Computational Rules for Chemotaxis in the Nematode C. elegans

To investigate the behavioral mechanism of chemotaxis in Caenorhabditis elegans, we recorded the instantaneous position, speed, and turning rate of single worms as a function of time during chemotaxis in gradients of the attractants ammonium chloride or biotin. Analysis of turning rate showed that each worm track could be divided into periods of smooth swimming (runs) and periods of frequent turning (pirouettes). The initiation of pirouettes was correlated with the rate of change of concentration (dC/dt) but not with absolute concentration. Pirouettes were most likely to occur when a worm was heading down the gradient (dC/dt Ͻ 0) and least likely to occur when a worm was heading up the gradient (dC/dt Ͼ 0). Further analysis revealed that the average direction of movement after a pirouette was up the gradient. These observations suggest that chemotaxis is produced by a series of pirouettes that reorient the animal to the gradient. We tested this idea by imposing the correlation between pirouettes and dC/dt on a stochastic point model of worm motion. The model exhibited chemotaxis behavior in a radial gradient and also in a novel planar gradient. Thus, the pirouette model of C. elegans chemotaxis is sufficient and general.

Journal of Neuroscience, 2010

Chemotaxis during sinusoidal locomotion in nematodes captures in simplified form the general problem of how dynamical interactions between the nervous system, body, and environment are exploited in the generation of adaptive behavior. We used an evolutionary algorithm to generate neural networks that exhibit klinotaxis, a common form of chemotaxis in which the direction of locomotion in a chemical gradient closely follows the line of steepest ascent. Sensory inputs and motor outputs of the model networks were constrained to match the inputs and outputs of the C. elegans klinotaxis network. We found that a minimalistic neural network, comprised of an ON-OFF pair of chemosensory neurons and a pair of neck muscle motor neurons, is sufficient to generate realistic klinotaxis behavior. Importantly, emergent properties of model networks reproduced two key experimental observations that they were not designed to fit, suggesting that the model may be operating according to principles similar to those of the biological network. A dynamical systems analysis of 77 evolved networks revealed a novel neural mechanism for spatial orientation behavior. This mechanism provides a testable hypothesis that is likely to accelerate the discovery and analysis of the biological circuitry for chemotaxis in C. elegans.

HFSP Journal, 2009

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 worm's 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 worm's 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.

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 worm's locomotion subsystem.

Proceedings of the 2nd International Congress on Neurotechnology, Electronics and Informatics, 2014

Biological neural systems are powerful, robust and highly adaptive computational entities that outperform conventional computers in almost all aspects of sensory-motor integration. Despite dramatic progress in information technology, there is a big performance discrepancy between artificial computational systems and brains in seemingly simple orientation and navigation tasks. In fact, no system exists that can faithfully reproduce the rich behavioural repertoire of the tiny worm Caenorhabditis elegans which features one of the simplest nervous systems in nature made of 302 neurons and about 8000 connections. The Si elegans project aims at providing this missing link. This article is sketching out the main platform components.

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 worm's 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 worm's 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.

2013

The field of cognitive science deals with the scientific study of mind and the various processes being carried out in the mind, which are involved in interpreting the information available around us. In such a field of study, studying Brain and the nervous system becomes both essential and fundamental in nature. However, the nervous system, comprising of brain and spinal cord, functions in a very peculiar way. Its basic entity, known as nerve cell or neurons, always functions in groups. These groups are what we call as neural circuits. Generally, these ensembles specialize in processing a certain kind of information. In this project, a study of such a circuit which is responsible for motor control in Caenorhabditis elegans for gentle touch stimulation was carried out based on the model proposed by M Sujuki et al in their paper “A model of motor control of nematode C.elegans with neuronal circuits”(2005) and a computational model was generated. The model correctly predicted the respo...

Locomotion is a fundamental behavior of Caenorhabditis elegans (C. elegans). Previous works on kinetic simulations of animals helped researchers understand the physical mechanisms of locomotion and the muscle-controlling principles of neuronal circuits as an actuator part. It has yet to be understood how C. elegans utilizes the frictional forces caused by the tension of its muscles to perform sequenced locomotive behaviors. Here, we present a two-dimensional rigid body chain model for the locomotion of C. elegans by developing Newtonian equations of motion for each body segment of C. elegans. Having accounted for friction-coefficients of the surrounding environment, elastic constants of C. elegans, and its kymogram from experiments, our kinetic model (ElegansBot) reproduced various locomotion of C. elegans such as, but not limited to, forward-backward-(omega turn)-forward locomotion constituting escaping behavior and delta-turn navigation. Additionally, ElegansBot precisely quantifi...

2018

Animal locomotion describes the coordinated self-propelled movement of a body, subject to the combined effects of internal muscle forcing and external forces. Here we use an integrated neuromechanical computational model to study the combined effects of neural modulation, mechanical modulation and modulation of the external environments on undulatory forward locomotion in the nematodeC. elegans. In particular we use a proprioceptively driven neural control circuit to consider the effects of proprioception, body elasticity and environmental drag on the waveform, frequency and speed of undulations. We find qualitative differences in the frequency-wavelength relationship obtained under extrinsic modulation of the environmental fluid or body elasticity versus intrinsic modulation due to changes in the sensorimotor control. We consider possible targets of modulation by the worm and implications of our results for our understanding of the neural control of locomotion in this system.