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PubMed1989

Changes in visual evoked potentials in patients with multiple sclerosis treated with isoprinosine and amantadine.

We studied 30 patients with clinically definite MS according to the Mc Alpine et al. clinical criteria (20 patients received isoprinosine and 10 amantadine for a period of 12 months). In each patient pattern reversal stimulation was presented to each eye successively and potentials were recorded over both occipital lobes. For each condition the average evoked response to 200 pattern reversals was computed on DISA 2000. During the 24 month-lasting observation high clinical improvement and simultaneous shortening of the latency to peak of the first major positive component of the response in visual evoked potentials was observed in 12 cases with relapsing form treated 12 months with isoprinosine. In 3 cases, despite of the treatment with isoprinosine, new relapses were observed; in these patients delayed response in VEP was observed. In cases treated with amantadine no shortening of the latency to the major positive peak of the potential was observed, also no diminish of relapses frequency was observed.

Adolescent↗
PubMed1977

Visually evoked potentials from occipital and precentral cortex in visually deprived humans.

The visually evoked potential (VEP) was recorded from the scalp overlying precentral and occipital cortex in three monocularly deprived humans. The subjects had defects of the globe from birth that effectively created a condition of diffuse light rearing in one eye. In subject, BER, a 19-year-old with a recently removed congenital cataract, the occipital response evoked from the deprived eye was reduced by 53% compared with the response evoked from the good eye. In subject GUZ, age 20 with a congenital cataract, the occipital response evoked from the deprived eye was actually larger by 20% than was the response evoked from the good eye. For UTZ, age 5 with whitish cellular debri in the anterior vitreous of the eye, the occipital response evoked from the deprived eye was only 4% smaller than the response evoked from his good eye. In all three subjects, the precentral response evoked from the deprived eye was reduced in amplitude compared with the precentral response evoked from the good eye. In terms of relative effect of the deprivation upon the VEP from the two recording sites, the precentral VEP was altered to a greater extent than was the occipital VEP. These findings indicate that diffuse light rearing can affect the pathways projecting to precentral cortex independently of the specific visual pathways.

Adult↗
PubMed2000

A network inversion technique for estimating equivalent dipole description of visual evoked potential.

For the activation study of the brain, dipole localization from the scalp potential is one of the most promising techniques to realize a reasonable temporal resolution which cannot be realized in functional MR and PET. The goal of our study is to estimate inversely the electrical brain activity in the form of several dipoles from the scalp potential, using a network inversion technique. As a basic approach, we have inversely estimated several dipoles from the potential distribution on a spherical surface, in the homogeneous sphere model. In the training phase, by expanding the neural network input dimensions being redundant, the network can easily learn the forward mapping. In the inversion phase, the space of the expanded-network-input-vector can be narrowed by introducing a penalty term. Additionally, a consensus term was used to force several dipoles to have a similar orientation. We estimate that this is applicable to the localization of several dipoles that reflect the actual brain activity, especially in the visual evoked potentials.

Brain Mapping↗
PubMed2006

Binocular interactions in the guinea pig's visual-evoked potentials.

In this study, binocular interaction in guinea pigs is evaluated using bioelectrical activities. A difference potential, as evidence of an interaction, is calculated by subtracting the sum of visual-evoked potentials recorded by left and right monocular visual stimulations from the potential recorded by binocular stimulation. A negative monophasic wave with an average amplitude of 15.1 microV and an average latency of 106 ms is observed in the difference potential. This finding implies that the P100 is the main guinea pig visual-evoked potential wave that is affected by binocular interaction. Binocular interaction is also observed in the waves N75 and N140, although with a smaller amplitude. No interaction is observed in the segments of P55 and P200 waves.

Animals↗
PubMedDate not supplied

Pattern-reversal electroretinograms and visual evoked potentials in branch retinal vein occlusion.

