Fernando Martins Pereira Da Silva fmsilva | Universidade Federal do Rio Grande do Sul (original) (raw)

Papers by Fernando Martins Pereira Da Silva fmsilva

Physical Review E Statistical Nonlinear and Soft Matter Physics, Nov 1, 2008

It has been shown that the analysis of electroencephalographic (EEG) signals submitted to an appr... more It has been shown that the analysis of electroencephalographic (EEG) signals submitted to an appropriate external stimulation (active paradigm) is efficient with respect to anticipating epileptic seizures [S. Kalitzin , Clin. Neurophysiol. 116, 718 (2005)]. To better understand how an active paradigm is able to detect properties of EEG signals by means of which proictal states can be identified, we performed a simulation study using a computational model of seizure generation of a hippocampal network. Applying the active stimulation methodology, we investigated (i) how changes in model parameters that lead to a transition from the normal ongoing EEG to an ictal pattern are reflected in the properties of the simulated EEG output signals and (ii) how the evolution of neuronal excitability towards seizures can be reconstructed from EEG data using an active paradigm, rather than passively, using only ongoing EEG signals. The simulations indicate that a stimulation paradigm combined with appropriate analytical tools, as proposed here, may yield information about the change in excitability that precedes the transition to a seizure. Such information is apparently not fully reflected in the ongoing EEG activity. These findings give strong support to the development and application of active paradigms with the aim of predicting the occurrence of a transition to an epileptic seizure.

European Journal of Pharmacology, Dec 18, 1998

The involvement of the protein kinase C substrate, B-50 (GAP-43), in the release of glutamate fro... more The involvement of the protein kinase C substrate, B-50 (GAP-43), in the release of glutamate from small clear-cored vesicles in streptolysin-O-permeated synaptosomes was studied by using anti-B-50 antibodies. Glutamate release was induced from endogenous as well as 3H-labelled pools in a [Ca(2+)]-dependent manner. This Ca(2+)-induced release was partially ATP dependent and blocked by the light-chain fragment of tetanus toxin, demonstrating its vesicular nature. Comparison of the effects of anti-B-50 antibodies on glutamate and noradrenaline release from permeated synaptosomes revealed two major differences. Firstly, Ca(2+)-induced glutamate release was decreased only partially by anti-B-50 antibodies, whereas Ca(2+)-induced noradrenaline release was inhibited almost completely. Secondly, anti-B-50 antibodies significantly reduced basal glutamate release, but did not affect basal noradrenaline release. In view of the differences in exocytotic mechanisms of small clear-cored vesicles and large dense-cored vesicles, these data indicate that B-50 is important in the regulation of exocytosis of both types of neurotransmitters, probably at stages of vesicle recycling and/or vesicle recruitment, rather than in the Ca(2+)-induced fusion step.

Eur Spine J, 2005

ABSTRACT BACKGROUND: After Pokemon viewing triggered an epidemic of seizures in Japan, many effor... more ABSTRACT BACKGROUND: After Pokemon viewing triggered an epidemic of seizures in Japan, many efforts have been made to design safety guidelines and systems to protect subjects with photosensitivity. The authors developed a new method based upon nonlinear diffusion techniques capable of filtering the epileptogenic content of a video sequence related to color without altering its spatial and luminance content. METHODS: The authors showed to 25 photosensitive patients (18 women, mean age: 22 years) the original Pokemon sequence and a modified one in an ABBA protocol using two television (TV) sets (100 and 50 Hz). RESULTS: Twenty-three patients had a photoparoxysmal response (PPR) according to Waltz classification with at least one of the scenes. The modified sequence triggered fewer and less severe PPRs than the original version in both TVs (p < 0.001). Original sequences elicited generalized PPRs in 56.5% of the trials for the 50 Hz TV and in 41.3% for the 100 Hz TV, whereas modified sequences elicited these responses in only 8.7% (50 Hz) and 4.3% (100 Hz TV) of the trials (p < 0.001). Sensitivity to the modified version on the 50 Hz TV correlated with pattern sensitivity (p < 0.05). CONCLUSION: Specific manipulations of the color modulation-depth could be enough to decrease dramatically the risk of triggering seizures in susceptible subjects exposed to provocative visual scenes. This new method can be implemented in protective devices able to filter out the epileptogenic video sequences in which color plays a fundamental role while leaving intact the spatial content, frequency, and average luminance

