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At least 955 records · Page 53Linked to original sources
PubMed1999

The effect of odour priming on long latency visual evoked potentials of matching and mismatching objects.

This study reports a cross-modal, olfactory/visual event related potential (ERP) using odours as olfactory primes. The results show a difference in the ERP waveform for the N400 waveform when a visual image does not match the priming odour. An N400 peak was produced for both the matched and mismatched conditions but the peaks were significantly more negative for the mismatched condition. By the use of non-food odours this study extends an earlier finding by Grigor, who, using the same ERP paradigm, obtained similar results for food odours and photographs of food.

Adult↗
PubMed1979

Visual evoked potentials: a noninvasive technique to monitor patients with shunted hydrocephalus.

Visual evoked potentials (VEPs) to repetitive flash stimuli were abnormal in 10 patients with documented hydrocephalus. Abnormalities included latency delays, fatigability, and asymmetries. Both latency and wave form disturbances improved in the postshunt period. Clinical progression of the hydrocephalus occurred in several patients, and this correlated well with worsening of the VEPs. We suggest that this noninvasive technique may be valuable in following patients with cerebrospinal fluid shunts, patients with presumed "arrested" hydrocephalus, and patients who are being weaned from their shunts.

Adult↗
PubMed1980

Macula and periphery: their contributions to the visual evoked potentials (VEP) in humans.

An alternating checkerboard pattern subtending a visual angle of 25 min arc is capable of eliciting remarkably high amplitudes of visually evoked potentials (VEP) outside a visual angle of 2.5 degree. These contributions cannot be neglected when evaluating a VEP response obtained with a larger field of stimulation. When the retina is consecutively stimulated by concentric frame-shaped stimuli, the algebraic sum of all single cortical responses augmented the cortical response obtained when stimulating the whole field simultaneously by approximately 30%. This finding may be explained by the inhibiting interactions within the receptive field organisation of the retina.

Evoked Potentials↗
PubMed1994

Pattern reversal visual evoked potentials following early treatment of unilateral, congenital cataract.

OBJECTIVE: To describe the pattern reversal visual evoked potentials (VEPs) that were used to monitor and quantify early visual development following treatment for dense, unilateral, congenital cataract. DESIGN: Longitudinal prospective study. PATIENTS: Six infants who underwent surgery and contact lens correction before age 5 months and who had good compliance with occlusion therapy throughout the first 3 years of life. RESULTS: Initially, VEPs from aphakic eyes showed marked abnormalities, including small amplitudes, prolonged latencies, missing components, and absent VEPs to small check sizes. Threshold check size was elevated by 3 octaves or more. With part-time occlusion of the opposite eye, VEPs normalized rapidly in the first year, but residual deficits remained to age 4 years when visual acuities were between 20/50 and 20/120 in aphakic eyes. Threshold check size clearly differentiated between aphakic and normal eyes and was the only VEP parameter that was correlated with single-letter visual acuity. Thus, threshold check size had greater clinical use than measures of pattern VEPs based on latency, amplitude, or waveform. CONCLUSIONS: Patients treated for unilateral congenital cataract, who have early surgery and contact lens correction and comply with occlusion therapy, show a period of rapid VEP maturation and have a good visual prognosis.

Aphakia, Postcataract↗
PubMed1987

Effects of scopolamine parenteral administration on the electroretinogram, visual evoked potentials, and quantitative electroencephalogram of healthy volunteers.

Single intramuscular doses of scopolamine and matching placebo were administered to young, healthy, and emmetropic volunteers. Electroretinograms and visual evoked potentials (flash and pattern stimuli) were recorded prior to and 30, 90, and 120 min after administration. The effects of scopolamine at the central nervous system level were monitored also by quantitative electroencephalographic methods. Scopolamine reduced the peak-to-peak amplitude of the late components of the flash-evoked potential without affecting latencies. A decrease of the N75 latency and increment of N175 latency of pattern-evoked potentials were observed without any apparent modification of the amplitude values. These changes were not produced by administering topical cyclopentholate. Electroencephalographic effects were apparent with a longer delay after administration than were those on the visual evoked potentials. No significant modification was observed in the electroretinogram under these recording conditions.

Adult↗
PubMed1990

[Visual evoked potentials to a light flash in patients with optic nerve atrophy].

