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Results for “Evoked Potentials, Visual”

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PubMed2004

Visual evoked potentials in workers with chronic solvent encephalopathy.

OBJECTIVES: Two promising variations of visual evoked potentials (VEPs) were studied in solvent-exposed workers: the effect of a low-contrast stimulus in comparison with the usually applied high contrast, and the ability of pattern-onset VEP to reveal damage to specific visual cortical areas. In addition, we studied disturbances of a visual event-related potential (P300). METHODS: Thirty male patients (48 +/- 9 years of age) with solvent-induced chronic encephalopathy, and 41 controls (46 +/- 8 years) without solvent exposure, participated. Pattern-reversal checkerboards with low (11%) contrast and with high (93%) contrast between the checks were used. For onset VEPs two dedicated stimulus patterns were used. P300 was elicited with an "oddball" paradigm. RESULTS: At low contrast the N75-P100 peak-to-peak amplitude in the controls was 9.6 +/- 4.9 microV, i.e. 57% of the amplitude at high contrast (16.3 +/- 7.2 microV). In the patients the response at low contrast was only 48% of that at high contrast; the corresponding amplitudes were 7.5 +/- 3.5 microV and 15.8+/-4.9 microV. For the pattern-onset VEPs no effect of exposure was found. With regard to the P300, the patients missed more targets (average 3.6%) than did the controls (average 0.5%). Patients had a smaller P300 amplitude (8.8 +/- 4.5 microV) than the controls (11.5 +/- 5.3 microV), and a longer latency (390 +/- 34 ms compared to 376 +/- 24 ms). CONCLUSION: The results point to a physiological basis for the solvent-induced decrease of visual contrast sensitivity as found by others by means of psychophysical methods. The results also suggest that the neurophysiological examination of the visual system in persons who have undergone exposure to toxins might be benefited by the addition of low-contrast stimuli.

Adult↗

PubMed1990

[A dual process model for on and off visual evoked potentials].

A model of consisting of excitatory and inhibitory processes was proposed for visual evoked potentials (VEPs) from the midline occiput (Oz). On and off stimulation of circular lights subtending 2 degrees and 5 degrees in visual angle were presented with luminance contrast of 1.0, 2.2, and 3.4. The typical triphasic data from a well trained male subject were analysed and decomposed into the two monophasic processes by using the optimal model parameters (amplitude, delay, and peak latency). Then those parameters were predicted by the multiple regression method with the variables for the present experimental conditions. The shapes of the model VEPs were fairly well fitted for ones of the raw data. The model was discussed with its relation to other perceptional phenomena, especially, flickering, forward and backward masking, and spatio-temporal properties, as well as with the physiological aspects. Finally, it was suggested that the dual process model for VEPs would be useful to investigate as well as to explain the spatio-temporal characteristics of the human visual system.

Electroencephalography↗

PubMed1985

Cortical visual evoked potentials during the sleep-wakefulness cycle in the freely moving cat. A dynamic study.

The dynamic features of visual evoked potentials, elicited by a light emitting diode chronically implanted in the frontal sinus of the freely moving cat, were studied during sleep stages by means of calculation of the power spectra of the EEG prior to the stimulus and the poststimulus EEG which contain the single evoked potential. The statistical analysis between mean frequencies from both EEG prior to the stimulus and single evoked potential, within each sleep stage, showed that the main changes occurred during slow sleep, with a significant increase in the percentage of the alpha band. These results are interpreted as a partial desynchronization evoked by the visual stimulation during the synchronized phase of sleep.

Animals↗

PubMed2006

Attention induces synchronization-based response gain in steady-state visual evoked potentials.

