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At least 937 records · Page 52Linked to original sources
PubMed1991

[Visual evoked potentials in Alzheimer's and Parkinson disease].

Harding et al. suggested at first that an increase of P2 latency in flash VEP without an increase of P2 latency in pattern reversal VEP may be a diagnostic marker of Alzheimer's disease. Up to now there is no convincing evidence for this hypothesis. The purpose of the present study was to examine this hypotheses in an extended group of patients with Alzheimer's disease (n = 36). In addition, a group of patients with Parkinson's disease (n = 8) without dementia syndrome and a group of healthy elderly controls (n = 46) was investigated in order to determine the sensitivity and specificity of these VEP parameters. The results confirmed significant group differences between patients with Alzheimer's disease and healthy controls concerning the increase of Flash P2 latency and unchanged latency of P2 in the pattern reversal VEP. No significant correlations were found between duration of illness and mental test scores. The group differences of P2 latency in the flash VEP for patients with Parkinson's disease and healthy controls were also significant. Therefore, the increase of flash P2 latency in VEP does not seem to be specific for Alzheimer's disease nor for dementia syndrome. The pathological mechanism causing the flash P2 latency increase in a remarkable number of neuropsychiatric patients should be elucidated in further experimental investigations.

Aged↗
PubMed1991

Visually evoked potentials and electroretinography in neurologic evaluation.

Electrophysiologic testing of the visual system requires primarily the ERG and the VEP. The flash electroretinogram provides information about the outer retina only. The pattern electroretinogram is derived from both the outer retina and the innermost retinal layers including the ganglion cell layer. The VEP is based on electrical information recorded from the visual cortex in response to stimulation of the retina. Thus, the integrity of the entire visual pathway can be tested. Localizing ability of the VEP is limited. Since the visual cortex is heavily weighted by representation of the central retina, peripheral lesions, including those producing peripheral visual field abnormalities that do not impinge upon central fixation, may produce relatively little disturbance of the VEP. As with most tests, electrophysiologic studies of the visual system must be placed in context of the entire examination, including the patient's history and neurologic and especially neuro-ophthalmologic evaluation. Electrophysiologic testing has three main uses in neurology. Pattern-reversal VEPs may be useful in detecting hidden visual loss in multiple sclerosis; VEPs and ERGs can distinguish function from organic visual loss; and VEPs and ERGs can be useful in the diagnosis of visual loss in nonverbal patients, especially in children.

Electroretinography↗
PubMed1990

[Visual pattern-stimulation in the early diagnosis of demyelinating diseases of the central nervous system].

A high incidence of the visual pathway involvement into the pathological process at an early stage of derangement was revealed in patients with multiple sclerosis and retrobulbar neuritis by means of visual pattern-stimulation. The data obtained point to the information content of the suggested method for examining the visual analyzer in patients with suspected multiple sclerosis.

Evoked Potentials, Visual↗
PubMed1990

Flash electroretinograms and pattern visually evoked cortical potentials in Behçet's disease.

Behçet's disease with posterior uveitis was studied in 12 cases by flash electroretinography (FERG) and pattern visually evoked cortical potential (PVECP). Disappearance of oscillatory potentials was the initial change noted in FERG. Subnormal FERG and a delay in peak latency of the P100 component of PVECP were observed in patients with poor visual acuity and long-standing Behçet's disease. Amplitudes of PVECP were significantly decreased in these patients. It was suggested that FERG together with PVECP were good indicators for monitoring posterior segment changes and visual prognosis in Behçet's disease.

Adult↗
PubMed1990

Simultaneous pattern reversal ERG and VER recordings. Effect of stimulus field and central scotoma.

