Zur Beeinflussung der Bewegungsweise eines Beines von Carausius morosus durch Amputation anderer Beine

Amputation of a leg alters the amplitude of the adjacent ipsilateral legs during walking: Amputation of a middle leg encreases the amplitude of the foreleg especially by changing the rear extreme position. Amputation of a foreleg reduces the amplitude of the middle leg especially by changing the front extreme position. There is no significant influence observable on contralateral legs.     

Control of leg protraction in the stick insect: a targeted movement showing compensation for externally applied forces

Summary In stick insects, the swing of each rear leg is aimed at the ipsilateral middle leg. The control of this targeted movement was investigated by applying external force to aid or oppose protraction of one rear leg as stick insects walked on a treadwheel.In the first condition studied, the target middle leg was stationary during the protraction of the rear leg (Figs. 1a, 2). The opposing forces tested were 14 and 32 times greater than the peak force exerted during unobstructed protraction. Nevertheless, the rear leg continued to step to a constant position behind the middle leg (Fig. 3).In the second condition, the target middle leg also walked on the wheel. As the force opposing protraction increased, the endpoint of rear leg protraction shifted caudally, the speed of protraction decreased, and the total protraction duration increased (Fig. 5; Table 1). The middle leg's position at the end of rear leg protraction shifted caudally but its posterior extreme position remained virtually unchanged. When the onset of the external force was abrupt, compensation often occurred within 20 ms (Fig. 6a).External forces aiding protraction increased protraction speed only slightly (Table 2). When the force was suddenly removed, the leg continued moving forward but with reduced velocity (Fig. 6b).It is concluded that position information is used only to determine the swing endpoint and that velocity is controlled during the movement. The results are compared with movements to a target by vertebrates and with models of motor control in general.Abbreviations AEP anterior extreme position - PEP posterior extreme position     

A model of leg coordination in the stick insect,Carausius morosus

Mechanisms dependent upon leg position coordinate the alternate stepping of adjacent ipsilateral and contralateral legs in the stick insect. In this insect, swing duration and step amplitude are independent of walking speed. A simple geometrical model of the leg controller is used here to test different mechanisms for compatibility with these two invariant features. Leg position is the state variable of a relaxation oscillator and position thresholds determine the transitions between swing and stance. The coordination mechanisms alter these thresholds. The position-dependent mechanisms considered differ either in the form or the speed-dependence of the function relating the shift in the posterior threshold of the receiving leg to the position of the sending leg. The results identify parameter combinations leading to alternate stepping with symmetric or asymmetric phase distributions, to shifts in the posterior extreme position as a function of speed, to double stepping or to in-phase stepping. An optimal position-dependent excitatory mechanism is described. Finally the consequences of adding either inhibitory influences or time-dependent excitatory influences are analyzed.     

Walking in the American cockroach: the timing of motor activity in the legs during straight walking

The timing of bursts of motor activity in extensor muscles in the coxae of pairs of legs in intact freely walking American cockroaches was studied. The timing of bursts in adjacent and non-adjacent leg pairs generally reflected the common alternating tripod gait of these insects. Detailed study of the timing further revealed two previously unreported features. (1) The timing of extensor bursts in the middle legs relative to bursts in the rear legs was more variable than it was relative to those in the front legs. This difference in variability was statistically significant for the means of bursts when all insects were considered together as well as for bursts in individual insects. An apparent difference in variability of the timing of burst starts compared to burst ends for any one leg pair was not significant. (2) There was a shift in the timing of motor bursts relative to one another when an insect walked fast such that motor bursts in the middle legs tended to lag farther behind those in the front legs, and those in the rear legs tended to lag farther behind those in the middle legs compared to the timing during slow walking. This shift was apparent in both burst starts and burst ends, although more obvious in the former. It occurred in both ipsilateral and contralateral leg pairs, and in both the mean data and the data for individual insects. The implications of these characteristics of the timing data are discussed in terms of the neural organization of insect walking.     

