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At least 991 records · Page 55Linked to original sources
PubMed2005

Effect of fixation tasks on multifocal visual evoked potentials.

PURPOSE: This study investigated the effects of cognitive influence on the multifocal visual evoked potential (mVEP) at different levels of eccentricity. Three different foveal fixation conditions were utilized involving varying levels of task complexity. A more complex visual fixation task has been known to suppress peripheral signals in subjective testing. METHODS: Twenty normal subjects had monocular mVEPs recorded using the AccuMap objective perimeter. This allowed simultaneous stimulation of 58 segments of the visual field to an eccentricity of 24 degrees. The mVEP was recorded using three different fixation conditions in random order. During task 1 the subject passively viewed the central fixation area. For task 2 alternating numbers were displayed within the fixation area; the subject on viewing the number '3' in the central fixation area indicated recognition by pressing a button. Throughout task 3, numbers were displayed as in task 2. The subject had the cognitive task of summating all the numbers. RESULTS: Analysis revealed that the increased attention and concentration demanded by tasks 2 and 3 in comparison with task 1 resulted in significantly enhanced central amplitudes of 9.41% (Mann-Whitney P = 0.0002) and 13.45% (P = 0.0002), respectively. These amplitudes became reduced in the periphery and approached those of task 1, resulting in no significant difference between the three tasks. Latencies demonstrated no significant difference between each task nor at any eccentricity (P > 0.05). As the complexity of each task increased the amount of alpha rhythm was significantly reduced. CONCLUSIONS: Our findings indicate that task 1 required a minimal demand of cognition and was associated with the greatest amount of alpha rhythm. It was also the most difficult to perform because of loss of interest. The other two tasks required a greater demand of higher order cognitive skills resulting in significantly enhanced amplitudes centrally and the attenuation of alpha rhythm. Therefore, amplitudes are increased around the area of attention.

Adult↗
PubMed2005

Recovery of visual evoked potentials after regeneration of cut retinal ganglion cell axons within the ascending visual pathway in adult rats.

PURPOSE: Following optic nerve damage, retinal ganglion cells (RGCs) fail to regenerate their axons and soon undergo apoptosis. However, many RGCs survive axotomy and regenerate lengthy axons after a lens injury (LI). If the cut optic nerve is re-sutured, RGC axons grow into the distal part of the optic nerve and reach their natural targets within the thalamus and midbrain. In this study, we check time-dependence and extent of restoration of flash visual evoked potentials (FVEPs) to examine the functional relevance of the regenerated retinogeniculate pathway. METHODS: The optic nerve in adult rats was cut and re-sutured. The lens was injured transsclerally using a pointed glass capillary. FVEPs were measured starting at the time point of surgery, and then repeatedly up to an age of several months. RESULTS: Detectable FVEPs appeared approximately ten weeks after the surgery, and their amplitudes increased during the next months to reach eventually 15-40% of their values before surgery. CONCLUSIONS: Partial restoration of FVEPs indicates that some regenerating RGC axons have "bridged" the distance between the eye and the central targets forming a functional re-connection of the corresponding RGC with thalamic target neurones to elicit recordable activation of the visual cortex.

Animals↗
PubMed1986

Effects of hyperventilation on pattern-reversal visual evoked potentials in patients with demyelination.

The effects of hyperventilation on the pattern-reversal visual evoked potential (VEP) were studied in seven normal subjects and 13 multiple sclerosis patients with visual pathway involvement. Significantly greater reductions in P100 latency occurred in the multiple sclerosis patients than in controls and normalisation of the half-field response topography occurred in one patient after hyperventilation. The VEP changes are attributed to improved impulse transmission in demyelinated fibres in the visual pathway as a result of the alkalosis and changes in ionised calcium levels induced by hyperventilation.

Adult↗
PubMed1982

Visual evoked potentials (VEP) recorded from the hippocampus of the chronically-implanted unanesthetized hedgehog.

Visual evoked potentials (VEPs) were recorded from the dorsal hippocampus of chronically-implanted unanesthetized European hedgehogs (Erinaceus europaeus). The hippocampal VEP is less complex in appearance than the VEP recorded from the visual cortex. It consists of several distinct, reliably reproducible peaks and one distinct afterpotential (AP). The ease of recording and the reliability of the elicited electrophysiological responses recommended this primitive placental insectivore for use in comparative electrophysiological and psychophysiological studies.

Animals↗
PubMed1990

Visually evoked potentials in response to rotating plane-polarized blue light.

