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Results for “Evoked Potentials, Visual”

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PubMed1987

Single sweep analysis of visual evoked potentials through a model of parametric identification.

An original method is presented for the single sweep analysis of visual evoked potentials (VEP's). The introduced algorithm bases upon an AutoRegressive with eXogenous input (ARX) modeling. A Least Squares procedure estimates the coefficients of the model and allows to obtain a complete black-box description of the signal generation mechanism, besides providing a filtered version of the single sweep potential. The performance of the algorithm is verified on proper simulation tests and the experimental results put into evidence the noticeable improvement of signal-to-noise ratio with a consequent better recognition of the classical parameters of the peaks (latencies and amplitudes). The possibility of measuring these parameters on a single sweep basis enables to evaluate the dynamics of the Central Nervous System response during the entire course of the examination. A classification of the estimated evoked potentials in a small number of subsets, on the basis of their morphology, is also possible.

Algorithms↗

PubMed1994

Periodic synchronous discharges and visual evoked potentials in Creutzfeldt-Jakob disease: PSD-triggered flash VEPs.

We have developed the technique of flash visual evoked potentials (VEPs) triggered by periodic synchronous discharges (PSDs) to investigate the interaction between PSDs and VEPs in 3 patients with Creutzfeldt-Jakob disease (CJD). This technique enables us to explore the cerebral pathophysiology underlying CJD. Unexpectedly, we found that PSDs and VEPs did not interact even when VEPs were evoked in close temporal proximity to PSDs. Thus, it appears that PSDs are generated by a different neuronal mechanism from that involved in VEP generation.

Adult↗

PubMed1995

Comparison of the pattern reversal visual evoked potential mediated by separate cone systems.

With the purpose of recording responses mediated by the 3 cone systems visual evoked potentials (VEPs) were elicited by the reversal of monochromatic checkerboards superimposed upon strong monochromatic backgrounds (yellow, purple and blue-green). The sensitivity to light of various wave lengths were measured as the reciprocal of the intensity necessary to elicit a VEP amplitude of 3 microV. The spectral sensitivity curves based on this VEP amplitude criterion in the presence of blue-green, purple and yellow adaptation showed peak sensitivities in the red, the green and the blue part of the spectrum, respectively. This indicates that the responses reflect separate modulation of the 3 different cone mechanisms. The potentials obtained with yellow adaptation differed from those obtained with purple and blue-green adaptation. The amplitude versus log intensity function was flatter and the latency of the major positive peak was increased by 20-25 msec. Repeated examinations of 4 subjects suggest that the method yields reliable latency measurements of responses mediated by separate cone mechanisms.

Adult↗

PubMed2004

The evolutionary change of flash visual evoked potentials in preterm infants with periventricular leukomalacia.

OBJECTIVE: The aim of this study was to prospectively investigate flash visual evoked potential (VEP) findings and their chronological changes in preterm infants with cystic periventricular leukomalacia (PVL) during the early neonatal period. METHODS: The subjects of this study were 14 preterm infants with cystic PVL. The patients underwent serial cranial ultrasonography and diagnosed as having cystic PVL. Flash VEPs were diagnosed at least twice within the first 3 weeks of life. RESULTS: All infants had at least one or more flash VEP abnormalities. The most common finding was 'absent VEP', which was seen in 13 infants (93%). 'Delayed latency' was seen in two infants and 'abnormal waveform' was seen in one infant. Concerning the chronological changes, all records were abnormal in 4 infants, and the other 10 had transient normal VEP findings. Among them, flash VEPs changed from normal to abnormal within 10 days after birth in most cases. CONCLUSIONS: Almost all infants with cystic PVL had abnormal flash VEPs within the first 3 weeks of life, but chronological changes of flash VEP findings were seen during the period. SIGNIFICANCE: This manuscript may be useful as a reference to the flash VEPs in preterm infants with cystic PVL.

Cerebral Cortex↗

PubMed1999

Edge detection and surface 'filling in' as shown by texture visual evoked potentials.

OBJECTIVES: We designed a stimulation paradigm that was designed to ascertain whether specific components of the texture visual evoked potentials were attributable to edge detection or to surface 'filling-in' processes. METHODS: The stimuli were textures of parallel line elements, which were either uniform (all horizontal or vertical lines) or segregated (checkerboards in which texture line elements of neighbor checks were oriented orthogonally). A sequence of 4 stimuli, two uniform followed by two segregated stimuli, was repeated cyclically. Accordingly, segregation could appear from a uniform display; it could also be maintained, with the checkerboard illusory margin location unchanged but with alteration in the orientation of all line elements. Each stimulus was presented for 487 ms and instantly replaced by the following one. RESULTS: Segregation-related components for segregation-appearance (Sa) and for segregation-maintenance (Sm) conditions were obtained separately by subtraction. In both conditions, a negative component was obtained with a peak latency of about 140-150 ms. However, the onset of Sa was earlier than that of Sm, whereas the respective offsets were almost identical. CONCLUSIONS: We hypothesize that the segregation component in VEPs is composed of two subcomponents: an early part, which is related to the segregation of edges, and a final part, which is related to the 'filling-in' of the homogeneous texture surface within the boundary defined by these edges.