When attention is voluntarily directed to a spatial location, visual sensitivity increases at that location. What causes this improved sensitivity? Studies of single neuron spike rates in monkeys have provided mixed results in regard to whether attending to a stimulus increases its effective contrast (contrast gain) or multiplicatively boosts stimulus-driven neural responses (response or activity gain). We monitored frequency-tagged steady-state visual evoked potentials (SSVEPs) in humans and found that voluntary sustained attention multiplicatively increased stimulus-driven population electrophysiological activity. Analyses of intertrial phase coherence showed that this attentional response gain was at least partially due to the increased synchronization of SSVEPs to stimulus flicker. These results suggest that attention operates in a complementary manner at different levels; attention seems to increase single-neuron spike rates in a variety of ways, including contrast, response and activity gains, while also inducing a multiplicative boost on neural population activity via enhanced response synchronization.

Adult↗

PubMed1993

Visual evoked potentials in adrenoleukodystrophy: a trial with glycerol trioleate and Lorenzo oil.

Adrenoleukodystrophy is an X-linked metabolic disorder with very-long-chain fatty acid (VLCFA) accumulation and multifocal nervous system demyelination, often with early involvement of visual pathways. Dietary therapy with glycerol trioleate and glycerol trierucate (Lorenzo oil) diminishes VLCFA levels. In a study of patients with the adrenomyeloneuropathy phenotype of adrenoleukodystrophy, we used pattern-reversal visual evoked potentials to evaluate visual pathways before and after treatment. Of 108 patients tested, all 26 women and 68 of the 82 men had normal potentials at baseline. Seventy patients were retested at 1 year, at which time VLCFA levels were markedly diminished. Of them, the responses in the 10 men who showed abnormalities at baseline remained abnormal; the latencies in 4 men with initially normal responses became abnormal. No patients improved. There were no correlations between disease duration prior to treatment, baseline P100 latencies, VLCFA levels, or the change in P100 latencies and VLCFA levels after dietary treatment for 1 year. Pattern-reversal visual evoked potentials were abnormal in 17% of the men with adrenoleukodystrophy, and there was no evidence that reduction of VLCFA levels improved or retarded visual pathway demyelination.

Adolescent↗

PubMed1994

[Stereoscopic visual evoked potential elicited by static random dot stereogram].

Using 16.56' visual disparity stimulation produced by television random dot stereogram (TVRDS), we recorded visual evoked potentials (VEPs) elicited from 35 normal subjects with and without breaking their stereopsis and 28 stereoblind subjects. The results showed that a constant negative-positive wave complex was observed in 33 of 35 normal subjects; this negative-positive wave-complex disappeared when the stereopsis was artificially inhibited by a prism and in the stereoblind group, and no VEP wave was elicited in all of the stereoblind patients except in one with paralytic strabismus. The results revealed that under this condition the VEPs elicited by TVRDS were specific VEPs related to visual disparity stimulation and were stereoscopic ones. The TVRDS is an effective electro-physiological means to examine the stereopsis objectively and a new way to approach the occurrence and development of stereopsis.

Adolescent↗

PubMed2006

The acute effect of cigarette smoking on pattern visual evoked potentials.

Reports of tobacco-induced electrocortical activation and decrements in ocular blood flow in the acute phase indicated that this effect is mediated via nicotine's action or neuronal systems. In this study, pattern visual evoked potentials were investigated in a group of male smokers (22 right eyes of 22 subjects) in separate real smoking and sham smoking sessions. On each session, pattern visual evoked potentials were recorded before smoking, immediately after smoking, and five minutes after smoking. Latency and amplitude values for P100 peaks were assessed and analyzed in each smoking condition for both real smoking and sham smoking sessions. Real smoking significantly decreased P100 latency values (p value related to difference between pre-smoking and immediately after smoking conditions is 0.009) and increased P100 amplitude values (p value related to difference between pre-smoking and fifth minute after smoking is 0.039). Statistically no significant difference was observed in sham smoking sessions. Our results are consistent with smoking-induced stimulant effects on pattern visual evoked potentials.

Adult↗

PubMed2005

Early visual evoked potentials in callosal agenesis.