We recorded pattern electroretinograms and visual evoked potentials in a group of selected patients with unilateral uncomplicated branch retinal vein occlusion. To document the effects of preexisting risk factors, patients were divided into three groups: diabetes mellitus, hypertension with hyperlipidemia and no systemic disease. The transient and steady-state pattern electroretinogram and visual evoked potential amplitudes were significantly reduced and visual evoked potential peak times were delayed relative to the fellow eyes and age-matched normal subjects. There was a second amplitude reduction relative to the other patient groups in both the affected and fellow eyes of the diabetes mellitus group, which was indicative of an additive effect of diabetes mellitus.

Aged↗
PubMed1987

Scalp distribution of visual evoked potentials to foveal pattern and luminance stimuli.

Scalp potentials elicited by pattern reversal, pattern onset, and flash stimulation have been studied in normal subjects by means of a 16-channel brain mapping system. In two groups of experiments the topography of the major positive component in each response was compared with 4 degrees full- and lateral half-field stimuli and, for more detailed exploration of the pattern components by M-scaled stimuli selected to activate 1 cm2-patches of striate cortex and associated extrastriate re-projections. The 4 degrees stimuli were found to elicit scalp distributions for the pattern reversal P100 and the pattern onset C1 consistent with striate and extrastriate visual cortical origins respectively. Data on the flash P2 component suggest that stimulation was not localized accurately; this may have been due to lateral spread of neural activity in the retina. Predictably, the M-scaled stimuli showed extensive inter- and intraindividual variations depending on stimulus type and location relative to fixation. The manner in which, in some subjects, the region of maximal activity on the map appears to migrate with change of stimulus position possibly reflects local retinotopic order in visual evoked potential generator areas. However, data are neither extensive nor detailed enough to be conclusive.

Adult↗
PubMed1984

Visual evoked potential: a diagnostic tool for the assessment of hepatic encephalopathy.

Visual evoked potential recordings were examined in 45 liver cirrhosis patients with (n = 29) and without (n = 16) encephalopathy, in 15 normal volunteers, and in one patient with an opioid induced stupor state. Visual evoked potential parameters were classified on the basis of EEG recordings. Plasma concentrations of amino acids, octopamine, and ammonia were assayed in order to document the metabolic change of hepatic encephalopathy. Latencies and wave patterns recorded after flash stimulation differentiated the four degrees of the coma one from another according to EEG classification in the 29 patients with encephalopathy. In the group of 16 patients without clinical and EEG evidence of encephalopathy the visual potential recordings discriminated a group of patients (n = 10) in a preclinical stage of encephalopathy. Biochemical parameters and subsequent clinical observation of patients confirmed our judgement of a preclinical stage of encephalopathy. These results suggest that visual evoked potentials are a simple, suitable and objective method for differentiating the degrees of encephalopathy and for identifying the preclinical stage of encephalopathy.

Adult↗
PubMed1998

Multifocal topographic visual evoked potential: improving objective detection of local visual field defects.

PURPOSE: To investigate the relationships between the pattern stimulation of different parts of the visual field (up to 25 degrees of eccentricity), the electrode position, and the cortical response to improve objective detection of local visual field defects. METHODS: The human visual evoked potential (VEP) was assessed using multifocal pseudorandomly alternated pattern stimuli that were cortically scaled in size. Monopolar and bipolar electrode positions were used. The visual field was investigated up to 26 degrees of eccentricity. Twelve normal subjects and seven subjects with visual field defects of different nature were studied. RESULTS: Although the monopolar response is heavily biased toward the lower hemifield, bipolar leads overlying the active occipital cortex (straddling the inion) demonstrate good signals from all areas of the visual field tested. The amplitude is almost equal for the averaged upper and lower hemifields, but the polarity is opposite, causing partial cancellation of the full-field VEP. The degree of cancellation depends mainly on latency differences between the vertical hemifields. The bipolar VEP corresponded well with Humphrey visual field defects, and it showed a loss of signal in the scotoma area. CONCLUSIONS: The multifocal VEP demonstrates good correspondence with the topography of the visual field. Recording with occipital bipolar electrode placement is superior to standard monopolar recording. To avoid a full-field cancellation effect, a separate evaluation of upper and lower hemifields should be used for the best assessment of retinocortical pathways. This technique represents a significant step toward the possible application of the multifocal VEP to objective detection of local defects in the visual field.