The effect of amputation and leg restraint on the free walking coordination of the stick insectCarausius morosus

Summary The stepping patterns of intact, amputated and leg restrained first instar stick insects were examined by analysing video tape records of their free walking behaviour. Amputation produced changes in the relative timing of protraction movements both along and across the body axis. Restraint of individual front or rear legs produced walking behaviour similar to that of the amputee animal but restraint of middle legs caused a breakdown in the coordination of front and rear legs. The changes in behaviour produced by leg autotomy and restraint were used to test certain assumptions of a model for generating the step pattern of these insects and to investigate how the tonic influence of proprioceptive input might be incorporated into the model.I would like to thank Professor P.N.R. Usherwood and Drs. M.D. Burns and W.J.P. Barnes for their comments and ideas on this work. A special acknowledgement goes to Dr. F. Delcomyn whose Fortran step analysis programs assisted greatly in the data reduction. I wish to thank S.R.C. for a returning scientist award and the support and equipment provided by grant B/SR/9774 to Professor Usherwood. A preliminary survey of some of the amputees was carried out at the Biology Department, Case Western Reserve University and I would like to acknowledge the support provided by a P.H.S. grant NB-06054 to Professor R.K. Josephson.     

A model of leg coordination in the stick insect,Carausius morosus

A model of interleg coordination presented in a separate report is evaluated here by perturbing the step pattern in three ways. First, when the initial leg configuration is varied, the simulated leg movements assume a stable coordination from natural starting configurations in a natural way (Fig. 1a). They also rapidly re-establish the normal coordination when started from unnatural configurations (Fig. 1b-d). An explicit hierarchy of natural frequencies for the legs of the three thoracic segments is not required. Second, when the coordination is perturbed by assigning one or more legs a retraction velocity different from the rest, gliding coordination or various integer step ratios can be produced (Figs. 2–4). Third, when the swing of one leg is obstructed, characteristic changes in the stepping of other legs occur (Fig. 5). Overall differences between the step patterns of the model and those of the stick insect are related to the form of the coordinating mechanisms. Errors made by the model, such as overlapping swings by adjacent legs or discrepancies in step timing and step end-points, point out the limitations of a model restricted to kinematic parameters.     

Basic processes of locomotor coordination in the rock lobster

Rock lobsters are able to perform long and stereotyped stepping sequences above a motor driven treadmill. Forward walking samples are estimated by mean of statistical methods to draw out the basic rules involved in the locomotor behaviour (Fig. 1).

- The spatial and temporal parameters defined in a single propulsive leg are either invariable in respect to the imposed speed, as the mean step length (L), the return stroke duration (Tr) and the pause times (T's, T'r), or speed dependent as the power stroke duration (Ts) and the whole period (Figs. 2 and 3).

- The interleg phase coupling is strong and stable in the ipsilateral rear pairs (4–5), these legs acting most of the time in absolute coordination (1:1) or in harmonic ratio (2:1). In the contralateral pairs (R4-L4, R5-L5) the legs roughly operate in antiphase, but the relationship appears much weaker and variable, with frequent episodes of relative coordination (Fig. 4).

- The time intervals between the ground contact of any leg and the swing initiation in the nearest ones appear somewhat constant and could be closely related to the mechanism of stepping synchronization. The “5 on - 4 off” delay, very stable and always positive, suggests that the rear legs could exert a predominant influence upon the rhythmical movements of the next anterior ipsilateral appendages (Fig. 5).

- To test the contralateral relationships, the treadmill belts can be decoupled in order to impose different walking speeds on each side. Such a conflicting stimulus reveals that:

1. The relative hierarchy always observed between the ipsilateral legs can be artificially created between the two sides (Fig. 6).
2. The driving influence of a given leg is closely linked to the intensity of EMG's discharges in its power stroke muscles.
3. The contralateral appendages are able to walk in absolute coordination despite a large speed difference between the two sides (up to 4 cm/s). Under such a constraint, the walking legs alter its invariable parameters (L and Tr) to reach a common step period and steadily maintain the alternating pattern (Figs. 6 and 7).

