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Results for “Evoked Potentials, Visual”

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PubMed1990

Objective measurement of contrast sensitivity using the steady-state visual evoked potential.

Contrast sensitivity functions (CSFs) were determined electrophysiologically with the steady-state visual evoked potential (VEP). Psychophysical CSFs obtained by the method of increasing contrasts were also measured concurrently with the VEP trials. The VEP contrast thresholds were obtained using a rapid recording technique in which the contrast of a counterphase sinewave modulated at a temporal frequency of 7.5 Hz was swept from 0.5% to 40% over a period of 22 s in 39 equal logarithmic steps. For this pattern reversal stimulus, the amplitude and phase of the second harmonic response as a function of contrast were measured using a discrete Fourier transform (DFT). Contrast sensitivities at five spatial frequencies ranging from 0.5 to 14.9 cpd were measured. The VEP contrast thresholds were determined by a linear extrapolation to zero amplitude. The contrast threshold obtained by the two methods correlated at 0.816 for 14 subjects. For all five spatial frequencies there were no significant differences between the contrast sensitivities derived from the two methods.

Adult↗

PubMed1983

Visual evoked potentials and CSF IgG at different stages of multiple sclerosis: a possible correlation.

Visual Evoked Potentials (VEP) have been investigated in 102 patients affected by Multiple Sclerosis (MS), classified both by disease stage and by optic pathway status. VEP abnormalities were significantly correlated with the clinical stage and increased CSF IgG levels. The delay in the VEP latencies and the CSF IgG values proved to be increased in parallel in the worsening phases of MS. The diagnostic value of these findings is also discussed.

Adult↗

PubMed1984

Colour and brightness components of foveal visual evoked potentials in man.

The different effects of colour and brightness on the transient visual evoked potentials to a foveal stimulus have been investigated in a psycho-physically controlled stimulus set-up, in which equally bright red, orange and green stimuli were substituted for a standard yellow stimulus. These colour-evoked responses were compared with the responses to additional brightness increments and decrements of each of the colour stimuli. An initial component of small amplitude, P55, was followed by a colour-dominated component, N87, and a luminance-dominated component, P120, with a maximum at the occipital electrode. Both N87 and P120 showed a decline in amplitude at the parietal electrode and P120 had a reversed polarity at FZ. These results indicate that the responses to equally bright green and red stimuli have closely similar wave forms, but that this changes rapidly with additional brightness differences. Comparison with the reports of subdural recording of colour-evoked potentials in the macaque striate cortex suggests that P55 corresponds with the primary excitation via geniculo-cortical fibres and that N87 and P120 represent later stages of cortical processing.

Color Perception↗

PubMed1986

Source geometry and dynamics of the visual evoked potential.

A method is developed for the analysis of the steady-state visual evoked potential (VEP) recorded at an array of electrodes. The VEP is assumed to result from the sum of a number of independent mechanisms. Each mechanism proves to have a fixed intracerebral source (independent of stimulus paradigm) and dynamics which depend on the stimulus. The steps in the analysis are: Fourier analysis of the responses and retention of the first 4 even harmonics; factor analysis in the frequency domain; an invariant representation ('the invariant fingerprint') of the geometric information contained in the factor analysis; and interpretation of the invariant fingerprint in terms of a simple biophysical model. This analysis is applied to responses elicited by a contrast-reversing checkerboard. The dependence of the midline VEP wave form on reversal frequency, check size, and area of stimulation (upper, lower, and full-field) reflects a change in the dynamics of the generators, rather than a change in their geometry.

Evoked Potentials, Visual↗

PubMed1994

Visual evoked potentials in three-dimensional color space: correlates of spatio-chromatic processing.

Visual evoked potentials (VEPs) were measured for sinusoidal gratings with spatio-chromatic modulation defined in a three-dimensional color space. The spatio-chromatic modulation of the gratings can be decomposed into contributions from an achromatic luminance varying component, an isoluminant component which modulates only the activities of L cones and M cones, and an isoluminant component corresponding to modulation of only S-cone activity. The emphasis of this report is the nature of VEPs resulting from isoluminant spatio-chromatic modulation. The VEP response was characterized along a number of spatial, temporal, and chromatic stimulus dimensions: contrast, spatial frequency, chromaticity in the isoluminant plane, chrominance/luminance ratio, orientation, and temporal frequency. Isoluminant VEPs resulting from stimuli modulating L and M cones are compared with those from S-cone modulation. When appropriate spatiotemporal conditions are employed, both types produce robust VEPs; however, the S-pathway VEPs show considerably longer latencies than do those from LM-pathway activation. The VEP results are compared to psychophysical and single unit electrophysiological observations. VEP latencies exhibit the lowpass character of psychophysical chromatic contrast sensitivity functions but VEP amplitudes show bandpass tuning along both the S and LM axes. An oblique effect, i.e. shorter latencies for horizontal and vertical gratings than for diagonal, is observed in the isoluminant VEP. S-pathway VEPs are used to demonstrate an electophysiological correlate of transient tritanopia. Normative amplitude and latency data for VEPs from selectivity stimulated chromatic mechanisms provide a baseline for clinical electrodiagnostic applications.

