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Results for “Evoked Potentials, Visual”

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PubMed2001

The role of visual evoked potentials in the diagnosis of optic nerve injury as a result of mild head trauma.

The curve of visual evoked potentials was observed and compared with changes of visual acuity and visual field during a 24-month period in a group of 39 patients with optic nerve injury as a result of mild cerebral trauma. Results of the study showed great improvement of visual acuity and visual field after treatment, and slower and continuous improvement of visual evoked potentials. The main abnormality of visual evoked potentials is the shortening of amplitude, which is recorded to gradually recede after treatment in half of the patients. Authors conclude that the shortening of amplitude can be partially explained by the edema and the compression of fibers in the optic canal. Also, they emphasize that in this type of optic nerve injury visual acuity testing is the best indicator of the promptness and scope of the injury, while visual field research presents the best method for following later delicate changes of visual function.

Adult↗

PubMed1985

Abnormal visual-evoked potentials in leukemic children after cranial radiation.

Visual-evoked potentials (VEPs) were studied in 55 asymptomatic children with leukemia or solid tumors in remission in order to detect subclinical demyelination of the optic pathway after CNS prophylaxis. In group I (11 patients with ALL studied prospectively), VEP latency was increased in ten after cranial radiation (CR) as compared with previous values. Group II (18 patients with ALL in maintenance) and group III (16 patients with ALL off therapy) were studied retrospectively and VEP latency was found above normal limits in 33 and 31%, respectively. In group IV (four patients with solid tumors and six with leukemia, all of whom received no CR), VEP latency was normal despite periodical intrathecal methotrexate administrations to five of them. We conclude that CR determines a slowing of conduction on VEP test, probably due to demyelination of the optic pathway, in a high proportion of patients. The future clinical significance of these findings must be established throughout a prolonged follow-up period.

Brain↗

PubMed1989

Effect of levodopa on the human pattern electroretinogram and pattern visual evoked potentials.

Pattern electroretinograms (P-ERGs) and pattern visual evoked potentials (P-VEPs) were recorded at three luminance levels and five different check sizes in a group of 16 control subjects before and after the oral administration of levodopa. At the lower luminance levels, significant decrease in P-ERG and P-VEP latencies were found. For P-VEPs the latency changes occurred only at small check sizes. No changes were observed in control experiments without levodopa administration. Our results show that levodopa-induced changes even occur at the retinal level and support a dopaminergic involvement in light and dark adaptation. Our observations are in agreement with a VEP delay found in Parkinson's disease and with a VEP latency increase in rats after dopamine depletion.

Administration, Oral↗

PubMed1983

Visual evoked potentials in mild senile dementia of Alzheimer type.

Visual evoked potentials (VEPs) to chessboard shift and to flash stimulation were recorded from 40 subjects with senile dementia of Alzheimer type (SDAT) and 40 individually matched control subjects. All of the SDAT subjects had only a mild degree of dementia and were still living in the community. Analysis of variance showed significant differences between demented and control group means for 3 chessboard shift VEP measures, the demented group having longer latency of peaks P3 and N3, and larger amplitude of segment N2-P3. These three are the earliest reported changes in the VEP in Alzheimer disease, since the flash VEPs showed no measure in which the demented and control group means differed significantly.

Aged↗

PubMed1994

Visual evoked potentials following abrupt contrast changes.