     

The contralateral coordination of walking legs in the crayfish Astacus leptodactylus

The coupling mechanisms which coordinate the movement of ipsilateral walking legs in the crayfish have been described in earlier investigations. Concerning the coupling between contralateral legs it was only known that these influences are weaker than those acting between ipsilateral legs. The nature of these coupling mechanisms between contralateral legs of the crayfish are investigated here by running left and right legs on separate walking belts at different speeds. The results show that coordination is performed by a phase-dependent shift of the anterior extreme position of the influenced leg. This backward shift leads to a shortening of both the return stroke and the following power stroke. As the coupling influence is only weak, several steps might be necessary to retain normal coordination after a disturbance. This corresponds to v. Holst's relative coordination. The influences act in both directions, from left to right and vice versa. However, one side may be more or less dominant. A gradient was found in the way that anterior leg pairs show less strong coordination than posterior legs. In some cases the coupling between diagonally neighbouring legs was found to be stronger than between contralateral legs of the same segment. The interpretation of this result is still open.     

The function of auditory neurons in cricket phonotaxis

Summary The activity of auditory receptor cells and prothoracic auditory neurons of the cricket,Gryllus bimaculatus, was recorded intracellularly while the animal walked on a sphere or while passive movement was imposed on a foreleg.During walking the responses to simulated calling song is altered since (i) the auditory sensory cells and interneurons discharged impulses in the absence of sound stimuli (Figs. 1, 3) and (ii) the number of action potentials in response to sound is reduced in interneurons (Figs. 2, 3).These two effects occurred in different phases of the leg movement during walking and therefore masked, suppressed or did not affect the responses to auditory stimuli (Figs. 3, 4). Hence there is a time window within which the calling song can be detected during walking (Fig. 5).The extra excitation of receptors and interneurons is probably produced by vibration of the tympanum because (i) the excitation occurred at the same time as the leg placement (Fig. 4), (ii) during walking on only middle and hindlegs, no extra action potentials were observed (Fig. 6), (iii) in certain phases of passive movements receptor cells and interneurons were excited as long as the ipsilateral ear was not blocked (Figs. 8, 9).Suppression of auditory responses seems to be peripheral as well as central in origin because (i) it occurred at particular phases during active and passive leg movements in receptor cells and interneurons (Figs. 1, 4, 9), (ii) it disappeared if the ear was blocked during passive leg movements (Fig. 9) and (iii) it persisted if the animal walked only on the middle and hind legs (Fig. 6).     

Righting kinematics in beetles (Insecta: Coleoptera)

Twenty modes of stereotyped righting motions were observed in 116 representative species of coleoptera. Methods included cine and stereocine recording with further frame by frame analysis, stereogrammetry, inverse kinematic reconstruction of joint angles, stroboscopic photography, recording of electromyograms, 3D measurements of the articulations, etc. The basic mode consists of a search phase, ending up with grasping the substrate, and a righting, overturning phase. Leg coordination within the search cycle differs from the walking cycle with respect to phasing of certain muscle groups. Search movements of all legs appear chaotic, but the tendency to move in antiphase is still present in adjacent ipsilateral and contralateral leg pairs. The system of leg coordination might be split: legs of one side might search, while contralateral legs walk, or fore and middle legs walk while hind legs search. Elaborated types of righting include somersaults with the aid of contralateral or diagonal legs, pitch on elytra, jumps with previous energy storage with the aid of unbending between thoracic segments (well-known for Elateridae), or quick folding of elytra (originally described in Histeridae). Righting in beetles is compared with righting modes known in locusts and cockroaches. Search in a righting beetle is directed dorsad, while a walking insect searches for the ground downwards. Main righting modes were schematized for possible application to robotics.     

