Stride length and speed for adults, children, and fossil hominids

Research workers studying the relationship between stride length (L) and speed (u) in human walking have often expressed their results as multiples of stature (h): they have given values of L/h and u/h. They have claimed or implied that this takes account of differences of body size and that L/h should be the same function of u/h for people of all sizes. It is shown that this is not true for comparisons of children with adults. Further, it is argued by dimensional analysis that u/square root gh is a more appropriate speed parameter that u/h (g is the acceleration of free fall). It is shown that L/h is approximately the same function of u/square root gh for children aged 4 or more years as for adults. The empirical relationship between L/h and u/square root gh is used to make new estimates of walking speed for the early hominid footprints found at Laetoli, Tanzania. The speeds obtained are equivalent to mean speeds of human walking observed in small towns (i.e., they give approximately equal values of u/square root gh).     

Evolving experience-dependent robust behaviour in embodied agents

In this work, based on behavioural and dynamical evidence, a study of simulated agents with the capacity to change feedback from their bodies to accomplish a one-legged walking task is proposed to understand the emergence of coupled dynamics for robust behaviour. Agents evolve with evolutionary-defined biases that modify incoming body signals (sensory offsets). Analyses on whether these agents show further dependence to their environmental coupled dynamics than others with no feedback control is described in this article. The ability to sustain behaviours is tested during lifetime experiments with mutational and sensory perturbations after evolution. Using dynamical systems analysis, this work identifies conditions for the emergence of dynamical mechanisms that remain functional despite sensory perturbations. Results indicate that evolved agents with evolvable sensory offset depends not only on where in neural space the state of the neural system operates, but also on the transients to which the inner-system was being driven by sensory signals from its interactions with the environment, controller, and agent body. Experimental evidence here leads discussions on a dynamical systems perspective on behavioural robustness that goes beyond attractors of controller phase space.     

Effect of stable and unstable load carriage on walking gait variability,dynamic stability and muscle activity of older adults

Load carriage perturbs the neuromuscular system, which can be impaired due to ageing. The ability to counteract perturbations is an indicator of neuromuscular function but if the response is insufficient the risk of falls will increase. However, it is unknown how load carriage affects older adults. Fourteen older adults (65 ± 6 years) attended a single visit during which they performed 4 min of walking in 3 conditions, unloaded, stable backpack load and unstable backpack load. During each walking trial, 3-dimensional kinematics of the lower limb and trunk movements and electromyographic activity of 6 lower limb muscles were recorded. The local dynamic stability (local divergence exponents), joint angle variability and spatio-temporal variability were determined along with muscle activation magnitudes. Medio-lateral dynamic stability was lower (p = 0.018) and step width (p = 0.019) and step width variability (p = 0.015) were greater in unstable load walking and step width variability was greater in stable load walking (p = 0.009) compared to unloaded walking. However, there was no effect on joint angle variability. Unstable load carriage increased activity of the Rectus Femoris (p = 0.001) and Soleus (p = 0.043) and stable load carriage increased Rectus Femoris activity (p = 0.006). These results suggest that loaded walking alters the gait of older adults and that unstable load carriage reduces dynamic stability compared to unloaded walking. This can potentially increase the risk of falls, but also offers the potential to use unstable loads as part of fall prevention programmes.     

Leg coordination during turning on an extremely narrow substrate in a bug, Mesocerus marginatus (Heteroptera, Coreidae)

The turning movement of a bug, Mesocerus marginatus, is observed when it walks upside-down below a horizontal beam and, at the end of the beam, performs a sharp turn by 180 degrees . The turn at the end of the beam is accomplished in three to five steps, without strong temporal coordination among legs. During the stance, leg endpoints (tarsi) run through rounded trajectories, rotating to the same side in all legs. During certain phases of the turn, a leg is strongly depressed and the tarsus crosses the midline. Swing movements rotate to the same side as do leg endpoints in stance, in strong contrast to the typical swing movements found in turns or straight walk on a flat surface. Terminal location is found after the search through a trajectory that first moves away from the body and then loops back to find substrate. When a leg during stance has crossed the midline, in the following swing movement the leg may move even stronger on the contralateral side, i.e. is stronger depressed, in contrast to swing movements in normal walking, where the leg is elevated. These results suggest that the animals apply a different control strategy compared to walking and turning on a flat surface.     

长穗偃麦草DREB类基因EeAP2.2 的克隆与序列分析

由于一些基因的特殊碱基序列限制,使得应用一种技术获得基因的全长cDNA序列比较困难。本研究结合RACE和Genome Walking技术从十倍体长穗偃麦草（Elytrigia elongata,2n=70）中克隆了AP2家族的一个全长cDNA序列,命名为EeAP2.2。序列分析表明,该基因具有一个837bp的开放阅读框,编码279个氨基酸残基,含有一个保守的AP2结构域,是AP2大家族的一个新成员。该基因编码的氨基酸序列与GenBank已有的普通小麦AP2家族两个同源基因编码蛋白TaDREB1和TaDREBW50（登录号分别为：AAL01124.1和AAY44605.1）具有98%的氨基酸序列一致性, 与大麦AP2蛋白HvDREB1-a（登录号AAY25517.1）,高羊茅AP2蛋白FaDREB2A （登录号CAG30547.1） 及水稻OsDREB2.2（登录号AY064403）的氨基酸序列一致性分别为 93%、86%、69%。说明该基因与小麦AP2家族基因的同源性最高。本研究除获得了长穗偃麦草一个重要抗逆转录因子基因EeAP2.2的全长cDNA序列外,也提供了一种快速、有效克隆功能基因的方法。     

