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Results for “Evoked Potentials, Visual”

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PubMed1992

Activation state of the cortex could be changed by reinforcement of low-amplitude visual evoked potentials in rabbits.

Visually evoked potentials (VEP) were recorded chronically from occipital cortex in awake rabbits. The VEP typically consisted of a triphasic response (positive deflection P60--negative deflection N205--positive deflection P450) that was followed by a late negative shift starting about 750 ms after the eliciting flash. After computation of a discriminating amplitude value (200 or 250 microV) the VEP were divided for comparison in high- and low-amplitude groups. Significant differences between these groups existed in amplitudes and latencies of the early VEP components. High-amplitude VEP were followed by larger late negative shifts and had significantly (P less than 0.01) earlier second positive deflections. In these high-amplitude cases, the EEG-baseline was more negative than in the low-amplitude VEP. In addition, we found a more synchronized background EEG in the low-amplitude VEP group. We conclude that different VEP amplitudes depended on different activation states of the cortex which could be changed by reinforcement.

Animals↗

PubMed2003

Adaptation characteristics of steady-state motion visual evoked potentials.

OBJECTIVE: Motion visual evoked potentials (motion VEPs) are used in clinical diagnosis and basic research. Employing steady-state rather than the usual transient motion VEPs simplifies statistical evaluation and might drastically reduce examination durations. Protocols for recording transient motion-onset VEPs usually involve fairly long recovery intervals between trials to avoid neural adaptation. This is not feasible for steady-state VEPs. We investigated how adaptation affects the steady-state motion VEP. METHODS: Oscillatory (13.3rev/s) and continuous uni-directional random-dot motion served as adaptation stimuli. Steady-state motion VEPs and, for comparison, transient motion VEPs were recorded. RESULTS: In the first experiment, we investigated how adaptation affects the recordings. Contrary to our expectation, we did not find any sizable effect. However, there was a large inter-individual variability in steady-state amplitude and no correlation across subjects between transient and steady-state amplitude. In the second experiment, we confirmed that the steady-state VEP reflects veridical motion processing by assessing its susceptibility to uni-directional pre-adaptation. CONCLUSIONS: Taken together, the results suggest that steady-state motion VEPs provide a fast method of recording motion responses without suffering from adaptation, but at the expense of inter-individual reproducibility.

Adaptation, Physiological↗

PubMed1983

Visual evoked potentials in alcoholics.

Visual evoked potentials were obtained in nineteen patients during the early phase of alcohol intoxication. Out of the thirty-eight responses recorded in the nineteen patients, 13% were found to be abnormal (5 responses). Repeated testing was done in all patients with abnormal responses at three to four week intervals following treatment with vitamins and balanced diets. In three patients the major positive peaks returned to normal after treatment.

Adult↗

PubMed1990

The clinical significance of the bifid or "W" pattern reversal visual evoked potential.

Although the visual evoked potential (VEP) to an alternating checkerboard stimulus is usually recorded from the occipital midline as an N-P-N complex with a major positive deflection at 100 ms (P100), a wave form exhibiting a P-N-P or "W" morphology is occasionally encountered and its interpretation is the source of some controversy. A retrospective chart review identified 15 patients exhibiting the "W" VEP. This represented 7.6 percent of 197 VEP studies and 5.1 percent of 394 eyes. The response was encountered in 1.7 percent of 57 normal patients and 21.4 percent of 56 patients with definite, probable or possible multiple sclerosis (P less than .001). The "W" response was considered normal in only one patient. Of the remaining 14 cases, 13 had definite, probable or possible MS and one had ischemic optic neuropathy. It is concluded that the "W" VEP is an aberrant response that is rarely seen in normals and may have the same significance as a delayed P100 latency.

Adult↗

PubMed2002

Early detection of hepatic encephalopathy by recording visual evoked potential (VEP).