Reflex modulation in locusts walking on a treadwheel intracellular recordings from motoneurons

Summary In locusts (Locusta migratoria) walking on a treadwheel, afferents of tarsal hair sensilla were stimulated via chronically implanted hook electrodes (Fig. 1). Stimuli applied to the middle leg tarsus elicited avoidance reflexes (Fig. 2). In quiescent animals, the leg was lifted off the ground and the femur adducted. In walking locusts, the response was phase-dependent. During the stance phase, no reaction was observed except occasional, premature triggering of swing movements; stimuli applied near the end of the swing phase were able to elicit an additional, short leg protraction.Central nervous correlates of phase-dependent reflex modulation were observed by recording intracellularly from motoneuron somata in walking animals. As a rule, motoneurons recruited during the swing phase showed excitatory stimulus-related responses around the end of the swing movement, correlated to the triggering of additional leg protractions (Figs. 3, 4, 5). Motoneurons active during the stance phase were often inhibited by tarsal stimulation, some showed only weak responses (Figs. 8, 9, 10). Common inhibitory motoneuron 1 was excited by tarsal stimulation during all phases of the leg movement (Figs. 6, 7). In one type of flexor tibiae motoneuron, a complex response pattern was observed, involving the inversion of stimulus-related synaptic potentials from excitatory, recorded during rest, to inhibitory, observed during long-lasting stance phases (Figs. 11, 12).The results demonstrate how reflex modulation is represented on the level of synaptic input to motoneurons. They further suggest independent gain control in parallel, antagonistic pathways converging onto the same motoneuron as a mechanism for reflex reversal during locomotion.Abbreviations CI ₁ common inhibitory motoneuron (1) - EMG electromyogram - Feti fast extensor muscle of the tibia     

Sensory control of leg movement in the stick insect Carausius morosus

Hind legs with crossed receptor-apodemes of the femoral chordotonal organ when making a step during walking often do not release the ground after reaching the extreme posterior position. After putting a clamp on the trochanter (stimulation of the campaniform sensilla) the leg is no longer protracted during walking. However, during searching-movements the same leg is moved very far forwards. The anatomical situation of the campaniform sensilla on the trochanter and the sensory innervation of the trochanter is described. After removal of the hair-rows and continuously stimulating the hair-plate at the thorax-coxa-joint the extreme anterior and posterior positions of the leg in walking are displaced in the posterior direction. Front and middle legs operated in this way sometimes do not release the ground at the end of retraction. In searching-movements the same leg is moved in a normal way. If only one side of a decerebrated animal goes over a step, then on the other side a compensatory effect is observed. The main source of this compensatory information appears to be the BF1-hair-plates. If the animal has to drag a weight the extreme anterior and posterior positions of the middle and hind legs are displaced in the anterior direction. Crossing the receptor-apodeme of the femoral chordotonal organ, when it causes the leg to remain in the protraction phase, displaces the extreme posterior position of the ipsilateral leg in front of the operated one in the posterior direction. Influences of different sources on the extreme posterior position can superimpose. A model is presented which combines both a central programme and peripheral sensory influence. The word programme used here means that it does not only determine the motor output but also determines the reactions to particular afferences. The fact that the reaction to a stimulus depends on the internal state of the CNS is also represented by the model.Supported by Deutsche Forschungsgemeinschaft     

A mathematical modeling study of inter-segmental coordination during stick insect walking

The biomechanical conditions for walking in the stick insect require a modeling approach that is based on the control of pairs of antagonistic motoneuron (MN) pools for each leg joint by independent central pattern generators (CPGs). Each CPG controls a pair of antagonistic MN pools. Furthermore, specific sensory feedback signals play an important role in the control of single leg movement and in the generation of inter-leg coordination or the interplay between both tasks. Currently, however, no mathematical model exists that provides a theoretical approach to understanding the generation of coordinated locomotion in such a multi-legged locomotor system. In the present study, I created such a theoretical model for the stick insect walking system, which describes the MN activity of a single forward stepping middle leg and helps to explain the neuronal mechanisms underlying coordinating information transfer between ipsilateral legs. In this model, CPGs that belong to the same leg, as well as those belonging to different legs, are connected by specific sensory feedback pathways that convey information about movements and forces generated during locomotion. The model emphasizes the importance of sensory feedback, which is used by the central nervous system to enhance weak excitatory and inhibitory synaptic connections from front to rear between the three thorax-coxa-joint CPGs. Thereby the sensory feedback activates caudal pattern generation networks and helps to coordinate leg movements by generating in-phase and out-of-phase thoracic MN activity.     

