory bulb (medOB) or indirectly through the main olfactory bulb and the lateral pallium (LPal). Here, we characterized the transmission of olfactory inputs to the PT in the sea lamprey, Petromyzon marinus. Abundant projections from the medOB were observed close to DA neurons of the PT. Moreover, electrophysiological experiments revealed that PT neurons are activated by both the medOB and LPal, and calcium imaging indicated that the olfactory signal is then relayed to the mesencephalic locomotor region to initiate locomotion. In semi-intact preparations, stimulation of the medOB and LPal induced locomotion that was tightly associated with neural activity in the PT. Moreover, PT neurons were active throughout spontaneously occurring locomotor bouts. Altogether, our observations suggest that the medOB and LPal convey olfactory inputs to DA neurons of the PT, which in turn activate the brainstem motor command system to elicit locomotion.