Adolescent↗

PubMed2003

The effects of certain H(1)-antagonists on visual evoked potential in rats.

The present study was undertaken to clarify the effects of certain H(1)-antagonists on visual evoked potential (VEP) in rats. Pyrilamine (5 and 10 mg/kg), diphenhydramine (5 and 10 mg/kg) and chlorpheniramine (10 and 20 mg/kg) caused a significant reduction in the amplitude of late VEP components (P(3)-N(3), N(3)-P(4)), although these drugs showed no significant changes in early VEP components (P(1)-N(1), N(1)-P(2)). Cyproheptadine caused a slight enhancement of late components of VEP at a dose of 20 mg/kg. On the other hand, epinastine caused no significant effect on late VEP components even at a dose of 20 mg/kg. The reduction in the late VEP components induced by pyrilamine and diphenhydramine was significantly antagonised by pre-treatment of histidine (200 and 500 mg/kg), but not by physostigmine even at a dose of 0.01 mg/kg. The effect induced by cyproheptadine was significantly potentiated by histidine (500 mg/kg), and significantly reduced by DOI (2 mg/kg). These results indicate that an inhibition of the late VEP components induced by H(1)-antagonist pyrilamine, diphenhydramine and chlorpheniramine may be due to an inhibition of specific sensory system relating the histaminergic mechanisms. In addition, slight enhancement of these components induced by cyproheptadine may be attributable to its anti-serotonergic effects.

Administration, Oral↗

PubMedDate not supplied

Visual evoked potentials for reversals of red-green gratings with different chromatic contrasts: asymmetries with respect to isoluminance.

Human visual evoked potentials (VEPs) were recorded for abrupt 6.25-Hz reversals of 2 c/deg square-wave gratings combining red-green contrast with different levels of luminance contrast. Response characteristics-- amplitudes and peak latencies as a function of luminance contrast--were compared for four different pairs of red-green colors and an isochromatic yellow grating. For each of the red-green color pairs, the plots of VEP amplitudes and latencies were nonsymmetrical with respect to isoluminance. The amplitude dropped to a minimum within a region of rapid phase change, at a different contrast for each color pair but always at a luminance contrast for which the greener color had the higher luminance. When the contrast-response curve for each of the four red-green pairs was modeled by a simple |CL - CM| opponency of L- and M-cone contrast using a fixed CL/CM weighting ratio of about two, there was a close correspondence between the contrast giving a null in the modeled response and that giving a minimum in the VEP amplitude. So for the stimulus parameters applied here, the reversal VEP appeared to be dominated by L/M-opponent response contributions for which the signed CL/CM-cone weighting ratio was close to a value of minus two rather than to a value of minus one, which is characteristic of the psychophysical red-green detection mechanism and representative of CL/CM weighting ratios for precortical cells in the parvocellular pathway.

Adult↗

PubMed2003

Diagnostic utility of visual evoked potential changes in Alzheimer's disease.

Previous studies have consistently found a selective delay of the P2 flash visual evoked potential (VEP) component among groups of patients with Alzheimer's dementia (AD) compared with control groups. Several authors have termed the selective P2 delay a "marker" for AD and have called for its use in clinical diagnosis. This study examined the diagnostic utility of the selective P2 delay in a retrospective sample of 45 AD patients and 60 age-equivalent healthy control subjects. Although significant between-group differences were found, classification accuracies for individual patients and controls were too low for the P2 delay to contribute meaningfully to clinical diagnosis.

Aged↗

PubMedDate not supplied

Inverse relationship between nonverbal intelligence and the parameters of pattern reversal visual evoked potentials in left-handed male subjects: importance of right brain and testosterone.