Adult↗
PubMed1989

The clinical utility of visual-evoked potential acuity testing.

We assessed the clinical utility of objectively measured acuity using visual-evoked potentials. The technique was first standardized in normal emmetropic subjects and then applied to uncorrected myopic subjects. We found that visual-evoked potential acuity could accurately indicate Snellen acuity in emmetropia and corrected myopia; however, the two measures were highly correlated only in those uncorrected myopic subjects with visual acuities of 20/100 or better. In subjects with poorer than 20/200 uncorrected visual acuity caused by myopia, estimates of visual-evoked potential acuity could not be obtained. The correlation between these two measures of visual acuity was also lower in patients with decreased Snellen acuity attributable to retinal or ocular disease. We found that patients with unexplainable claims of decreased visual acuity could be diagnosed as having functional visual loss based on objective visual-evoked potential acuities.

Adolescent↗
PubMed1996

Processing visual evoked potentials based on matched filtering of single trial responses.

Physiological signals recorded after presentation of a stimulus can be considered as the sum of an evoked sensory response and uncorrelated noise corresponding to the spontaneous neural background activity. In case of low signal-to-noise ratio, the sensory signal is estimated by averaging a large number of single trial records sampled under the same experimental conditions. The averaging technique, however, is inappropriate for displaying trial-to-trial variations that may occur during a recording session. A method based on matched filtering was developed for processing single visual evoked potentials (VEPs). To illustrate the performance of this method, a set of VEPs for grating patches of 8 different contrasts (including 0) was evaluated. The VEPs were subjected to signal detection analysis by computing for each contrast similarity indices between the single trial records and the averaged response used as a template. The signals were analysed in terms of probability density distributions, expressing the goodness of fit between template and each single waveform.

Cluster Analysis↗
PubMed1995

Visual evoked potentials in early Alzheimer's dementia: an exploratory study.

Topographical maps of visual evoked potentials (VEPs) were recorded from 10 possible Alzheimer's disease (AD) patients and 10 control subjects. The purpose of the study was to determine if the two types of VEPs could function as a diagnostic screening for AD. Results of the statistical analysis did not reveal any latency differences between VEPs for the components elicited by either the pattern shift visual evoked potential (PSVEP)--or flash visual evoked potential (FVEP)--elicited components for AD patients compared with the control subjects; however, the information provided insight into results that are frequently lost with conventional evoked potential data. Statistically significant differences in amplitude were found between the P1 and the N2 of the PSVEP at 124, 126, and 130 ms, and at 116 ms for the FVEP.

Aged↗
PubMed1983

Pattern electroretinograms and visual-evoked potentials in glaucoma and multiple sclerosis.

Steady-state visual-evoked potentials and electroretinograms were simultaneously recorded in four patients with glaucoma and in five patients with multiple sclerosis. The stimuli included a homogenous field and a 2.3 cycles per degree sinusoidal grating that were counter-phase modulated at the rate of 7.5 Hz. We used narrow bandwidth spectral analysis to measure the response amplitudes and signal-to-noise ratios. Transient pattern visual-evoked potentials (1 Hz) were also measured for latency in each eye. We found abnormal pattern electroretinograms, based on the absence of a significant second harmonic component, in three of the four glaucomatous eyes although the homogenous field electroretinograms were normal. In the patients with multiple sclerosis, the pattern electroretinograms were abnormal in two eyes, but the transient visual-evoked potential latency had the highest diagnostic yield (seven of ten eyes).