Visually evoked cortical potentials closely related to the appearance and disappearance of Haidinger's brushes were obtained in response to onset and offset of rotation of plane-polarized blue light. The method provides a means of investigating macular function in man; it is fairly independent of ocular opacities and relates, for the first time, entoptic phenomena to those evoked by extrinsic light stimulation.

Adult↗
PubMed1988

Visual evoked potentials in tumors from orbita to occipital lobe in childhood.

68 infants and children with proven tumours along the visual pathway visually evoked potentials with pattern reversal and flash were investigated. Subdivided in 5 locational groups (orbital, optic nerve, chiasmatic, retrochiasmatic and occipital lobe) best results were obtained by stimulation with pattern reversal using variable checksizes (91.2%) versus 61.8% by using flash evoked responses. Furthermore, using patterned stimuli not only latency shifts are best detected but also hints for visual function correlating to visual acuity could be given also in nonverbal or disabled children. For long term follow-up studies in known space-occupying lesions along the visual pathway, the use of pattern VEP is extraordinary because of its high sensitivity and complete harmlessness. Pattern VEP are even more sensitive than visual acuity testing in cooperative patients. The close interdisciplinary follow-up controls in these children between pediatric neurophysiologists and neurosurgeons are, therefore, strongly recommended.

Adolescent↗
PubMed1978

Pattern-reversal visual evoked potential. Method of analysis and results in multiple sclerosis.

A detailed method of analysis of the pattern-reversal visual evoked potential is presented. This method takes into account a number of parameters in addition to the latency of the major surface-positive component (P2) and has been tested in a group of 50 normal subjects and in 98 patients with established or suspected multiple sclerosis (MS). It was found that this more detailed form of analysis improved the detection rate of abnormal responses in the MS subjects particularly in those classified in the suspected category. The potential value of this form of analysis, particularly in clinical neurophysiology laboratories where the recording of visual evoked potentials is the only technique employed in the investigation of patients with suspected MS, is discussed.

Adolescent↗
PubMed1999

Localization of the optic tract by using subcortical visual evoked potentials (VEPs) in cats.

OBJECTIVES: This study was aimed to clarify the relationship between the amplitudes of visual evoked near field potentials and distance from the optic tract, and to determine the adequate filter settings to record these potentials from the optic tract separately from the far field potentials. METHODS: The visual evoked near field potentials from the optic tract were consecutively recorded through intracerebral electrodes in 6 cats' brains. Different filter settings were tried and the amplitudes of visual evoked potentials (VEPs) were compared with the distance from the optic tract. RESULTS: The filter settings of 100 Hz to 1 kHz were the best to obtain only the near field potentials separately from the far field potentials. Histological sections revealed that the potentials of the surface of the optic tract showed sudden increase of amplitude, above the 50% of the maximum VEPs amplitudes. CONCLUSIONS: The optic tract can be identified using these methods. These results can be applied to localize the optic tract during such an operative procedure as postero-ventral pallidotomy.

Animals↗
PubMed1990

A procedure for recording electroretinogram and visual evoked potential in freely moving cats.

A procedure for recording the electroretinogram (ERG) and the visual evoked potential (VEP) in freely moving cats was developed and used to test the visual toxicity of nalidixic acid. The electrodes for recording the ERG and VEP were implanted chronically in the sclera of the eye and on the surface of the visual cortex, respectively. Both the ERG and VEP were simultaneously recorded in freely moving cats using a slip ring that allows the cat to move freely without twisting the cables. After a 15-min dark-adaptation period, 20 responses to repetitive photic stimulation with an intensity of 2 joules and a 10-sec interstimulus interval were averaged by means of a minicomputer. The waveform of the ERG consisted of a negative wave (a-wave) followed by a positive wave (b-wave) with 2 to 3 oscillatory potentials on the rising slope. The VEP consisted of initial positive wave (P1 wave) followed by a negative wave (N1 wave) and late positive and negative deflections. The amplitude of the components of the ERG and VEP varied considerably from animal to animal, whereas within the same animal they were very stable. Using this technique, the effects of nalidixic acid, a retinotoxic compound, on the ERG and VEP were studied. Nalidixic acid produced a marked, but transient, decrease in the amplitude of the ERG b-wave after a single intravenous injection at a dose of 10 mg/kg. After repeated doses at 40 mg/kg/day for 2 weeks, the reduction in the amplitude of the b-wave was stronger, but remained transient. Upon ophthalmologic and histopathologic examination of the retina, no abnormalities indicating visual toxicity were observed. These results indicate that this procedure for recording the ERG and VEP is useful for evaluating the visual toxicity of drugs in freely moving cats.