Effects of circum-oesophageal lesion on the behaviour of the stick insect Carausius morosus

The co-ordination of the walking behaviour of decerebrate stick insects is examined and compared with normal behaviour. The walks are fully coordinated but undergo subtle changes in timing, have a longer average step period and show momentary pauses of 50 ms during the time course of protraction movements. In addition a new intersegmental reflex has been discovered. This tactile reflex is used to avoid errors in co-ordination that would be produced by posterior legs stepping onto the tarsi of the legs in front. The reflex has a latency of 100 ms and is easily observed in lesioned animals but is also active, although seldom seen, in slowly walking intact animals.     

Saxitoxin binding in nerves from walking legs of the lobster Homarus americanus. Two classes of receptors

The binding of exchange-labeled saxitoxin (STX) to sodium channels has been investigated in the nonmyelinated fibers of the walking leg nerves of the lobster. The properties of the STX binding site differed systematically among the nerves from different walking legs. The equilibrium dissociation constant for STX binding (KSTX) to the front legs is approximately twice that for the binding to the rear legs; the average ratio of KSTX (front): KSTX (rear) from five separate experiments was 1.80 +/- 0.21 (mean +/- SE). The actual KSTX values ranged from 124.0 to 22.7 nM for the front leg nerves and from 8.6 to 12.7 nM for the rear leg nerves. KSTX values for the middle two walking leg nerves fell between those for the front and rear legs. The inhibitory dissociation constant for tetrodotoxin (KTTX), calculated from tetrodotoxin's inhibition of labeled STX binding, was 3.02 +/- 0.27 nM for the front legs and 2.20 +/- 0.33 nM for the rear legs. The ratio KSTX: KTTX was different in the front and rear leg nerves, being 5.5 and 4.2, respectively. The apparent P pKa of the STX receptor also differed between the two legs, being 4.6 +/- 0.3 for the front legs and 5.1 +/- 0.1 for the rear legs. These results demonstrate that one tissue type in one organism can contain different toxin binding sites. The difference in the receptors can be qualitatively accounted for by the location of an additional negative charge near the receptor site of the rear walking leg.     

The two groups of sensilla in the ventral coxal hairplate of Carausius morosus have different roles during walking

Abstract. The ventral coxal hairplate (cxHPv) of the stick insect Carausius morosus Br. (Phasmida: Bacteriidae) contains two morphologically distinct groups of sensilla designated as group 1 and 2 (Gl, G2). The function of these sensilla during walking was tested by selectively ablating one or both groups on one middle leg in thirty-four animals. It has previously been shown that ablation of the entire hairplate leads to two kinds of errors: the operated leg swings farther forward and the adjacent caudal leg ends its swing more to the rear relative to the operated leg. Following selective ablation of cxHPv Gl on the middle leg, the first kind of error is more pronounced, indicating that this group contributes more to limiting forward protraction during the swing. Following ablation of cxHPv G2, the second kind of error is more evident, indicating that during stance this group contributes more to the target information influencing the swing end-point of the adjacent caudal leg. These results are interpreted to reflect the phasic and phasic-tonic response characteristics of Gl and G2 hairs, respectively.     