Informativeness of different methods used for registration of optic generated potentials in response to light flash (FOP) has been studied in 27 healthy persons and 21 patients (32 eyes) with partial atrophy of the optic nerve. It is shown that the most informative one for diagnosing optic nerve atrophy and determining visual acuity in such patients is a method of investigation of the critical incidence of rythm reproduction of FOP light flickerings. Considering the complexity and difficulty of the mentioned method for its practical usage, a simplified method is proposed; a registration of FOP of a stable state with the incidence of stimulations of 33 Hz, that allows to detect cases of pathology with visual acuity not less than 0.2.

Evoked Potentials, Visual↗
PubMed2000

[The effect of dopamine injected into the lateral brain ventricle on flash visual evoked potential (FVEP) after prenatal intoxication with cadmium].

PURPOSE: Earlier studies demonstrated that exposure, especially prenatal, of mammalians to cadmium (Cd) results in disorders of visual evoked potentials (FVEP). The purpose of this study is to find out any influence of cadmium intoxications on the effect of dopamine (DA) on FVEP. METHOD: 18 Wistar albino rats in 3-6 months of age were divided into 3 groups: control (drinking tap water only), prenatal exposure of 5 ppm, and 50 ppm Cd. Flash visual evoked potentials (FVEP) were recorded before and after injections of dopamine (DA) 100 and 200 nmols into the lateral brain ventricle. The amplitude and latency of N1 and P2 were statistically analysed by the test of t-Student. p < 0.05 was used to indicate significant difference. RESULTS: There were no statistical differences of mean latency of P2 waves between initial records of FVEP and after both doses of DA in all observed groups. The amplitudes of both waves increased after DA injections compared to initial values in all groups. The differences were statistically significant. The mean latencies of N1 peak were prolonged after both DA doses (106-109%) compared to the initial records (100%) in the control group; however, there were no changes of it in the Cd-treated groups before and after DA injections. CONCLUSION: Cadmium blocked the dopamine effect on the latencies of N1 and P2 of FVEP (because it prolonged them alone); however, cadmium increased the stimulative effect of dopamine on their amplitudes.

Animals↗
PubMed1994

A personal computer-based visual evoked potential stimulus and recording system.

A system for recording electroretinograms and visual evoked cortical potentials has been constructed with the use of a personal computer and a digital signal processing card. The system is based on widely available commercial hardware. It has been designed to be capable of performing routine visual electrophysiology as well as allowing the development of novel visual stimuli and signal detection techniques. The system enables both transient and steady-state stimulation rates. Pattern stimuli can be presented in pattern-reversal, pattern-onset, pattern-offset or motion-onset modes. In addition to conventional signal averaging, the digital signal processing card can also provide on-line Fourier analysis and is facilitating the development of adaptive filtering techniques for the detection of steady-state visual evoked cortical potentials. This versatile system is in regular clinical use for the measurement of electroretinograms and visual evoked cortical potentials.

Electrophysiology↗
PubMed1997

Simultaneous recording of pattern reversal electroretinograms and visual evoked potentials in migraine.

We recorded full-field pattern reversal electroretinograms (PERGs) and visual evoked potentials (PVEPs) simultaneously in 15 migraine with aura, 14 migraine without aura patients during the interictal period, and in 23 sex- and age-matched normal subjects. All subjects had normal visual fields. The visual aura in all patients was hemianopsia or fortification spectra. Neither migraine group showed significant differences from normal in latency and amplitude of PERGs. In migraine with aura, the amplitudes of PVEPs in classic migraine at the mid-occipital electrode were significantly (p < 0.01) higher than normal. PVEP amplitudes were significantly (p < 0.01) higher on the contralateral side of the aura than the ipsilateral side in both visual aura and normal subjects, but there was no significant difference in latency. This high amplitude and asymmetry of PVEPs may contribute to defective inhibition between interhemispheric visual occipital areas or striate and peristriate areas.

Adult↗
PubMed1981

Life-span change in visually evoked potentials at central scalp.