Adaptation, Ocular↗

PubMedDate not supplied

Preservation of single-flash visual evoked potentials at very low cerebral oxygen delivery in preterm infants.

Single-flash visual evoked potentials (VEPs) were recorded in 32 preterm infants (mean gestational age: 29 weeks) during extreme physiologic conditions within the first day of life. The VEP configuration was normal in all patients at the onset of the investigation. Hypoxic episodes (PaO2 less than 3 kPa) caused rapid and consistent attenuation of the VEP mostly with an instantaneous recovery after normalization of PaO2. In contrast, VEP amplitude and latency were unaffected during episodes with low cerebral blood flow (4.5 ml/100 gm/min) and correspondingly low oxygen delivery to the brain (1 ml/100 gm/min), severe hypocapnia (PaCO2 1.6 kPa), and severe arterial hypotension (MABP 10 mm Hg), provided that the arterial oxygen tension was greater than 5 kPa. Absence of N1 was observed soon after the development of severe intracranial hemorrhage; however, this abnormality was short in duration. We conclude that the neurons generating VEPs are supported sufficiently during extreme physiologic episodes, except during severe hypoxia. The recovery time may be proportional to the cerebral insult.

Carbon Dioxide↗

PubMed1997

Visual evoked potentials in the vicinity of the optic tract during stereotactic pallidotomy.

We recorded visual evoked responses in eight patients with Parkinson's disease, using a depth electrode either at or below the stereotactic target in the ventral part of the globus pallidus internus (GPi), which is located immediately dorsal to the optic tract. Simultaneously, scalp visual evoked potentials (VEPs) were also recorded from a mid-occipital electrode with a mid-frontal reference electrode. A black-and-white checkerboard pattern was phase reversed at 1 Hz; check size was 50 min of arc . Pallidal VEPs to full field stimulation showed an initial positive deflection, with a latency of about 50 ms (P50), followed by a negatively with a mean latency of 80 ms (N80). The mean onset latency of P50 was about 30 ms. P50 and N80 were limited to the ventralmost of the GPi and the ansa lenticularis. Left half field stimulation evoked responses in the right ansa lenticularis region while right half field stimulation did not, and vice versa. These potentials thus seemed to originate posterior to the optic chiasm. The scalp VEPs showed typical triphasic wave forms consisting of N75, P100 and N145. The location of the recording electrode in the ansa lenticularis region did not modify the scalp VEP. These results suggest that P50 and N80 are near-field potentials reflecting the compound action potentials from the optic tract. Therefore, N75 of the scalp VEPs may represent an initial response of the striate cortex but not of the lateral geniculate nucleus.

Aged↗

PubMed1997

The effects of electroconvulsive shock on the flash visual evoked potential in the rat.

The effects of electroconvulsive shock (ECS) on the flash visual evoked potential (FVEP) were studied in the awake albino rat. Immediately after the induction of generalised seizure activity, the FVEP was totally abolished although accidentally averaged rhythmic epileptiform activity was often present in the trace. During the second recording, a potential had reappeared but this response was suspected of being a superior colliculus FVEP masquerading as a cortical response. By the third recording, the genuine cortical FVEP had returned, albert with an abnormally large amplitude. The waveform subsequently remained significantly distorted although it had regained an approximately normal morphology within 6-7 min of the administration of ECS. It was not possible to identify the principal site of action of ECS but it was concluded that ECS may impact on activity generated at more than one location within the optic pathways. The present findings are compared with a number of previous animal and human studies where the FVEP was apparently preserved following ECS and attempts are made to explain the discrepancy in results. The relevance of the present findings for understanding the pathophysiology of electrical stunning and of the loss or impairment of consciousness during generalised epileptic seizures is also discussed.

Animals↗

PubMed2003

Steady-state visual evoked potentials reveal frontally-mediated working memory activity in humans.

