Desenvolvimento pós-natal do EEG em cães normais: avaliação visual qualitativa e quantitativa até 45 dias de vida

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Investigação do potencial cortical provocado visual para padrão reverso em pacientes diagnosticados com epilepsia parcial e generalizada

Este trabalho avaliou o potencial cortical provocado visual de crianças com história de epilepsia com o objetivo de identificar marcadores eletrofisiológicos que indicassem alterações corticais em epilepsia. Foram estudados 34 sujeitos com história de epilepsia (18 sujeitos com epilepsia parcial e 16 com epilepsia generalizada). O grupo controle foi composto por 19 sujeitos sem história de crises epilépticas com faixa etária semelhante aos pacientes. Os componentes do potencial cortical provocado visual transiente para apresentação por padrão reverso de tabuleiros de xadrez foram avaliados quanto à amplitude, tempo implícito e razões de amplitude entre os componentes. Foi observado que os pacientes com epilepsia generalizada apresentaram componente N75 com amplitude maior que os demais grupos, enquanto as razões de amplitude N75/P100 e P100/N135foram menores em pacientes com epilepsia parcial que em outros grupos. Houve fraca correlação linear entre os parâmetros do potencial cortical provocado visual e a idade de início das crises epilépticas ou tempo de utilização das medicações antiepilépticas. Conclui-se que o componente N75 e as razões de amplitude N75/P100 e P100/N135 podem ser bons indicadores eletrofisiológicos para alterações funcionais corticais em epilepsia.

Seletividade espacial de cor do potencial cortical provocado visual pseudoaleatório

A seletividade espacial para cor tem sido investigada usando métodos eletrofisiológicos invasivos e não invasivos, e métodos psicofísicos. Em eletrofisiologia cortical visual não invasiva este tópico foi investigado usando métodos convencionais de estimulação periódica e extração de respostas por promediação simples. Novos métodos de estimulação (apresentação pseudo-aleatória) e extração de respostas corticais não invasivas (correlação cruzada) foram desenvolvidos e ainda não foram usados para investigar a seletividade espacial de cor de respostas corticais. Este trabalho objetivou introduzir esse novo método de eletrofisiologia pseudoaleatória para estudar a seletividade espacial de cor. Foram avaliados 14 tricromatas e 16 discromatópsicos com acuidade visual normal ou corrigida. Os voluntários foram avaliados pelo anomaloscópio HMC e teste de figuras de Ishihara para caracterizar a visão de cores quanto à presença de tricromacia. Foram usadas redes senoidais, 8º de ângulo visual, vermelho-verde para 8 frequências espaciais entre 0,2 a 10 cpg. O estímulo foi temporalmente modulado por uma sequência-m binária em um modo de apresentação de padrão reverso. O sistema VERIS foi usado para extrair o primeiro e o segundo slice do kernel de segunda ordem (K2.1 e K2.2, respectivamente). Após a modelagem da resposta às frequências espaciais com função de diferença de gaussianas, extraiu-se a frequência espacial ótima e banda de frequências com amplitudes acima de ¾ da amplitude máxima da função para servirem como indicadores da seletividade espacial da função. Também foi estimada a acuidade visual cromática pelo ajuste de uma função linear aos dados de amplitude a partir da frequência espacial do pico de amplitude até a mais alta frequência espacial testada. Em tricromatas, foi encontrada respostas cromáticas no K2.1 e no K2.2 que apresentaram seletividade espacial diferentes. Os componentes negativos do K2.1 e do K2.2 apresentaram sintonia passa-banda e o componente positivo do K2.1 apresentou sintonia passa-baixa. A acuidade visual estimada de todos os componentes estudados foi próxima àquelas encontradas por Mullen (1985) e Kelly (1983). Diferentes componentes celulares podem estar contribuindo para a geração do VECP pseudoaleatório. Este novo método se candidata a ser uma importante ferramenta para a avaliação não invasiva da visão de cores em humanos.

