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Results for “Evoked Potentials, Visual”

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PubMed1991

Naloxone effects on the visual evoked potentials recorded from the main and accessory visual pathways of the cat.

1. The effects produced by repetitive i.v. administration of naloxone (1, 2 or 4 mg/kg) on the visual evoked potentials (VEPs) recorded along the main and accessory visual pathways were investigated in a modified "encéphale isolé" cat preparation. 2. Naloxone provoked a progressive amplitude enhancement and latency reduction of some components, depending on the structure analyzed, the dose used and the number of administrations applied. Electroretinogram (ERG) and N1-P1 VEP components of optic chiasm (OCh), lateral geniculate body (LGB) and visual cortex (VC) did not present significant changes. 3. Late-latency components (more than 200 msec) appeared in the VEPs of LGB and VC, mainly when 4 mg/kg were used. 4. Our results suggest that endogenous opioids have a modulatory role in the processing of sensory information at different levels of the visual system.

Animals↗

PubMed2006

Visual evoked potentials in neonatal hyperbilirubinemia.

The management of neonatal hyperbilirubinemia is very standardized. However, there is a lack of an objective method to evaluate the cerebral effects of bilirubin apart from brainstem auditory evoked potentials. There were few studies evaluating the effects of hyperbilirubinemia or phototherapy on the visual pathway in infants with hyperbilirubinemia. Serial visual evoked potentials of two groups of term neonates (N = 24)--group 1 with moderate hyperbilirubinemia (n = 16) and group 2 with severe hyperbilirubinemia (n = 8)--were evaluated prospectively. All infants had regular physical, neurologic, visual, and auditory evaluations until 3 years. Four (16%) had abnormal visual evoked potentials before 1 year, and the abnormalities returned to normal thereafter. There was no significant difference in visual evoked potentials between the two groups. All had normal neurodevelopmental status by 3 years, with the exception of one child from the severe group with ABO incompatibility with transient mild motor delay, hypotonia, and abnormal visual evoked potential. There were no abnormal effects of phototherapy on visual evoked potentials in infants with neonatal hyperbilirubinemia after 1 year of age. Although our sample size was small, the results suggest that the effects of hyperbilirubinemia on visual evoked potentials might be transient. (J Child Neurol 2006;21:58-62).

Child Development↗

PubMed1993

Pattern electroretinogram and visual evoked potential amplitudes are influenced by different stimulus field sizes and scotomata.

The pattern electroretinogram and the visual evoked potential were recorded simultaneously with various stimulus fields and artificial scotomata of increasing sizes. In contrast to an earlier study, a smaller check size (20') and two stimulus field sizes (20 degrees x 20 degrees and 10 degrees x 10 degrees) for the scotomata were used. With a concentric decreasing stimulus field, a reduction of both the pattern electroretinogram and visual evoked potential was found. Both showed a simultaneous reduction of amplitudes, but, compared with the amplitude in the full field, the reduction was more extensive for the pattern electroretinogram at each test field size. This implies a greater contribution to the pattern electroretinogram from more eccentric retinal parts. An artificial central scotoma of increasing size in the 20 degrees x 20 degrees field had less influence on the pattern electroretinogram than on the visual evoked potential. The percentage amplitude loss of the visual evoked potential was more pronounced. The visual evoked potential was eventually abolished by a scotoma size from 10 degrees x 10 degrees upward, while the pattern electroretinogram was still registrable. When scotomata of similar size were introduced in a smaller (10 degrees x 10 degrees) field, percentage pattern electroretinogram and visual evoked potential amplitude losses were less separated than in a larger (20 degrees x 20 degrees) test field.

Adult↗

PubMed1981

Age-related changes in the latency of the visual evoked potential: influence of check size.

Pattern reversal visual evoked potentials were recorded from visually normal adults between 10 and 80 years of age. Two check sizes, 12 and 48 min, were used. The results showed that the latency of the first major positive component, P1, increased with age for both check sizes. This rate of increase was nearly twice as fast for 12 min checks. This difference is most likely a reflection of the differential effects of aging processes on the various spatial frequency channels in the human visual system.