The timing of visual evoked potential (VEP) amplitude and phase changes following abrupt increases or decreases in contrast was examined. Gratings (1 c/deg) were presented at a low contrast for 8 sec, increased to a higher contrast for 8 sec, and then decreased to the initial lower contrast for another 8 sec. Second harmonic VEP amplitude and phase were recorded continuously and averaged in 1 sec epochs. Both amplitude and phase exhibited delays in reaching a stable level following the contrast change. For amplitude, the length of the delay was dependent on the magnitude and direction of the contrast step and on the spatial frequency of the stimulus. Time constants for the change in amplitude following step increases in contrast ranged from 0.2 sec for a 12% contrast step to 1.34 sec for a 37% contrast step. The timing of phase changes, however, was independent of the size of the contrast increases (tau = 0.7 sec). For step decreases in contrast, both amplitude and phase were relatively independent of the size of the change (tau = approx. 0.9 sec for amplitude and tau = 0.15 sec for phase). Amplitude time constants also increased with increasing spatial frequency (tau = 1.2 sec for 1 c/deg, tau = 1.6 sec for 4 c/deg and tau = 2.3 sec for 8 c/deg); phase time constants, however, did not change as a function of spatial frequency (tau = 0.7 for all spatial frequencies). These findings demonstrate that a unitary process may not always be tapped by signal averaging techniques. Additionally, swept stimulus VEP techniques may produce considerable errors in threshold estimation depending on the stimulus spatial frequency and on the slope and direction of the contrast change.

Contrast Sensitivity↗

PubMed1986

The visual evoked potential in neonates with occipital lesions and holoprosencephaly.

Visual evoked potentials (VEPs) were studied in 4 preterm and 2 fullterm infants in whom unilateral lesions of the occipital cortex were demonstrable on cranial ultrasonography. In the neonatal period, symmetrical responses were recorded from the two hemispheres, and the VEPs only became asymmetrical at the age of 2-3 months. Evoked responses to flash stimulation were also recorded initially in an infant with complete holoprosencephaly. These findings, together with previous reports on the maturation of the VEPs in the neonatal period, suggest that the early evoked response may be subcortical rather than cortical in origin.

Brain↗

PubMed1998

Component wave analysis of flash visual evoked potentials in preterm infants.

Waveform analyses of flash visual evoked potentials (VEPs) in neurologically normal preterm infants (postconceptional age 31-42 weeks) were performed using an autoregressive moving average (ARMA) model to interpret the evoked potentials as dynamic high-order responses to natural and experimental stimulation. Averaged VEP waveforms obtained were decomposed into 7-11 component impulse response waveforms by an ARMA component wave analysis. Based on the histogram of damping frequencies of different component impulse response waveforms, the waveforms were divided into 6 groups. All characteristic values in Group IV (6.5-12.0 Hz), such as the energy, the percent energy and the damping time of component impulse responses, changed significantly with increasing postconceptional age. Among the component impulse responses, neuronal networks generating impulse responses classified into Group IV appeared to be important to the developmental change of VEPs in preterm infants. The identification of an impulse response component with a dominant frequency which undergoes a well-identified change with age might prove to be a useful tool for discriminating between normal and abnormal changes in the VEP with age in preterm infants and could aid in the early diagnosis of abnormalities.

Child Development↗

PubMed1988

Developmental changes of pattern reversal visual evoked potentials.

Analysis of developmental changes in pattern reversal visual evoked potentials (PVEPs) was performed on 141 normal children ranging in age from 1 month to 19 years 4 months. The stimulus was a black and white checkerboard pattern on a television screen, and the check edge subtended 50 min of retinal arc. The major positive peak (P2) was observed in all subjects, and the incidence of other peaks tended to increase with age. The P2 latency decreased rapidly during the first six months of life and reached a constant value after the age of 2 years. The P2 latency with monocular stimulation was significantly longer than that with binocular stimulation in most age groups. Developmental changes of the N1-P2 or P2-N2 amplitudes were unclear, and the standard deviation of the amplitude in each age was too large for clinical application. The P2 latency with binocular stimulation was shorter for females than for males only at the age of 8-11 years.

Adolescent↗

PubMed1985

Effect of contrast on fusional visual evoked potential (VEP): a model and experimental results.

A visual evoked potential (VEP) component that appears in the power spectrum only during binocular fusion has recently been discovered. When both eyes are stimulated with the same checkerboard but at different pattern reversal rates, this fusional component appears at a frequency intermediate between the two stimulus frequencies. We have proposed a model to explain the appearance of this intermediate component and have tested the model's predictions that the fusional component will remain constant independent of binocular or monocular changes in stimulus contrast. As predicted by the model, changes in contrast over the range of 10 to 90% produced no significant change in the power of the fusional component.