Chromatic spatial contrast sensitivity estimated by visual evoked cortical potential and psychophysics

The purpose of the present study was to measure contrast sensitivity to equiluminant gratings using steady-state visual evoked cortical potential (ssVECP) and psychophysics. Six healthy volunteers were evaluated with ssVECPs and psychophysics. The visual stimuli were red-green or blue-yellow horizontal sinusoidal gratings, 5^° × 5^°, 34.3 cd/m2 mean luminance, presented at 6 Hz. Eight spatial frequencies from 0.2 to 8 cpd were used, each presented at 8 contrast levels. Contrast threshold was obtained by extrapolating second harmonic amplitude values to zero. Psychophysical contrast thresholds were measured using stimuli at 6 Hz and static presentation. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. ssVECP and both psychophysical contrast sensitivity functions (CSFs) were low-pass functions for red-green gratings. For electrophysiology, the highest contrast sensitivity values were found at 0.4 cpd (1.95 ± 0.15). ssVECP CSF was similar to dynamic psychophysical CSF, while static CSF had higher values ranging from 0.4 to 6 cpd (P < 0.05, ANOVA). Blue-yellow chromatic functions showed no specific tuning shape; however, at high spatial frequencies the evoked potentials showed higher contrast sensitivity than the psychophysical methods (P < 0.05, ANOVA). Evoked potentials can be used reliably to evaluate chromatic red-green CSFs in agreement with psychophysical thresholds, mainly if the same temporal properties are applied to the stimulus. For blue-yellow CSF, correlation between electrophysiology and psychophysics was poor at high spatial frequency, possibly due to a greater effect of chromatic aberration on this kind of stimulus.

Poesia visual e poética postal

Ce travail cherche montrer quelques caractéristiques de la Poésie Visuel, expresion artistique qui melange le langage verbal et le langage visuel à tel point qu´on ne peut pas afirmer une classification appuyée sur les genres traditionnels. Aprés une curte presentation des chemins et des points polémiques de cette esthétique, on analyse comme exemple deux compositions sorties de le grand réseau de communication de l´Art Postal qui est né les années soixante et survit aujourd´hui avec intensité. L´Art Postal a une structure fondé sur la simultanéité de l´information que ressamble à la forme de la poésie visuel. Cettes compositions contemporaines sont confrontées à la tradition du poème visuel qui commence peut-être à l´époque des premiers écrits de hiéroglyphe. Elles sont analysées, donc, dans son originalité. A partir des analyses realisées dans le but de révéler les significations, on arrive à la question proposé par Wilcon Joia Pereira : la nécessité de se comprendre d´une façon nouvelle les expériences esthétiques oú les mots deviennent des images

Mercury toxicity in Amazon gold miners: Visual dysfunction assessed by retinal and cortical electrophysiology

Amazonian gold mining activity results in human exposure to mercury vapor. We evaluated the visual system of two Amazonian gold miners (29 and 37 years old) by recording the transient pattern electroretinogram (tPERG) and transient pattern visual evoked potential (tPVEP). We compared these results with those obtained from a regional group of control subjects. For both tPERG and tPVEP, checkerboards with 0.5 or 2 cycles per degree (cpd) of spatial frequency were presented in a 16 degrees squared area, 100% Michelson contrast, 50cd/m(2) mean luminance, and 1 Hz square-wave pattern-reversal presentation. Two averaged waveforms (n = 240 sweeps, Is each) were monocularly obtained for each subject in each condition. Both eyes were monocularly tested only in gold miners. Normative data were calculated using a final pooled waveforin with 480 sweeps. The first gold miner, LCS, had normal tPERG responses. The second one, RNP, showed low tPERG (P50 component) amplitudes at 0.5cpd for both eyes, outside the normative data, and absence of response at 2 cpd for his right eye. Delayed tPVEP responses (P 100 component) were found at 2 cpd for LCS but the implicit times were inside the normative data. Subject RNP also showed delayed tPVEP responses (all components), but only the implicit time obtained with his right eye was outside the normative data at 2cpd. We conclude that mercury exposure levels found in the Amazon gold miners is high enough to damage the visual system and can be assessed by non-invasive electrophysiological techniques. (C) 2007 Elsevier Inc. All rights reserved.