The visual evoked potential (VEP) record in response to a pattern stimulus is a non invasive and reliable method of detecting central and peripheral nerve system abnormalities. VEP recording have been used in animals with fulminant hepatic failure, and also in-patients with hepatic encephalopathy and acute severe hepatitis. Our aims were: a. to evaluate the potency of PVEP in assessing hepatic encephalopathy. b. to find the rate of pathologic PVEP in patients with advanced liver cirrhosis. VEP was recorded in 14 chronic liver cirrhotic patients (6 alcoholic, 6 HCV-related, 2 cryptogenic) and 14 controls. Patients with any neurologic abnormalities were excluded from the study. All patients were subjected to the Mental State Score (MSS) test, and venous blood ammonia was measured on the same day of VEP recording. In 10/14 (71%) patients some VEP recording abnormality was detected. In the cirrhotic patients, P100 latency was significantly longer (P < 0.05) than in controls. Low amplitude was observed in 8 patients compared to controls. Marked increase of N75 (3 patients) and marked increase of N145 (2 patients) were observed. Mean blood ammonia and MSS score were normal in all patients. No correlation was found between both MSS score and blood ammonia levels and the P100 delay. Five out of 10 patients with pathologic VEP developed hepatic encephalpathy during a follow-up of one year, compared to one out of 4 patients with no pathology on VEP recording. VEP recording may be a valuable tool in assessing patients with early hepatic encephalopathy and in predicting encephalopathy.

Adult↗

PubMed1990

Pattern-reversal visual evoked potentials in children with migraine: a correlation analysis.

Visual potentials evoked by pattern reversal (PRVEPs) were studied in 64 normal children (age range 7 to 15 years) and in 20 age-matched patients with common and complicated migraine (age range 6 to 16 years). Most of them were studied before and during prophylactic therapy. A Quadristim set (Alvar) was used to present checkerboard patterns on a TV monitor, to amplify the EEG signals and to average and plot the evoked potentials. The potentials were elicited by binocular full-field 2/s checkerboard reversal, recorded from an electrode 4 cm above the inion, and analyzed for latency, amplitude and waveform morphology. The degree of similarity between pairs of PRVEPs was determined by the correlation coefficient. In all our patients no pronounced influence of the disease itself was demonstrated on the PRVEP latencies and amplitudes, but in most of them the correlation coefficients were significantly different from that showing the measure of normal PRVEP variations. Prophylactic medication influenced non-significant increase of the coefficient. This increase seems to be related to recovery from medication in terms of attack frequency. No significant difference in PRVEP results of common and complicated migraine was noticed. The PRVEP distortion can be revealed by the correlation coefficient but not by other PRVEP parameters. Therefore, this parameter may be useful as a sensitive measure of both PRVEP distortion and PRVEP improvement. Our results give further evidence that non-demyelinating disorders, but with ischemic damage and abnormalities in neurotransmitters, can produce measurable changes in PRVEP morphology.

Adolescent↗

PubMed2003

Differential effects of low-frequency rTMS at the occipital pole on visual-induced alpha desynchronization and visual-evoked potentials.

Visual-induced alpha desynchronization (VID) and visual-evoked potentials (VEPs) characterize occipital activation in response to visual stimulation but their exact relationship is unclear. Here, we tested the hypothesis that VID and VEPs reflect different aspects of cortical activation. For this purpose, we determined whether VID and VEPs are differentially modulated by low-frequency repetitive transcranial magnetic stimulation (rTMS) over the occipital pole. Scalp EEG responses to visual stimuli (flashed either to the left or to the right visual field) were recorded for 8 min in six healthy subjects (1) before, (2) immediately following, and (3) 20 min after left occipital rTMS (1 Hz, 10 min). The parameters aimed to reduce cortical excitability beyond the end of the TMS train. In addition, simple reaction times to visual stimulation were recorded (left or right hand in separate blocks). In all subjects, VID was significantly and prominently reduced by rTMS (P = 0.0001). In contrast, rTMS failed to modulate early VEP components (P1/N1). A moderate effect was found on a late VEP component close to manual response onset (P = 0.014) but this effect was in the opposite direction to the VID change. All changes were restricted to the targeted left occipital cortex. The effects were present only after right visual field stimulation when a right hand response was required, were associated with a behavioral effect, and had washed out 20 min after rTMS. We conclude that VID and early VEPs represent different aspects of cortical activation. The findings that rTMS did not change early VEPs and selectively affected VID and late VEPs in conditions where the visual input must be transferred intrahemispherically for visuomotor integration (right visual field/right hand) are suggestive of rTMS interference with higher-order visual functions beyond visual input. This is consistent with the idea that alpha desynchronization serves an integrative role through a corticocortical "gating function."

Adult↗

PubMedDate not supplied

The effect of motion on pattern-onset visual evoked potentials in adults and children.