Adolescent↗

PubMed1984

Visually evoked potentials in eccentrically and centrally fixing amblyopes.

Visually evoked potentials to checkerboard pattern reversal were found to be nearly five times larger in eccentrically fixing amblyopic eyes than in centrally fixing amblyopic eyes when compared with the fellow non-amblyopic eye. The two groups of amblyopes had comparably poor visual acuity and differed in no other way save in their fixation behaviour. This suggests that at least two neurodevelopmental mechanisms subserve human amblyopia and that only one of these resembles the animal model of visual deprivation.

Adult↗

PubMed1997

The prognostic value of flash visual evoked potentials in the assessment of non-ocular visual impairment in infancy.

The results of flash visual evoked potentials (VEPs) in 44 infants blind or severely visually impaired from non-ocular causes are presented, and related to the subsequent visual outcome. Ocular causes of visual impairment were excluded by clinical examination and electroretinography. Using a 2 x 2 contingency table, a significant association between VEP and outcome was demonstrated (chi 2 = 3.51, 1 d.f., p = 0.05). Of 13 infants with normal VEPs, 11 demonstrated substantial visual improvement (negative predictive value = 84.6%). However, of the 31 with abnormal VEPs, only 14 remained severely impaired/blind; the other 17 demonstrating visual improvement (positive predictive value = 45.1%). The sensitivity of the method was high in that 14 of 16 (87.5%) infants who remained impaired/blind had abnormal VEPs, but specificity was low as only 11 of 28 (39.3%) who showed visual improvement had normal VEPs. The accuracy of the technique was therefore low, 25 of 44 (56.8%) being true positive/ negative. With regard to visual outcome when faced with an apparently blind infant, it is important not to be too pessimistic for, as is shown in this study, 28 of 44 demonstrated substantial improvement. There are no absolute indicators of prognosis, but the presence of structural cerebral lesions and a history of either neonatal meningitis or encephalopathy are relatively bad prognostic signs. The flash VEP, despite its limitations, is a useful prognostic tool, particularly in those apparently blind infants whose normal ocular examination/electroretinogram is accompanied by normal VEPs. Those with abnormal VEPs, however, do not necessarily have a poor prognosis, but should be followed-up as maturational changes and/or improvements in function of the sensory pathway will be reflected in the evoked potentials.

Blindness, Cortical↗

PubMed1986

Isolation of components due to intracortical processing in the visual evoked potential.

A class of stochastic visual textures are used to analyze the components of the visual evoked potential (VEP). This procedure exploits the differential sensitivity of populations of visual neurons to aspects of contrast and pattern. A simple transformation of VEP responses elicited by these stimuli separates components that reflect complex aspects of visual processing from those that reflect elementary aspects. Simultaneous recordings of the VEP and cellular activity in the cat lateral geniculate nucleus are obtained. Responses to traditional VEP stimuli contain a mixture of intracortically generated and precortically generated components. A theoretical and experimental analysis demonstrates that the present approach cleanly separates intracortical generators of the VEP from precortical generators.

Animals↗

PubMed1978

Visual evoked potential characteristics and subtypes of schizophrenia.

Visual evoked potentials (VEPs) were recorded from the midoccipital area of 72 schizophrenic patients. The amplitude of wave VI (100- to 115-millisecond latency) was reduced after the addition test for 15 minutes. It recovered to the pretest level later, and four types of recovery curves were found; marked reduction in amplitude occurred in A1 (A1 type), in A3 with fast recovery (A3f type), in A3 with slow recovery (A3s type), and in A5 (A5 type) (A1, A3, A5: averaged potentials evoked by 1-Hz flashes which started 1 minute, 3 minutes, and 5 minutes after the end of the test). Each type closely corresponded to paranoid, atypical hebephrenic, typical hebephrenic, and simple schizophrenia, respectively.

Electroencephalography↗

PubMed1977

Changes in visual evoked potentials of schizophrenics after addition test.