Visual scanning in sports actions: comparison between soccer goalkeepers and judo fighters

Visual search and oculomotor behaviour are believed to be very relevant for athlete performance, especially for sports requiring refined visuo-motor coordination skills. Modern coaches believe that a correct visuo-motor strategy may be part of advanced training programs. In this thesis two experiments are reported in which gaze behaviour of expert and novice athletes were investigated while they were doing a real sport specific task. The experiments concern two different sports: judo and soccer. In each experiment, number of fixations, fixation locations and mean fixation duration (ms) were considered. An observational analysis was done at the end of the paper to see perceptual differences between near and far space. Purpose: The aim of the judo study was to delineate differences in gaze behaviour characteristics between a population of athletes and one of non athletes. Aspects specifically investigated were: search rate, search order and viewing time across different conditions in a real-world task. The second study was aimed at identifying gaze behaviour in varsity soccer goalkeepers while facing a penalty kick executed with instep and inside foot. Then an attempt has been done to compare the gaze strategies of expert judoka and soccer goalkeepers in order to delineate possible differences related to the different conditions of reacting to events occurring in near (peripersonal) or far (extrapersonal) space. Judo Methods: A sample of 9 judoka (black belt) and 11 near judoka (white belt) were studied. Eye movements were recorded at 500Hz using a video based eye tracker (EyeLink II). Each subject participated in 40 sessions for about 40 minutes. Gaze behaviour was considered as average number of locations fixated per trial, the average number of fixations per trial, and mean fixation duration. Soccer Methods: Seven (n = 7) intermediate level male volunteered for the experiment. The kickers and goalkeepers, had at least varsity level soccer experience. The vision-in-action (VIA) system (Vickers 1996; Vickers 2007) was used to collect the coupled gaze and motor behaviours of the goalkeepers. This system integrated input from a mobile eye tracking system (Applied Sciences Laboratories) with an external video of the goalkeeper’s saving actions. The goalkeepers took 30 penalty kicks on a synthetic pitch in accordance with FIFA (2008) laws. Judo Results: Results indicate that experts group differed significantly from near expert for fixations duration, and number of fixations per trial. The expert judokas used a less exhaustive search strategy involving fewer fixations of longer duration than their novice counterparts and focused on central regions of the body. The results showed that in defence and attack situation expert group did a greater number of transitions with respect to their novice counterpart. Soccer Results: We found significant main effect for the number of locations fixated across outcome (goal/save) but not for foot contact (instep/inside). Participants spent more time fixating the areas in instep than inside kick and in goal than in save situation. Mean and standard error in search strategy as a result of foot contact and outcome indicate that the most gaze behaviour start and finish on ball interest areas. Conclusions: Expert goalkeepers tend to spend more time in inside-save than instep-save penalty, differences that was opposite in scored penalty kick. Judo results show that differences in visual behaviour related to the level of expertise appear mainly when the test presentation is continuous, last for a relatively long period of time and present a high level of uncertainty with regard to the chronology and the nature of events. Expert judoist performers “anchor” the fovea on central regions of the scene (lapel and face) while using peripheral vision to monitor opponents’ limb movements. The differences between judo and soccer gaze strategies are discussed on the light of physiological and neuropsychological differences between near and far space perception.

Callosal connections of primary visual cortex predict the spatial spreading of binocular rivalry across the visual hemifields

In binocular rivalry, presentation of different images to the separate eyes leads to conscious perception alternating between the two possible interpretations every few seconds. During perceptual transitions, a stimulus emerging into dominance can spread in a wave-like manner across the visual field. These traveling waves of rivalry dominance have been successfully related to the cortical magnification properties and functional activity of early visual areas, including the primary visual cortex (V1). Curiously however, these traveling waves undergo a delay when passing from one hemifield to another. In the current study, we used diffusion tensor imaging (DTI) to investigate whether the strength of interhemispheric connections between the left and right visual cortex might be related to the delay of traveling waves across hemifields. We measured the delay in traveling wave times (ΔTWT) in 19 participants and repeated this test 6 weeks later to evaluate the reliability of our behavioral measures. We found large interindividual variability but also good test-retest reliability for individual measures of ΔTWT. Using DTI in connection with fiber tractography, we identified parts of the corpus callosum connecting functionally defined visual areas V1-V3. We found that individual differences in ΔTWT was reliably predicted by the diffusion properties of transcallosal fibers connecting left and right V1, but observed no such effect for neighboring transcallosal visual fibers connecting V2 and V3. Our results demonstrate that the anatomical characteristics of topographically specific transcallosal connections predict the individual delay of interhemispheric traveling waves, providing further evidence that V1 is an important site for neural processes underlying binocular rivalry.