Steady-state visual evoked potentials (SSVEPs) reflect power changes at the stimulus driving frequency and have been used to assess brain activity reflecting cognitive processing. Only one study has demonstrated SSVEP modulation associated with working memory (WM), and none have compared the spatial localization of SSVEP modulations during WM performance with other brain imaging methods. Here we examined WM-related activity recorded with dense-array SSVEPs, analyzed using low resolution electromagnetic tomography, and compared the results to our previous findings using functional magnetic resonance imaging (fMRI). WM was associated with increased SSVEP activity over the right dorsolateral prefrontal cortex, paralleling our previous fMRI findings. Frontal WM-related SSVEP power correlated selectively with task performance. These results demonstrate the utility of SSVEPs for studying representational aspects of cognition.

Adolescent↗

PubMed1997

Analysis of pattern reversal visual evoked potentials (PRVEP's) by spline wavelets.

In this study, the pattern-reversal visual evoked potentials (PRVEP's) collected from normal and demented subjects are investigated by applying the quadratic spline wavelet analysis. The data are decomposed into six octave frequency bands. For quantitative purposes, the wavelet coefficients in the residual waveform representing the delta-theta band activity (0-8 Hz) are explored to characterize the (N70-P100-N130) complex. Specifically, the coefficients corresponding to the location of N70, P100, and N130 peaks are investigated for their sign in order to test whether they represent a consistent (N70-P100-N130) complex in the averaged waveform. Waveforms with normal latency (N70-P100-N130) complex are observed to have positive second, negative third, and positive fourth coefficients in amplitude in their residual scale standing for the delta-theta (0-8 Hz) band activity. The method allows for the analysis of oscillatory-phase behavior of the normal and pathological PRVEP's in their delta-theta band based on a few quantitative measures consistent with the time-frequency occurrence of the major components of the evoked potential.

Alzheimer Disease↗

PubMed1985

Primary presenile dementia: the use of the visual evoked potential as a diagnostic indicator.

The use of the flash and pattern reversal visual evoked potential (VEP) in the diagnosis of primary presenile dementia was investigated. The results from 20 patients with primary presenile dementia were compared with those from a control group of normals of equivalent age and from a control group of 20 patients with cortical atrophy but no dementia. Presenile dementia caused a slowing of the major positive (P2) component of the VEP to flash stimulation. However, the VEP to pattern reversal stimulation (P100) was of normal latency. The difference between these two latencies characterises this unusual combination of results and is found to be a more specific diagnostic indicator of primary presenile dementia than the EEG or CT scan.

Aged↗

PubMed1981

Relationship between visual evoked potentials and intracranial pressure.

The relationship between intracranial pressure (ICP) and latency of visual evoked potentials (VEP) was investigated in hydrocephalic patients with severe head trauma. A positive correlation of increase in latency of wave N2 (normal latency 71 +/- 9.2 msec) of the VEP with elevations in ICP was observed. A potential role for VEP in both the assessment of shunt function and the monitoring of patients with severe head injury is suggested by these findings.

Adolescent↗

PubMed1992

[Pattern shift visual evoked potentials in diabetes mellitus].

Functional exploration of the optic pathways with pattern shift visual evoked potentials (PSVEP) has been rapidly accepted as a non-invasive method of investigation of diabetics. For this article, we conducted the PSVEPs study on 46 cases of NIDDM and 13 cases of IDDM. The peak latency, interpeak latency and evoked amplitude of P100 were analyzed in each case. For further correlation, the motor and sensory nerve conduction velocities of the median nerve, blood sugar, serum HbA1c, and duration of DM were measured simultaneously. Two nondiabetic control groups which matched the age and sex of the NIDDM and IDDM groups were used for comparison. In the IDDM group, the results showed prolongation of all peak and interpeak latencies (IPL) except the peak latency of N75 on the right side. The P100 amplitude was reduced as compared with the age-matched young control group. The interocular P100 latency difference (ILD) was not statistically significant between the IDDM group and the age-matched control group. The results of the NIDDM group revealed prolongation of all peak latencies and IPLs. The P100 amplitude and ILD showed no statistically significant difference between NIDDM and the age-matched control group. The prolongation of N 75 peak latency exhibited a linear correlation with duration, HbA1c and median nerve SNCV.

Adult↗

PubMedDate not supplied

[Visual evoked potentials and their relation to fundus oculi changes in patients with subacute sclerosing panencephalitis (SSPE)].

The results of 634 determinations of visual evoked potentials in 110 cases of SSPE are presented. The determinations were repeated many times in successive stages of the disease and were compared with findings obtained during eye fundus examinations. A statistically significant correlation was found between these potentials and changes in the fundus involving the optic disc and macula, and increasing abnormalities of the potentials in successive stages of the disease with their complete disappearance in the last stages. Visual evoked potential determination is regarded by the authors as a valuable diagnostic factor in early stages of the disease and as an additional source providing information about the degree of visual system damage with progression of the pathological process.