Evoked Potentials, Visual↗

PubMed1988

Visual evoked potentials of mildly mentally retarded and control children.

Visual evoked potentials (VEPs) were recorded from 25 10- to 13-year-old mildly mentally retarded children and compared with those from 31 control children of the same age-range. Correlations of VEPs with age were weak, but a relationship between VEPs and IQ was demonstrated for the control group. The retarded group had significantly longer latencies and higher amplitude peaks than the control group, with the differences occurring primarily over non-specific cortex and for secondary components. Analysis also showed that the retarded group were neurophysiologically heterogeneous. Since the same children had been analyzed earlier by quantitative EEG methods, comparisons are made with respect to these two methods of investigating brain function.

Adolescent↗

PubMed1983

Transient visually evoked potentials to sinusoidal gratings in optic neuritis.

Transient visually evoked potentials (VEPs) to sinusoidal gratings over a range of spatial frequencies have been recorded in cases of optic neuritis. The use of the response to pattern onset in addition to the response to pattern reversal extended the range to higher spatial frequencies by up to two octaves. There was an increase in VEP delay and a greater degree of discrimination from a control group at higher spatial frequencies. This finding is discussed in the light of previous reports of luminance and checkerboard VEPs in demyelinating optic nerve disease. An attempt is made to relate amplitude changes in various VEP components to contrast sensitivity measurements in this group of patients.

Evoked Potentials, Visual↗

PubMed1986

Anterior ischaemic optic neuropathy. A correlative clinical and visual evoked potential study of 18 patients.

The clinical and visual evoked potential (VEP) findings were analysed in 18 patients with anterior ischaemic optic neuropathy. The VEP studies showed a variety of abnormalities which could be interpreted as being the result of subcomponent interaction consequent upon loss or attenuation of the normal macular-derived P100 component. Delay of normal VEP subcomponents was not seen. The VEP findings were non-specific but pointed to a severe disturbance of transmission in optic nerve fibres subserving central vision. No significant changes were observed with time in most cases indicating a static monophasic process with no significant recovery.

Aged↗

PubMed1983

Visual evoked potentials in schizophrenia. Intensity effects and hemispheric asymmetry.

Visual evoked potentials (VEP) to different flash intensities were recorded at a central site (Cz) plus at homologous temporal and occipital locations in normal and unmedicated schizophrenic subjects. Schizophrenic patients showed an hemisphere asymmetry of the P100-N120 peak-trough amplitude with smaller left but larger right hemisphere amplitudes than normal. Further, two subgroups of patients were found with abnormalities lateralized to the left hemisphere. One group was found to have abnormal P100 amplitude-intensity patterns at the left temporal site while the other group showed deviant N120 amplitude-intensity patterns at the left occipital location. The clinical significance of these results can be seen in the higher nuclear schizophrenia (PSE-CATEGO) scores in the left temporal subgroup and the higher hypomania and situational anxiety scores in the left occipital group. Patients also showed slower than normal P100 and N120 peak latencies.

Adult↗

PubMed1991

Changes in the visual evoked potentials with different photic conditions in guinea pigs.

Visual evoked potential (VEP) was studied in five adult male guinea pigs weighing 350-750 g. VEPs were recorded with chronically implanted electrodes. Photic stimulation was presented in the following order: binocular, left eye, right eye, and screened binocular. The averages of the responses were made from 140 samples. When a single eye was exposed to photic stimulation, the ipsilateral VEP was different from the contralateral VEP; the peaks N140 and P200 disappeared, and the peak latencies of N75 and P100 were significantly (P less than 0.05) longer than those in the contralateral hemisphere. Peak-to-peak amplitude N40-P55 in the ipsilateral VEP was significantly (P less than 0.05) lower than that in the contralateral VEP. The contralateral VEP by monocular stimulation was generally indistinguishable from the response to binocular stimulation. As described above, when only a single eye was exposed to flashes, the ipsilateral dural VEP was different from the contralateral dural VEP.

