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Results for “Evoked Potentials, Visual”

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PubMed1975

[A simple method for the evaluation of differences in averaged evoked potentials as demonstrated of visual evoked potentials changed through hippocampal stimulation].

A simple method is presented which by subtraction of amplitudes of averaged evoked potentials (AEP) within regular time-intervals enables us to estimate differences in the course of the potential. First results demonstrate that all parts of the potential may be influenced and that most striking differences must not necessarily occur in the peak region of the AEP. The late negative complex of the AEP is likely to be a result of summation of some subcomponents, which may be altered differently. The method presented allows exact measurements of each of them.

Animals↗

PubMed1996

Emotional information processing and visual evoked brain potentials.

Visual evoked potentials to emotional slides presented for 2 sec. were investigated in 13 subjects. 73 emotional slides (pleasant, unpleasant, and neutral) were selected from a standardized set of photographic slides, the 1988 International Affective Picture System of Lang, Ohman, and Vaitl Visual evoked potentials were recorded from three head locations, frontal, central and parietal (Fz, Cz, and Pz). Analyses were performed in the two latency ranges: 300-400 msec. and 400-500 msec. Analyses showed an arousal effect, as indicated by a quadratic trend, indicating that emotional slides (both pleasant and unpleasant) gave higher cortical positivity than neutral ones, for all components. In addition, in the two latency epochs, larger positivities were found at Pz, compared to Fz and Cz, whereas Fz and Cz did not differ from each other.

Adult↗

PubMed1994

Comparison of visual evoked potentials elicited by light-emitting diodes and TV monitor stimulation in patients with multiple sclerosis and potentially related conditions.

Visual evoked potentials elicited by reversal of a checkerboard pattern constructed of square, red light-emitting diodes (LEDs) were compared with a conventional black and white pattern displayed on a TV monitor in control subjects and in 71 patients with established or suspected multiple sclerosis. Both stimuli elicited distinct responses in the control groups: the latencies were longer with LED stimulation while the amplitudes of the various components were differently altered. The frequency of abnormal responses among the patients was higher with LED stimulation than with TV stimulation, but the highest diagnostic yield was obtained when both methods were combined.

Adolescent↗

PubMed1976

Pattern reversal visually evoked potentials in infants.

Visually evoked potentials (VEP) were recorded from infants two to six months of age using a checkerboard pattern reversal stimulus. By six months, infants produced the largest amplitude VEP to checks subtending visual angles of 7.5 or 15 minutes of arc, as do adults with 20/20 acuity. This finding indicates that by six months an infant's sensory capacity for a visual acuity of 20/20 is established.

Adult↗

PubMed1975

Stimulus novelty, task relevance and the visual evoked potential in man.

Visual evoked potentials (VEPs) were recorded from normal adult subjects performing in a visual discrimination task. Subjects counted the number of presentations of the numeral 4 which was interposed rarely and randomly within a sequence of tachistoscopically flashed background stimuli (numeral 2s). Intrusive, task-irrelevant (not counted) stimuli were also interspersed rarely and randomly in the sequence of 2s; these stimuli were of two types: simples, which were easily recognizable (e.g., geometric figures), and novels, which were completely unrecognizable (i.e., complex, colorful patterns). It was found that the simples and the counted 4s evoked posteriorly distributed P3 waves (latency 380-430 msec) while the irrelevant novels evoked large, frontally distributed P3 waves (latency 360-380 msec). These large, frontal P3 waves to novels were also found to be preceded by large N2 waves (latency 278 msec). These findings indicate that "the P3" wave is not a unitary phenomenon but should be considered in terms of a family of waves, differing in their brain generators and in their psychological correlates. These late positive components are discussed in terms of task-relevance, recognition and Pavlov's "what is it" response.

Attention↗

PubMed1998

Auditory and visual event-related potentials and flash visual evoked potentials in Alzheimer's disease: correlations with Mini-Mental State Examination and Raven's Coloured Progressive Matrices.