Adult↗
PubMed1983

[Statistical analysis of the parameters defining the cortical visual evoked potentials in the phases of the sleep-wake cycle].

Visual evoked potential parameters (latencies, intervals of latencies and amplitudes) obtained by photic stimulation using a light-emitting diode implanted in the frontal sinus of cats were studied by statistical methods (analysis of variance) during the stages of wakefulness, slow sleep and paradoxical sleep. The results show: a) greater intraindividual homogeneity in all cases with special emphasis on the latencies; b) the greatest homogeneity of responses was found during slow sleep and paradoxical sleep stages; c) in relation to the influences exerted by the sleep-wakefulness cycle on the visual evoked potentials, the parameters most affected were those closely related to the secondary complex. We conclude, that latency, due to its great homogeneity, is the most useful parameter in this kind of experiments and secondly, that it is the secondary complex of the visual evoked potentials that is affected by the endogenous conditions of the subject (in our case the sleep-wakefulness cycle stage).

Activity Cycles↗
PubMedDate not supplied

Visual evoked potential in young adults: a normative study.

It is important to acquire adequate normative data of visual evoked potential before using it as a diagnostic tool. A study using visual evoked potential with pattern (VEP-P) was conducted in Twenty male and seven female young healthy subjects of 17-35 years age. Ag/Agcl electrodes anchored on scalp with collodion at O1-A1, O2-A2 (10-20 system), with transition skin to electrode impedence kept at less than 5 K ohms were connected to MEB 5200 Evoked potential Recorder (Nihon Kohden, Japan). The evoked responses to 256 visual stimuli were recorded using transient pattern reversal (checker size 32'), frequency 1/sec and contrast between black and white checks 67%. The responses were averaged by the computer and absolute peak latency values for P100 alongwith other positive and negative waves worked out. P100 latency of 95.37 +/- 6.85, amp. 6.4 +/- 2.38 for males and 91.07 +/- 49 msec, amp. 6.88 +/- 2.79 microv for females are being reported. The P100 latency values of present study are similar to those reported in age and sex matched subjects of the western world, indicating that there are no ethnic variations in P100 of VEP.

Adolescent↗
PubMed1997

[Evaluation of visual evoked potentials in partial optic nerve atrophy].

PURPOSE: Parameters of visual evoked potentials in partial optic nerve atrophy in different aetiology were studied. MATERIALS AND METHODS: The study involved 48 patients (68 eyes) with partial optic nerve atrophy from neuritis, toxic, arteriosclerosis and trauma. The tests of visual evoked potentials were performed by the use of UTAS E-1000 computer system in all patients with the use of pattern and flash stimulation. RESULTS: Amplitude of all waves were reduced in 74% patients using "pattern" and in 61% patients using "flash" stimulation. Latency of wave P2 was delayed in all patients with optic nerve atrophy from arteriosclerosis. Latency of P100 wave and N1 wave were not delayed in patients with optic nerve atrophy from toxic neuropathy. CONCLUSIONS: Estimation of latency of the VEP may be useful in diagnosis of the partial optic nerve atrophy. Variety of records of VEP indicate different degree of disturbances of nerve conduction.

Adult↗
PubMed1978

A reconsideration of visual evoked potentials for fast automated ophthalmic refractions.

Visual evoked potentials (VEP's) recorded from the scalp are sensitive to retinal image sharpness and thus to changes in the refractive state of the eye. Initially the responses to checkerboard flash or reversal stimuli were computer-averaged in order to raise the signal above the noise, primarily the electroencephalogram (EEG). Recently analogue Fourier signal analysis has been proposed for using the VEP for rapid clinical refraction. We have confirmed that this method can measure the spherical refractive state to within +/- 0.50D. However, because of large slow-wave fluctuations, measurements of changes within +/- 1.00D are not always clear. Despite its promise the method does not appear to be clinically useful at present.

Diagnosis, Computer-Assisted↗