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Results for “Evoked Potentials, Visual”

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At least 289 records · Page 16Linked to original sources

PubMed1979

Visual evoked potentials in Reye's syndrome.

Visual evoked potentials (VEPs) induced by flash stimulation in a child who was recovering from Reye's syndrome with complaints of poor left-eye vision were recorded. Ophthalmological examination disclosed intact visual fields and normal visual acuity. Analysis of VEP's, however, showed a grossly abnormal configuration of wave forms, marked prolongation in latency and reduction in amplitude when the left eye was stimulated. Follow-up observation 3 weeks later showed parallel improvements in VEPs and subjective complaints. Thus, from VEP analysis, it may be possible to detect subtle changes in the visual system that have diagnostic and prognostic value.

Adolescent↗

PubMed1982

Dopaminergic deficiency and delayed visual evoked potentials in humans.

Abnormal delay in visual evoked potential (VEP) could be normalized in 9 of 14 previously untreated parkinsonian patients under the influence of levodopa/carbidopa therapy. In 6 of 11 previously untreated schizophrenic patients the VEP latency became abnormal following therapy with agents known to cause dopaminergic blockade. Besides defects in retrobulbar conduction secondary to demyelination, synaptic dysfunction due to neurotransmitter deficiency or receptor blockade must also be considered as a mechanism underlying VEP delays in humans.

Adult↗

PubMed1982

Dopaminergic deficiency causes delayed visual evoked potentials in rats.

Flash and pattern visual evoked potentials (VEPs) to two temporal frequencies of stimulation were studied in nineteen rats. The effect of a tyrosine hydroxylase inhibitor and of a dopamine receptor blocker on the VEP was explored in ten animals. Significant latency change occurred following injection of either drug, while only the hydroxylase inhibitor reduced the VEP amplitude. These changes were not caused by the anesthesia used in these experiments, although the same anesthetics in higher doses did depress VEP amplitudes. When dopamine blockade was followed by administration of apomorphine, a dopamine agonist, VEP delays could be partially reversed. Besides conduction defects of myelinated axons, synaptic malfunction may also cause delays in sensory evoked potentials.

Animals↗

PubMed1986

Delayed visual evoked potentials in chronic alcoholism.

Pattern reversal visual evoked potentials (VEPs) were studied in 80 chronic alcoholics and in 43 normal subjects. In the patient group, P2 latencies and inter-eye differences were found above the 98% confidence limit in 30%, and above the 99.9% confidence limit in 10%. An abnormal waveform was observed in 12.5% and 7.5% of the patients. VEP abnormalities showed some statistical correlation with the gamma-type of alcoholism of Jellinek, but almost no correlation was observed with a variety of clinical and laboratory data. This suggest that VEP abnormalities are unrelated to other toxic effects of alcohol on the peripheral and central nervous systems or on metabolism.

Adult↗

PubMed1992

The effects of low-pass filtering on the flash visual evoked potential of the albino rat.

Flash visual evoked potentials (FVEPs) were recorded from the rat in order to determine the effects of low-pass filtering on the wave form. The low-frequency (high pass) filter remained fixed at 3.2 Hz while the setting of the high-frequency (low-pass) filter was progressively raised from 32 Hz to 3.2 kHz. The amplitude of the primary cortical potential (P30) steadily increased while its latency decreased until asymptotic values were recorded with a low-pass cut-off of 320 Hz. Thereafter, there was little additional change in wave form. It is concluded that a bandpass of 3.2-320 Hz is optimal to record the primary cortical response of the FVEP, and this is consistent with the theory that the P30 potential is generated by comparatively slow post-synaptic activity. In a second experiment the effects of low-pass filtering were examined on the later and more labile secondary components of the FVEP wave form. These were found to be less responsive to low-pass filtering than the early components and assumed a near optimal configuration when the high-frequency cut-off was raised to 80 Hz. The high-frequency filter setting which is most appropriate to record the primary component of the FVEP therefore appears to be more than adequate also to record the secondary responses. It is also shown that the same principles of low-pass filtering on the FVEP will apply irrespective of whether the subject is awake or anaesthetised.

Anesthesia↗

PubMedDate not supplied

Visual evoked potentials in a patient with prosopagnosia.