Visual evoked potentials were obtained for schizophrenics, neurotics and patients with affective disorders, and comparison between those before and after an addition test for 15 min was made. Reduction in amplitude and prolongation of latency of the potential were observed in schizophrenics after the test, while there was no change after that in neurotics and patients with affective psychosis. In schizophrenics, 4 types of changes in amplitude of the potential could be seen after the test. Namely, marked reduction occurred in A1 (A1 type), in A3 with fast recovery (A3f type), in A3 with slow recovery (A3s type), and in A5 (A5 type). (A1, A3, A5: Averaged potentials evoked by 1c/sec flashes which started 1 min, 3 min and 5 min after the end of the test.) Each type closely corresponded to paranoid schizophrenia, atypical hebephrenia, typical hebephrenia and simple schizophrenia, respectively.

Adolescent↗

PubMedDate not supplied

[Visual evoked potentials to illusory contours (Kanizsa's square)].

Visual evoked potentials (VEP) were studied in 10 subjects to presentation of illusory Kanizsa's square and control visual stimulus with similar spatial organization, which did not produce a visual illusion. The VEPs to the applied stimuli were expressed in the occipital, parietal, and inferiotemporal areas. It was shown that during presentation of the illusory configuration the amplitude of VEP variation between the N180 and P230 peaks was higher and the N300 latency lower than during presentation of stimuli with real configuration. The difference between VEPs in amplitude were observed in the left and right occipital and left inferiotemporal areas, and differences in latency were pronounced in the left occipital derivation. It is suggested that there exist two contour-encoding regions in the visual system which participate in different kinds of the visual analysis. First, associative visual fields which encode the information on single sings and their complexes and inferiotemporal fields which compare the sensory and memory codes.

Adult↗

PubMedDate not supplied

The effect of oral prednisolone on visual evoked potential latencies in acute optic neuritis monitored in a prospective, randomized, controlled study.

The Tübingen study of optic neuritis treatment was started in 1980 to apply new and sensitive tests for monitoring a potential therapeutical steroid effect on the course of acute optic neuritis. Visual evoked potentials were used to assess an effect of oral methylprednisolone in a randomized, controlled trial. Forty-eight patients with acute optic neuritis were treated orally either with methylprednisolone (100 mg per day initially, dosage reduction every 3 days; n = 15) or with thiamine (100 mg per day; n = 33) in the control group, 36 of them in a double-blind procedure. A comparison of the two treatment groups indicated that oral methylprednisolone resulted in a faster improvement in visual evoked potential latency in the initial phase (p = 0.015, 4 weeks after onset), but had no benefit after 12 weeks and 12 months. Follow-up showed different types of courses in the visual evoked potential latencies. The visual evoked potential latencies were correlated to other outcome variables, such as visual evoked potential amplitudes, visual acuity, Aulhorn flicker test and perimetry. We were able to handle nonmeasurable latencies in highly pathologic cases by means of ranks (taking into account censored observations).

Acute Disease↗

PubMed1979

n-Hexane-induced changes in visual evoked potentials and electroretinograms of industrial workers.

Visual evoked potentials (VEPs) and averaged extraocular electroretinograms (ERGs) were recorded from 15 workers occupationally exposed to n-hexane for 5-21 years and from 10 healthy control persons. The amplitude of the VEP components was clearly smaller among the exposed subjects with the exception of N0, which tended to be larger. In addition, the latencies of P1 and N1 were longer among the exposed workers, while that of P2 was slightly shorter. The peak-to-peak amplitude of the ERGs was also diministed among the exposed subjects. The changes were interpreted to indicate cerebral dysfunction, probably conduction block in intracerebral axons. n-Hexane is an aliphatic hydrocarbon found in gasoline and used in various industrial applications. It has been shown to cause axonal neuropathy of the dying-back type in both experimental animals and humans. According to the present findings the central nervous system is alos susceptible to the toxic effects of n-hexane.

Adult↗

PubMed1993

Colored focal visual evoked potentials by cathode ray tube versus scanning laser ophthalmoscope.

