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At least 865 records · Page 48Linked to original sources
PubMed1991

Visual evoked potentials in dementia: selective delay of flash P2 in probable Alzheimer's disease.

The flash visual evoked potential P2 component is delayed in etiologically mixed groups of demented patients compared to healthy controls or nondemented patients. This study compared patients meeting both DSM-III-R criteria for dementia and NINCDS-ADRDA criteria for probable Alzheimer's disease (AD) with healthy elderly controls and found the P2 delay in the probable AD group. Additional comparisons found no evidence of a P2 delay in demented unlikely AD patients. These results suggest that earlier findings of a delayed P2 in etiologically mixed demented groups may have been due to inclusion of AD patients.

Aged↗
PubMed1988

Electroencephalography and visually evoked potentials during moderate hypoglycemia.

The effects of hypoglycemia per se on the electroencephalogram (EEG) and visually evoked potentials (VEPs) were studied in eight normal young adults. The EEG and VEPs were recorded before and during hypoglycemic clamp studies, carried out at plasma insulin and glucose concentrations of about 287 pmol/L and 2.38 mmol/L, respectively. From the mean power EEG spectra obtained during each testing condition, several parameters in each frequency band considered were compared statistically. During the eyes closed recording, the mean frequency of the alpha-band (8-13 Hz) decreased from 10.1 +/- 0.2 (+/- SE) Hz in both the right and left frontal leads during euglycemia to 8.8 +/- 0.2 and 8.8 +/- 0.1 Hz (left and right frontal leads, respectively; P less than 0.05) during hypoglycemia. In the same leads, the peak frequency decreased from 10.6 +/- 0.4 and 10.3 +/- 0.4 Hz to 9.6 +/- 0.4 and 9.5 +/- 0.3 Hz, respectively (P less than 0.05). A similar pattern of variation was found during the eyes open recording. In contrast, mean VEP latencies did not vary significantly; they were 118 +/- 3 ms (smallest image size; square wave signals subtending 30 min of arc) and 116 +/- 3 ms (largest image size; square wave signals subtending 60 min of arc) during euglycemia to 121 +/- 3 and 119 +/- 3 ms, respectively, during hypoglycemia. This study demonstrates that the earliest hypoglycemia-induced EEG alterations occur in the frontal regions and can be quantified in terms of decreased mean and peak frequencies of the alpha-band. VEP latency is less sensitive. If confirmed in diabetic patients, these data may provide a theoretical basis for developing a portable device to detect early hypoglycemia in those patients who lack warning symptoms.

Adult↗
PubMed1995

Variability analysis of visual evoked potentials in humans by pattern recognition in phase domain.

A novel approach to single trial visually evoked potentials (VEP) variability analysis based on a new model of post-stimulus brain electrical activity is presented. The convolution model introduced by the author is experimentally verified by the analysis of flash stimulus effects on EEG amplitude and phase spectra. Pattern recognition in the signal phase domain is proposed for detection of any time locked transient signals. This is illustrated by an application of a clustering algorithm in two-dimensional unwrapped phase of EEG Fourier transform space for occipitally recorded VEPs in human subjects.

Adult↗
PubMedDate not supplied

[Standards for carrying out and interpreting visual evoked potentials in children].

INTRODUCTION: An essential step, prior to the introduction into paediatric practice of visual evoked potentials (VEP) caused by stimulation with light emitting diodes (LED) is their description at different stages of maturity of the nervous system. PATIENTS AND METHODS: We obtained VEP to LED in a group of 60 children aged between 1 and 5 years, who were functionally healthy and equally distributed with regard to age and sex. In each case we recorded the responses to monocular stimulation (right and left), binocular stimulation and without stimulation (replicas of each condition). The recordings were made under sedation with secobarbital at a dose of 3 mg/kg body weight. RESULTS: Our results showed a significant reduction in the latency of all components (except P3) and the amplitude of N1 and P1, as a function of the age of the child. The response to LED is reproducible (especially intra individual) with up to three types of morphology observed. Sedation did not affect detection of the response. The only significant effect was a reduction in the amplitude of P1. CONCLUSIONS: We confirmed the changes due to maturity, reflected in a significant reduction of the latency of most components with increasing age. By between 4 and 6 years old the figures obtained were similar to those in adults. The results obtained give us the opportunity chance of publishing this standard data so that better use and interpretation of VEP to LED at an early age may be possible.