Visual evoked potentials (VEPs) were recorded from a 53-year-old man with prosopagnosia during presentation of slides of known and unknown faces and under two control conditions. ANOVA comparisons with a normal male group showed no differences in P100 amplitude, P300 amplitude or P300 latency. There were no significant evoked potential differences between the patient and controls specifically related to the face conditions. There was, however, a significant delay in the latency of P100 from both hemispheres during all types of stimuli. This prolonged latency was asymmetrical, showing a right sided emphasis with the control conditions: pattern reversal and slides of geometric designs. This finding, of a dissociation in the interhemispheric delay, provides physiological evidence of stimulus-specific organisation at an early, sensory level. The fact that the P100 component showed a marked delay, yet P300 fell within normal limits for amplitude and latency, suggests that this patient's problem lies at a perceptual level.

Agnosia↗

PubMedDate not supplied

Three-dimensional human pattern visual evoked potentials. II. Multiple sclerosis patients.

Pattern visual evoked potentials were obtained from 46 patients with definite relapsing/remitting multiple sclerosis, using both a conventional 5-channel occipital array and a 3-D recording technique consisting of three bipolar derivations approximating the three dimensions of space. These three orthogonal wave forms were displayed as a 3-D Lissajous trajectory for each subject. Two of the 15 patients with completely normal conventional pattern VEPs had abnormalities of the orientation of the B-C curvilinear segment of the 3-D pattern VEPs. Delays in the first major occipital positive component (P100) were evident using both techniques; the correlation between P100 latency and the latency of the corresponding trajectory apex was r = 0.99 (P less than 0.01). Post-chiasmal MRI abnormalities were associated with 3-D VEP orientation abnormalities. Three-dimensional pattern VEPs are moderately more sensitive than conventional pattern VEPs at detecting dysfunction posterior to the optic chiasm in demyelinating disease and do not require the use of eccentric fixation to do so.

Adult↗

PubMedDate not supplied

Serial visual evoked potential recordings in geriatric psychiatry.

Serial visual evoked potentials to flash and pattern reversal stimuli were recorded in elderly patients with senile dementia of the Alzheimer type (SDAT), multi-infarct dementia (MID) and functional psychiatric illness, and in a group of elderly control subjects. Recordings were made at 6 monthly intervals over a 2 year period. Latency and amplitude of the main components were measured and the flash P2-pattern reversal P100 latency difference value was calculated. In all groups significant changes over time did not occur for any parameters but in the SDAT group the regression coefficient for the latency of the flash P2 component and the flash P2-pattern reversal P100 latency difference was significant, reflecting a trend towards increasing flash P2 latency as time progressed. The flash P2-pattern reversal P100 latency difference was longer in the SDAT and MID groups than in the functional patients, confirming the findings of previous reports. The latency difference in the SDAT group only was significantly greater than that in the control group.

Aged↗

PubMed2001

Visual evoked potentials elicited by chromatic motion onset.

Visually Evoked Potentials (VEPs) were recorded in response to the onset of chromatic and luminance motion gratings of 1 cpd and luminance 40 cd m(-2) subtending a 7 degrees field. At slow speeds (< or =2 cycles s(-1)) the motion onset response exhibits a clear amplitude minimum at isoluminance. Over the Michelson contrast range tested (0.05-0.75) the chromatic response at 2 cycles s(-1) possesses a linear response function compared to the saturating function of the luminance response and the contrast dependency of the former is a factor of 5-6 times greater than for the latter. These differences are suggestive of different neural substrates for the chromatic and luminance motion VEPs at slow speeds. At 10 cycles s(-1) the chromatic motion onset VEP exhibits no amplitude minimum at isoluminance and becomes more like its luminance counterpart in terms of its saturating contrast response function. Furthermore, the contrast dependency of the chromatic and luminance responses differs by only a factor of 1.6 at this faster rate. These findings are consistent with the idea of separate motion mechanisms that operate at fast and slow speeds, the latter having separate channels for colour and luminance motion.

Adult↗

PubMed1991

Visual evoked potentials: differences related to physical activity.

