1,721,033 research outputs found
Experimental validation of a hybrid computationalmodel for selective stimulation using transverseintrafascicular multichannel electrodes
No full textRecently a hybrid model based on the finite element method and on a compartmental biophysical representation of peripheral nerve fibers and intraneural electrodes was developed founded on experimental physiological and histological data. The model appeared to be robust when dealing with uncertainties in parameter selection. However, an experimental validation of the findings provided by the model is required to fully characterize the potential of this approach. The recruitment properties of selective nerve stimulation using transverse intrafas- cicular multichannel electrodes (TIME) were investigated in this work in experiments with rats and were compared to model predictions. Animal experiments were performed using the same stimulation protocol as in the computer simulations in order to rigorously validate the model predictions and understand its limitations. Two different selectivity indices were used, and new indices for measuring electrode performance are proposed. The model predictions are in decent agreement with experimental results both in terms of recruitment curves and selectivity values. Results show that these models can be used for extensive studies targeting electrode shape design, active sites shape, and multipolar stimulation paradigms. From a neurophysiological point of view, the topographic organization of the rat sciatic nerve, on which the model was based, has been confirmed
A computational model for the stimulation of ratsciatic nerve using a transverse intrafascicularmultichannel electrode
No full textNeuroprostheses based on electrical stimulation
could potentially help disabled persons. They are based on
neural interface that aim at creating an intimate contact with
neural cells. The efficacy of neuroprostheses can be improved by
increasing the selectivity of the neural interfaces used to stimulate
specific subsets of cells. Selectivity is strongly influenced by interface
design. Computer models can be useful for exploring the high
dimensional space of design parameters with the aim to provide
guidelines for the development of more efficient electrodes, with
minimal animal use and optimization of manufacturing processes.
The purpose of this study was to implement a realistic model
of the performance of a transverse intrafascicular multichannel
electrode (TIME) implanted into the rat sciatic nerve. A realistic
finite element method (FEM) model was developed taking into
account the anatomical and physiological features of the rat
sciatic nerve. Electric potentials were calculated and interpolated
voltages were applied to the model of a rat sciatic nerve axon,
based on experimental biophysical data. Results indicate that
high intra-fascicular and inter-fascicular selectivity values with
low current levels can be achieved with TIMEs. The selectivity of
TIMEs was also compared to one of the extraneural electrodes,
showing that higher selectivity with less current can be obtained.
Using this model, the robustness of electrode performances for
translational and rotational displacements were evaluated
Finite element and biophysics modelling of intraneural transversal electrodes: Influence of active site shape.
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Mechanisms underlying the neuromodulation of spinal circuits for correcting gait and balance deficits after spinal cord injury
No full textMechanisms Underlying the Neuromodulation of Spinal Circuits for Correcting Gait and Balance Deficits after Spinal Cord Injury
Full text linkEpidural electrical stimulation of lumbar segments facilitates standing and walking in animal models and humans with spinal cord injury. However, the mechanisms through which this neuromodulation therapy engages spinal circuits remain enigmatic. Using computer simulations and behavioral experiments, we provide evidence that epidural electrical stimulation interacts with muscle spindle feedback circuits to modulate muscle activity during locomotion. Hypothesis-driven strategies emerging from simulations steered the design of stimulation protocols that adjust bilateral hindlimb kinematics throughout gait execution. These stimulation strategies corrected subject-specific gait and balance deficits in rats with incomplete and complete spinal cord injury. The conservation of muscle spindle feedback circuits across mammals suggests that the same mechanisms may facilitate motor control in humans. These results provide a conceptual framework to improve stimulation protocols for clinical applications. Computer simulations validated experimentally revealed that epidural electrical stimulation of lumbar segments facilitates motor control through the modulation of muscle spindle feedback circuits. Simulations established a clinical framework to design stimulation protocols correcting gait symmetry and balance deficits after injury
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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