We investigated possible correlations among neurophysiological examinations [auditory and visual event-related potentials (A-ERPs, V-ERPs), and flash visual evoked potentials (F-VEPs)] and neuropsychological tests [Mini-Mental State Examination (MMSE) and Raven's Coloured Progressive Matrices (RCPM)] in 15 subjects with probable or possible Alzheimer's disease (AD) according to the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria. The P300 latency of A-ERPs was correlated with the scores of MMSE but not with those of RCPM. The P300 latency of V-ERPs was more significantly correlated with the scores of RCPM than with those of MMSE. The P2 latency of F-VEPs was more significantly correlated with the scores of RCPM than with those of MMSE. The P2 latency of F-VEPs was not correlated with the P300 latency of A-ERPs but was correlated with the P300 latency of V-ERPs. The close relationship among V-ERPs, F-VEPs and RCPM suggests that these examinations at least partly reflect the functions of visual association areas in AD. Furthermore, discrepancy between P300 latency by A-ERPs and V-ERPs suggests that the mechanism responsible for P300 generation is not identical between these two stimulus modalities.

Aged↗

PubMed1979

Visual evoked potentials in monkeys.

Visual evoked potentials (VEPs) were recorded from 2 cortical sites in stump-tailed macaques. VEPs recorded from striate cortex were basically consistent between animals (especially at low light intensity), remained remarkably stable over time, and compared favorably to VEPs reported by other investigators. We concluded that the VEP recorded from the striate cortex of day-active monkeys consists of 5 major peaks within the first 250 msec. The potentials recorded from post-central gyrus were simpler and more individualized and did not show intensity-related latency changes or increases in inter-subject variability. However, amplitudes of potentials recorded from both electrode placements increased with light intensity apparently reflecting the amplitude of individual potentials rather than the variability of these potentials from which the average VEPs were derived.

Animals↗

PubMed1998

Multimodality visual evoked potentials in evaluating visual dysfunction in optic neuritis.

Visual information is processed via multiple, parallel channels. The present study examined the clinical feasibility of multimodality visual evoked potentials (VEPs) in optic neuritis. We recorded transient VEPs to 30' checkerboard patterns, chromatic and achromatic sinusoidal gratings and apparent motion, and steady-state VEPs to achromatic gratings in 15 normal controls and 14 patients. VEPs to 30' checks were abnormal in 10 eyes (7 patients); however, considering all five modalities, abnormal responses were seen in 20 eyes (12 patients). Abnormality rates were not equal among the visual stimuli, which thus suggested possible dysfunction of individual subdivisions in the visual pathways. We conclude that use of multimodality VEPs may increase both understanding of the pathophysiology of the visual pathways and diagnostic yield.

Adult↗

PubMed1982

[Effect of neuroleptanalgesia on the visual evoked potential (VEP) in man].

Visual evoked potentials (VEP) were monitored intraoperatively in 35 urological patients during modified neuroleptanalgesia. Control measurements were made in 18 awake, premedicated patients prior to induction of anesthesia. The latencies of the negative peaks (designed n1, n2, n3) increased significantly (p = 0.001) during anesthesia: n1 from 50,6 ms to 57,1 ms, n2 from 80 ms to 89,4 ms, n3 from 124,5 ms to 139,6 ms, no significant change in amplitude was seen. Changing paCO2 in the range from 20 mmHg to 50 mmHg during controlled ventilation did not affect latencies and amplitudes of visual evoked potentials (n = 10 patients). These influences of neuroleptanalgesia must be considered when recording visual evoked potentials intraoperatively during neurosurgical procedures (aneurysm-, pituar gland surgery) for monitoring optic nerve function.

Adolescent↗

PubMed2006

Spatial frequency-specific potentiation of human visual-evoked potentials.

Recent research has suggested that cortical long-term potentiation can be induced non-invasively in humans by using rapid visual stimulation. The present study extends these findings by investigating the specificity of this long-term potentiation effect to the inducing stimulus. One group of study participants were tetanized using a one cycle-per-degree sine grating, while a second group was tetanized using a five cycles-per-degree sine grating. Using electroencephalography, we found that an increase in the N1b potential was specific to sine gratings of the same frequency as the tetanus. No effect was observed in the N1b for sine gratings of a different spatial frequency. These results suggest that the long-term potentiation effect induced by the sensory tetanus is isolated to a discrete neural population in the visual cortex.