... Marques da Silva F: (2004) Natural Ventilation Air Change Rates Considering Atmospheric Turb... more ... Marques da Silva F: (2004) Natural Ventilation Air Change Rates Considering Atmospheric Turbulence. ... Orme M, Liddament M and Wilson A: (1998) Numerical Data for Air Infiltration and Natural ... Saraiva J, Dias J and Borges AJ: (1985), Um programa de cálculo automático de ...

Neuroimage, 2008

Considering that there are several theoretical reasons why fMRI data is correlated to variations ... more Considering that there are several theoretical reasons why fMRI data is correlated to variations in heart rate, these correlations are explored using experimental resting state data. In particular, the possibility is discussed that the “default network”, being a brain area that deactivates during non-specific general tasks, is a hemodynamic effect caused by heart rate variations.Of fifteen healthy controls ECG, EEG and fMRI were co-registered. Slice time dependent heart rate regressors were derived from the ECG data and correlated to fMRI using a linear correlation analysis where the impulse response is estimated from the data.It was found that in most subjects substantial correlations between heart rate variations and fMRI exist, both within the brain and at the ventricles. The brain areas with high correlation to heart rate are different from the “default network” and the response functions deviate from the canonical hemodynamic response function. Furthermore, a general negative correlation was found between heart beat intervals (reverse of heart rate) and alpha power. We interpret this finding by assuming that subject's state varies between drowsiness and wakefulness. Finally, given this large correlation, we re-examined the contribution of heart rate variations to earlier reported fMRI/alpha band correlations, by adding heart rate regressors as confounders. It was found that inclusion of these confounders most often had a negligible effect.From its strong correlation to alpha power, we conclude that the heart rate variations contain important physiological information about subject's resting state. However, it does not provide a full explanation of the behaviour of the “default network”. Its application as confounder in fMRI experiments is a relatively small computational effort, but may have a substantial impact in paradigms where heart rate is controlled by the stimulus.

Mol Brain Res, 1995

To investigate the molecular changes underlying kindling epileptogenesis in the rat hippocampus, ... more To investigate the molecular changes underlying kindling epileptogenesis in the rat hippocampus, the expression levels of the genes encoding for 13 different γ-aminobutyric acid type-A receptor (GABAAR) subunits were measured in hippocampal principal neurons using in situ hybridization techniques and semi-quantitative analysis of the autoradiograms. Schaffer collateral-commissural pathway kindled rats were investigated at three different stages of kindling acquisition, at 24 h after the last seizure and at long-term (28 days) after termination of kindling stimulations. Changes were distinct for the different subunits in the three analyzed regions (CA1, CA3, fascia dentata) and also different for the various kindling stages. In all hippocampal areas at the early phases of kindling epileptogenesis, before the appearance of generalized seizures, an increase was found of those transcripts that constituted the majority of the expressed variants in control animals (α1, α2, α4, β1, β2, β3, mRNA). In these stages, the increased levels of different variants in the granular neurons of the fascia dentata were more pronounced when compared to the pattern of changes in pyramidal cells of CA1 and CA3. In fully kindled animals, the expression levels of several subunits returned to control levels, whereas β3 and mRNA expression was still significantly enhanced in all areas. At long-term, few changes were encountered. The long-splice variant of γ2 was decreased within pyramidal and granular neurons while the total level of γ2 mRNA was not different from controls. The increased GABAAR subunit expression in the fascia dentata may underly the reported increased GABAAR ligand binding and the increased GABA mediated inhibition. However, the decreased GABAAR binding and the attenuation of GABAergic inhibition in CA1, could not be explained by a decrement of receptor subunit expression.