The relationships between latencies of visual evoked potentials (VEPs) and nonverbal intelligence test scores (IQs from Cattell's Culture Fair Intelligence Test) and correlations between serum testosterone level and VEP latencies were studied to examine the neural speed hypothesis of intelligence and its hormonal mechanisms in left-handed male subjects (Geschwind Scores). In accordance with the speed theory of intelligence, N1 and P1 latencies (and amplitudes) were found to be inversely related to IQ. However, this was true only for the right brain; the left brain did not contribute to this relationship. There was an inverse relationship between serum testosterone level and P1 latency; left minus right N1 latency, depending on N1 latency from right brain, linearly increased with testosterone. It was concluded that nonverbal intelligence largely depends on speed of information processing only by the right brain, not by the left brain in left-handed male subjects. This may have been created by testosterone in these subjects. Inconsistencies in the IQ literature concerning the speed hypothesis of intelligence may be explained by differences in cerebral lateralization.

Adolescent↗

PubMedDate not supplied

[Visual evoked potentials and the P300 component in different courses of the posttraumatic vegetative state].

The late latency components of visual evoked potentials (VEP) and the component P300 AEP were analyzed to evaluate their informative value in the process of mental function restoration in patient after long-term traumatic coma. VEP components with latencies of 70 to 320 msec were studied in 24 patients. Topographical mapping of the power of the study VEP components and components P300 was made by the peak amplitude. Long-term VEP components and component P300 were examined by the method of three-dimensional localization of equivalent dipole sources. In 16 patients with positive tendencies in the condition there was a stable localization of the maximum VEP power in the parietal, sagittal, and occipital regions, component P300 showed its maximum amplitude in the central and parietal regions in the left hemisphere. Eight patients with negative tendencies in the status had the maximum VEP and component P300 in the frontal and temporal regions, predominantly in the right hemisphere. The paper shows it important to evaluate not only time-amplitude parameters and analyzes the tomographic features of its formation in dynamics.

Acoustic Stimulation↗

PubMed2000

[Application of numeric integration in waveform morphology of visual evoked potentials in optic nerve diseases. Numeric integration method].

PURPOSE: Presentation of new waveform analysis of pattern and flash visual evoked potentials (VEPs) in patients with optic neuropathy. MATERIAL AND METHODS: The study involved 48 patients with acute optic neuritis (2nd group), 60 patients with demyelinating (3rd group), 32 patients with compressive (4th group), 24 patients with nonarteritic anterior ischemic optic neuropathy (5th group) and 32 healthy subjects (1st group). Using computer system UTAS E-1000 (pattern and flash stimulation) the VEPs tests were performed. Amplitude, latency of 8 VEP components, 4 gradients, mean waveform and 16 areas of numeric integrals were calculated. Results were analysed with the use of AN-STAT software. RESULTS: Statistical difference recorded under pattern stimulation was obtained in latency of 3rd, 4th, 5th components of VEP in comparing 3th and 4th groups, as well as amplitude of 3rd waveform, second gradient, areas of integrals between cursors number 2 and 4 in comparing 3rd and 5th groups (p < 0.001). Statistical difference recorded under flash stimulation was obtained in latency of 4th component in comparing 2nd and 5th groups, in amplitude of 7th waveform, areas of integrals covering 160 and 224, 224 and 256 ms, between cursors number 2 and 4 in comparing 4th and 5th groups, as well as in a range of areas of integrals covering 160 and 192 ms in comparing 4th and 5th groups (p < 0.001). CONCLUSION: Results prove clinical potency of the presented new comprehensive method in analysis of VEP in optic nerve diseases.

Acute Disease↗

PubMed2002

[Flash visual evoked potentials (FVEP) examination under midazolam sedation of non-cooperating children].

PURPOSE: To find the optimal conditions for visual evoked potential (VEP) examination of non-cooperative children using midazolam maleate sedation. PATIENTS: 32 children aged from 8 months to 13 years (mean 3.5 years) with mental disorders, emotional problems and/or very low vision due to various reasons. METHODS: VEP--flash and bright flash according to ISCEV standards. Midazolam maleate sedation 0.4-0.5 mg per kilo body weight, given orally. RESULTS: Only 6 children aged from 11 months to 3.5 years (mean 2.5 years) required sedation for VEP examination. Midazolam sedation unabled VEP examination, was safe for children and well-tolerated. CONCLUSION: Second degree sedation in Ramsey score is effective for good VEP examination of non-cooperative children.

Anxiety↗

PubMedDate not supplied

Reliability and upper normal variability limits of pattern reversal visual evoked potential parameters.

Twenty healthy volunteers aged 21-48 years (10 males, 10 females) were submitted to pattern reversal visual evoked potentials with 15' and 30' checks. The recordings were repeated after 7 days to assess reliability and upper normal variability limits of the following parameters: latencies of N70, P100, N140 and peak-to peak amplitudes of N70-P100, P100-N140. Reliability was tested with intraclass correlation coefficient, which was excellent or good for all parameters. Test-retest variability limits were computed with = 0.01 for absolute latency differences and relative amplitude differences.