Central Nervous System↗
PubMedDate not supplied

Visual evoked potential & brainstem auditory evoked potentials in acute attack & after the attack of migraine.

PURPOSE: To study the effect on visual evoked potential (VEP) and brainstem auditory evoked potential (BAEP) at time of acute attack and after 7 days of the attack of migraine. MATERIAL AND METHODS: We studied BAEP and pattern reversal VEP in 25 patients during acute attack and after 7 days of the attack. The diagnosis of migraine was established according to criteria given by international headache society (IHS). Peak and interpeak latencies (IPL's) of BAEP and P100 latency of VEP were the main criteria to judge abnormalities. RESULTS: There were prolonged peak and interpeak latencies in BAEP and prolonged peak latency (P100) in VEP at the time of acute attack of migraine. The data of these abnormal recording were highly significant. After 7 days when the attack was over, we recorded the BAEP and VEP again. The observation obtained at this time was comparable to normal values. CONCLUSIONS: From the observation of this study we can safely conclude that in acute attacks of migraine there may be some pathological changes in different areas of brain and brainstem, producing changes in evoked potential which are statistically highly significant. However, these changes are reversible, as the values of BAEP & VEP on 7th day after the attack were comparable to those observed in normal healthy control.

Acute Disease↗
PubMed1991

Visual evoked potentials in the white New Zealand rabbit: source localization and normative aspects.

Normative data of visual evoked potentials were obtained from occipital screw electrodes referenced to a nasal electrode in 10 white New Zealand rabbits. Two time-bases were used (200 and 400 ms) in order to reliably identify both early components (of retinal and cortical origin), as well as late components. The putative origin of the single components was established by simultaneous recording of ERG and by stereotaxic recordings from the lateral geniculate body. Test-retest variability was measured repeating the recordings after 24 hours.

Animals↗
PubMed1990

[Visual evoked potentials produced by monocular flash stimuli in the cerebral cortex of the rabbit. I. Typology].

Visually evoked potentials obtained from the cerebral cortex of pigmented rabbits in response to monocularly applied flashes were studied. In agreement with their morphology, the VEP of the cerebral cortex of the rabbit were classified in three fundamental types: the first one is characterized by the presence of a large positive wave, (P1), followed by a negative wave, (N1), and finally, another positive wave, (P2); these last two being of quite variable amplitudes. The second one is characterized by an initial large negative wave, (N1), followed by a usually large positive wave, (P2). Should a positive, (P1), appear previous to N1 there would be little amplitude. The third one is characterized by the presentation of an early negative wave, (N0), of variable amplitude. This is usually followed by a large wave, (P1). N1 and P2 are present but their amplitude is variable.

Animals↗
PubMed1985

Behaviour-dependent changes of visually evoked potential components in the superior colliculus of freely moving rats.

Amplitudes and peak times of visually evoked potential (VEP) components in superficial and deeper layers of the superior colliculus of 24 rats were measured during slow wave sleep (S), relaxed wakefulness (RW), grooming (G) and exploratory behaviour (E). All peaks occurred later during S than during RW, whereas only a few peak times were significantly longer in activated states compared with RW. Positive and negative peaks between 35 and 60 ms were significantly (p less than 0.01) prolonged during G and E. Corresponding peaks of the polarity reversed VEP appear 1-4 ms later than in the superficial VEP when compared in identical behavioural states. Significant amplitude decrease (p less than 0.01) of almost all components related to RW was found in G and E and of components N-39-P51 and N60-P71 in S. These changes were relatively different for each component and each behavioural state. The amplitude changes of the polarity reversed VEP were similar but not identical (as a mirror image) with superficial VEP. The different behaviour-dependent patterns of the VEP components indicate different interactions in the neuron pools of superior colliculus.

Animals↗
PubMed1993

Perceptual ranking versus visual evoked potentials for different local features in texture segregation.