Cadernos De Agroecologia, Nov 15, 2011

Neuroscience letters, Jan 6, 1992

Monosynaptic evoked field potentials (EPs) in response to paired-pulse stimulation (20 ms interva... more Monosynaptic evoked field potentials (EPs) in response to paired-pulse stimulation (20 ms interval) were recorded in area CA1 and fascia dentata of the same animal in the course of development of a kindled focus in the CA1 region. A significant reduction of paired pulse depression in response to medium and high stimulation intensity was found in CA1. A similar change was found in the fascia dentata in response to medium intensity stimulation of the angular bundle. In contrast, at high intensity, paired pulse depression was enhanced in the fascia dentata in the course of kindling. These results indicate that kindling epileptogenesis is accompanied by regionally different changes in recurrent inhibition: a reduction in CA1 and intensity dependent changes in fascia dentata.

Proceedings 13th Brazilian Symposium on Computer Graphics and Image Processing (Cat. No.PR00878), 2000

A Control Theory Approach for Real-time Animation of Artificial Agents * Fernando Wagner da Silva... more A Control Theory Approach for Real-time Animation of Artificial Agents * Fernando Wagner da Silva',Luiz M. Garcia2, Ricardo С. Farias3, Antonio AF Oliveira1, 1 Universidade Federal do Rio de Janeiro (LCG/UFRJ) CP 68511, 21945-970, Rio de Janeiro, RJ, Brasil ...

Proceedings Computer Animation 2000, 2000

... neous path by using a standard planning technique that solves a harmonic function 2]. Once th... more ... neous path by using a standard planning technique that solves a harmonic function 2]. Once the instantaneous displacements are computed in C-space coordinates, the ... They have used the same architecture described above to sim-ulate/perform their animated behaviors. ...

IECON Proceedings (Industrial Electronics Conference), 2009

Page 1. Single Stage Inverter for PV Applications with One Cycle Sampling Technique in the MPPT A... more Page 1. Single Stage Inverter for PV Applications with One Cycle Sampling Technique in the MPPT Algorithm Hugo Ribeiro1,3, Fernando Silva2, Sónia Pinto2, Beatriz Borges1 1Instituto de Telecomunicações, Instituto Superior Técnico, 1049-001 Lisboa, Portugal ...

2010 IEEE Energy Conversion Congress and Exposition, ECCE 2010 - Proceedings, 2010

Abstract - This paper presents a bridgeless single-stage, single phase circuit topology consistin... more Abstract - This paper presents a bridgeless single-stage, single phase circuit topology consisting in the association of a full-bridge isolated DC-DC converter with only one input inductor connected to the grid and two rectifier diodes, to provide sinusoidal input current wave shaping. The ...

EUROCON 2011 - International Conference on Computer as a Tool - Joint with Conftele 2011, 2011

Page 1. Digital LQR Control with Kalman Estimator for DC-DC Buck Converter Carlos O. Moreira IST ... more Page 1. Digital LQR Control with Kalman Estimator for DC-DC Buck Converter Carlos O. Moreira IST / INESC-ID Lisbon, Portugal cmoreira@ieee.org Fernando A. Silva IST / Cie3 Lisbon, Portugal fernando.alves@ist.utl.pt Sónia ...

Lecture Notes in Business Information Processing, 2009

Revista Brasileira de Sementes, 2012

Physiological Measurement, 2000

NeuroReport, 1995

The editing status of mRNA at the Q/R site of the AMPA/kainate type glutamate receptor (GluR) sub... more The editing status of mRNA at the Q/R site of the AMPA/kainate type glutamate receptor (GluR) subunits A, B, 5 and 6 modulates the ion selectivity of glutamate receptor operated ion channels. We hypothesized that a long-lasting dysfunction of this editing process after an ischeamic insult may be involved in the process of delayed neuronal cell death. In order to test this hypothesis, the editing status of the GluRs was determined in the hippocampus of rats up to 24 h after 10 min of global ischaemia. No statistical significant differences were found in the hippocampus of animals after ischaemia compared with controls. It is concluded that delayed neuronal cell death is not mediated by a less selective or less efficient mRNA editing process of the different glutamate receptor subunits in the hippocampus.