Dissertações em Neurociências e Biologia Celular (Mestrado) - PPGNBC/ICB

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2375

O Mestrado Acadêmico pertence ao Programa de Pós-Graduação em Neurociências e Biologia Celular (PPGNBC) do Instituto de Ciências Biológicas (ICB) da Universidade Federal do Pará (UFPA).

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Acesso aberto (Open Access)
Entropia conjunta de espaço e reqüência espacial estimada através da discriminação de estímulos espaciais com luminância e cromaticidade moduladas por funções de Gábor: implicações para o processamento paralelo de informação no sistema visual humano
(Universidade Federal do Pará, 2013-12-06) SILVEIRA, Vladímir de Aquino; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
The objective of this study was to estimate the joint entropy of the human visual system in the domains of space and spatial frequency by using psychometric functions. The psychometric functions were obtained from stimulus discrimination that had luminance or chromaticity modulated by Gábor functions. The method consisted in evaluating the entropy in the space domain by testing subject capacity to discriminate stimuli that differed only in their spatial extent and in evaluating the entropy in the spatial frequency domain by testing subject capacity to discriminate stimuli that differed only in their spatial frequency. The joint entropy was then estimated from these two individual entropy values. Three visual conditions were studied: achromatic, chromatic without fine tuning correction of equiluminance, and chromatic with full equiluminance correction by using heterochromatic flickker photometry. Four subjects were tested in all conditions, two additional subjects were tested in the chromatic condition without fine equiluminance adjustment and a seventh subject also performed the acrhomatic test. All subjects were examined by an ophthalmologist, their eyes and visual system were considered normals, and presented no report, symptoms or signs of visual dysfunctions or diseases that could have affected their visual system. The subjects had their normal or corrected visual acuity of 20/30 minimum. The work was approved by the Comissão de Ética em Pesquisa (Núcleo de Medicina Tropical, UFPA) and followed the recomendations of the Helsinki Declaration. The Gábor functions used for luminance or chromaticity modulation comprised unidimensional horizontal sinusoidal gratings, modulated in the vertical direction, with bidimensional Gaussian envelopes whose spatial extent was measured by their standard deviation. Stimuli were generated by using a software written in Pascal in a Delphi 7 Enterprise environment. A Dell Precision 390 Workstation was used together with a CRS VSG ViSaGe stimulus generator to display the stimuli in a CRT monitor, 20”, 800 x 600 pixels, 120 Hz, RGB, Mitsubishi Diamond Pro 2070SB. In the achromatic experiments, the stimuli were generated by white luminance modulation (CIE1931: x = 0.270, y = 0.280; CIE1976: u’ = 0.186, v’ = 0.433), 44,5 cd/m2 mean luminance. In the chromatic experiments, mean luminance was kept in 15 cd/m2, and two series of red-green stimuli were used. In the first series, two chromaticities defined on the M-L axes of the DKL color space were used (CIE1976: green, u’=0.131, v’=0.380; red, u’=0.216, v’=0.371). In the second series, two chromaticities were defined along a red-green horizontal axis across the CIE1976 color space (CIE1976: green, u’=0.150, v’=0.480; red, u’=0.255, v’=0.480). Throughout the experiment, the reference stimuli comprised gratings with three different spatial frequencies (0.4, 2, and 10 cycles per degree) and a Gaussian envelope with 1 degree standard deviation. The test stimuli comprised 19 different spatial frequencies in the region of the reference spatial frequency and 21 different Gaussian envelopes in the region of the reference standard deviation. In the achromatic condition, four levels of Michelson contrast were studied: 2%, 5%, 10% e 100%. In the two chromatic conditions, the highest level of pooled cone contrast allowed by the CRT gamut was used, 17%. The procedure consisted of a two interval forced choice with the following steps: i) 1 s display of the reference stimulus; ii) 1 s replacement of the reference stimulus by a background with the same luminance and chromaticity; iii) 1 s display of the test stimulus which differed from the reference stimulus either in spatial frequency or spatial extent, together with a beep to tell the subject that it was now neccessary to provide a response if the two stimuli were equal or different; iv) replacement of the test stimulus by the background. The spatial extent or spatial frequency of the test stimulus was randomly changed from trial to trial by usind the method of constant stimuli. In a series comprising 300 trials, the spatial frequency was changed while in another series also comprising 300 trials, the spatial extent was changed, each test stimulus in each series being displayed at least 10 times. The subject response in every trial was stored as correct or incorrect for further use to estimate the psychometric function. The experimental data of the psychometric functions for spatial extent and spatial frequency at each contrast level, which corresponded to percent of correct responses, were fitted with Gaussian functions using the Least Square Method. For each contrast level, the spatial extent entropy and spatial frequency entropy were estimated from the standard deviations of these Gaussian functions. The joint entropy was then calculated by multiplying the square root of the spatial extent entropy by the spatial frequency entropy. The joint entropy values were compared with the theoretical minimum predicted for linear systems, 1/4π or 0.0796. For low and intermediate spatial frequencies at high contrasts, the joint entropy reached very low levels, below this minimum, suggesting that there were nonlinear interactions between two or more visual mechanisms. This phenomenon occurred in all conditions (achromatic, chromatic, and chromatic with fine equiluminance adjustment) and was more pronounced for spatial frequency 0.4 cycles / degree. A possible explanation for this phenomenon is the occurrence of nonlinear interactions between the retino-geniculo-striate visual pathways, such as the K, M, and P pathways, in the primary visual area or in higher levels of neural processing of visual information.