Three participants with callosal agenesis and 12 neurologically normal participants were tested on a simple reaction time task, with visual evoked potentials collected using a high-density 128-channel system. Independent-components analyses were performed on the averaged visual evoked potentials to isolate the components of interest. Contrary to previous research with acallosals, evidence of ipsilateral activation was present in all 3 participants. Although ipsilateral visual components were present in all 4 unilateral conditions in the 2 related acallosal participants, in the 3rd, these were present only in the crossed visual field-hand conditions and not in the uncrossed conditions. Suggestions are made as to why these results differ from earlier findings and as to the neural mechanisms facilitating this ipsilateral activation.

Adult↗

PubMed1998

A periodogram-based method for the detection of steady-state visually evoked potentials.

The task of objective perimetry is to scan the visual field and find an answer about the function of the visual system. Flicker-burst stimulation--a physiological sensible combination of transient and steady-state stimulation--is used to generate deterministic sinusoidal responses or visually evoked potentials (VEP's) at the visual cortex, which are derived from the electroencephalogram by a suitable electrode array. In this paper we develop a new method for the detection of VEP's. Based on the periodogram of a time-series, we test the data for the presence of hidden periodic components, which correspond to steady-state VEP's. The method is applied successfully to real data.

Electroencephalography↗

PubMed1997

Local luminance and pattern reversal stimuli yield different visual evoked potential topography.

We studied how the stimulation of quadrants of the visual field affect brain potential topography, and we compared activity elicited by conventional pattern reversal or by local luminance stimuli. The method of quasi-simultaneous stimulation of many small visual field elements by binary m-sequences allowed us to reconstruct the potentials evoked at each of 54 visual field locations independently. Data from all field elements within each quadrant and in the whole stimulation field were summed and compared to those elicited by checkerboard reversal stimuli presented in the four quadrants or as full field stimuli. In twenty-two healthy adults evoked brain activity was recorded in 30 channels with an electrode array densely spaced over the occipital brain areas. With local flash stimuli as well as with checkerboard reversal the topographical distributions of cortical activation changed significantly with retinal stimulus location. Analysis of three components occurring between 50 and 240 ms revealed significant differences between pattern reversal and local luminance evoked brain activity. Reversal stimuli yielded not only larger amplitudes but also a completely different component structure and topography. Our results illustrate that different neuronal generators are activated by pattern reversal and local luminance stimuli although visual field location of the stimuli was identical indicating that the same retinal and cortical structures respond in a different way depending on stimulation mode.

Adult↗

PubMedDate not supplied

[The negative components of visual evoked potentials in the mechanisms of the classification of incomplete images].

Event-related brain potentials were recorded in 16 young adult subjects in response to a short presentation of recognizable and nonrecognizable visual images with an incomplete set of signs. Sequential brain maps and amplitude-temporal ERP parameters in 1000 ms poststimulus epoch were estimated (BMDP 4M and 7M, 1987). The results suggested that the component N450 was specifically related to a perception of nonrecognizable visual images. N70 and N150 reflected voluntary attention during invariant recognition and the late negative waves (600-1000 ms) reflected an "exhaustive search" for categorization of new information.

Adult↗

PubMed1997

Nonlinear analysis of visual evoked potentials elicited by color stimulation.

The relationship between chromatically modulated stimuli and visual evoked potentials (VEPs) was considered. VEPs of normal subjects elicited by chromatically modulated stimuli were measured under several color adaptations, and their binary kernels were estimated. Up to the second-order, binary kernels obtained from VEPs were so characteristic that the VEP-chromatic modulation system showed second-order nonlinearity. First-order binary kernels depended on the color of the stimulus and adaptation, whereas second-order kernels showed almost no difference. This result indicates that the waveforms of first-order binary kernels reflect perceived color (hue). This supports the suggestion that kernels of VEPs include color responses, and could be used as a probe with which to examine the color visual system.