Visually evoked potentials to patterned stimuli were recorded from tennis players, rowers and non-athlete control subjects. Each group consisted of 12 males and 12 females of similar age. Tennis players showed shorter P100 latencies compared to those of control subjects and rowers. This difference exists, in the same range, both in the male and in the females. The analysis of covariance and multiple linear regressions show that these shorter latencies cannot be explained by head circumference or by height. The hypothesis of a relationship between these shorter latencies and the specific qualities of racket players is suggested. A second experiment with squash players seems to confirm these first results.

Adolescent↗

PubMedDate not supplied

Visual evoked potentials in the clinically normal dog.

Visual evoked potentials (VEP) in response to flashes of white light were recorded from 15 adult beagles of both sexes to provide a normative data base. Separate recordings were taken by stimulating each eye of every dog. Responses were recorded from a needle electrode placed over the nuchal crest referenced to an electrode just caudal to the eyes. Five positive and negative peaks were present in each VEP; P1, N1, P2, N2, and P3. Peak P2 was the most prominent. Mean (+/- standard deviation [SD]) latencies for peaks P1, N1, P2, N2, and P3 were 14.3 +/- 2.4, 29.2 +/- 2.2, 54.5 +/- 7.4, 78.0 +/- 13.1, and 98.1 +/- 12.6 msec, respectively. Peak-to-peak mean amplitudes ranged from 5.88 to 13.30 microV. Recordings were accomplished without sedation, anesthesia, or mydriatic drugs.

Animals↗

PubMed1991

Visual evoked potential from scalp in guinea pigs.

Visual evoked potentials (VEPs) recorded from the scalp in guinea pigs were compared with those from the dura. The study was performed with ten adult male guinea pigs weighing 350-750 g. VEPs recorded from the scalp had large negative components (N40 and N75) and a large positive component (P55). The waveform of the VEP in the scalp recording was similar to that in the dural recording in that N40 was a major early negative component. Great differences between the scalp and the dural recording were observed in the late negative components (N75 and N140). In the dural recording, the peak N75 was a very small component, and the peak N140 was very large. There was no significant difference between the peak latencies of the two kinds of VEPs except for the peaks P55 and P100. Peak-to-peak amplitudes of VEPs recorded from the scalp were smaller than those from the dura except for P55-N75. The peak-to-peak amplitude in the scalp recording compared to that in the dural recording varied from a ratio as low as 1.0:2.9 to as high as 1.0:36.2, and was markedly variable in each component. The scalp recording correlated with the dural recording as regards the early component.

Animals↗

PubMed1990

[The normal response process of the dynamic topography of pattern visual evoked potentials].

The dynamic topography of pattern visual evoked potentials (PVEPs) were studied in 20 normal subjects. PVEPs, recorded from 16 electrodes referenced to balanced non-cephalic electrode (BNE), were elicited by a binocular checkerboard pattern (15 min) that alternated at 1 Hz rate on a 14 x 8.5 degree TV monitor 1m distant from the eyes. N70, P100, N100, N150 and P200 components were recorded each time. In 65% of subjects the P100 components appeared in the lateral region in 120-150 msec. In flash VEP, the P100 component did not appear in the lateral region. Recorded on lateral electrodes, N100 components first appeared in the deep frontal region and gradually distributed throughout the frontal region while the P100 component was localized at the occipital pole. In the focused state, the peak latency of the N100 component was the same as that of the P100 component, but in the moderately defocused state, the peak latency of the N100 component was delayed compared with that of the P100 component. This study suggested that the appearance of the P100 component in the lateral region is related to form recognition, and that the N100 component is not the inverse dipole of the P100 component.

Adult↗

PubMed1986

[Oscillating visual evoked potential in epilepsy].

The authors studied visual evoked potentials (VEP) at the O, P, C and T leads in response to light flashes of 0.09, 0.18 and 0.36 W/s in 19 normal and 43 epileptic subjects. In 75% of the patients the VEPs were characterized by a high amplitude oscillatory response (OVEP) in the form of a series of 5.5 oscillations with a 10 Hz frequency, the mean latent period of its development being 230 ms. In the normal subjects the OVEP was observed in only 30% of cases and had a lower amplitude, longer latent period and corresponded to the normal after-discharge according to all parameters. Some common features characteristic of the OVEP in epilepsy and the after-discharge in normal conditions suggest that the OVEP is generated by thalamic rhythmogenic mechanisms which are involved in the reaction earlier and more actively as a result of disinhibition of the subcortical multisynaptic systems. The OVEP is an indicator confirming the diagnosis of epilepsy.