Visual evoked potentials can be elicited by a variety of visual stimuli, including pattern-onset and motion-onset. It may be desirable to combine pattern-onset with motion-onset stimuli, for example, to make a direct comparison between optokinetic nystagmus and visual evoked potential acuity thresholds. Both procedures employ grating stimuli; however, the gratings must be moving to produce optokinetic nystagmus. We compared pattern-onset visual evoked potentials with both a static and a moving pattern to investigate the effect of motion on the pattern-onset visual evoked potential waveform. Visual evoked potential recordings were made from 10 adults (aged 20-37 years) and 10 children (aged 5-7 years) with the active electrode at Oz. Stimuli consisted of onset of high-contrast vertical bars of three sizes (12', 30' and 60') both with and without motion (3 cycles/s). In a subgroup of subjects, visual evoked potentials were recorded to motion onset of constantly present gratings. Motion of the pattern had no significant effect on any of the latency components of the visual evoked potential waveform in adults or children. The amplitude of the C2-C3 component was significantly increased (p < 0.001) in adults. The motion appears to add a late negative component to the visual evoked potential similar to that produced by the motion-only stimulus. The latency of the early components of the pattern-onset visual evoked potential was unaffected by the presence of motion. Therefore, pattern-onset visual evoked potentials with moving gratings could be used to estimate visual acuity, and direct comparisons could be made between visual evoked potential and optokinetic nystagmus acuity thresholds with the use of the same stimulus parameters.

Adult↗

PubMed1992

Use of 10-Hz flash visual evoked potentials in prediction of final visual acuity in diabetic eyes with vitreous hemorrhage.

In 44 diabetic eyes with vitreous hemorrhage, monocular steady-state visual evoked potentials were elicited through closed eyes by a 10-Hz flash. Visual evoked potentials were rated as normal or abnormal on the basis of amplitude and waveform. Abnormal visual evoked potentials were subdivided into mildly abnormal, markedly abnormal and nonrecordable categories. Patients with normal potentials were predicted to have visual acuities of 6/15 (20/50) or better. Patients with abnormal potentials were predicted to have visual acuities of 6/18 (20/60) or worse. Final visual acuities were the best visual acuities recorded in the 6 months after vitreous surgery (vitrectomy) or spontaneous clearing of the vitreous hemorrhage. The visual evoked potential categories and final acuities were compared with a 2 x 2 contingency table. The accuracy was 86%. The visual evoked potential categories and final acuities were associated at a statistically significant level.

Adult↗

PubMed2006

Clinical ability of pattern electroretinograms and visual evoked potentials in detecting visual dysfunction in ocular hypertension and glaucoma.

OBJECTIVE: To assess the presence of normal or abnormal pattern electroretinogram (PERG) and visual evoked potential (VEP) responses in patients with ocular hypertension or open-angle glaucoma (OAG). DESIGN: Retrospective, cross-sectional, case-control study. PARTICIPANTS: Eighty normal control subjects (mean age, 51.77+/-6.04 years; 80 eyes), 68 ocular hypertension patients (mean age, 51.58+/-7.12; 68 eyes; intraocular pressure [IOP] < 18 mmHg under pharmacological treatment; Humphrey field analysis [HFA] 24/2 mean deviation [MD] > -2 decibels [dB]), and 84 OAG patients (mean age, 52.77+/-5.28; 84 eyes; IOP < 18 mmHg under pharmacological treatment; HFA 24/2 mean deviation between -2 and -23 dB) were enrolled. METHODS: Simultaneous recording of PERGs and VEPs using high-contrast (80%) 15' checkerboard stimuli reversed at the rate of 2 reversals per second. MAIN OUTCOME MEASURES: Pattern electroretinogram P50 and VEP P100 implicit times were considered delayed when exceeding the limit of mean values of controls plus 2 standard deviations (SDs). Pattern electroretinogram P50 to N95 and VEP N75 to P100 amplitudes were considered reduced when exceeding the limit of mean values of controls minus 2 SDs. RESULTS: Pattern electroretinogram: P50 implicit times were delayed in 58 of 68 (85.30%) ocular hypertension eyes and 83 of 84 (98.80%) OAG eyes; P50 to N95 amplitudes were reduced in 47 (69.12%) ocular hypertension eyes and 84 (100%) OAG eyes. Visual evoked potential: P100 implicit times were delayed in 58 (85.30%) ocular hypertension eyes and 84 (100%) OAG eyes; reduced N75 to P100 amplitudes were observed in 39 (57.35%) ocular hypertension eyes and 73 (86.90%) OAG eyes. Ocular hypertension eyes showed no significant correlations (Pearson test, P>0.01) between electrophysiological parameters and age, IOP before or under medical treatment, HFA, and corneal thickness values. Significant correlations (P<0.01) were observed in OAG eyes between electrophysiological results and HFA values. Pattern electroretinogram and VEP responses were normal in all control eyes. CONCLUSIONS: Combined PERG/VEP recordings identified a large percentage of ocular hypertension eyes with impairment of the innermost retinal layers, notwithstanding normal optic disc morphology and normal HFA. In OAG eyes, PERG P50 to N95 amplitude and VEP P100 implicit time showed the highest sensitivity/specificity for the detection of a visual dysfunction. The presence of abnormal PERG and/or VEP responses did not allow a clearcut separation between ocular hypertension and OAG eyes.