PURPOSE: To validate recent reports of specific visual evoked potentials associated with preattentive texture segregation (tsVEPs) and to quantitatively compare perceptual segregation strength and tsVEP amplitudes across different local features. METHODS: Four local features were selected: crossed vs noncrossed, line segments differing in orientation by 90 degrees, U-shapes differing in orientation by 90 degrees, and U-shapes differing in orientation by 180 degrees. The two variants of each local feature were spatially arranged in a checkerboard pattern; for the first three features this led to pop-out of a "preattentive checkerboard." In seven subjects, perceptual segregation strength was assessed using ranking, and tsVEPs were recorded in these and three additional subjects. RESULTS: Statistically significant tsVEPs were obtained for the features crossed vs noncrossed and 90 degrees-line segments. Ranking results and tsVEP amplitudes were highly correlated (P < 0.001); the order of perceptual ranking and the order of tsVEP amplitudes were identical; 180 degrees-U-shapes had lowest ranking, mean tsVEP amplitude was 0.1 microV, close to noise. Line segments had maximal ranking, tsVEP amplitude was 1.5 microV. CONCLUSIONS: The results suggest that tsVEPs quantitatively reflect the activity of cortical mechanisms involved in texture segregation across various features.

Adult↗
PubMed1993

Spatial modulation transfer function of vision by pattern visual-evoked potentials in patients with early glaucoma.

We applied subjective and psychophysical methods and pattern visual-evoked potential (VEP) P100peak latency as an objective index to measure spatial modulation transfer function (MTF) in normal subjects and patients with early primary open-angle glaucoma (POAG) in an effort to detect impairment of the spatial MTF of vision. To estimate spatial MTF objectively, the peak latency of the P100 component of pattern VEP was investigated. The mean contrast sensitivity in normal subjects derived from the pattern VEP peak latency was found to be maximum at the check size of 14.4 minutes of arc (i.e., 2.08 cycles per degree of spatial frequency), and the objective spatial MTF curve coincided well with that of the subjective one at all spatial frequencies examined. A statistically significant positive correlation was found between the objective (VEP) contrast threshold and the subjective one. Deterioration of the objective contrast sensitivity derived from the VEP peak latency was found to be much prominent that of the subjective one in patients with early glaucoma.

Adolescent↗
PubMed1993

[Evaluation of visual evoked potentials and static perimetry in chiasmal tumors and retrobulbar neuritis].

The author presented results of visual evoked potentials and static perimetry examinations performed in 17 patients with chiasmal tumors and in 27 with retrobulbar neuritis. A comparative analysis of the gathered parameters was done, using computer programs. The results suggest that the applied non-invasive methods of examination could be useful in differential diagnosis of these diseases.

Adolescent↗
PubMed1996

[Lateralization in dissociated vertical deviation with flash visual evoked potentials].

Lateralization, suggesting misrouting of optic nerve fibers in albinism, was examined by the flash visual evoked potentials (flash VEP) test in dissociated vertical deviation (DVD). Eighteen cases of DVD were studied and compared with 5 cases of X-recessive ocular albinism and 4 normal controls. Full-field monocular and binocular stimulation was employed with electroencepharograph electrodes on O1 and O2 (10/20 system), and the latency of P100 was statistically analysed with two-way analysis of variance. The difference in the P100 latency between contralateral and ipsilateral stimulation was significant (p < 0.05) in albinism, but not in DVD and normal controls. Therefore, DVD is probably not associated with misrouting of optic nerve fibers.

Adolescent↗
PubMed1996

[Quadrant pattern visual evoked potential in normal eyes].

OBJECTIVE: The study was designed to approach the difference in pattern visual evoked potential (PVEP) among quadrants of the normal eye. METHODS: Quadrant transient PVEP method was used to record quadrant PVEP for 70 eyes of 35 normal subjects. RESULTS: The latency of P100 in lower temporal and lower nasal fields was significantly shorter than that in upper temporal and upper nasal fields; the amplitude of P100 in lower temporal and lower nasal fields was significantly higher than that in upper temporal and upper nasal fields. Generally, in lower field, the P100's latency is shorter and its amplitude higher. CONCLUSION: The difference in P100 between upper and lower field of normal person is possibly related to the fact that the lower field is used more frequently than the upper in ordinary human or animal life, and to the differences in distribution of retinal ganglion cells and in retina-cortex pathway between the upper and lower retina.