We compared the focal visual evoked potentials obtained in 52 young subjects with normal vision, evoked by means of three alternating black/color checkerboards generated by a trichromic cathode ray tube (dominant wavelength, 514 nm; colorimetric purity, 0.45) and by means of a scanning laser ophthalmoscope (argon laser beam, 514 nm; colorimetric purity, approximately 1). These three checkerboards, with an area of 3.5 degrees x 3.5 degrees (stimulating the fovea), then with an area of 3.5 degrees x 3.5 degrees with a central exclusion of 1.5 degrees x 1.5 degrees (stimulating the perifoveola) and finally with an area of 1.5 degrees x 1.5 degrees (stimulating the foveola) were presented within a field (8 degrees x 8 degrees) of homogeneous luminance of 170 cd/m2 and 1500 cd/m2, respectively. Their check sizes were 30', with a reversal temporal frequency of 0.75 Hz. The transient focal visual evoked potentials recorded with these three stimuli generated by the two types of stimulators were clearly detected for at least 85% of subjects. Their characteristics (waveform, amplitude and culmination times of the different waves) were comparable, regardless of the stimulator used (cathode ray tube or scanning laser ophthalmoscope). These results suggest that, under these various conditions of luminance and colorimetric purity, the neurophysiologic circuits tested function in identical ways. The focal visual evoked potential signs, now clearly defined by means of stimuli generated by cathode ray tubes, therefore apparently can be applied to the focal visual evoked potential evoked by stimuli generated by the scanning laser ophthalmoscope.

Adult↗

PubMed1990

Properties of visual evoked potentials to onset of movement on a television screen.

In 80 subjects the dependence of movement-onset visual evoked potentials on some measures of stimulation was examined, and these responses were compared with pattern-reversal visual evoked potentials to verify the effectiveness of pattern movement application for visual evoked potential acquisition. Horizontally moving vertical gratings were generated on a television screen. The typical movement-onset reactions were characterized by one marked negative peak only, with a peak time between 140 and 200 ms. In all subjects the sufficient stimulus duration for acquisition of movement-onset-related visual evoked potentials was 100 ms; in some cases it was only 20 ms. Higher velocity (5.6 degree/s) produced higher amplitudes of movement-onset visual evoked potentials than did the lower velocity (2.8 degrees/s). In 80% of subjects, the more distinct reactions were found in the leads from lateral occipital areas (in 60% from the right hemisphere), with no correlation to handedness of subjects. Unlike pattern-reversal visual evoked potentials, the movement-onset responses tended to be larger to extramacular stimulation (annular target of 5 degrees-9 degrees) than to macular stimulation (circular target of 5 degrees diameter).

Adult↗

PubMed2003

Analysis of visual evoked potentials and background electroencephalographic activity in young and elderly subjects.

OBJECTIVE: New techniques developed in this laboratory to overcome the loss of information involved in conventional evoked potential averaging are applied here to visual evoked potential (VEP) in young and elderly normal subjects. METHODS: The techniques are based on statistical descriptions of the times and amplitudes of the electroencephalographic deflections recorded before (background) and after (evoked) a series of pattern reversal visual stimuli. RESULTS: The elderly had a higher rate of background deflections at all electrode sites, but lower amplitudes at the occipital electrodes. The elderly had a lower rate of deflections during the period of evoked activity compared with the background period. The young had a higher degree of response deflection time locking and amplitude. The mean amplitude of the deflections recorded during the period of evoked activity was significantly greater in amplitude than the background deflections and greater than the amplitudes of the conventionally averaged VEP derived from the same data. Thus the lower amplitude VEPs seen in the elderly are due to their poor time locking and reduced amplification. Only 79% of the stimulus trials contributed deflections to the P1 response component in both young and elderly subjects and 63% to the N1. In young subjects, several of the new response parameters showed the presence of evoked response components that were not apparent in the conventionally averaged VEP derived from the same data. CONCLUSIONS: The novel methods presented here provide a great deal of additional information that is unavailable when analyzing data using only conventional evoked potential averaging.