Atypical findings in delayed presentation of unilateral acute idiopathic maculopathy

Unilateral acute idiopathic maculopathy is a rare disease affecting young healthy patients resulting in moderate to severe unilateral visual loss preceded by prodromal flu-like illness. We present a case of delayed presentation of unilateral acute idiopathic maculopathy associated with hand, foot and mouth disease.

An unusual stroke-like clinical presentation of Creutzfeldt-Jakob disease: acute vestibular syndrome

INTRODUCTION Vertigo and dizziness are common neurological symptoms in general practice. Most patients have benign peripheral vestibular disorders, but some have dangerous central causes. Recent research has shown that bedside oculomotor examinations accurately discriminate central from peripheral lesions in those with new, acute, continuous vertigo/dizziness with nausea/vomiting, gait unsteadiness, and nystagmus, known as the acute vestibular syndrome. CASE REPORT A 56-year-old man presented to the emergency department with acute vestibular syndrome for 1 week. The patient had no focal neurological symptoms or signs. The presence of direction-fixed, horizontal nystagmus suppressed by visual fixation without vertical ocular misalignment (skew deviation) was consistent with an acute peripheral vestibulopathy, but bilaterally normal vestibuloocular reflexes, confirmed by quantitative horizontal head impulse testing, strongly indicated a central localization. Because of a long delay in care, the patient left the emergency department without treatment. He returned 1 week later with progressive gait disturbance, limb ataxia, myoclonus, and new cognitive deficits. His subsequent course included a rapid neurological decline culminating in home hospice placement and death within 1 month. Magnetic resonance imaging revealed restricted diffusion involving the basal ganglia and cerebral cortex. Spinal fluid 14-3-3 protein was elevated. The rapidly progressive clinical course with dementia, ataxia, and myoclonus plus corroborative neuroimaging and spinal fluid findings confirmed a clinicoradiographic diagnosis of Creutzfeldt-Jacob disease. CONCLUSIONS To our knowledge, this is the first report of an initial presentation of Creutzfeldt-Jacob disease closely mimicking vestibular neuritis, expanding the known clinical spectrum of prion disease presentations. Despite the initial absence of neurological signs, the central lesion location was differentiated from a benign peripheral vestibulopathy at the first visit using simple bedside vestibular tests. Familiarity with these tests could help providers prevent initial misdiagnosis of important central disorders in patients presenting vertigo or dizziness.

Dynamic population coding in primary visual cortex

More than a century ago Ramon y Cajal pioneered the description of neural circuits. Currently, new techniques are being developed to streamline the characterization of entire neural circuits. Even if this 'connectome' approach is successful, it will represent only a static description of neural circuits. Thus, a fundamental question in neuroscience is to understand how information is dynamically represented by neural populations. In this thesis, I studied two main aspects of dynamical population codes. ^ First, I studied how the exposure or adaptation, for a fraction of a second to oriented gratings dynamically changes the population response of primary visual cortex neurons. The effects of adaptation to oriented gratings have been extensively explored in psychophysical and electrophysiological experiments. However, whether rapid adaptation might induce a change in the primary visual cortex's functional connectivity to dynamically impact the population coding accuracy is currently unknown. To address this issue, we performed multi-electrode recordings in primary visual cortex, where adaptation has been previously shown to induce changes in the selectivity and response amplitude of individual neurons. We found that adaptation improves the population coding accuracy. The improvement was more prominent for iso- and orthogonal orientation adaptation, consistent with previously reported psychophysical experiments. We propose that selective decorrelation is a metabolically inexpensive mechanism that the visual system employs to dynamically adapt the neural responses to the statistics of the input stimuli to improve coding efficiency. ^ Second, I investigated how ongoing activity modulates orientation coding in single neurons, neural populations and behavior. Cortical networks are never silent even in the absence of external stimulation. The ongoing activity can account for up to 80% of the metabolic energy consumed by the brain. Thus, a fundamental question is to understand the functional role of ongoing activity and its impact on neural computations. I studied how the orientation coding by individual neurons and cell populations in primary visual cortex depend on the spontaneous activity before stimulus presentation. We hypothesized that since the ongoing activity of nearby neurons is strongly correlated, it would influence the ability of the entire population of orientation-selective cells to process orientation depending on the prestimulus spontaneous state. Our findings demonstrate that ongoing activity dynamically filters incoming stimuli to shape the accuracy of orientation coding by individual neurons and cell populations and this interaction affects behavioral performance. In summary, this thesis is a contribution to the study of how dynamic internal states such as rapid adaptation and ongoing activity modulate the population code accuracy. ^