The effects of the sizes of the stimulus field and of an artificially created central scotoma on simultaneously recorded pattern-reversal electroretinogram (P-ERG) and pattern-reversal visual-evoked response (P-VER) were investigated. With an increase in the stimulus field from 4 degrees X 4 degrees to 12 degrees X 12 degrees, the amplitude of the P-ERG increased steadily. The amplitude of the P-VER also showed an increase up to a stimulus field of 6 degrees X 6 degrees or 8 degrees X 8 degrees, but showed no increase with further expansion of the stimulus field. A central scotoma, created by placing a square of black paper at the center of the 12 degrees X 12 degrees stimulus field, was increased from 4 degrees X 4 degrees to 10 degrees X 10 degrees by 2-degree increments. Amplitudes of both the P-ERG and the P-VER decreased with increasing central scotoma size. The P-VER decreased significantly with a 4 degrees X 4 degrees central scotoma. Although both the P-ERG and the P-VER were influenced by the overall stimulus field and the central scotoma, there was a distinct difference in their behavior. The P-VER showed saturation above a certain stimulus field size and, with a central scotoma of 4 degrees X 4 degrees, much more reduction than the P-ERG, suggesting that the P-VER depends more on the macular area than does the P-ERG. The P-ERG also exhibited a substantial macular dependency, which, however, was not as great as that of the P-VER. The greater macular dependency of the P-VER compared to the P-ERG, as observed in our study, reflects the larger anatomic representation of the macula at the higher visual level.

Adult↗
PubMed1989

[Changes in the EEG frequency spectrum in various phases of mental stress].

To obtain evidence about the relationship between spontaneous EEG activity and mental activity, an experiment was designed and executed with EEG recordings during a concept-learning task. We varied task performance (self-paced vs. machine-paced) and distinguished different stages of information processing during task performance. Using factor analysis calculated on all spectral coefficients, we found two orthogonal variables in the clinical alpha band. Alpha 2 power (10.5-12 Hz) seems to reflect the overall processing demands imposed on the individuals. Furthermore, there are different EEG frequency patterns during perceptual-central- compared with response-related processing as well as during processing of positive vs. negative feedback. The results suggest using (1) conservative procedures in hypothesis testing and (2) procedures to reduce between subject variability (a posteriori defined frequency variables, relative power values, scaling of reaction values) in further studies relating EEG activity to mental activity during task performance.

Adolescent↗
PubMed1989

The visual evoked potentials and the spatial vision in old people.

The latency of the visual evoked potentials elicited by pattern-reversal and onset-offset stimulation was measured in 75 healthy subjects aged 21 to 80 years. In 24 of these subjects the contrast sensitivity threshold was recorded by electrofunctional method. There is a close correlation between increasing latency of visual evoked potentials and age increase. This finding is of greater importance after 60 years. The delayed latencies are obtained with both pattern-reversal and onset-offset stimulation, and are more striking using stimuli of small size. In the old people the contrast sensitivity shows a raised threshold, especially for small stimuli. These age-related changes of the visual evoked potentials and contrast sensitivity are due to optical factors--the most important is the reduction of the retinal illuminance caused by senile miosis--and to neural factors as degeneration and demyelination of the optic nerve axons and abnormalities of the neurotransmitters.

Adult↗
PubMed1988

[Topography of the movement visual evoked potential in the human].

The amplitudes of the motion VEP waves P100, N200 and P300 were investigated on 12 subjects at six electrode positions (2.5, 5, 7.5 and 10 cm above the inion and 5 cm bilaterally from the 2.5 cm midline point). The evaluation was performed on the basis of in general 45 (for P100 32) averaged potentials per subject. Each averaged potential was obtained from 40 single potentials. P100: The amplitudes were nearly equal at all electrodes. N200: The greatest amplitudes could be found at the lateral electrodes. The amplitudes decreased in the midline in occipito-frontal direction reaching the lowest value at the electrode most frontally situated. P300: This wave had its greatest amplitude at the most frontal lead position. The amplitude decreased systematically in occipital direction. The differences in the position of the amplitude maxima and in the topographical distribution of the remaining amplitude values suggest different generator structures of the waves N200 and P300.

Brain Mapping↗
PubMedDate not supplied

[Electrophysiologic analysis of the process of recognizing target and non-target stimuli in healthy and oligophrenic children].

