1,720,990 research outputs found
Stimulation strategies for tinnitus suppression in a neuron model
Full text linkTinnitus is a debilitating perception of sound in the absence of external auditory stimuli. It may have either a central or a peripheral origin in the cochlea. Experimental studies evidenced that an electrical stimulation of peripheral auditory fibers may alleviate symptoms but the underlying mechanisms are still unknown. In this work, a stochastic neuron model is used, that mimics an auditory fiber affected by tinnitus, to check the effects, in terms of firing reduction, of different kinds of electric stimulations, i.e., continuous wave signals and white Gaussian noise. Results show that both white Gaussian noise and continuous waves at tens of kHz induce a neuronal firing reduction; however, for the same amplitude of fluctuations, Gaussian noise is more efficient than continuous waves. When contemporary applied, signal and noise exhibit a cooperative effect in retrieving neuronal firing to physiological values. These results are a proof of concept that a combination of signal and noise could be delivered through cochlear prosthesis for tinnitus suppression
Revealing spectrum features of stochastic neuron spike trains
Full text linkPower spectra of spike trains reveal important properties of neuronal behavior. They exhibit several peaks, whose shape and position depend on applied stimuli and intrinsic biophysical properties, such as input current density and channel noise. The position of the spectral peaks in the frequency domain is not straightforwardly predictable from statistical averages of the interspike intervals, especially when stochastic behavior prevails. In this work, we provide a model for the neuronal power spectrum, obtained from Discrete Fourier Transform and expressed as a series of expected value of sinusoidal terms. The first term of the series allows us to estimate the frequencies of the spectral peaks to a maximum error of a few Hz, and to interpret why they are not harmonics of the first peak frequency. Thus, the simple expression of the proposed power spectral density (PSD) model makes it a powerful interpretative tool of PSD shape, and also useful for neurophysiological studies aimed at extracting information on neuronal behavior from spike train spectra
Characterization of a portable and low cost system for practical dielectric spectroscopy
No full textA portable setup for measurements of complex permittivity based on ad-hoc arrangements is proposed and its performance compared to the ones of a bench system. The measurement setup consists of a portable spectrum analyzer (used as vector network analyzer, VNA) connected to an open-end coaxial cable for S 11 acquisition. Scattering parameters were processed using custom Labview software specifically developed to obtain complex permittivity of liquids and soft materials in real-time. A suitable calibration procedure, based on a differential principle, enables accurate measurements. Raw results showed that the portable setup provides noisier traces if compared to the performance of a high precision laboratory VNA. However, accurate permittivity data have been achieved introducing filtering to eliminate signal oscillations and spurious noise without loss of information associated to liquid dielectric relaxations. This procedure, applied to standard liquids (ethanol, ethanediol, 2-propanol) showed good performance in terms of bias and precision. Water solutions, used for cell culturing purposes, both conductive and non-conductive, were also successfully measured. The obtained results are a proof of concept that the proposed procedure is a reliable technique to perform fast, low-cost and on site permittivity measurements, useful for diagnostic or therapeutic applications
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
Experimental Characterization of a Figure of Eight Coil for Transcranial Magnetic Stimulation
No full textIn order to accurately evaluate the induced E field distribution inside the brain due to a transcranial magnetic stimulation (TMS) procedure, a complete characterization of the stimulating source is needed. In this paper, a full experimental characterization of a typical TMS coil is given, providing spatial distribution of the generated B field as well as input impedance and waveform of the current. Measurements show a slight deviation in the field distribution with respect to the one coming from idealized coil models, particularly for what concerns symmetry
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
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
Acute exposure to CW 900 MHz radiofrequency does not affect synaptic transmission in the rat perirhinal cortex.
No full textAn in vivo exposure-system for wide-band electric pulses
No full textIn this paper, the dosimetry of small animals arranged on a monopolar patch antenna for bioelectromagnetic experiments is reported. Numerical simulations were carried out to verify the matching of the antenna in the presence of a dielectric box to accommodate the small animals. This strategy, reducing the dielectric differences between the various irradiated materials, improves largely the efficiency of the setup. The induced electric field in the biological samples reached tens of V/m for an input voltage of 1 V, which is one of the highest efficiency obtained so far for these types of exposure setup. A very short electric pulse (on-time duration of 1 ns) is transferred mostly undistorted to the biological sample guaranteeing controlled experimental exposure conditions. Optimization of the positioning of the small animals was also analyzed. Our setup can be used to study effects of short and intense electric pulses in vivo only poorly addressed so far
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