Adolescent↗

PubMed1994

Monitoring vigilance during single and serial visual evoked potentials.

Full- and half-field visual evoked potentials (VEPs) are used to evaluate functional effects of optic chiasm compression by pituitary tumours. Reduction in VEP amplitude, typically from the temporal fields of vision, can occur even without demonstrable clinical deficit. An inherent problem of prolonged or serial testing is that changing levels of vigilance may affect the VEP. Gradual decrease in vigilance during a test sequence or with serial testing may cause a reduction in amplitude of the response mimicking the abnormality sought. This has serious implications when monitoring the effect of medical treatment since it may give a false impression of tumour growth requiring urgent surgery to prevent blindness. This report illustrates the nature of the problem and describes techniques using electroencephalograms (EEG), which have been used in an attempt to monitor vigilance. The ultimate aim is to produce a system to automate such monitoring during VEP recording.

Constriction, Pathologic↗

PubMedDate not supplied

[Diagnosis of demyelination processes based on the visual evoked potential test using a checkerboard reversal pattern].

Visual evoked potentials in response to checkerboard reversal pattern were evaluated in 160 patients: 24 with isolated retrobulbar optic neuritis, 100 with unquestionable and probable multiple sclerosis, 36 with paraparesis or with disseminated changes of unestablished aetiology (degenerative or inflammatory) and in 80 healthy controls. Normal visual evoked potentials were obtained in all controls. In all cases of present or past optic neuritis abnormal potentials were observed, usually unilateral. In multiple sclerosis patients with unquestionable diagnosis abnormal potentials were present in 92% of cases, and in patients with probable multiple sclerosis they were found in 58%, and in cases without retrobulbar neuritis they were present in 71% and 48% of cases respectively. The abnormalities were found most frequently in both optic nerves. It was tried to find out other correlations making possible partial differentiation of the axonal and demyelinating type of damage to the anterior part of the visual pathways.

Adolescent↗

PubMed2006

[Multifocal visual evoked potential in retinitis pigmentosa and its comparison with visual field].

PURPOSE: To investigate the characteristics of the multifocal visual evoked potential (mfVEP) and to evaluate the potential of mfVEP as a way of objective perimetry in retinitis pigmentosa (RP). METHODS: The mfVEPs were obtained by using VERIS 4.9 visual evoked response imaging system for 12 RP patients (19 eyes) and 15 normal control subjects (30 eyes). The stimulative field consisted of 60 sectors in a dartboard configuration, the visual angle of one side was 26 degrees. The amplitude sums of P1 wave of the first slice of the second order kernel from patients with RP were compared with values from control subjects. The central 30 degrees visual fields were obtained in the RP patients. Correlation between sensitivity sums of visual field and amplitude sums of P1 wave was performed in the same area. RESULTS: The amplitude sums of P1 wave decreased significantly at all rings in RP group compared with those of normal control group (P < 0.05). Except for inferior ring 1 and inferior ring 2, there was correlation between sensitivity sums of visual field and amplitude sums of P1 wave at the other rings (P < 0.05). CONCLUSION: There was a certain correlation between visual field and mfVEP. The mfVEP can be a method to evaluate visual function objectively in RP.

Adult↗

PubMed1978

Sex and strain differences in the visual evoked potentials of albino and hooded rats.

Visually evoked potentials were recorded n male and female rats from albino and hooded strains. Recordings were made at 4 different flash intensities in unanesthetized animals. Clear sex and strain differences were observed. Females had larger amplitude P1-N1 and N1-P2 components and shorter latency N1 peaks than males. Albino rats had larger amplitude P1-N1, N2-Pe and P3-N3 components and longer latency P2 and P3 peaks than hooded rats. Variations in flash intensity produced greater alterations in latencies and N1-P2 amplitudes in hooded rats than in albino rats, but greater alterations in N1, N2 and P3 latencies in albino rats than in hooded rats. Hooded rats are recommended as more valuable for studies of chemically induced change in the visual evoked potential.

Animals↗