Adaptation, Ocular↗

PubMed2006

Myelin deficiencies visualized in vivo: visually evoked potentials and T2-weighted magnetic resonance images of shiverer mutant and wild-type mice.

Visually evoked potentials (VEPs) and micro magnetic resonance imaging (micro MRI) are widely used as noninvasive techniques for diagnosis of central nervous system (CNS) diseases, especially myelin diseases, such as multiple sclerosis. Here we use these techniques in tandem to validate the in vivo data in mouse models. We used the shiverer mutant mouse, which has little or no CNS myelin, as a test model. These data show that shiverer (MBP(shi)/MBP(shi)) has a VEP latency that is 30% longer than that of its wild-type sibling. Surprisingly, the heterozygous (MBP(shi)/+) mouse, with apparently normal myelin, nevertheless has a 7% increase in its VEP latency vs. wild type. The micro MRIs of the same animals show that myelinated white matter is hypointense compared with gray matter as a result of the shorter T2 in myelinated regions of the CNS. T2-weighted images of wild-type and heterozygous shiverer mice show regions of hypointensity corresponding to the major myelinated tracts, including the optic nerve and the optic tract of the CNS, whereas shiverer mice have no regions of low intensity and therefore no detectable myelinated areas. In shiverer mice, micro MRI can discern hypomyelination throughout the brain, including the optic tract, and these changes correlate with longer VEP latencies. In addition, VEPs can also detect changes in the molecular make up of myelin that are not discernible with histology or micro MR. These data show the potential of using micro MRI in combination with VEPs to follow changes in both the quality and the quantity of myelin in vivo. These combined methods would be useful for longitudinal studies and therapy testing.

Animals↗

PubMed1991

Color pattern-reversal visual evoked potential in eyes with ocular hypertension and primary open-angle glaucoma.

Color pattern-reversal visual evoked potential testing was performed in 99 normal eyes, 27 eyes with ocular hypertension and 30 eyes with primary open-angle glaucoma with the use of black-white, black-red and black-blue color checkerboard stimuli. The P1 wave peak time and amplitude of the eyes with ocular hypertension and glaucoma were significantly different from those of age-similar normal eyes, especially on the black-red and black-blue checkerboards (p less than 0.001). The differences between the ocular hypertensive and glaucomatous eyes were of less significance. The P1 peak time difference between black-white and black-red checkerboards may serve as an important parameter in the early diagnosis of glaucoma.

Adolescent↗

PubMed1982

The visually evoked potential in humans with amblyopia: pseudorandom modulation of uniform field and sine-wave gratings.

The visually evoked potential was recorded in response to pseudorandom modulation of a uniform field and sine-wave gratings in humans with naturally occurring amblyopia. Analysis in the frequency domain showed similar temporal tuning when the nonamblyopic and amblyopic eye were stimulated with a uniform field and with spatial stimuli. Although most observers showed some reduction in the cortical response to stimulation of the amblyopic eye with uniform field modulation, all observers showed reductions in the response obtained for stimulation of the amblyopic eye with spatial stimuli. This decrease in the cortical response to stimulation of the amblyopic eye for sine-wave gratings was present at either the low and middle temporal frequencies or over the range of temporal frequencies tested, and was greater than that observed in those amblyopes who also showed reductions with uniform field modulation. Latency measures in the time domain showed increases in the response of the early components when the amblyopic eye was stimulated with a uniform field and with sine-wave gratings above 2 c/deg. These electrophysiological results confirm the results obtained psychophysically which suggest that although amblyopia is primarily a spatial anomaly, the response is influenced by the temporal attributes of the stimulus as well.

Adolescent↗

PubMed1995

Source model and scalp topography of pattern reversal visual evoked potentials to altitudinal stimuli suggest that infoldings of calcarine fissure are not part of VEP generators.

