Jordan H. Boyle

Forward locomotion of the nematode C. elegans is achieved through modulation of a single gait

The ability of an animal to locomote through its environment depends crucially on the interplay between its active endogenous control and the physics of its interactions with the environment. The nematode worm Caenorhabditis elegans serves as an ideal model system for studying the respective roles of neural control and biomechanics, as well as the interaction between them. With only 302 neurons in a hard‐wired neural circuit, the worms apparent anatomical simplicity belies its behavioural complexity. Indeed, C. elegans exhibits a rich repertoire of complex behaviors, the majority of which are mediated by its adaptive undulatory locomotion. The conventional wisdom is that two kinematically distinct C. elegans locomotion behaviors—swimming in liquids and crawling on dense gel‐like media—correspond to distinct locomotory gaits. Here we analyze the worms motion through a series of different media and reveal a smooth transition from swimming to crawling, marked by a linear relationship between key locomotion metrics. These results point to a single locomotory gait, governed by the same underlying control mechanism. We further show that environmental forces play only a small role in determining the shape of the worm, placing conditions on the minimal pattern of internal forces driving locomotion.

Gait Modulation in C. elegans: An Integrated Neuromechanical Model.

Equipped with its 302-cell nervous system, the nematode Caenorhabditis elegans adapts its locomotion in different environments, exhibiting so-called swimming in liquids and crawling on dense gels. Recent experiments have demonstrated that the worm displays the full range of intermediate behaviors when placed in intermediate environments. The continuous nature of this transition strongly suggests that these behaviors all stem from modulation of a single underlying mechanism. We present a model of C. elegans forward locomotion that includes a neuromuscular control system that relies on a sensory feedback mechanism to generate undulations and is integrated with a physical model of the body and environment. We find that the model reproduces the entire swim-crawl transition, as well as locomotion in complex and heterogeneous environments. This is achieved with no modulatory mechanism, except via the proprioceptive response to the physical environment. Manipulations of the model are used to dissect the proposed pattern generation mechanism and its modulation. The model suggests a possible role for GABAergic D-class neurons in forward locomotion and makes a number of experimental predictions, in particular with respect to non-linearities in the model and to symmetry breaking between the neuromuscular systems on the ventral and dorsal sides of the body.

Swimming at low Reynolds number: a beginners guide to undulatory locomotion

Undulatory locomotion is a means of self-propulsion that relies on the generation and propagation of waves along a body. As a mode of locomotion it is primitive and relatively simple, yet can be remarkably robust. No wonder then, that it is so prevalent across a range of biological scales from motile bacteria to gigantic prehistoric snakes. Key to understanding undulatory locomotion is the bodys interplay with the physical environment, which the swimmer or crawler will exploit to generate propulsion, and in some cases, even to generate the underlying undulations. This review focuses by and large on undulators in the low Reynolds number regime, where the physics of the environment can be much more tractable. We review some key concepts and theoretical advances, as well as simulation tools and results applied to selected examples of biological swimmers. In particular, we extend the discussion to some simple cases of locomotion in non-Newtonian media as well as to small animals, in which the nervous system, motor control, body properties and the environment must all be considered to understand how undulations are generated and modulated. To conclude, we review recent progress in microrobotic undulators that may one day become commonplace in applications ranging from toxic waste disposal to minimally invasive surgery.

Caenorhabditis elegans body wall muscles are simple actuators

Over the past four decades, one of the simplest nervous systems across the animal kingdom, that of the nematode worm Caenorhabditis elegans, has drawn increasing attention. This system is the subject of an intensive concerted effort to understand the behaviour of an entire living animal, from the bottom up and the top down. C. elegans locomotion, in particular, has been the subject of a number of models, but there is as yet no general agreement about the key (rhythm generating) elements. In this paper we investigate the role of one component of the locomotion subsystem, namely the body wall muscles, with a focus on the role of inter-muscular gap junctions. We construct a detailed electrophysiological model which suggests that these muscles function, to a first approximation, as mere actuators and have no obvious rhythm generating role. Furthermore, we show that within our model inter-muscular coupling is too weak to have a significant electrical effect. These results rule out muscles as key generators of locomotion, pointing instead to neural activity patterns. More specifically, the results imply that the reduced locomotion velocity observed in unc-9 mutants is likely to be due to reduced neuronal rather than inter-muscular coupling.

