Spared cognitive processing of visual oddballs despite delayed visual evoked potentials in patient with partial recovery of vision after 53years of blindness (original) (raw)
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Aging effect in visual evoked potentials to pattern, motion and cognitive stimuli
Vision Research, 2012
An electrophysiological study on the effect of aging on the visual pathway and various levels of visual information processing (primary cortex, associate visual motion processing cortex and cognitive cortical areas) was performed. We examined visual evoked potentials (VEPs) to pattern-reversal, motion-onset (translation and radial motion) and visual stimuli with a cognitive task (cognitive VEPs – P300 wave) at luminance of 17 cd/m2 . The most significant age-related change in a group of 150 healthy volunteers (15–85 years of age) was the increase in the P300 wave latency (2 ms per 1 year of age). Delays of the motion-onset VEPs (0.47 ms/year in translation and 0.46 ms/year in radial motion) and the pattern-reversal VEPs (0.26 ms/ year) and the reductions of their amplitudes with increasing subject age (primarily in P300) were also found to be significant. The amplitude of the motion-onset VEPs to radial motion remained the most constant parameter with increasing age. Age-related changes were stronger in males. Our results indicate that cognitive VEPs, despite larger variability of their parameters, could be a useful criterion for an objective evaluation of the aging processes within the CNS. Possible differences in aging between the motion-processing system and the form-processing system within the visual pathway might be indicated by the more pronounced delay in the motion-onset VEPs and by their preserved size for radial motion (a biologically significant variant of motion) compared to the changes in pattern-reversal VEPs.
Study of voluntary alteration of visual evoked potentials: Evaluating role in functional visual loss
International Journal of Research in Medical Sciences, 2015
Background: Pattern reversal visual evoked potentials (PRVEP) are one of the recommended tests for detection of functional visual loss. However, voluntary alterations producing abnormal records have been reported in the normal subjects limiting the role of the test. Hence, this study aimed to record voluntarily altered PRVEP responses and to study the role of various modifications in the technique for detection of the condition. Methods: 20 normal subjects in the age-group of 18-25 years were studied. PRVEP records were obtained in the normal perceiving states and then with voluntary alterations in different stimulus conditions and the changes in the mean P100 latency and N75-P100 amplitude were compared and analysed using paired t-test. Results: 15 out of 20 subjects could voluntarily alter their PRVEP records with 26 out of 30 eyes demonstrating statistically significant abnormal records in terms of latency delay or amplitude reduction or both. Modifications in the technique with increased check size, field size and binocular stimulation reduced the number of abnormal records. But, mean P100 latency and N75-P100 amplitude recorded from the above stimulus conditions in voluntarily altered states were still statistically significantly altered from those in the normal perceiving conditions (p<0.05). Conclusion: Normal subjects can voluntarily produce abnormal PRVEP responses. Various modifications in the technique like increase in the check-size, field size and binocular stimulation should be employed if voluntary alteration is suspected, but interpretation should be made carefully in the context of clinical findings of the subject.
Italian Journal of Neurological Sciences - ITAL J NEUROL SCI, 1997
Monocular and binocular visual evoked potentials (VEPs) in response to different check sizes (15-21-38-84 minutes of arc) were studied in 14 subjects with normal visual acuity and stereopsis.The binocular VEP amplitude is slightly higher than the VEP amplitude on stimulation of the better eye and significantly higher than the VEP amplitude on stimulation of the worse eye; this effect is observed using small checks and almost exclusively involves N75-P100.Both the N75 and P100 peaks occur earlier after binocular than monocular stimulation. The shortening of the N75 mean latency is significantly greater than that of the P100 mean latency when larger check sizes are used.The mean latency of the N145 potential is not significantly different in monocular and binocular stimulus conditions. The slight summation effect and latency shortening in the binocular VEPs are not consistent with the hypothesis that it is the sum of separate monocular signals originating from the visual cortex that g...
Effect of age on pattern-reversal visual evoked potentials in Indian population
International Journal of Clinical and Experimental Physiology, 2014
Evoked potentials provide a measure of the functional changes of the sensory systems during different stages of life. [1] For the visual cells starting from the retina upto the visual cortex and beyond, the activities can be partly recorded by electroretinographs (ERGs) and partly by the visual evoked potentials (VEPs); ERGs measure the retinal activities and VEPs records the activity of the neuronal circuitary beyond it and the cortical responses. [2] Comparisons between pattern evoked ERG and cortical evoked potentials in the same individuals suggested that some neural change occurs between the retina and the striate cortex, though the exact location and nature of change was not established. [2] Among the VEPs, the most sensitive measure of signal transduction is considered to be the transient pattern reversal VEPs (t-PRVEPs) showing 3 major waveforms-N70, P100, and N155. [3] However, amongst known physiological and physical parameters [3-6] that
Aging effect in pattern, motion and cognitive visual evoked potentials
An electrophysiological study on the effect of aging on the visual pathway and various levels of visual information processing (primary cortex, associate visual motion processing cortex and cognitive cortical areas) was performed. We examined visual evoked potentials (VEPs) to patternreversal, motion-onset (translation and radial motion) and visual stimuli with a cognitive task (cognitive VEPs -P300 wave) at luminance of 17 cd/m 2 . The most significant age-related change in a group of 150 healthy volunteers (15 -85 years of age) was the increase in the P300 wave latency (2 ms per one year of age). Delays of the motion-onset VEPs (0.47 ms/year in translation and 0.46 ms/year in radial motion) and the pattern-reversal VEPs (0.26 ms/year) and the reductions of their amplitudes with increasing subject age (primarily in P300) were also found to be significant. The amplitude of the motion-onset VEPs to radial motion remained the most constant parameter with increasing age. Age-related changes were stronger in males.