In an automatized experiment, with a computer on line, amplitude-temporal parameters of evoked potentials (EPs) to purposive and non-purposive stimuli (digits), were analyzed in normal and mental retarded children. At unilateral stimuli presentation to the left or right visual half-fields EPs were recorded simultaneously in projection, TPO, parietal and central areas of the left and right hemispheres. It has been shown that in normal children, differential involvement of projection and associative structures in the analysis of sensory information takes place in both hemispheres. The amplitudes of most EP components in the range of 100-400 ms to the purposive stimuli are higher than to the non-purposive ones. Considerable similarity of EPs developing in response to ipsi- and contralateral stimulations of visual fields ("direct" and "transmitted" EP) is observed. In mental retarded children significant changes are revealed in intra- and interhemisphere organization of the process of perception of purposive and non-purposive stimuli. In the right hemisphere structures there are no differential EP reactions to the two types of stimuli. Significant, in comparison with the norm, prolongation of the latencies of most EP components is noted, especially in the structures of the left hemisphere, to the purposive stimuli. In the process of perception, changes are seen of the integration of functions of both hemispheres. The totality of disturbances of systemic brain organization at perceptive activity in mental retarded children may reflect neurophysiological mechanisms of mental deficiency.

Association↗
PubMed1985

The pattern evoked electroretinogram: its variability in normals and its relationship to amblyopia.

Electroretinograms evoked by pattern stimuli (contrast reversing gratings) were measured under steady state conditions in the normal and amblyopic eyes of 14 amblyopic individuals having Snellen acuities in the range 20/100 to 20/600. These ERGs were measured as a function of spatial frequency, and compared with the psychophysical threshold losses to the same stimuli. In all cases the authors compared the normal and fellow amblyopic eye's response while taking into account the variability of right-left eye comparisons of normal individuals for these psychophysical and electrophysiological tests. When factors such as optical focus, fixation alignment, and fixation stability have been individually optimized, no pattern ERG deficit was observed in a spatial frequency range where there were obvious psychophysical deficits to the same stimuli. Our results do not substantiate previous claims of a pattern ERG anomaly in many severely amblyopic eyes.

Adolescent↗
PubMed1983

[Visual evoked potentials in pattern motion].

Our intention was to obtain a visual evoked potential (VEP) consisting only of a movement-related component for the purpose of further investigations of movement detection. This was attempted by selection of appropriate stimulus conditions. Evoked by initial movement a VEP with five typical waves was observed at the human occipital scalp. The N2-wave with a peak latency of 180-200 ms was most prominent. Following results were yielded in the experiments carried out: 1. Adaptation to a pattern movement: The amplitude of N2 and P1 is significantly reduced (Fig. 4). 2. Relation between amplitude and velocity: The experimental data could be approximated by a power function with an exponent of m = 0.3 for N2 and lower m for later waves (Fig. 5). 3. Pattern variation (grating, checkerboard, zig-zag) had no influence on N2 but on P1 and possibly also on later waves (Fig. 6). These results suggest that the wave N2 is movement-related under our experimental conditions. A pattern-related component may additionally be assumed in wave P2. Components, evoked by further reasons, may be included in the waves following N2. Their specification demands supplementary experiments.

Evoked Potentials, Visual↗
PubMed1980

Pattern ERGs are abnormal in many amblyopes.

We have used a pattern-reversing chequerboard (1 degree squares, or smaller: 84 per cent contrast, or less: 2 to 16 reversals/sec: field size 22 degrees x 16 degrees: mean luminance 50 cd/m2) to evoke responses from the eyes of young adults and children. ERGs were recorded with gold foil electrodes, which did not interfere with the normal optics. All patients were affected accurately. The fixation point was adjusted so that squinters received the stimulus on corresponding areas of each retina. The normal ERG obtained is 1.5 to 3 mu V in amplitude, and in thirteen normal subjects right and left eyes gave equal responses. The extreme asymmetry detected was c. 10 per cent. In all amblyopes, including children of 6 years old and upwards, satisfactory recordings were obtained. In most amblyopes, the response from the affected eye was 50 per cent or less of the response from the fellow eye. In all cases of failure to respond to treatment, the asymmetry was highly significant. In adults, occluding the screen area corresponding to the area of amblyopic suppression, reduces the ERG in the fellow eye, but does not reduce the ERG in the amblyopic eye. We conclude that amblyopic retina produces very little electrical activity that we can record. The timing, response to frequency of stimulation, and other parameters in the pattern ERG are dissimilar from those in the ERG produced by small changes of luminance. We have little evidence about the class of cell generating the response we observe, but evidently there is peripheral abnormality in the visual system even of amblyopic children.

Adolescent↗