Programa de Pós-Graduação em Neurociências e Biologia Celular - PPGNBC/ICB
URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2374
O Programa de Pós-Graduação em Neurociências e Biologia Celular (PPGNBC) é parte integrante do Instituto de Ciências Biológicas (ICB) da Universidade Federal do Pará (UFPA), sendo constituído por: Mestrado e Doutorado em Neurociências e Biologia Celular, com área de concentração em Neurociências ou Biologia Celular.
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Item Acesso aberto (Open Access) Estudos de mecanismos cromáticos e acromáticos para o potencial cortical provocado visual (VECP) e multifocal (mfVEP)(Universidade Federal do Pará, 2017-10-06) ARAÚJO, Carolina dos Santos; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718Visual evoked potentials (VECPs) and multifocal visual evoked potentials (mfVEPs) are being widely used to investigate cortical information processing in response to stimuli at different sites of the visual field and present the potential for complement information to conventional VEPs on chromatic and achromatic mechanisms of human vision. The objective of this work was to investigate the contribution of chromatic and achromatic mechanisms to VECP and mfVEP from two experiments: in the first, 9 healthy trichromates subjects with normal or corrected to 20/20 visual acuity were submitted to a visual stimulation of 8º of size, formed by achromatic sinusoidal gratings in 7 spatial frequencies (from 0.4 to 10 cpd) and in six contrast levels (from 3.12% to 99%); in the second, a multifocal dartboard with 60 sectors covering 40° of visual angle was shown for 14 healthy subjects (12 trichromates, 1 protan and 1 deutan discromatopsic type) in 7 different ratios of red-green luminance (R/R+G) and in one achromatic condition (99%). The two stimuli were presented as a reverse pattern, temporally controlled by m-sequences. The first slice (K2.1) and the second slice (K2.2) of the second order kernel were extracted. In experiment 1, were analyzed the main components of the waveforms recorded and in experiment 2 the signal-to-noise ratio (SNR) of the waveforms was analyzed to classify them as reliable (SNR> 1.35) or unreliable (SNR <1.35) and the number of reliable waveforms in 6 different rings with the same visual eccentricity (R1 being the central ring and R6 the most peripheral ring) was quantified. The results of experiment 1 indicated that responses in K2.1 were dominated by M pathway, and responses in K2.2 reflected the contribution of P pathway. The results of experiment 2 were similar for K2.1 and K2.2. In the R1-R4 rings, all red-green luminance ratios showed a similar number of reliable waveforms. In the R5-R6 rings, there are more reliable waveforms in the red-green luminance ratios with high luminance contrast, while the equiluminant condition has the fewest reliable responses. Protan and deutan subjects showed inverted results: stimulus conditions with green brighter than red generated more reliable waveforms in the protan subject (0.2-0.4), while the opposite combination generated more reliable waveforms in the deutan subject. The two second-order kernel slices are useful for studying the chromatic and achromatic mfVEP mechanisms. The results in R1-R4 indicated a similar contribution of chromatic and achromatic mechanisms for mfVEP, while R5-R6 show the most pronounced contribution of the achromatic mechanism to mfVEP. The method used allowed to identificate specific characteristics of protan and deutan discromatopsic type from obtained data. discromatopsic type from obtained data.Item Acesso aberto (Open Access) Influência de parâmetros espaciais sobre potenciais corticais provocados visuais gerados por estimulação pseudoaleatória(Universidade Federal do Pará, 2013-03-08) ARAÚJO, Carolina dos Santos; GOMES, Bruno Duarte; http://lattes.cnpq.br/4932238030330851; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718The contributions of contrast detection mechanisms to the visual cortical evoked potential (VECP) have been investigated studying the contrast-response and spatial frequency-response functions. Previously, the use of m-sequences for stimulus control has been almost restricted to multifocal electrophysiology stimulation and, in some aspects, it substantially differs from conventional VECP. Single stimulation with spatial contrast temporally controlled by msequences was not extensively tested or compared to multifocal techniques. Our purpose was to evaluate the influence of spatial frequency and contrast of sinusoidal gratings on the VECP elicited by pseudo-random stimulation. Nine normal subjects were stimulated by achromatic sinusoidal gratings driven by a pseudo-random binary m-sequence at seven spatial frequencies (0.4-10 cpd) and three stimulus sizes (4º, 8º, and 16º of visual angle). At 8º of visual angle, it was also used six contrasts levels (3.12-99%). First order kernel had not provided a consistent measurable signal across spatial frequencies and contrasts that were tested – signal was very small or absent – while the second order kernel first and second slices exhibited reliable responses for the stimulus range. The main differences between results obtained with the first and second slices of the second order kernel were the shape of the amplitude versus contrast and amplitude versus spatial frequency functions. The results indicated that the second order kernel first slice was dominated by M pathway, but for some stimulus condition some P pathway contribution could be found, while the second order kernel second slice reflected the P pathway contribution. The present work extended previous findings of the visual pathways contribution to VECP elicited by pseudo-random stimulation for a wider range of spatial frequencies.