Adult↗

PubMed1991

Pattern reversal visual evoked potentials in fencers.

Visual evoked potentials were recorded from occipital and temporal leads in the two cerebral hemispheres of eight fencers and eight control subjects. The stimulus was a checkerboard subtending a small (1 degree) or large (30 degrees) visual field. Significant differences in P60, N75 and P100 latency and amplitude were found between the two subject groups, especially during the processing of the large visual field. In fencers and left-handers shorter latencies were found for the large visual field condition, whereas right-handers showed an opposite trend. The results give further evidence of special patterns of visual processing in athletes, like fencers, in agreement with the literature.

Adolescent↗

PubMedDate not supplied

[Effect of abstinence on visual evoked potentials in alcoholics].

Visual evoked potentials (VEP) were studied in 61 alcohol-dependent subjects analysing the amplitude and latency of the first major positive wave (P100) and carrying out the determinations three times, in the 1st, 2nd and 3rd weeks of abstinence. The results were compared with similar ones obtained in healthy subjects without a history of alcohol abuse. In the acute stage of alcohol withdrawal a significant rise was observed in the amplitude of the cortical P100/N120 complex. With regression of the clinical symptoms of withdrawal syndrome the amplitude of visual potentials decreased and demonstrated partial normalization. The mean P100 latency was significantly longer in relation to the control group and was not changed during the withdrawal period. Amplitude increase was regarded as an evidence of hyperexcitability of the central nervous system, and latency prolongation as a result of the toxic effects of alcohol and nicotine on the optic nerve.

Acute Disease↗

PubMedDate not supplied

[Effect of the spatial frequency of sinusoidal gratings on amplitude and temporal parameters of visual evoked potentials in man].

Visual evoked potentials (EPs) in response to sinusoidal gratings of different contrast, with spatial frequencies of 0,5-15 cycles/grad presented in "on-off" order, were studied in six grown-up subjects with normal sight. Peak latencies of all EP components and the amplitude of the relatively early N95-130-P-120-190 complex increased with increasing spatial frequency. Presentation of low-frequency gratings led to an increase of the late EP complex (N150-230-P 210-290). The EP configuration in response to sinusoidal gratings of different spatial frequencies determined by the dominance of the early or late EP complex is supposed to reflect involvement of independent mechanisms of processing of information on low or high spatial frequency differently localized in the visual cortex.

Adult↗

PubMed1998

Spontaneous EEG theta activity controls frontal visual evoked potential amplitudes.

Frontal visual evoked potentials (VEPs) were studied in order to extend the application of a recently introduced algorithm for selective averaging of evoked potentials. This algorithm is based on the inverse relationship between amplitudes of alpha or theta components of the spontaneous EEG activity and evoked potential (EP) amplitudes. Stimuli were only applied if the root mean square (RMS) value of the ongoing EEG at the lead F4 was below an individual threshold level ('selective stimulation'). For this comparison, the EEG was filtered in one of the frequency ranges 'alpha', 'theta' and 'alpha and theta', respectively. 'Alpha' and 'alpha-and-theta-dependent' selective stimulation conditions resulted in significant amplitude increases (P < 0.05) at the input reference channel F4 and partly at ipsihemispherical temporal and parietal leads and at Cz. The largest increase of 35% at F4 (P < 0.01) was obtained with visual stimulation during low prestimulus theta activity. We conclude that spontaneous theta activity of the frontal cortex may be a factor influencing the amplitudes of frontal VEPs. A sophisticated analysis of frontal EPs, mainly in the framework of cognitive studies, should consider the theta activity prior to stimulation.