An Integrated Neuro-mechanical Model of C. elegans Forward Locomotion

One of the most tractable organisms for the study of nervous systems is the nematode Caenorhabditis elegans, whose locomotion in particular has been the subject of a number of models. In this paper we present a first integrated neuro-mechanical model of forward locomotion. We find that a previous neural model is robust to the addition of a body with mechanical properties, and that the integrated model produces oscillations with a more realistic frequency and waveform than the neural model alone. We conclude that the body and environment are likely to be important components of the worms locomotion subsystem.

Adaptive Undulatory Locomotion of a C. elegans Inspired Robot

Although significant progress has been made in the development of robots with serpentine properties, the issues of motion control and adaptation to environmental constraints still require substantial research. This is particularly true for search and rescue applications, where reliable operation in extremely difficult terrain is essential. This paper presents a novel robot design based on the mechanics and neural control of locomotion in Caenorhabditis elegans, a tiny nematode worm. Equipped with an extremely simple yet powerful neurally-inspired decentralized control system, the robot presented here is capable of effective serpentine locomotion. More importantly, it exhibits sensorless path finding, in which obstacles in the environment are overcome, based purely on proprioceptive feedback encoding body shape. Indeed, the robot lacks any form of external sensory capability. The design and implementation of the prototype robot and its control strategy are discussed. In order to validate the control strategy for path finding, experiments and analyses have been performed. The results show that the robot can find its path successfully in the majority of cases. The current limitations have also been discussed.

Gait Modulation in C. Elegans: It's Not a Choice, It's a Reflex!

In their perspectives article, Mesce and Pierce-Shimomura (2010) make a case for the existence of two locomotion gaits in C. elegans, and for the ability of this nematode worm to choose between them. Here, we offer a counter-perspective, namely, that the variety of observed behaviors are more appropriately described as a single gait. In what follows we focus on pure forward locomotion, which is generally believed to be controlled by a dedicated circuit, distinct from the circuits that control backward locomotion and head motor behavior. With regard to our question of gaits, we are not aware of any evidence that links head swings with the generation of propulsive (forward/backward) locomotion, so these will not be considered here.

A C. elegans-inspired micro-robot with polymeric actuators and online vision

The 1mm long nematode worm Caenorhabditis elegans (C. elegans) is one of the best characterized animals and an important biological model for studies of nervous system function and behavior. C. elegans locomotion is generated by the rhythmic contraction of muscles under the control and regulation of the animals nervous system. The final goal of this research is to build a robotic model mimicking this undulatory locomotion. Towards this end, a first prototype invertebrate wormbot using electroactive polymer is presented in this paper. The 25mm wormbot is made of a single ionic polymer-metal composite consisting of five segments that are controlled individually and can propagate a sinusoidal wave along the robot body similar to the movement of C. elegans. Solutions to the technical challenges of miniaturization, IPMC segmentation and small scale electrical wiring are also described. Finally, a digital image processing technique was developed for online sensory feedback. The system operates in real time and includes robust image noise removal.

C. elegans locomotion: a unified multidisciplinary perspective

Address: 1School of Computing, University of Leeds, Leeds LS2 9JT, UK, 2School of Physics, University of Leeds, Leeds LS2 9JT, UK, 3Bioelectronics Research Centre, Department of Electronics and Electrical Engineering, University of Glasgow G12 8LT, UK, 4Institute of Integrative and Comparative Biology, University of Leeds, Leeds LS2 9JT, UK and 5Institute of Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, UK

Integrated Manufacturing: The Future of Fabricating Mechatronic Devices

This chapter explores current and future technologies for physically creating mechatronic devices, and in particular robotic systems. Robots consist of electronics, actuators and sensors within a self-contained mechanical structure and have the ability to exert controlled external forces to enable them to physically interact with the world around them. There is no doubt that robots have the potential to revolutionise many sectors [Willetts in Eight great technologies. Government Report, 2013 1], but there are many barriers to widespread use including public perceptions and difficulties in physically and computationally integrating robots into real-world environments. The cost of both designing and manufacturing robots is also very high. Improving manufacturing techniques for robots and providing better integration between the mechanical and electrical systems could help robots become physically robust, small, sealed, mobile and appropriate for the many challenging environments where their use could have a big impact.