Three intensities of patterned flash were used to elicit visually evoked potentials (VEPs) from central scalp of 220 healthy males aged 4-90 years. Intensities were based on visual thresholds. VEP components from children and oldsters were generally larger than those of subjects of intermediate ages and, in response to increased flash intensity, demonstrated greater amplitude enhancement. This pattern of age changes is thought to reflect decreased cortical inhibition in the young and the old with inhibitory capacity being maximal during late adolescent and early adult years. Hemispheric asymmetries were observed. VEP amplitudes from the right hemisphere were larger than those from the left and demonstrated a greater amplitude augmentation to brighter flashes.

Adolescent↗
PubMed1988

Visual evoked potentials to multiple temporal frequencies. Use in the differential diagnosis of optic neuropathy.

The usefulness of the visual evoked potential (VEP) in differential diagnosis increases when stimulus parameters such as check size and grating orientation are varied. In this study we varied the stimulation frequency. Temporal frequency-specific abnormalities were compared in three patient categories, including retrobulbar optic neuritis (eight patients), pseudotumor cerebri (11 patients), and thyroid eye disease (seven patients). All patients had minimal clinical evidence of optic nerve damage when tested. A 2.3 cycle-per-degree sinusoidal grating of 55% contrast was phase reversed at either 1 or 4 Hz. The P1 latency of the 1-Hz data and the phase at 8 Hz, the second harmonic of the 4-Hz input frequency, were measured. In retrobulbar neuritis, latency (phase) was severely abnormal at both temporal frequencies. In thyroid eye disease, VEP phase was abnormal at 8 Hz while the P1 latency was normal at 1 Hz. The P1 latency and phase were normal in most cases of pseudotumor cerebri. The results suggest differing mechanisms for damage in compressive vs primary demyelinating neuropathies.

Adolescent↗
PubMed2006

Steady-state visual evoked potentials: distributed local sources and wave-like dynamics are sensitive to flicker frequency.

Steady-state visual evoked potentials (SSVEPs) are used in cognitive and clinical studies of brain function because of excellent signal-to-noise ratios and relative immunity to artifacts. SSVEPs also provide a means to characterize preferred frequencies of neocortical dynamic processes. In this study, SSVEPs were recorded with 110 electrodes while subjects viewed random dot patterns flickered between 3 and 30 Hz. Peaks in SSVEP power were observed at delta (3 Hz), lower alpha (7 and 8 Hz), and upper alpha band (12 and 13 Hz) frequencies; the spatial distribution of SSVEP power is also strongly dependent on the input frequency suggesting cortical resonances. We characterized the cortical sources that generate SSVEPs at different input frequencies by applying surface Laplacians and spatial spectral analysis. Laplacian SSVEPs recorded are sensitive to small changes (1-2 Hz) in the input frequency at occipital and parietal electrodes indicating distinct local sources. At 10 Hz, local source activity occurs in multiple cortical regions; Laplacian SSVEPs are also observed in lateral frontal electrodes. Laplacian SSVEPs are negligible at many frontal electrodes that elicit strong potential SSVEPs at delta, lower alpha, and upper alpha bands. One-dimensional (anterior-posterior) spatial spectra indicate that distinct large-scale source distributions contribute SSVEP power in these frequency bands. In the upper alpha band, spatial spectra indicate the presence of long-wavelength (> 15 cm) traveling waves propagating from occipital to prefrontal electrodes. In the delta and lower alpha band, spatial spectra indicate that long-wavelength source distributions over posterior and anterior regions form standing-wave patterns. These results suggest that the SSVEP is generated by both (relatively stationary) localized sources and distributed sources that exhibit characteristics of wave phenomena.

Adult↗
PubMed1979

Possibilities of simultaneous analysis of phasic pupillary light reflex and visual evoked potentials.

A report of first results of a simultaneous analysis of the phasic pupillary light reflex and visual evoked potentials (VEP). It is shown that combination of pupillography with VEP analysis can be of some use in the diagnosis of conductive defects of the optic nerve (e.g. optic neuritis). Furthermore, the simultaneous analysis allows distinction between subclinical disturbances of the afferent and efferent arcs of the pupillary light reflex. Assuming a lesion of the afferent arc secondary to damage to the optic nerve, an increase of both the pupillomotor and the VEP latencies is seen. With lesions of the efferent arc (e.g. in the case of a third nerve palsy) only the pupillomotor latency is altered. Potentialities and disadvantages of the method are discussed.