Child↗

PubMed1984

Developmental and aging changes in somatosensory, auditory and visual evoked potentials.

To assess developmental and aging changes in human sensory systems, components of short-latency somatosensory, brain-stem auditory and pattern-reversal visual evoked potentials, thought to originate in specific structures of these systems, were recorded in 286 normal subjects ranging in age from 4 to 95 years. Analysis was primarily restricted to peak and interpeak latencies; visual evoked potential amplitudes were also analyzed. Major results and conclusions are: (1) 'Developmental' changes (that is, decreases in latency attributable to decreased conduction time in younger subjects) were not seen in the median nerve, in brain-stem auditory pathways, or in some portions of visual cortex. Small developmental changes were seen in the somatosensory afferent pathway from the cervical spinal cord to thalamus, and large changes were seen in somatosensory and visual cortex. Cortical developmental changes appeared not to be complete until 17 years of age or later. (2) 'Aging' changes (that is, increases in latency attributable to increased conduction time in older subjects) were observed in the median nerve, cervical spinal cord, brain-stem auditory pathways, and somatosensory and visual cortex. (3) Visual evoked potential amplitudes tended to decrease with age, particularly during development; amplitude and latency effects were dissimilar for most components. (4) Males tended to show larger aging effects than females. (5) The results suggest that age-related changes in human sensory systems are not uniform, but rather are different in specific portions of these systems, different at particular epochs of the life span, and stronger in males than in females.

Adolescent↗

PubMed2004

[Flash visual evoked potentials on newborns and infants].

OBJECTIVE: To explore the feasibility of applying flash visual evoked potentials (FVEPs) for visual function test newborns and infants and bring out the consultable laboratory values of FVEPs. The technology of FVEP could be used as diagnostic tests for those who failed the screening and the infants who were cared for in the NICU. METHODS: 41 normal neonates (<or= 4 days) and 18 normal infants (<or= 5 months) were tested with FVEP by Nicolet Viking-IV model evoked potentials apparatus. RESULTS: Get the normal reference range of FVEPs latency in both groups and the consulting value of the difference between the left and right eyes. It has been observed from the paper that the latency of FVEPs has the tendency to shorten with the age increasing. It also shows that there are extreme significant changes of FVEPs (P < 0.05) by different frequency of stimulating light. CONCLUSION: The latency of FVEPs P1 is steady and could be applied to newborns-infants visual function test. While, the references of FVEPs according to different age group should be taken into account when we using this measure in clinic.

Age Factors↗

PubMed1989

Miniature fiber-optic pattern-reversal stimulator for determination of the visual evoked potential threshold; comparison with Snellen acuity.

In this report we recommend the estimation of visual acuity by detection of the visual evoked potential (VEP) threshold, defined by the smallest visual angle of a constant check size that evokes potentials. This approach was implemented using a fiber-optic pattern-reversal stimulator placed at measured, increasing distances from the examined eye. Snellen visual acuity as determined in 113 subjects was correlated with the VEP detection threshold. A highly significant correlation was found between visual acuity and the threshold visual angle of check size in subjects whose vision was impaired due to opacity in ocular media. For any given visual acuity a somewhat wide range of threshold check sizes, typically 5-10 min of arc was observed. Technical difficulties that need to be overcome to improve these results are discussed.

Adult↗

PubMed1986

The fetal visual evoked potential.

Five singleton fetal lambs were surgically instrumented at 110-121 days gestation (term gestation = 145 days) for measurement of visual evoked potentials (VEP) in utero. Light flashes were generated by a small incandescent bulb secured under the right fetal eyelids and the visual responses were recorded through stainless steel electrodes implanted in the fetal scalp. Four of the five fetal lambs were surgically instrumented between 110-113 days. VEPs recorded in these four animals from 111-114 days exhibited N1, P1, and N2, but lacked the P2 component. All VEP components (N1, P1, N2, P2) were measureable by 115-118 days in these fetuses. One fetus was surgically instrumented at 121 days and VEPs containing all components were measurable until 125 days gestation when the equipment dislodged in utero. Serial VEP recordings from all five fetal lambs from 111-128 days indicated no change in latency to N1 while significant latency changes occurred in P1, N2, and P2 suggesting maturational development of the visual system. Histological assessment of the eyes from three animals at delivery revealed only thickening and increased vascularity of the cornea in response to the light source resting on the fetal eye. In conclusion, these results suggest that the fetal visual evoked potential has application in the longitudinal study of normal visual development in utero and offers a technique for studying visual response changes to adverse perinatal events.

Animals↗