Animals↗
PubMed1996

A dynamic and quantitative study of pattern visual evoked potentials and gamma-aminobutyric acid neurones in the lateral geniculate nucleus and the visual cortex of monocular deprivation cats.

PURPOSE: To assess the effects of monocular lid closure during critical period on cortical activity. METHOD: Pattern visual evoked potentials (PVEP) of the normal and the monocular deprivation (MD) cats were dynamically measured and the number of gammaaminobutyric acid immunopositive (GABA-IP) neurones of the area 17 of the visual cortex and the lateral geniculate nucleus (LGN) was quantitatively compared by using immunohistochemical method (ABC). RESULTS: The amplitude of the N1-P1 attenuated in deprived eyes (DE), NE/DE at postnatal week (PNW) 7-8 (P < 0.05), NE/DE at PNW 15-16 (P < 0.01); while P1 latency delayed, NE/DE at PNW 7-8 (P > 0.05), NE/DE at PNW 15-16 (P< 0.05). The numbers of GABA-IP neurones in layer A1 of the ipsilateral LGN and in layer A of the contralateral LGN, compared to those in the corresponding normal laminae, were not significant at PNW 7-8 and PNW 11-12 (P > 0.05), while in the same cats a reduction in the number of GABA-IP neurones was found in layer IV of area 17 at PNW 11-12 (P < 0.05). However, with longer survival of 3-4 weeks in duration, the numbers of GABA-IP neurones in the deprived laminae of LGN were remarkably reduced (P < 0.05). CONCLUSIONS: The amplitude of N1-P1 components is sensitive to the effects of monocular deprivation. Monocular deprivation in cats during critical period leads to dramatic changes of the number of GABA-IP neurones in the LGN and cortical layer IV receiving inputs from the deprived eye in cats. The deprivation-induced reduction in GABA-IP neurones is delayed in the LGN compared with the visual cortex. PVEP of the MD cats is consistent with the damage of its GABA system in visual cortex.

Animals↗
PubMed1994

Single P100 visual evoked potential analyses in man.

Standards evoked potential averaging leads to a loss of information inherent in the moment to moment variability of the amplitude and latency of single evoked potentials. In order to extract this information, attempts were made to develop procedures which would allow recording of single visual evoked potentials in at least a selected group of subjects. In 11 out of 25 non-selected subjects, 43% to 86% of all stimuli (reversal checkerboard pattern elicited single visual evoked potentials (VEP) which were recognized as such by a group of independent observers. The mean amplitude and latency obtained by directly measuring the peak to peak amplitudes and peak latencies of these single VEPs (arithmetic averaging) were compared to those obtained following conventional time-locked averaging of the same data. During long-term continuous stimulation, the arithmetic averaged VEPs increased in amplitude to a steady state while the time-locked averages of the same sets of responses decreased in amplitude. This reduction was found to be closely related to the latency jitter. It may provide a better understanding of the phenomenon of habituation. This finding was confirmed in model single VEPs obtained by summing on-going pre-stimulus EEG activity with a time-locked average VEP stationary wave form. The variability of the true single VEPs was found to be less than the variability of the model single VEPs. The latency and amplitude parameters of the true single VEPs were strongly correlated with each other while those of the model single VEPs were not. These findings show that single VEPs have an inherent variability which may reflect brain processing.

Adult↗
PubMed1992

Contribution of pattern electroretinogram and pattern visual evoked potential in early diagnosis of primary open angle glaucoma.

Pattern electroretinogram (PERG) combined with visual evoked potential (VEP) has become increasingly useful in clinical assessment of the anterior visual pathways. In regard to the PERG dependence on ganglion cell activity, we studied monocular PERG in 36 patients (71 eyes) with intraocular hypertension (6 eyes under topical beta-blockers) and in 10 patients (18 eyes) with advanced glaucoma, to estimate the potential effect of increased IOP on ganglion cells. We recorded simultaneous VEP to evaluate the retino-cortical conduction time. Referring to normal values obtained from 19 eyes (12 subjects), we found clear-cut PERG abnormalities in 20 eyes among ocular hypertensive patients with increased IOP. They were more altered in the advanced glaucomatous group. Two or three control exams were performed in 10 patients every 6 months: however such a short-time follow-up seems too limited to define the ERG prognosis value in this pathology. Comparing the PERG with the clinical routine assessments, we discuss its place in the diagnosis and in the follow-up of patients with ocular hypertension.

Adult↗
PubMed1997

[Visual acuity measured by pattern visual evoked potential].