A comparative analysis of visual strategy in elite and amateur handball goalkeepers

The aim of the present study was to analyze the visual strategies prior to a throw from 7 metres in elite and amateur handball goalkeepers. To this end we analyzed the visual fixations in number and order of 10 goalkeepers (29.7±5.4 years; 14.7±8.6 years of experience), 3 elite and 7 amateurs, during the life size projection of 14 different throws, made by different players. During each throw the movement of the eyeballs, the dilation of the pupil (pupillometry) and the subject?s blinking were recorded thanks to a technological system which permitted eye tracking with high speed cameras, and the subsequent presentation of the visual data for each action studied. The elite goalkeepers performed a greater number of visual fixations than the amateur goalkeepers, revealing large and significant differences. Equally the priority zones observed were differed, with the amateur goalkeepers fixating more on the thrower?s face, and the elite goalkeepers paying more attention to the area of the arm/ball. It can therefore be inferred that elite goalkeepers have a greater perceptive capacity and also use different visual strategies from the amateur goalkeepers.

A perceptual memory for low-contrast visual signals

Detection of a visual signal can be facilitated by simultaneous presentation of a similar subthreshold signal. Here we show that the facilitatory effect of a subthreshold signal can persist for more than 16 s. Presenting a near-threshold Gabor signal (prime) produced a phase-independent increase in contrast sensitivity (40%) to similar successive signals (target) for a period of up to 16 s. This effect was obtained only when both prime and target were presented to the same eye. We further show that the memory trace is inactivated by presenting high-contrast signals before the target. These results suggest that activated neurons in the primary visual cortex retain a near-threshold memory trace that persists until reactivated.

A recuperação da informação da memória de trabalho: evidências baseadas em tarefas de imagem mental e de memória visual

A imagem mental e a memória visual têm sido consideradas como componentes distintos na codificação da informação, e associados a processos diferentes da memória de trabalho. Evidências experimentais mostram, por exemplo, que o desempenho em tarefas de memória baseadas na geração de imagem mentais (imaginação visual) sofre a interferência do ruído visual dinâmico (RVD), mas não se observa o mesmo efeito em tarefas de memória visual baseadas na percepção visual (memória visual). Embora várias evidências mostrem que tarefas de imaginação e de memória visual sejam baseadas em processos cognitivos diferentes, isso não descarta a possibilidade de utilizarem também processos em comum e que alguns resultados experimentais que apontam diferenças entre as duas tarefas resultem de diferenças metodológicas entre os paradigmas utilizados para estuda-las. Nosso objetivo foi equiparar as tarefas de imagem mental visual e memória visual por meio de tarefas de reconhecimento, com o paradigma de dicas retroativas espaciais. Sequências de letras romanas na forma visual (tarefa de memória visual) e acústicas (tarefa de imagem mental visual) foram apresentadas em quatro localizações espaciais diferentes. No primeiro e segundo experimento analisou-se o tempo do curso de recuperação tanto para o processo de imagem quanto para o processo de memória. No terceiro experimento, comparou-se a estrutura das representações dos dois componentes, por meio da apresentação do RVD durante a etapa de geração e recuperação. Nossos resultados mostram que não há diferenças no armazenamento da informação visual durante o período proposto, porém o RVD afeta a eficiência do processo de recuperação, isto é o tempo de resposta, sendo a representação da imagem mental visual mais suscetível ao ruído. No entanto, o processo temporal da recuperação é diferente para os dois componentes, principalmente para imaginação que requer mais tempo para recuperar a informação do que a memória. Os dados corroboram a relevância do paradigma de dicas retroativas que indica que a atenção espacial é requisitada em representações de organização espacial, independente se são visualizadas ou imaginadas.

Look-up table of quadrics applied to corneal topography [Presentation]

Presentación oral realizada en el 6th EOS Topical Meeting on Visual and Physiological Optics (EMVPO 2012), Dublín, 20-22 Agosto 2012.