Cognitive, Affective, & Behavioral Neuroscience, 2003
The purpose of this study was to compare the lambda response of eye-fixation-related potentials (EFRPs) with the P100 component of pattern-reversal visual-evoked potentials. EFRPs were obtained by averaging EEGs time-locked to the offset of the saccade. The dipole of the lambda response and that of the P100 component were estimated by the dipole-tracing method . The locations of their dipoles at the occipital sites were very close to each other when the difference waveform, which was calculatedby subtracting the EFRP to the patternless stimulus from the EFRP to the patterned stimulus, was used for the lambda response. This finding implies that the lambda response and P100 have a common neural generator in the visual cortex. However, the peak latency of the lambda response was shorter than that of P100. The saccades in the EFRP trial were considered to be the cause of the difference.
Effect of different stimulus configurations on the visual evoked potential (VEP)
Documenta Ophthalmologica, 2012
The purpose of this study was to assess changes in the response profile of the pattern visual evoked potential (VEP) using three stimulus configurations simulating visual-field scotomas: central circular and central blank fields increasing incrementally in diameter from 1°to 15°, hemi-field, and quadrant patterns. Five visually normal adult subjects (ages 22-68 years) were tested binocularly at 1 m for each stimulus configuration on 5 separate days. A checkerboard test pattern (64 9 64 black-and-white checks, 85 % contrast, 64 cd/m 2 luminance, 20 s of stimulus duration, 2-Hz temporal frequency) was used. The group mean VEP amplitude increased in a linear manner with increase in the central circular diameter (y = 0.805x ? 2.00; r = 0.986) and decrease in central blank field diameter (y =-0.769x ? 16.22; r = 0.987). There was no significant change in latency in nearly all cases. The group mean coefficient of variability results indicated that the VEP amplitude was repeatable for the different stimulus configurations. The finding of VEP response linearity for the circular stimulus fields, and repeatability for all stimulus configurations, suggests that the clinician may be able to use the VEP technique with the suggested test patterns as a rapid and simple tool for objective assessment for several types of visual-field defects for a range of abnormal visual conditions and special populations.
Studies of human visual pathophysiology with visual evoked potentials
Clinical Neurophysiology, 2006
Visual evoked potentials (VEPs) offer reproducible and quantitative data on the function of the visual pathways and the visual cortex. Pattern reversal VEPs to full-field stimulation are best suited to evaluate anterior visual pathways while hemi-field stimulation is most effective in the assessment of post-chiasmal function. However, visual information is processed simultaneously via multiple parallel channels and each channel constitutes a set of sequential processes. We outline the major parallel pathways of the visual system from the retina to the primary visual cortex and higher visual areas via lateral geniculate nucleus that receive visual input. There is no best method of stimulus selection, rather visual stimuli and VEPs' recording should be tailored to answer specific clinical and/or research questions. Newly developed techniques that can assess the functions of extrastriate as well as striate cortices are discussed. Finally, an algorithm of sequential steps to evaluate the various levels of visual processing is proposed and its clinical use revisited.
Visual evoked responses in humans with abnormal visual experience
The Journal of Physiology, 1975
1. The visual evoked response to a grating target of varying spatial frequency was examined for normal subjects and for subjects with meridional amblyopia. This condition, reduced visual resolution for specific target orientations, is associated with, and thought to result from, marked ocular astigmatism. 2. For normal subjects, the general relation between spatial frequency and the evoked response is similar to psychophysical contrast sensitivity data. Evoked response amplitudes to oblique gratings are typically reduced and this is analogous to the lower acuity for oblique compared to horizontal and vertical detail. 3. In addition to the oblique effect, the magnitude of the evoked response for meridional amblyopes depends upon grating orientation over most of the spatial frequency range tested (0‐5‐16 cycles/deg). The lowest evoked amplitude is found when stimulus grating orientation matches that for which acuity is reduced. 4. The evoked potentials spatial frequency response funct...