Adult↗
PubMed2006

Visual evoked potential in the newborn: does it have predictive value?

We reviewed studies on the predictive value of visual evoked potentials (VEPs) in the newborn. VEPs demonstrated a good correlation with neurodevelopmental outcome in full-term infants with birth asphyxia. However, their prognostic value in preterm infants is controversial. In preterm infants, most studies showed high specificities for neurodevelopmental outcome, but some studies demonstrated lower sensitivities.

Electroencephalography↗
PubMedDate not supplied

Temporal frequency responsivity shows multiple maturational phases: state-dependent visual evoked potential luminance flicker fusion from birth to 9 months.

Maturation of temporal resolution was investigated in a visual evoked potential study in 77 infants from birth to 9 months of age. Luminance evoked potential measures in response to homogeneous sinusoidal flickering light (1-64 Hz) were recorded under behavioral state-defined conditions. Behavioral state was determined by direct observation and by polygraphic recording of the electroencephalogram (EEG), eye movements (EOG), muscle activity (EMG), heart rate (ECG), and respiration. Temporal-frequency functions of the amplitude of the fundamental response across the temporal-frequency range were recorded during sleep and wakefulness. The highest temporal-frequency response recorded during wakefulness was accepted as a measure for inclusion in a growth function of temporal-frequency responsiveness. The resulting temporal resolution frequency vs. age function showed three separate maturational phases. Maturational phases were defined as (1) an initial slow phase from 1-32 days postnatal during which maturation of temporal vision is unremarkable; (2) an intermediate rapid phase of improvement from age 26 to 170 days; and (3) an overlapping but final slow phase from 151 to at least 270 days during which adult-like flicker resolution is approximated. This study suggests that the multiple maturational phases of the infant's responses to flickering light are due to maturational differences, which correspond with maturation of structural factors of brain function. Finally, across the age span tested, high-frequency responsivity was influenced significantly by the degree of infant arousal.

Adult↗
PubMedDate not supplied

Visual evoked potentials for red-green gratings reversing at different temporal frequencies: asymmetries with respect to isoluminance.

Human visual evoked potentials (VEPs) were recorded for abrupt reversals of 2 cycles/deg (c/deg) square-wave gratings combining high red-green contrast with different levels of luminance contrast. Response characteristics--2nd harmonic amplitudes and peak latencies as a function of luminance contrast--were compared for four different reversal rates ranging from 6.25 Hz to 12.5 Hz. At every reversal frequency, the VEP amplitude and latency plots were nonsymmetrical with respect to isoluminance. The amplitude dropped to a minimum within a region of rapid phase change, always at a red-green luminance contrast for which the green color had the higher luminance, at about 40% or 50% Michelson luminance contrast. The rapid phase shift around this contrast suggested a sudden change in the relative impact of VEP generators with different latencies, possibly dominated by parvocellular or magnocellular input. The most prominent VEP waveform through most of the luminance contrast range, P110, is interpreted in terms of a parvo-mediated response that is attenuated with increasing reversal frequency. Contrast-dependent changes in the P110 amplitude appear to be responsible for the VEP asymmetries reported here.

Adult↗
PubMed2001

Effects of attention on pattern-reversal visual evoked potentials: foveal field stimulation versus peripheral field stimulation.

The effects of foveal field attention on pattern reversal visual evoked potential (VEP) were investigated in thirteen normal subjects. Conventional monocular VEP was recorded during the three conditions of control, foveal concentration and reaction time task. Three patterns of checker-board, which were full field (radius, 0-9 degrees), peripheral field (2.5-9 degrees) and foveal field (0-2.5 degrees), were presented for the stimulation in each condition. The P100 and N145 amplitude of the peripheral field VEP were significantly smaller during the concentration and the reaction time task conditions that that in the control session, while the foveal field VEP amplitudes were enhanced in the concentration and reaction time tasks conditions. The full field VEP amplitudes were not significantly changed by the conditions. We concluded that the act of concentration to the foveal field or the task requiring attention to the foveal field, enhanced the VEP response to foveal field stimulation and suppressed the VEP to the peripheral field. A gating effect in area V1 was speculated, although extra-striate cortex might contribute.

Adult↗