Adult↗

PubMed1985

Comparisons among Snellen, psychophysical, and evoked potential visual acuity determinations.

Acuity limits were determined for gratings of progressively finer spatial frequency directly from the visually evoked potential. The evoked potential was retrieved in real time, while spatial frequency was electronically changed or swept. The results of the swept evoked potential technique are compared to acuity thresholds determined psychophysically with similar gratings, and with Snellen acuity determinations over the range 6/60 (20/200) to 6/3.6 (20/12), obtained by defocusing with positive spherical lenses. One line of Snellen acuity is easily discriminated; the absolute Snellen level can often be identified to within two lines with 95% certainty. Correlations between visually evoked response (VER) grating and Snellen optotype acuity levels are poorer than correlations between VER- and psychophysically-determined grating acuity limits, perhaps because of variability inherent in the Snellen task itself. The swept evoked potential affords a rapid, objective, and potentially useful measure of acuity in young or minimally cooperative subjects.

Adult↗

PubMed1994

Topographic mapping of the visual evoked potential after source derivation.

Visual Evoked Potentials (VEP) have been considered an important complementary diagnostic method for the study of the physiology of the visual pathways and cortex. It is suggested that topographic maps of Visual Evoked Potentials (VEP) generate information related to the anatomy and physiology of the visual cortex. The source derivation technique applied to electroencephalographic signals has been shown to improve the sensitivity and spatial selectivity of the results. Mapping VEP after source derivation was implemented in order to facilitate the interpretation of the VEP signals and as an aid in identifying the distribution of the sources generating them. The signals were obtained from normal individuals stimulated with full-field and half-field pattern reversal checker-boards. The electrode system used (16 channels) was that proposed by Bodis-Wollner; this system concentrates the electrodes in the scalp areas related to the visual cortex. Signals were sampled simultaneously with a 10-bit A/D converter, saved and, thereafter, processed in an IBM/PC compatible microcomputer. After coherently averaging the responses, source derivation considering inter-electrode distances was applied. It was observed that the spatial spreading of the signals was reduced, leading to an improved spatial selectivity, locating the VEP sources in the expected brain regions and suggesting the existence of electrical dipoles.

Adult↗

PubMed1991

[A preliminary report of evoked potential marker study of pattern shift visual evoked potentials (PS-VEP) and auditory evoked potentials (AEP) on schizophrenic twins].

This paper reports the result of electroneurophysiological study of the pattern shift visual evoked potentials (PS-VEP) and auditory evoked potentials (AEP) on six pairs of schizophrenic twins. The result indicated that there were significant differences in the inter-pair variance between MZ and DZ in latency P2, amplitude P2-N2 and P2 of using PS-VEP. AEP was also used for this group cases, and the result showed the presence of statistical differences in the inter-pair variance of latency N2, amplitude N1-P2 and P2. The authors speculated upon that the above six electrophysiological markers may be related to genetic factors, which had been proved by the blood group, character, clinical symptoms and treatment response of those patients.

Adolescent↗

PubMed2001

Spatial property of motion visual evoked potentials.

The cortical evoked response to drifting patterns (motion visual evoked potentials) was investigated. When the direction of motion of the stimulus pattern was reversed upward or downward at intervals, the cortical evoked response was triggered at the moment when the pattern changed direction. The polarity reversal of the main negative component occurred between upper and lower visual field stimulations as seen in pattern reversal visual evoked potentials. Our study indicates these potentials have a compound property reflecting the visual field.

Adult↗

PubMed1989

Waveform analysis and reproducibility of visual-evoked potentials in dogs.

