Robert McNeill Alexander. 7 July 1934—21 March 2016

Neill Alexander graduated in natural sciences at the University of Cambridge in 1955. After a PhD at Cambridge and a lecturership at the University College of North Wales in Bangor, he was appointed to the chair of the Department of Pure and Applied Zoology at the University of Leeds in 1969. At that stage, he switched his research interests abruptly from fishes to the mechanics of legged locomotion. He conducted experiments with a variety of mammals, calculating forces, stresses and strains in muscle fibres, bones and tendons. His speciality became the application of mathematical models to animal locomotion, including repurposing the Froude number, devised by the Victorian engineer William Froude (FRS 1870) for use with ships, to estimate the speed of dinosaurs based on the spacing of their fossil footprints. Subsequent work included modelling the optimization of mammal performance and the minimization of energy costs. In 1992, following an announcement that London Zoo would have to close as a result of shortage of funds, Neill was appointed secretary of the Zoological Society of London. During the period of his secretaryship, the Society's finances recovered, with both its zoos (London and Whipsnade) breaking even in 1993 and the Society returning a surplus in each subsequent year. Neill was awarded the CBE in 2000. The National Portrait Gallery holds his portrait by John Arnison.

The BCM rule allows a spinal cord model to learn rhythmic movements

Animal locomotion is hypothesized to be controlled by a central pattern generator in the spinal cord. Experiments and models show that rhythm generating neurons and genetically determined network properties could sustain oscillatory output activity suitable for locomotion. However, current CPG models do not explain how a spinal cord circuitry, which has the same basic genetic plan across species, can adapt to control the different biomechanical properties and locomotion patterns existing in these species. Here we demonstrate that rhythmic and alternating movements in pendulum models can be learned by a monolayer spinal cord circuitry model using the BCM learning rule, which has been previously proposed to explain learning in the visual cortex. These results provide an alternative theory to CPG models, because rhythm generating neurons and genetically defined connectivity are not required in our model.

Robots with Tails

Until recently, most four-legged robots have lacked a feature that is found again and again in nature—a tail. Studies of animal locomotion and robots in the laboratory indicate that leaving out tails has been a design drawback. In fact, research conducted by our lab at Virginia Tech has shown that an articulated robotic tail can effectively maneuver and stabilize a quadruped both for static and dynamic locomotion.

Inhibitory hippocampo–septal projection controls locomotion and exploratory behavior

Although the hippocampus is generally considered a cognitive center for spatial representation, learning and memory, increasing evidence supports its roles in regulation of locomotion. However, the neuronal mechanisms of hippocampal regulation of locomotion and exploratory behavior remain unclear. Here we found that the inhibitory hippocampo-septal projection bi–directionally controls locomotion speed of mice. Pharmacogenetic activation of these septum–projecting interneurons decreased locomotion and exploratory behavior. Similarly, activation of the hippocampus–originated inhibitory terminal in the medial septum reduced locomotion. On the other hand, inhibition of the hippocampus–originated inhibitory terminal increased locomotion. The locomotion-regulative roles were specific to the septal projecting interneurons as activation of hippocampal interneurons projecting to the retrosplenial cortex did not change animal locomotion. Therefore, this study reveals a specific long-range inhibitory output from the hippocampus in the regulation of animal locomotion.

A terrain treadmill to study small animal locomotion through large obstacles

A major challenge to understanding locomotion in complex 3-D terrain with large obstacles is to create tools for controlled, systematic lab experiments. Existing terrain arenas only allow observations at small spatiotemporal scales (~10 body length, ~10 stride cycles). Here, we create a terrain treadmill to enable high-resolution observations of small animal locomotion through large obstacles over large spatiotemporal scales. An animal moves through modular obstacles on an inner sphere, while a rigidly-attached, concentric, transparent outer sphere rotated with the opposite velocity via closed-loop feedback to keep the animal on top. During sustained locomotion, a discoid cockroach moved through pillar obstacles for 25 minutes (≈ 2500 strides) over 67 m (≈ 1500 body lengths), and was contained within a radius of 4 cm (0.9 body length) for 83% of the duration, even at speeds of up to 10 body length/s. The treadmill enabled observation of diverse locomotor behaviors and quantification of animal-obstacle interaction.

Learning quadrupedal locomotion over challenging terrain

Legged locomotion can extend the operational domain of robots to some of the most challenging environments on Earth. However, conventional controllers for legged locomotion are based on elaborate state machines that explicitly trigger the execution of motion primitives and reflexes. These designs have increased in complexity but fallen short of the generality and robustness of animal locomotion. Here, we present a robust controller for blind quadrupedal locomotion in challenging natural environments. Our approach incorporates proprioceptive feedback in locomotion control and demonstrates zero-shot generalization from simulation to natural environments. The controller is trained by reinforcement learning in simulation. The controller is driven by a neural network policy that acts on a stream of proprioceptive signals. The controller retains its robustness under conditions that were never encountered during training: deformable terrains such as mud and snow, dynamic footholds such as rubble, and overground impediments such as thick vegetation and gushing water. The presented work indicates that robust locomotion in natural environments can be achieved by training in simple domains.

A Region of UNC-89 (obscurin) Lying Between Two Protein Kinase Domains is a Highly Elastic Spring Required for Proper Sarcomere Assembly

In C. elegans, unc-89 encodes a set of giant multi-domain proteins (up 8,081 residues) localized to the M-lines of muscle sarcomeres and required for normal sarcomere organization and whole-animal locomotion. Multiple UNC-89 isoforms contain two protein kinase domains. There is conservation in arrangement of domains between UNC-89 and its two mammalian homologs, obscurin and SPEG: kinase, a non-domain region of 647-742 residues, Ig domain, Fn3 domain and a second kinase domain. In all three proteins, this non-domain “interkinase region” has low sequence complexity, high proline content and lacks predicted secondary structure. We report that a major portion of this interkinase (571 residues out of 647 residues) when examined by single molecule force spectroscopy in vitro displays the properties of a random coil and acts as an entropic spring. We used CRISPR/Cas9 to create nematodes carrying an in-frame deletion of the same 571-residue portion of the interkinase. These animals express normal levels of giant internally deleted UNC-89 proteins, and yet show severe disorganization of all portions of the sarcomere in body wall muscle. Super-resolution microscopy reveals extra, short-A-bands lying close to the outer muscle cell membrane and between normally spaced A-bands. Nematodes with this in-frame deletion show defective locomotion and muscle force generation. We designed our CRISPR-generated in-frame deletion to contain an HA tag at the N-terminus of the large UNC-89 isoforms. This HA tag results in normal organization of body wall muscle, but dis-organization of pharyngeal muscle, small body size, and reduced muscle force, likely due to poor nutritional uptake.HighlightsThe giant muscle proteins UNC-89 and its mammalian homologs have an ∼700 aa non-domain region lying between two protein kinase domainsBy single molecule force spectroscopy UNC-89 non-domain region is an elastic random coilNematodes lacking this non-domain region have disorganized sarcomeres and reduced whole animal locomotionUNC-89 non-domain region is required for proper assembly of A-bands from thick filaments