Acesso aberto (Open Access)
Potencial cortical provocado visual gerado por estímulos pseudoisocromáticos
(Universidade Federal do Pará, 2016-10-11) SALOMÃO, Railson Cruz; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Visual evoked cortical potentials (VECP) are useful the investigation of color vision mechanisms and color vision dysfunctions. Chromatic sinusoidal gratings are generally used to elicit VECP, but they require long psychophysical measurements to match the perceptual brightness between their stripes. An alternative is to replace them by pseudoisochromatic stimuli which make use of luminance noise to mask brightness clues and force the target perception to be dependent of chromatic contrast. In this work, we compared VECPs generated by sinusoidal and pseudoisochromatic gratings. This research was approved by the Comitê de Ética em Pesquisa, Núcleo de Medicina Tropical, Universidade Federal do Pará, Protocol #570434. Seven normal trichromats were tested with chromatic sinusoidal gratings and illusory gratings provided by the pseudoisochromatic design of 0.33, 0.66, 1, 1.33, 1.66, and 2 cpd, presented in pattern reversal (1 Hz) and pattern onset (300 ms) – offset (700 ms) modes. The signals were recorded using surface electrodes, amplified x30,000, digitized at 1 kHz, and filtered between 0.1-100 Hz. Pattern reversal VECPs elicited by pseudoisochromatic gratings had similar amplitude and latency compared to those elicited by sinusoidal gratings. Onsetoffset VECPs elicited by sinusoidal gratings had larger amplitude and shorter latency than those obtained with pseudoisochromatic stimuli. Different visual mechanisms are responsible for the cortical responses evoked by illusory stimuli when presented in different stimulation modes.
Acesso aberto (Open Access)
Potencial cortical provocado visual pseudoaleatório gerado por estímulos compostos: efeito do modo de apresentação e do tempo de adaptação da resposta
(Universidade Federal do Pará, 2016-09-28) RISUENHO, Bárbara Begot Oliveira; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Conventional pattern-reversal visual evoked cortical potential (VECP) shows positivity for luminance and chromatic equiluminant stimuli while conventional pattern-onset VECP shows positivity for luminance pattern-onset and negativity for chromatic pattern-onset. We evaluated how the presentation mode affects VECPs elicited by luminance and compound (luminance plus chromatic) pseudo-random stimulation. Eleven normal trichromats and 17 red-green color-blinds were studied. Pattern-reversal and pattern-onset luminance and compound (luminance plus red-green) gratings were temporally modulated by m-sequence. We used a cross-correlation routine to extract the first order kernel (K1) and the first and second slices of the second order kernel (K2.1 and K2.2, respectively) from the VECP response. We integrated the amplitude of VECP components as a function of time in order to estimate its magnitude for each stimulus condition. We also used a normalized cross-correlation method in order to test the similarity of the VECP components. In order to assess how the interection time afects the VECP’s amplitude we calculate de root mean square (RMS) amplitude into differents time windows and correlated it with the response time interval relative to the sencond order kernel slice avaliated. The VECP components varied with the presentation mode and the presence of red-green contrast in the stimuli. In trichromats, for compound conditions, pattern-onset K1, K2.1, and K2.2, and pattern-reversal K2.1 and K2.2 had negative-dominated waveforms at 100 ms. Small negativity or small positivity were observed in dichromats. Trichromats had larger VECP magnitude than color-blinds for compound pattern-onset K1 (with large variability across subjects), compound pattern-onset and pattern-reversal K2.1, and compound pattern-reversal K2.2. Trichromats and color-blinds had similar VECP amplitude for compound pattern-reversal K1 and compound pattern-onset K2.2, as well as for all luminance conditions. The cross-correlation analysis showed high similarity between waveforms of compound pattern-onset K2.1 and pattern-reversal K2.2 as well as pattern-reversal K2.1 and K2.2. The amplitude of VECP was smaller as higher was the response time interval. We suggest that compound pattern-reversal K2.1 is an appropriate response to study red-green color-opponent activity.