Animals↗

PubMed1997

Temporal response characteristics of the spatiochromatic visual evoked potential: nonlinearities and departures from psychophysics.

Although the visual evoked potential (VEP) for isoluminant stimuli has been characterized in terms of spatiochromatic parameters, temporal tuning along various chromatic directions has received less systematic attention. Additionally, there has been little categorical comparison of psychophysical appearance with VEP responses obtained for temporal variation of these patterns. At appropriate contrasts the VEP's for color axes (LM, S) show a robust and contrast-sensitive temporal tuning peak at 4 Hz. Contrast response functions at 4 Hz for the LM color axis are markedly nonmonotonic. However, there is a clear monotonicity with contrast for VEP latencies along these color axes. The anomalous behavior does not appear to be due to interactions between chromatic signals, to luminance artifact, or to rod intrusion. These anomalies in the temporal characteristics of the chromatic VEP may reflect interactions between chromatic responses and inherent cortical responsivity not linked to psychophysical behavior.

Color Perception↗

PubMedDate not supplied

P2 latency of the flash visual evoked potential in dementia.

P2 latency of the flash visual evoked potential was found not to be prolonged in 13 demented patients compared to age normative predictions derived from a control group. This finding contrasts with a number of studies of demented patients that found P2 latency to exceed normative data. It was stated that the result of normal latency in dementia can hardly be explained only in terms of the sampling method used in this study (unselected dements) and that the finding is possibly due to the increase in latency across the adult life span in normal aging which was found to be much higher than previously reported.

Aged↗

PubMed1999

Early magnocellular loss in glaucoma demonstrated using the pseudorandomly stimulated flash visual evoked potential.

PURPOSE: Components of the pseudorandomly stimulated flash visual evoked potential (VEP) have now been identified that appear to arise predominantly from each of the magnocellular (M-cell) and parvocellular (P-cell) systems. In this study, the relative damage to magnocellular and parvocellular systems at different stages of glaucoma using pseudorandomly stimulated flash VEP was investigated. METHODS: Pseudorandomly stimulated flash VEP was recorded in 15 normal eyes and 28 eyes with different stages of glaucoma using the VERIS-3 recording system (Electro-Diagnostic Imaging, San Francisco, CA). Two levels of luminance contrast of the stimulus (32% and 99%) were tested. The first slice of the second-order kernel from only the central (8 degrees) stimulated area was extracted for analysis. RESULTS: Data recorded from normal eyes demonstrated early saturation of the response/contrast function of the first slice of the second-order kernel. The ratio of the VEP amplitude recorded at 32% and 99% of the luminance contrast was close to unity. In eyes with early glaucoma, although the amplitude of the responses to both low- and high-contrast stimulation decreased, the relative reduction of the low-contrast VEP (M-cell) was more prominent. However, the amplitude of the high-contrast response (P-cell) declined more rapidly later in the disease. CONCLUSION: These results are consistent with relatively earlier damage of the magnocellular pathway in glaucoma.

Adult↗

PubMed1991

Electroretinogram and visual-evoked potential measurements in sheep.

Electroretinogram (ERG) and visual-evoked potential (VEP) recordings were taken from ten Suffolk-cross sheep. Stimuli for VEP were 1.5 flashes of white light/s; ERG stimuli were single flashes. The ERG measurements of the a and b wave latencies and a-to-b amplitude were measured between the lower eyelid and the vertex, with ground on the nuchal crest. The VEP after monocular stimulation were measured between the nuchal crest and the interorbital line, with ground on the vertex. Measurements consisted of the latencies to seven alternating positive and negative peaks P1, N1, P2, N2, P3, N3 and P4, and six amplitudes, P1-N1, N1-P2, P2-N2, N2-P3, P3-N3 and N3-P4. Average latencies for the a and b waves were 13.6 and 28.2 ms; the mean ab amplitude was 131.68 microV. Average latencies for the seven VEP peaks were 35.0, 43.1, 52.8, 64.1, 74.5, 90.4 and 112.2 ms. Mean amplitudes ranged from 3.90 to 8.29 microV.

Animals↗