Adult↗

PubMedDate not supplied

[Studies on cerebral visual evoked potentials in the differential diagnosis of macular edema and obscration amblyopia in children with artiphakia].

The cerebral cortex visual evoked potentials (VEP) to chess pattern reversion have been examined in 41 healthy children (41 eyes) and in 25 children (25 eyes) with artiphakia after traumatic cataract extraction, with macular edemas (ME) in 12 of these and obscuration amblyopia (OA) in 13. Comparison of the amplitude-time parameters of the VEP and of treir relationship with the cell size and the chess pattern contrast has shown a characteristic feature of ME, i. e. an increased peak latency (PL) of the first negative deviation (H1 peak) of the VEP to reversion of the chess pattern with 90% contrast. The mean values of PLHI (M +/- m) have been as follows: 107.1 +/- 3.9 ms in children with ME, 93.1 +/- 2.3 ms in those with OA, and 84.9 +/- 0.8 ms in the controls. An elevation of PLHI over 100ms has been recorded in 9 of the 12 patients with ME and only in 1 child with OA. Involvement of the ganglion cells of the central area of the retina is considered as a possible reason of the detected VEP disorders in ME.

Adolescent↗

PubMed1996

[Use of pattern and flash visual evoked potentials in differential diagnosis of optic neuropathy].

PURPOSE: To assess the value of pattern and flash stimulus of visual evoked potentials (VEP) in patients with optic neuropathy. MATERIAL AND METHODS: The study involved 11 patients with compressive optic neuropathy, 19 with acute optic neuritis and 22 with demyelinating optic neuropathy. The control group included 20 persons without history of ocular and neuroophthalmologic diseases. In all patients VEP were performed using pattern and flash stimulus. Multidimensional analysis of variance (MANOVA) was used which allowed to evaluate the differentiation efficacy in respective parameters as well as the whole distinguishable classes. RESULTS: The efficacy of differential diagnosis of examined optic neuropathy with pattern or flash VEP was not sufficient. Better results were achieved when both types of stimulus were applied in the same patient.

Adolescent↗

PubMed1998

[Results of investigations of visual evoked potentials in the treatment of amblyopia].

PURPOSE: The aim of the study is to demonstrate the changes in visual evoked potentials (VEP) in treatment of amblyopia. MATERIAL AND METHODS: Pattern reversal VEP of 28 children treated because of amblyopia and 16 healthy persons were analysed. Before treatment and after treatment the results of the interocular amplitude difference ratio and interocular latency difference ratio were compared with standards. RESULTS: After treatment of amblyopia the percentage of normal interocular amplitude and latency difference ratios increased. CONCLUSION: Study of pattern VEP enables monitoring of amblyopia treatment.

Amblyopia↗

PubMedDate not supplied

[Operative memory and evoked visual potentials].

Changes in human EEG and event-related potentials to the complex color stimulus were studied during performance of three cognitive tasks: passive viewing, visual searching, and memorizing and storing of the stimulus in the operative memory. It was shown that involvement of memory mechanisms resulted in the alpha rhythm suppression in both occipital and frontal brain areas. It was also accompanied by a generation of the slow positive component in the evoked potential recorded in the frontal areas (in the occipital areas this wave was manifested as negative).

Adult↗

PubMed1983

Maturational sequence of the visual system: serial measurements of visual evoked potential and electroretinogram in the healthy neonatal lamb.

The value of measurements of visual evoked potential (VEP) for neurological assessment of the adult is widely accepted. Its use for neonatal evaluation following birth asphyxia has been limited by our knowledge of developmental changes occurring in the newborn brain. VEPs and electroretinograms (ERGs) were simultaneously recorded from five healthy newborn lambs from birth until 30 days of life. Newborn age was then compared with amplitude (height of the signal) and latency (time from stimulus to a specific wave deflection) measurements from these neuroelectrical signals. Latencies to A wave (photoreceptor activity) and B wave (bipolar and ganglion cells) of the ERG declined in a small but significant manner, while the latency interval from A to B wave did not change with age. Latency to wave N1 of the VEP remained stable while latency to P2 declined from birth to 30 days. The ERG and VEP signals exhibited linear increases in amplitude as the lambs became older. We conclude from these observations that ganglion and bipolar cells (B wave of the ERG) within the retina and primary nerve tracts (N1 of the VEP) along the visual system are mature at birth. In contrast, photoreceptor activity within the retina (A wave of the ERG) and nerve conduction through the visual cortex (P2 of the VEP) exhibit changes which are consistent with ongoing maturation of these more specialized areas through the early newborn period.

Animals↗