Adult↗

PubMed1995

[Abnormalities of pattern reversal evoked visual potential in patients with defined multiple sclerosis].

The pattern reversal visual evoked potential with checks of 14' and 28' was retrospectivelly studied in 28 patients with definite multiple sclerosis. We observed abnormal responses in 27/28 (96.4%) patients, in 31/36 (86%) of symptomatic eyes, and in 16/20 (80%) of asymptomatic eyes. When we classified the abnormalities in each eye according to the findings obtained with each check, there was a correlation between the pattern of abnormalities and the severity of visual involvement. Occasionally there were isolated abnormalities of N75 or only in P100 obtained with 28' checks. In conclusion the methodology applied was very sensible in detecting abnormalities in visual pathway. We could classify the findings in each eye and correlate them with the severity of visual involvement. The findings showed uneven distribution of lesions in visual pathway, affecting preferentially the central vision afferents.

Adult↗

PubMed1984

Visual evoked potentials to lateralized visual stimuli and the measurement of interhemispheric transmission time.

Visual evoked potentials (VEPs) to lateralized light flashes were recorded from the parietal midline, and from homologous occipital and central sites, in a GO/ NOGO reaction time task. The N160 component of the VEP was found to be larger over the hemisphere contralateral to the visual field of stimulus exposure at all pairs of lateral electrodes. At the occipital sites only, N160 latency was also shorter from the contralateral hemisphere, by an average of approximately 14 msec. This was not so centrally, where a non-significant value of approximately 4 msec was obtained. These data are considered to be consistent with Milner and Lines' hypothesis that callosal transmission occurs at different rates in different functional regions of the corpus callosum.

Cerebral Cortex↗

PubMed2005

Objective perimetry using the multifocal visual evoked potential in central visual pathway lesions.

AIMS: To examine the ability of the multifocal pattern visual evoked potential (mVEP) to detect field loss in neurological lesions affecting the visual pathway from the chiasm to the cortex. METHOD: The mVEPs recorded in the clinic were retrospectively reviewed for any cases involving central neurological lesions. Recordings had been performed with the AccuMap V1.3 objective perimeter, which used an array of four bipolar occipital electrodes to provide four differently oriented channels for simultaneous recording. 19 patients with hemianopias were identified. Of these there were 10 homonymous hemianopias with hemifield type loss, two bitemporal hemianopias, and seven homonymous hemianopias with quadrantanopic distribution. A comparison with subjective field results and CT/MRI findings was done to determine the relation between the two methods of visual field mapping and any relation with the anatomical location of the lesion and the mVEP results. RESULTS: In all hemianopic type cases (12) the defect was demonstrated on the mVEP and showed good correspondence in location of the scotoma (nine homonymous and two bitemporal). The topographic distribution was similar but not identical to subjective testing. Of the seven quadrantanopic type hemianopias, only four were found to have corresponding mVEP losses in the same areas. In the three cases where the mVEP was normal, the type of quadrantanopia had features consistent with an extra-striate lesion being very congruous, complete, and respecting the horizontal meridian. CONCLUSIONS: The mVEP can detect field loss from cortical lesions, but not in some cases of homonymous quadrantanopia, where the lesion may have been in the extra-striate cortex. This supports the concept that the mVEP is generated in V1 striate cortex and that it may be able to distinguish striate from extra-striate lesions. It implies caution should be used when interpreting "functional" loss using the mVEP if the visual field pattern is quadrantic.

Adult↗

PubMed1992

Visual evoked potential estimation of visual activity with a Laplacian derivation.

Visual acuity was estimated with visual evoked potentials in 13 healthy subjects. A Laplacian derivation of 5 electrodes was used to improve the signal-to-noise ratio and to enhance striate cortical activity selectively. In 6 subjects, the Laplacian derivation gave a more reliable estimation of visual acuity than did a single midline derivation. In the other 7 subjects, the quality of both estimations was comparable.

Electrodes↗