Acesso aberto (Open Access)
Seletividade espacial de cor do potencial cortical provocado visual pseudoaleatório
(Universidade Federal do Pará, 2014-04-23) MARTINS, Isabelle Christine Vieira da Silva; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Spatial selectivity to color stimulation has been investigated using invasive and non-invasive electrophysiological methods, and psychophysical methods. In non-invasive visual cortical electrophysiology, this issue was investigated using conventional methods of periodical stimulation; and averaging methods to extract responses. New methods of stimulation (pseudo-random presentation) and of signal extraction (cross-correlation) were developed and still lack their application to investigate the spatial selectivity of the cortical chromatic responses. The present study aimed to apply the new pseudo-random presentation electrophysiology method for study spatial selectivity of the color visual. Fourteen trichromats and 16 color-blind subjects were included in the sample. All the volunteers had normal or corrected visual acuity. They were evaluated by anomaloscopy HMC and Ishihara Plates test to be qualified the color vision in normal trichromacy or not. Sinusoidal gratings, 8º of visual angle, red-green contrast for 8 spatial frequencies among 0.2 a 10 cpd. The stimuli were temporally modulated by a binary m-sequence to simulate pattern reversal mode presentation. Veris system was used to extract the second order kernel, first and second slices (K2.1 e K2.2, respectively). After modeling of spatial frequencies response data with functions of difference of Gaussians, it was extracted the optimal spatial frequency and the bandwidth of spatial frequencies with amplitudes above of ¾ of the maximum amplitude of the spatial frequency-response function. Chromatic visual acuity also was estimated by the fit of a linear model to the amplitude data since from the optimal spatial frequency until the highest tested spatial frequency. In trichromats, the chromatic responses were found in the K2.1 and K2.2, whose showed different spatial selectivity. The negative components in the K2.1 and K2.2 showed band-pass tuning, and the positive component in the K2.1 showed low-pass tuning. The estimated chromatic visual acuity of the kernel components were comparable to those estimated by previous psychophysical studies. Different cellular components might contribute to the pseudo-random VECP generation. This new method is a potential candidate to an important tool for non-invasive evaluation of the human color vision.
Acesso aberto (Open Access)
O tratamento com glutationa potencializa o dano hepático em camundongos infectados com Plasmodium berghei (ANKA)
(Universidade Federal do Pará, 2016-05-10) KAUFFMANN, Nayara; OLIVEIRA, Karen Renata Herculano Matos; http://lattes.cnpq.br/3032008039259369
Malaria is a disease caused by protozoa of the genus Plasmodium and presents itself as a major public health problems in the world. To evaluate the malaria frame, murine models have been used for its similarities between species infective for mice and species infective to man. The increased production of reactive oxygen species and changes in the activity of enzymes such as glutathione peroxidase and superoxide dismutase have been characterized within the clinical picture of the disease, but little is known about the participation of antioxidant molecules such as glutathione in the evolution of the disease. Given the above, the main objective of this study is to evaluate the effect of glutathione in the evolution of murine malaria frame and front to damage caused by infection with Plasmodium berghei ANKA strain (PbA). To this were Balb-C mice, which were inoculated (~106 parasitized erythrocytes) intraperitoneally. The groups were divided into malaria group (PbA), PbA group + GSH 1 mg, PbA group + GSH 3 mg and PbA group + GSH 8 mg treated for 7 days consecutive. The development of the disease was monitored daily by determining the survival, body mass and parasitaemia was monitored every three days in blood strains, was also analyzed the histological sections of liver tissue was performed and the biochemical analysis of liver transaminases. Our data demonstrated that treatment with GSH (8mg/kg) accelerated mortality of infected animals once between days 13-14 after infection about 43% of the animals progressed to death. In the group infected with PbA that received no treatment with GSH, a similar reduction (40%) was observed only from 23-25 days post infection. In relation to PbA + GSH 1mg groups and GSH + PbA 3 mg, there was no difference when compared to the PbA group. Interestingly, although treatment with GSH 8mg has accelerated mortality in the infected group, no significant difference in parasitaemia level of the four groups analyzed. In relation to body mass was observed a difference between day 0 and 24 in all groups, but when analyzed between groups. In what concerns the histological and biochemical tests, we noted that listen both changes in histology and in transaminase, with the latter being expressed in PbA changes group was treated with glutathione 8mg / kg group than in PbA. Concluding that glutathione when administered intraperitoneally accelerates the mortality of mice infected with the ANKA strain, but this mortality is not associated with increased parasitemia, then indicating that mortality may result from liver changes.

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