The composition of Event-B models

The transition from classical B [2] to the Event-B language and method [3] has seen the removal of some forms of model structuring and composition, with the intention of reinventing them in future. This work contributes to thatreinvention. Inspired by a proposed method for state-based decomposition and refinement [5] of an Event-B model, we propose a familiar parallel event composition (over disjoint state variable lists), and the less familiar event fusion (over intersecting state variable lists). A brief motivation is provided for these and other forms of composition of models, in terms of feature-based modelling. We show that model consistency is preserved under such compositions. More significantly we show that model composition preserves refinement

The Inactivation Principle: Mathematical Solutions Minimizing the Absolute Work and Biological Implications for the Planning of Arm Movements

An important question in the literature focusing on motor control is to determine which laws drive biological limb movements. This question has prompted numerous investigations analyzing arm movements in both humans and monkeys. Many theories assume that among all possible movements the one actually performed satisfies an optimality criterion. In the framework of optimal control theory, a first approach is to choose a cost function and test whether the proposed model fits with experimental data. A second approach (generally considered as the more difficult) is to infer the cost function from behavioral data. The cost proposed here includes a term called the absolute work of forces, reflecting the mechanical energy expenditure. Contrary to most investigations studying optimality principles of arm movements, this model has the particularity of using a cost function that is not smooth. First, a mathematical theory related to both direct and inverse optimal control approaches is presented. The first theoretical result is the Inactivation Principle, according to which minimizing a term similar to the absolute work implies simultaneous inactivation of agonistic and antagonistic muscles acting on a single joint, near the time of peak velocity. The second theoretical result is that, conversely, the presence of non-smoothness in the cost function is a necessary condition for the existence of such inactivation. Second, during an experimental study, participants were asked to perform fast vertical arm movements with one, two, and three degrees of freedom. Observed trajectories, velocity profiles, and final postures were accurately simulated by the model. In accordance, electromyographic signals showed brief simultaneous inactivation of opposing muscles during movements. Thus, assuming that human movements are optimal with respect to a certain integral cost, the minimization of an absolute-work-like cost is supported by experimental observations. Such types of optimality criteria may be applied to a large range of biological movements

Etude et mise au point d'une chaine de polarisation stabilisee en gain pour des taux de comptage superieurs a 10 coups/s, pour PM2232

SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Activation of Akt/FKHR in the medulla oblongata contributes to ă spontaneous respiratory recovery after incomplete spinal cord injury in ă adult rats

International audienceAfter incomplete spinal cord injury (SCI), patients and animals may ă exhibit some spontaneous functional recovery which can be partly ă attributed to remodeling of injured neural circuitry. This post-lesion ă plasticity implies spinal remodeling but increasing evidences suggest ă that supraspinal structures contribute also to the functional recovery. ă Here we tested the hypothesis that partial SCI may activate ă cell-signaling pathway(s) at the supraspinal level and that this ă molecular response may contribute to spontaneous recovery. With this ă aim, we used a rat model of partial cervical hemisection which injures ă the bulbospinal respiratory tract originating from the medulla oblongata ă of the brainstem but leads to a time-dependent spontaneous functional ă recovery of the paralyzed hemidiaphragm. We first demonstrate that after ă SCI the PI3K/Akt signaling pathway is activated in the medulla oblongata ă of the brainstem, resulting in an inactivation of its pro-apoptotic ă downstream target, forkhead transcription factor (FKHR/FOXO1A). ă Retrograde labeling of medullary premotoneurons including respiratory ă ones which project to phrenic motoneurons reveals an increased FKHR ă phosphorylation in their cell bodies together with an unchanged cell ă number. Medulla infusion of the PI3K inhibitor, LY294002, prevents the ă SCI-induced Akt and FKHR phosphorylations and activates one of its ă death-promoting downstream targets, Fas ligand. Quantitative EMG ă analyses of diaphragmatic contractility demonstrate that the inhibition ă of medulla PI3K/Akt signaling prevents spontaneous respiratory recovery ă normally observed after partial cervical SCI. Such inhibition does not ă however affect either baseline contractile frequency or the ventilatory ă reactivity under acute respiratory challenge. Together, these findings ă provide novel evidence of supraspinal cellular contribution to the ă spontaneous respiratory recovery after partial SCI. (C) 2014 Elsevier ă Inc All rights reserved