The synganglion of the jumping spider Marpissa muscosa (Arachnida: Salticidae): Insights from histology,immunohistochemistry and microCT analysis

Jumping spiders are known for their extraordinary cognitive abilities. The underlying nervous system structures, however, are largely unknown. Here, we explore and describe the anatomy of the brain in the jumping spider Marpissa muscosa (Clerck, 1757) by means of paraffin histology, X-ray microCT analysis and immunohistochemistry as well as three-dimensional reconstruction. In the prosoma, the CNS is a clearly demarcated mass that surrounds the esophagus. The anteriormost neuromere, the protocerebrum, comprises nine bilaterally paired neuropils, including the mushroom bodies and one unpaired midline neuropil, the arcuate body. Further ventrally, the synganglion comprises the cheliceral (deutocerebrum) and pedipalpal neuropils (tritocerebrum). Synapsin-immunoreactivity in all neuropils is generally strong, while allatostatin-immunoreactivity is mostly present in association with the arcuate body and the stomodeal bridge. The most prominent neuropils in the spider brain, the mushroom bodies and the arcuate body, were suggested to be higher integrating centers of the arthropod brain. The mushroom body in M. muscosa is connected to first and second order visual neuropils of the lateral eyes, and the arcuate body to the second order neuropils of the anterior median eyes (primary eyes) through a visual tract. The connection of both, visual neuropils and eyes and arcuate body, as well as their large size corroborates the hypothesis that these neuropils play an important role in cognition and locomotion control of jumping spiders. In addition, we show that the architecture of the brain of M. muscosa and some previously investigated salticids differs significantly from that of the wandering spider Cupiennius salei, especially with regard to structure and arrangement of visual neuropils and mushroom body. Thus, we need to explore the anatomical conformities and specificities of the brains of different spider taxa in order to understand evolutionary transformations of the arthropod brain.     

Persistence of orientation toward a temporarily invisible landmark in Drosophila melanogaster

In arena experiments with the walking fruit fly, we found a remarkable persistence of orientation toward a landmark that disappeared during the fly's approach. The directional stability achieved by `after-fixation' allows a fly to continue pursuit under natural conditions, where a selected target is frequently concealed by surrounding structures. The persistence of after-fixation was investigated in Buridan's paradigm, where a fly walks persistently back and forth between two inaccessible landmarks. Upon disappearance of a selected target, the flies maintained their intended course for more than 15 body lengths of approximately 2.5 mm in about 50% of the trials. About 13% even exceeded 75 body lengths. About 88% of the approaches clustered in equal portions around peaks at 2.4 s and 8.6 s. About 12% of the approaches persisted even longer. In contrast, a single peak at about 2.2 s is sufficient to describe the persistence of orientation in a random walk. The ability to pursue an invisible landmark is disturbed neither by a transient angular deviation from the course toward this landmark, when this target disappeared, nor by a distracting second landmark. Accordingly, after-fixation seems to require an internal representation of the direction toward the concealed target, and idiothetical course control to maintain this direction. Accepted: 19 September 1997     

Reliability of medial-longitudinal-arch measures for skin-markers based kinematic analysis

The medial-longitudinal arch (MLA) is perhaps the most important feature characterizing foot morphology. While current skin-markers based models of the MLA angle used in stereophotogrammetry allow to estimate foot arch shape and deformation, these do not always appear consistent with foot anatomy and with standard clinical definitions. The aim of this study was to propose novel skin-markers based measures of MLA angle and investigate their reliability during common motor tasks.Markers on the calcaneus, navicular tuberosity, first metatarsal head and base, and on the two malleoli were exploited to test eight definitions of MLA angle consistent with foot anatomy, both as angles between two 3-dimensional vectors and as corresponding projections on the sagittal plane of the foot. The inter-trial, inter-session and inter-examiner reliability of each definition was assessed in multiple walking and running trials of two volunteers, tested by four examiners in three sessions.Inter-trial variability in walking was in the range 0.7–1.2 deg, the inter-session 2.8–7.5 deg, and the inter-examiner in the range 3.7–9.3 deg across all MLA definitions. The Rizzoli Foot Model definition showed the lowest inter-session and inter-examiner variability. MLA measures presented similar variability in walking and running.This study provides preliminary information on the reliability of MLA measurements based on skin-markers. According to the present study, angles between 3-dimensional vectors and minimal marker sets should be preferred over sagittal-plane projections. Further studies should be sought to investigate which definition is more accurate with respect to the real MLA deformation in different loading conditions.     

Bipedal locomotion: toward unified concepts in robotics and neuroscience

This review is the result of a joint reflection carried out by researchers in the fields of robotics and automatic control on the one hand and neuroscience on the other, both trying to answer the same question: what are the functional bases of bipedal locomotion and how can they be controlled? The originality of this work is to synthesize the two approaches in order to take advantage of the knowledge concerning the adaptability and reactivity performances of humans and of the rich tools and formal concepts available in biped robotics. Indeed, we claim that the theoretical framework of robotics can enhance our understanding of human postural control by formally expressing the experimental concepts used in neuroscience. Conversely, biological knowledge of human posture and gait can inspire biped robot design and control. Therefore, both neuroscientists and roboticists should find useful information in this paper.