We investigated the appropriateness of a method for the assessment of visual acuity using pattern visual evoked potentials (PVEP) in which retinal X-ganglion cells are predominantly stimulated. Eighteen normal eyes (average 22.2 years old) with normal acuity of 1.0 were examined. The stimulus consisted of white and black checkerboards (39', 26', 15' and 9') with a visual angle of eight degrees and a contrast level of 15%. The pattern reversal frequency was 0.7 Hz. This resulted in 100 averaged PVEP per session. We judged visual acuity from responses of the P100 component. Visual acuity was judged to be 0.1, so that there was response to the 39' checkerboard stimulus pattern, but not to the 26' pattern. Consequently, the accuracy for visual acuity was 76.9% for 0.1, 71.4% for 0.2, 70.0% for 0.5 and 58.3% for 1.0. This method, which uses a stimulus pattern with a small visual angle, low contrast, and low pattern reversal frequency, is useful for subjective measurement of the visual acuity of infants or handicapped children whom it is difficult to measure by the conventional objective method of measuring visual acuity with Landolt's rings.

Adult↗
PubMed1997

Visual evoked potentials relating to imagery: words for concrete objects versus absolute concepts.

We recorded visual evoked potentials (VEPs) elicited with high or low imaginable Chinese characters (HIC or LIC), representing concrete objects or absolute concepts, respectively. A closed circle (CC) acts as control stimulus. These were displayed (at 1.6 degrees visual angle) for 35 ms on a TV monitor. Twenty-one channel VEPs (band-pas filter: 0.05-60 Hz), using balanced non-cephalic electrodes, were recorded from -100 to 924 ms for 11 right-handed male volunteers. The VEPs were analyzed by multivariate analysis of variance (MANOVA) and comparison of topographies at four remarkable peaks (P110, N160, P230 and N320). MANOVA showed significant differences (p < 0.001) for both conditions of channel and stimuli (HIC, LIC or CC). P100 for the CC-VEPs, N160 for the HIC- and LIC-VEPs, P230 for the CC-VEPs, and N320 for the HIC-VEPs were remarkable in the posterior scalp regions. Topographies at P100 and N160 showed no difference between the HIC- and LIC-stimuli. However, those at N320 showed difference between the HIC- and LIC-stimuli over the occipital and posterior temporal areas. Those results suggest that the responses at P100 and N160 might segregate Chinese characters from non Chinese characters. N320 suggested certain processes in imagery on recognizing Chinese characters over the occipital and posterior temporal areas.

Adult↗
PubMed1994

Flash and pattern visual evoked potentials in the diagnosis and monitoring of dysthyroid optic neuropathy.

Flash and pattern visual evoked potentials were recorded in 8 patients (13 eyes) with dysthyroid optic neuropathy (DON), diagnosed using the American Thyroid Association classification. All were treated with systemic steroids, but 4 patients (6 eyes) also required orbital decompression. Flash VEP (P2) and pattern VEP (P100) were recorded prior to and 2 weeks after commencing steroid treatment or decompression. Fifteen patients with Graves orbitopathy but without DON, and 20 healthy subjects, acted as controls. Before treatment visual acuity was reduced in 10 eyes and visual fields were abnormal in 5, but the VEP was abnormal in all 13, with the group mean amplitude of P2 and P100 significantly less than controls, and the group mean P100 latency significantly greater than controls. After treatment with high-dose steroids or surgical decompression there were significant improvements in the group mean amplitude of P2 and P100, and significant reductions in P2 and P100 latency; however, individually, improvements in amplitude were more significant than improvements in latency. We conclude that the VEP to flash and pattern stimuli provides a useful diagnostic and monitoring tool in patients with DON, combining objectivity with quantitative analysis.

Adult↗
PubMed1993

[The clinical use of steady-state flash visual evoked potentials].

The authors applied 30Hz flash stimuli to record steady-state flash visual evoked potentials (FVEP) and extracted the amplitudes and phases of the first and second harmonics as the characteristic value by discrete Fourier transform (DFT). 46 normal controls (89 eyes) and 78 patients (109 eyes) were detected and analysed by this method. The result showed that the characteristic values of the normal controls are significantly different in three age groups and showed the positive in 35 eyes with the optic never diseases (82.9%), 25 eyes with age-related macular degeneration (92%), and 9 eyes with retinal detachment involved macular (100%). It indicates the method is a sensitive index to evaluate the macular visual function. After preliminary observation, the visual acuities of postoperation were found above 0.4 in cataracts (28 eyes) or opacities (12 eyes) if preoperative FVEP were normal and non-complicated, or less than 0.4 if preoperative FVEP were abnormal. This suggests the method is one of the effective index to detect the postoperative vision of the media opacities. The advantages, disadvantages and the clinical applications were discussed.

Adolescent↗