Adolescent↗

PubMed2003

Comparison between the lambda response of eye-fixation-related potentials and the P100 component of pattern-reversal visual evoked potentials.

The purpose of this study was to compare the lambda response of eye-fixation-related potentials (EFRPs) with the P100 component of pattern-reversal visual-evoked potentials. EFRPs were obtained by averaging EEGs time-locked to the offset of the saccade. The dipole of the lambda response and that of the P100 component were estimated by the dipole-tracing method (Musha & Homma, 1990). The locations of their dipoles at the occipital sites were very close to each other when the difference waveform, which was calculated by subtracting the EFRP to the patternless stimulus from the EFRP to the patterned stimulus, was used for the lambda response. This finding implies that the lambda response and P100 have a common neural generator in the visual cortex. However, the peak latency of the lambda response was shorter than that of P100. The saccades in the EFRP trial were considered to be the cause of the difference.

Adult↗

PubMed1998

Generators of visual evoked potentials investigated by dipole tracing in the human occipital cortex.

Current source generators (dipoles) of the human visual evoked potentials to pattern-onset stimuli were investigated with the dipole tracing method, using a realistic four-layer head model of scalp-skull-fluid-brain, which can equate the surface potential distributions on a scalp to one or two corresponding equivalent dipoles. Three healthy adult human subjects were used, and 29 electrodes were set on a scalp of each subject. Visual stimulus of a checkerboard pattern was presented for 250 ms in each of eight different visual fields (central and peripheral parts of each of four quadrant fields). The visual evoked potentials consisting of initial positive-late negative waves (CI and CII components designated by Jeffreys and Axford) were recorded mainly on the occipital region contralateral to stimulated visual fields. The initial positive wave (CI) of visual evoked potentials were divided into two components: early component of the CI (e-CI--an early small positive deflection with approximate peak latency of 70-90 ms) and late component of the CI (l-CI--a late large positive deflection with approximate peak latency of 100-120 ms). The dipole with a fit exceeding 98% dipolarity with our model at the shortest latencies was defined as an "earliest dipole" of the evoked potentials, produced by the primary responses in the occipital cortex to an afferent volley from the lateral geniculate body. These earliest dipoles, for eight different visual field stimulations, were estimated at the approximate peak of the e-CI. Estimated dipoles were superimposed on a three-dimensional magnetic resonance image of each subject's brain. Earliest dipoles for right upper and right lower quadrant-field stimulations were located at the left calcarine cortices below and above the calcarine fissure, respectively; earliest dipoles for left upper and left lower quadrant-field stimulations were located at the right calcarine cortices below and above the calcarine fissure, respectively. Furthermore, earliest dipoles for central and peripheral quadrant-field stimulations were located posteriorly and anteriorly in the calcarine cortex, respectively. The results from these non-invasive analyses of visual evoked potentials indicated topographic localization of the dipoles around the calcarine fissure based on the loci of the visual fields. This was comparable to the retinotopy of the human occipital lobe based on clinicopathological studies.

Adult↗

PubMed1979

[Visual evoked potential in multiple sclerosis].

Visual Evoked Responses (VER) by binocular flash stimulation were carried out in 30 cases of "definite" (15 cases-Group I) and of "probable" (15 cases-Group II) Multiple Sclerosis (MS). VER were recorded bilaterally by reference occiput-mastoid. Averaging of 50 responses (time base 200-500-1000 msec) was considered; measures were made by registration on X-Y Plotter. Abnormal VER by increased latencies of III and/or IV peak (Ciganek) were present uni- or bilaterally in most of the subjects (73,3% of the I Group; 66,6% of the II Group). Percentage of abnormal VER is quite higher than clinical involvement of visual pathways; it is present in 3 out of 5 patients also, in whom clinical findings were confined to spinal cord. The results are discussed with reference to the previous literature. Recording of VER seems useful in detecting involvement of visual pathways without clinical evidence.

Adult↗