Visual-evoked potentials (VEP) and electroretinograms (ERG) were recorded from 10 normal light-adapted adult dogs, using a 3 x 5 matrix of light-emitting diodes as a stimulator. Visual-evoked potentials were recorded from 4 scalp electrodes overlying cortical areas, whereas electroretinographic activity was recorded by 2 scalp electrodes placed near the eye and by a conjunctivally placed electrode. The waveform of the VEP consisted of 3 major positive waves (P1 through P3), with peak latencies in the 20- to 70-ms range. Waveform reproducibility was assessed by comparing peak latencies from VEP recorded on 2 separate days approximately 1 week apart. The peak latencies for P1 through P3 did not differ (P greater than or equal to 0.05) between first and second recording sessions. To substantiate the postretinal origin of VEP, recordings were made before and after unilateral optic nerve transsections in 4 dogs. Electroretinograms were also measured before and after surgery to assess the integrity of the retina. Postsurgically, VEP were absent when the eye on the surgically treated side was stimulated. Stimulation of the contralateral eye induced VEP with the same waveform shape, but latencies were slightly prolonged (P less than or equal to 0.05) compared with presurgical recordings. The only effect of optic nerve transsection on the ipsilateral ERG was a prolongation (P less than or equal to 0.05) of the b-wave. However, when postsurgical ERG values were compared with those from the intact side after surgery, there were no differences.

Animals↗

PubMed1985

Visual evoked potentials in pseudotumor cerebri.

Pattern reversal visual evoked potentials in 13 patients with pseudotumor cerebri were significantly delayed (99 +/- 7.3 ms [mean +/- SD]) compared with the findings in 20 normal subjects (94 +/- 2.7 ms), although only four patients had latencies outside the normal range. There was, however, a significant correlation between the intracranial pressure and the latency of visual evoked potentials. After medical treatment of the intracranial hypertension, visual evoked potential latencies decreased in patients who recovered and in whom the papilledema disappeared. In one patient with progressive visual failure, the visual evoked potentials were abnormal before disturbances of visual fields and visual acuity were evident. Repeated examinations of visual evoked potentials might be of value in patients with pseudotumor cerebri to ensure neurosurgical intervention in due time to prevent visual loss in patients with impending optic nerve atrophy.

Adolescent↗

PubMed1993

The effects of physostigmine on the response characteristics of the cat visual evoked potential.

Steady-state pattern visual evoked potentials were recorded from the surface of the cat primary visual cortex before and after the intravenous administration of physostigmine, an agent that blocks the enzyme responsible for the breakdown of synaptically released acetylcholine. Under pentobarbital anesthesia, physostigmine increased the amplitude and changed the phase of the second response harmonic of the visual evoked potential, whereas the amplitude and phase of the fourth harmonic were not affected. These effects persisted for 15 to 45 minutes and were blocked by prior treatment with scopolamine or atropine. In addition, scopolamine or atropine administered 5 to 10 minutes after physostigmine returned the visual evoked potential to the baseline state. In comparison, when nitrous oxide was used, physostigmine caused a marked reduction in visual evoked potential amplitude, an effect that was reversed by subsequent atropine. These results indicate that the cholinergic system influences the visual evoked potential via a muscarinic pathway and that this influence is strongly affected by the anesthetic regimen used.

Acetylcholine↗

PubMed1997

Neuronal generators of visual evoked potentials in humans: visual processing in the human cortex.

PURPOSE: We wished to define the localization of cortical generators of visual (pattern) evoked potentials (VEP) and the temporal sequence of activation in the occipital region. METHODS: In 4 candidates for epilepsy surgery, a large array of subdural electrodes was placed over occipital areas. Checkerboard pattern reversal stimuli were generated and the epileptogenic focus was localized and functionally mapped. Magnetic resonance imaging did not show any occipital lesions in any of the 4 patients. RESULTS: The area first activated was the lingual gyrus in the mesial occipital lobe (negative potential peaks at approximately 70 ms), followed by an area superior to the calcarine fissure (negative peaks at approximately 80 ms). Later (starting at approximately 90 ms), there were positive potentials over the occipital pole and lingual gyrus, followed by potentials at the lateral occipital lobe. CONCLUSIONS: These data support the idea that VEP are generated in the mesial and lateral occipital cortex by different circumscribed neuronal generators with different latencies of activation. The scalp-recorded N1 and P1 potential peaks most likely derive from the progressive activation of neuronal masses in different regions of the occipital lobe.

Brain Mapping↗