Effect of gaze direction on neck muscle activity during cervical rotation

Control of the neck muscles is coordinated with the sensory organs of vision, hearing and balance. For instance, activity of splenius capitis (SC) is modified with gaze shift. This interaction between eye movement and neck muscle activity is likely to influence the control of neck movement. The aim of this study was to investigate the effect of eye position on neck muscle activity during cervical rotation. In eleven subjects we recorded electromyographic activity (EMG) of muscles that rotate the neck to the right [right obliquus capitis inferior (OI), multifides (MF), and SC, and left sternocleidomastoid (SCM)] with intramuscular or surface electrodes. In sitting, subjects rotated the neck in each direction to specific points in range that were held statically with gaze either fixed to a guide (at three different positions) that moved with the head to maintain a constant intra-orbit eye position or to a panel in front of the subject. Although right SC and left SCM EMG increased with rotation to the right, contrary to anatomical texts, OI EMG increased with both directions and MF EMG did not change from the activity recorded at rest. During neck rotation SCM and MF EMG was less when the eyes were maintained with a constant intra-orbit position that was opposite to the direction of rotation compared to trials in which the eyes were maintained in the same direction as the head movement. The inter-relationship between eye position and neck muscle activity may affect the control of neck posture and movement

Bilateral otolith contribution to spatial coding in the vestibular system.

Recent work on the coding of spatial information in central otolith neurons has significantly advanced our knowledge of signal transformation from head-fixed otolith coordinates to space-centered coordinates during motion. In this review, emphasis is placed on the neural mechanisms by which signals generated at the bilateral labyrinths are recognized as gravity-dependent spatial information and in turn as substrate for otolithic reflexes. We first focus on the spatiotemporal neuronal response patterns (i.e. one- and two-dimensional neurons) to pure otolith stimulation, as assessed by single unit recording from the vestibular nucleus in labyrinth-intact animals. These spatiotemporal features are also analyzed in association with other electrophysiological properties to evaluate their role in the central construction of a spatial frame of reference in the otolith system. Data derived from animals with elimination of inputs from one labyrinth then provide evidence that during vestibular stimulation signals arising from a single utricle are operative at the level of both the ipsilateral and contralateral vestibular nuclei. Hemilabyrinthectomy also revealed neural asymmetries in spontaneous activity, response dynamics and spatial coding behavior between neuronal subpopulations on the two sides and as a result suggested a segregation of otolith signals reaching the ipsilateral and contralateral vestibular nuclei. Recent studies have confirmed and extended previous observations that the recovery of resting activity within the vestibular nuclear complex during vestibular compensation is related to changes in both intrinsic membrane properties and capacities to respond to extracellular factors. The bilateral imbalance provides the basis for deranged spatial coding and motor deficits accompanying hemilabyrinthectomy. Taken together, these experimental findings indicate that in the normal state converging inputs from bilateral vestibular labyrinths are essential to spatiotemporal signal transformation at the central otolith neurons during low-frequency head movements. Copyright 2002 National Science Council, ROC and S. Karger AG, Basellink_to_subscribed_fulltex

Tilt and translation motion perception during off-vertical axis rotation.

International audienceThe effect of stimulus frequency on tilt and translation motion perception was studied during constant velocity off-vertical axis rotation (OVAR), and compared to the effect of stimulus frequency on eye movements. Fourteen healthy subjects were rotated in darkness about their longitudinal axis 10 degrees and 20 degrees off-vertical at 45 degrees /s (0.125 Hz) and 20 degrees off-vertical at 180 degrees /s (0.5 Hz). Perceived motion was evaluated using verbal reports and a joystick capable of recording tilt and translation in both sagittal and lateral planes. Eye movements were also recorded using videography. At the lower frequency, subjects reported the perception of progressing along the edge of a cone, whereas at the higher frequency they had the sensation of progressing along the edge of an upright cylinder. Tilt perception and ocular torsion significantly increased as the tilt angle increased from 10 degrees to 20 degrees at the lower frequency, and then decreased at the higher frequency. The phase lag of ocular torsion increased as a function of frequency, while the phase lag of tilt perception did not change. Horizontal eye movements were small at the lower frequency and showed a phase lead relative to the linear acceleration stimulus. While the phase lead of horizontal eye movements decreased at 0.5 Hz, the phase of translation perception did not vary with stimulus frequency and was similar to the phase of tilt perception during all conditions. A second data set was obtained in 12 subjects to compare motion perception phase when using a simple push-button to indicate nose-up orientation, continuous setting of pitch tilt alone, or continuous setting of tilt and translation in both pitch and roll planes as in the first data set. This set of measurements indicated that in the frequency range studied subjects tend to lead the stimulus when using a push-button task while lagging the stimulus when using a continuous setting of tilt with a joystick. Both amplitude and phase of tilt perception using the joystick were not different whether concentrating on pitch tilt alone or attempting a more complex reporting of tilt and translation in both sagittal and lateral planes. During dynamic linear stimuli in the absence of canal and visual input, a change in stimulus frequency alone elicits similar changes in the amplitude of both self-motion perception and eye movements. However, in contrast to the eye movements, the phase of both perceived tilt and translation motion is not altered by stimulus frequency over this limited range. These results are consistent with the hypothesis that neural processing to distinguish tilt and translation stimuli differs between eye movements and motion perception