Adult↗
PubMed1993

[Possible advantages of visual evoked potentials and computerized static perimetry in early diagnosis of glaucoma].

Aim of the studies was to evaluate usefulness of the visual evoked potentials and static perimetry in diagnosis of an early glaucoma. There were 12 examined cases, divided into 3 equal groups: 1) patients suspected for glaucoma basing on the characteristic picture of the optic disc, 2) patients after acute glaucoma in one eye with no history of the disease in the fellow eye, 3) patients with open angle glaucoma diagnosed in one eye. Abnormal results of the examinations were found only in the second group. The authors concluded that visual evoked potentials and static perimetry could be helpful in proper diagnosis of many difficult cases suspected for glaucoma.

Diagnosis, Computer-Assisted↗
PubMed1985

The human visual evoked potential: analysis of components due to elementary and complex aspects of form.

The visual evoked potential (VEP) elicited by alternation between isodipole visual textures may be separated into an asymmetric and a symmetric part. The asymmetric part reflects processing of complex attributes of form. The spatial and temporal dependence of this response is used to evaluate models for the generation of this response. The symmetric part appears to reflect processing of local luminance and contrast changes. The relation of these components to the VEP elicited by contrast reversal, contrast modulation, and the windmill-dartboard stimulus is discussed.

Adult↗
PubMed1997

Fast visual evoked potential input into human area V5.

Studies of the human visual cortex have demonstrated that an area for motion processing (V5) is located in the lateral occipito-temporal cortex. To study the timing of arrival of signals in V5 we recorded multi-channel visual evoked potentials (VEPs) to checkerboard stimuli. We then applied dipole source analysis which was computed on a grand average of 10 subjects, and on five individual subjects, respectively. We demonstrate an early VEP component with onset before 30 ms and with a peak around 45 ms, located in the vicinity of V5. This early component was independent of a second activity, which started around 50 ms and peaked around 70 ms, and was located within the striate cortex (V1). These results provide further evidence for a very fast input to V5 before activation of V1.

Adult↗
PubMed2002

Field-specific visual-evoked potentials: identifying field defects in vigabatrin-treated children.

OBJECTIVE: To derive a visual-evoked potential (VEP) technique for identifying visual field defects in children with epilepsy treated with vigabatrin and unable to perform perimetry. BACKGROUND: Studies have linked vigabatrin to a specific pattern of visual field loss. Few studies have included the pediatric population because of difficulties in assessing the visual field by perimetry below a developmental age of 9 years. METHODS: A field-specific VEP was developed with a central (0 degrees to 5 degrees radius) and peripheral stimulus (30 degrees to 60 degrees radius). Stimuli consisted of black and white checks that increased in size with eccentricity. Checks reversed at different rates, allowing separate central and peripheral responses to be recorded. Five vigabatrin-treated young adults with field defects were identified using this stimulus. Electroretinograms (ERG) were recorded to examine the effects of vigabatrin on retinal function. Thirty-nine children aged 3 to 15 years were included in the study. Twelve patients were examined by both the field-specific stimulus test and perimetry. The diagnostic performance of the field-specific stimulus test was compared with that of perimetry. RESULTS: Thirty-five of 39 children complied with the field-specific stimulus, 26 of 39 complied with the ERG, and 12 of 39 complied with perimetry. Using the summed amplitude of the peripheral response from O(2) and O(1), responses below 10 microV were deemed abnormal. The field-specific stimulus identified 3 of 4 abnormal perimetry results and 7 of 8 normal perimetry results, giving a sensitivity of 75% and a specificity of 87.5%. When comparing perimetry results with the ERG parameters, only the 30-Hz flicker amplitude, with a cutoff below 70 microV, gave a useful indication of visual field loss. CONCLUSION: Field-specific VEP are well tolerated by children older than 2 years of age and are sensitive and specific in identifying vigabatrin-associated peripheral field defects.

Anticonvulsants↗