Identified nonspiking interneurons in leg reflexes and during walking in the stick insect

In the stick insect Carausius morosus identified nonspiking interneurons (type E4) were investigated in the mesothoracic ganglion during intraand intersegmental reflexes and during searching and walking.In the standing and in the actively moving animal interneurons of type E4 drive the excitatory extensor tibiae motoneurons, up to four excitatory protractor coxae motoneurons, and the common inhibitor 1 motoneuron (Figs. 1–4).In the standing animal a depolarization of this type of interneuron is induced by tactile stimuli to the tarsi of the ipsilateral front, middle and hind legs (Fig. 5). This response precedes and accompanies the observed activation of the affected middle leg motoneurons. The same is true when compensatory leg placement reflexes are elicited by tactile stimuli given to the tarsi of the legs (Fig. 6).During forward walking the membrane potential of interneurons of type E4 is strongly modulated in the step-cycle (Figs.8–10). The peak depolarization occurs at the transition from stance to swing. The oscillations in membrane potential are correlated with the activity profile of the extensor motoneurons and the common inhibitor 1 (Fig. 9).The described properties of interneuron type E4 in the actively behaving animal show that these interneurons are involved in the organization and coordination of the motor output of the proximal leg joints during reflex movements and during walking.Abbreviations CLP reflex, compensatory leg placement reflex - CI1 common inhibitor I motoneuron - fCO femoral chordotonal organ - FETi fast extensor tibiae motoneuron - FT femur-tibia - SETi slow extensor tibiae motoneuron     

Leg movements of stick insects walking with five legs on a treadwheel and with one leg on a motor-driven belt

Five legs of a fixed stick insect walked on a double treadwheel. The left hindleg (L3) walked on a motor-driven belt. When the belt was slower than the wheels L3 made less steps than the other legs and when the belt was faster than the wheels it made more steps than the other legs. In the case of slowlier stepping of the belt-leg, the motor neurons of the retractor coxae muscle of this leg showed a high activity when the leg was pulled backwards by the belt. This activity was modulated in the step rhythm of the wheel-legs. When all legs showed the same stepping frequency (1:1-coordination) the protraction duration of L3 was almost independent of step-period, as well as the lag between onset of protraction of L3 and that of L2. In some cases only L3 could be made to step on the belt even when all other legs did not walk.     

Mechanisms of stick insect locomotion in a gap-crossing paradigm

Locomotion of stick insects climbing over gaps of more than twice their step length has proved to be a useful paradigm to investigate how locomotor behaviour is adapted to external conditions. In this study, swing amplitudes and extreme positions of single steps from gap-crossing sequences have been analysed and compared to corresponding parameters of undisturbed walking. We show that adaptations of the basic mechanisms concern movements of single legs as well as the coordination between the legs. Slowing down of stance velocity, searching movements of legs in protraction and the generation of short steps are crucial prerequisites in the gap-crossing task. The rules of leg coordination described for stick insect walking seem to be modified, and load on the supporting legs is assumed to have a major effect on coordination especially in slow walking. Stepping into the gap with a front leg and antennal contact with the far edge of the gap provide information, as both events influence the following leg movements, whereas antennal non-contact seems not to contain information. Integration of these results into the model of the walking controller can improve our understanding of insect locomotion in highly irregular environments.Abbreviations AEP anterior extreme position - fAEP fictive anterior extreme position - PEP posterior extreme position - TOT treading-on-tarsus     

Responses of the lower limb to load carrying in walking man

Muscle activity patterns of several lower limb muscles were examined in the left leg of normal human subjects walking at comfortable speed on a treadmill. In addition knee angular changes and the durations of the swing and stance phases of the step cycle were recorded. Data were collected during a period of normal control walking and when the subject carried a load, either in his right or left hand or on his back. Load (up to 20% of body weight) carried in either hand caused minimal changes in the kinematic parameters investigated but evoked significant prolongation of the normal ongoing electromyographic activity in the contralateral Gluteus medius and in the ipsilateral Gastrocnemius, Vastus lateralis and Semimembranosus. Load (up to 50% of body weight) carried on the back significantly shortened the swing phase and prolonged the ongoing electromyographic activity of the Vastus lateralis. These findings would seem to indicate that the activity of the leg musculature during walking is so tightly controlled that deviation from the normal kinematic pattern of the legs is largely prevented even when body posture and balance are disturbed by carrying substantial additional load.