Visual evoked potentials (VEPs) to pattern reversal vertical bar stimuli were recorded from 19 scalp, 2 zygomatic and 3 inion derivations referenced to digitally linked earlobes in 50 controls. 1, 2 and 4 cycles per degree (cpd) patterns were presented as full field (FF) stimuli, on upper and lower hemifields (UHF-LHF), upper and lower quadrants and with the occlusion of central and peripheral UHF and LHF. VEPs to octant stimuli were also recorded with 2 cpd patterns. N1, P1 and N2 components were recorded from posterior and inion derivations with FF stimuli, from posterior derivations with LHF stimuli, only from inion leads with UHF stimuli, from derivations ipsilateral to stimuli with quadrants and octants, and from midline derivations only with lower quadrants. Polarity inverted sequences (iP1-iN1-iP2) were recorded from the other scalp derivations, with similar latency and spatial frequency sensitivity as N1-P1-N2. The orientation of Equivalent Dipoles (ED) was orthogonal with surface coordinates of mesial and occipito-polar calcarine cortex, measured on Magnetic Resonance Imaging. A model of VEP generators is proposed, suggesting that the VEP sequence is elicited only in mesial and occipito-polar surfaces of calcarine cortex.

Adult↗

PubMed1991

Aminophylline reduces cerebral blood flow in stable, preterm infants without affecting the visual evoked potential.

The effect of intravenous aminophylline (10 mg/kg) on cerebral blood flow (CBF) and single flash visual evoked potential (VEP) was investigated in 16 preterm infants (range 25-34 weeks). All infants were weaned from mechanical ventilation and had normal brain ultrasonograms. CBF, PaO2, PaCO2, mean arterial blood pressure and VEP were recorded before, immediately after and 1 h after the administration of aminophylline. When intra-individual changes in PaCO2 were taken into account, mean CBF was 5.5% lower than the baseline value immediately after administration of aminophylline, but this was not statistically significant (P = 0.14). After 1 h, however, CBF had decreased by a mean of 13.8% (P = 0.0003). The cerebral function estimated from VEP was not influenced by aminophylline since the VEP configuration and the VEP parameters remained constant throughout the study. It is concluded that aminophylline reduces cerebral blood flow in stable, preterm infants and apparently without inducing adverse effects on cerebral function.

Aminophylline↗

PubMed1986

Effect of central scotomata on pattern reversal visual evoked potentials in patients with maculopathy and healthy subjects.

The effect of central scotomata on pattern reversal visual evoked potential (PVEP) was investigated in patients with maculopathy and healthy subjects. PVEP was evoked monocularly by both full-field and half-field stimulations. Since the latency of 'the major positivity at Oz' (P100-Oz) is used as the most reliable parameter in the clinical application of PVEP, special attention was focused on its changes, comparing with 'ipsilateral major positivity of half-field PVEP' (P100-IHF). Although the incidence of modification was lower in the patients, central scotomata modified PVEPs of the healthy subjects and of the affected eye of the patients in a similar manner: full-field PVEP showed prolonged latency and reduced amplitude of P100-Oz. Half-field PVEP disclosed prolonged P100-Oz latency with intact P100-IHF latency. Only difference was that amplitude reduction of both P100-Oz and P100-IHF of half-field PVEP was observed only in the healthy subjects. The prolonged P100-Oz latency of half-field PVEP was accompanied, both in the healthy subjects and in the patients, by a contralateral negative-positive complex (N105-P135) which was augmented and extended to Oz. The prolonged P100-Oz latency, thus, was due to the pronounced P135. These observations suggested that an attenuation of the afferent impulses from the central retina may cause a prolongation of the P100-Oz latency in both healthy subjects and patients, but this is not a reflection of the truly prolonged P100-IHF latency. It was concluded that, in the clinical application of PVEP, recordings of half-field PVEP from the lateral electrodes seem to be essential to distinguish true prolongation of the P100-Oz latency.

Adolescent↗