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Results for “Evoked Potentials, Visual”

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PubMed1994

Temporal frequency deficit in patients with senile dementia of the Alzheimer type: a visual evoked potential study.

To study the temporal aspect of visual processing of senile dementia of the Alzheimer type (SDAT), we recorded the steady-state visual evoked potentials (VEPs) to LED goggle stimulation at five different temporal frequencies in 14 patients with SDAT and 14 control subjects. For comparison, we also studied 14 patients with vascular dementia (VD). All subjects were women, and their ages were closely matched. Temporal frequencies were 5, 10, 15, 20, and 30 Hz. The steady-state VEPs were Fourier analyzed, and both the amplitude and phase of the first and second harmonic responses were obtained. There was a significant difference in the amplitude across the three groups for stimulation at 15, 20, and 30 Hz, but no difference at a stimulation of 5 and 10 Hz. Multiple comparison tests revealed that patients with SDAT had a significantly smaller amplitude than normal controls. Patients with VD had lower amplitudes than normal subjects, but this was not statistically significant. In the phase data, there were also no statistically significant differences across the three groups for any of the temporal frequencies. These results indicate that a temporal frequency deficit exists in SDAT. This phenomenon may be explained by the pathology that affects the early stage of visual signal processing.

Aged↗
PubMed1987

Investigations of amitraz neurotoxicity in rats. II. Effects on visual evoked potentials.

As a part of a series of studies investigating the possible neurotoxicity of amitraz (AMZ), a formamidine pesticide, visual evoked potentials were recorded from Long-Evans rats following acute and short-term repeated exposures to AMZ. The first of three experiments examined the relationship between a single ip injection of AMZ (0, 50, and 100 mg/kg) and the latency and peak-to-peak amplitude of pattern-reversal (PREP) and flash-evoked potentials (FEP). The effects of another formamidine, chlordimeform (CDM; 40 mg/kg), were also studied for comparison purposes. Two hours after treatment, AMZ exposure produced large, dose-related increases in PREP amplitudes. Exposure to CDM produced similar changes. Neither compound changed FEP amplitudes. Body temperatures were reduced and evoked potential peak latencies were increased by both compounds. The latency increases were probably a secondary consequence of hypothermia. In the second experiment, PREPs were recorded before and 2, 24, 48, and 72 hr after treatment with AMZ (100 mg/kg). The time course of changes was biphasic in nature, with increases in amplitudes (N1P1, P1N2, and N2P3) 2 hr after treatment followed by subsequent depression in amplitude (P2N3) at 48 hr. Recovery occurred by 72 hr after treatment. The third experiment examined the effects of three daily treatments with either vehicle or 50 or 100 mg/kg AMZ. Body weights and body temperatures showed dose-related reductions which progressed with each additional treatment and recovered partially by 6 days after cessation of treatment. The PREPs of AMZ-treated rats agains showed biphasic changes, with N1P1 and P1N2 amplitudes significantly increased on each day of treatment and 1-2 days following the third treatment. Amplitude P2N3 showed an initial increase on the first 2 days of treatment, followed by subsequent, progressive amplitude reductions. In summary, AMZ produced two phases of change in visual evoked potentials. The first phase was characterized by large increases in PREP amplitudes without increasing FEP amplitudes in the same rats. The second phase was characterized by suppression of PREP P2N3 amplitude. Short-term repeated exposure produced signs of accumulating intoxication including progressive loss of body weight, lowered body temperature, and prolonged duration of evoked potential changes.

Animals↗
PubMed2004

Visual evoked potentials in migraine.

Migraine is a chronic disorder. Visual symptoms and hypersensitivity to light stimuli are common. The aim of this study is the analysis of visual system in migraineurs by visual evoked potentials (VEP). We studied 53 migraineurs (21 with prophylactic migraine treatment and 32 without preventive therapy) and 20 healthy control subjects. We found lower P100 latencies in migraineurs without therapy compared to controls. In treated patients, P100 latencies showed the same trend seen in the control group. We speculate a different responsiveness of the visual system in migraineurs probably due to a dysmodulation of sensor input leading to facilitation of visual processing.

Adult↗
PubMed2006

Sweep visual evoked potential grating acuity thresholds paradoxically improve in low-luminance conditions in children with cortical visual impairment.

PURPOSE: Children with cortical or cerebral visual impairment (CVI) often experience photophobia. In a study conducted to test whether this clinical phenomenon affects visual function, the sweep visual evoked potential (VEP) was used to evaluate cortical responses to grating stimuli in two luminance conditions: low and normal. METHODS: Twenty children (age range, 7 months to 4 years 10 months) with CVI and 17 age-matched control subjects were examined. Testing conditions consisted of a swept grating stimulus shown against a normal background luminance (109 cd/m2) and against a low-luminance background (20 cd/m2). Thresholds in these two luminance conditions were compared. Response amplitudes across the spatial frequency domain were also compared. RESULTS: Children with CVI paradoxically have improved grating acuity thresholds when the stimulus is shown using a low-luminance background (P=0.006). Response amplitudes are also increased in low luminance. In control children, luminance had no significant effect on response amplitudes or thresholds. CONCLUSIONS: Increased luminance causes a worsening of acuity thresholds in children with CVI. Response amplitudes are also diminished in normal luminance. This finding has implications for optimal viewing and learning conditions for children with CVI.

Blindness, Cortical↗
PubMed1991

The cause of increased pupillary light reflex latencies in diabetic patients: the relationship between pupillary light reflex and visual evoked potential latencies.

In 42 diabetic patients the relationship between the latency of the pupillary light reflex and the pattern reversal visual evoked potential (P100) was examined. Fifty-five percent of diabetic patients had pupillary light reflex latencies above the normal range. In 19% the visual evoked potentials were prolonged when compared to the normal range. Latencies of pupillary light reflexes and VEPs showed no correlation. There was a minimal correlation between the presence of retinopathy and prolongation of both the pupillary light reflex and the visual evoked response latency (kappa coefficients respectively: 0.31, P less than 0.01 and 0.36, P less than 0.02). The presence of an increased pupillary light reflex latency was positively correlated with a reduced respiratory sinus arrhythmia (kappa coefficient: 0.58, P less than 0.0001). Increased VEP latencies showed no correlation with signs of cardiovascular autonomic neuropathy. We conclude that the afferent optic pathway can be affected in diabetic patients. However, prolongation of pupillary light reflex latency in diabetic patients is primarily due to an efferent pupillary defect and represents parasympathetic dysfunction.

Adult↗
PubMed1996

[Voluntary changes of visual evoked potentials in cases with hysteria and/or simulation].

We report a 25-year-old woman with gradual loss of visual acuteness, during puerperium and blindness in fifteen days. Two months latter she remain steady. Visual evoked potentials using monocular checkerboard pattern-reversal, were abnormal. Clinical suspicion of voluntary alteration of VEP was considered. A second VEP exploration with binocular stimulation and maneuvers of distraction were carried out. Normal VEP were recorded. Deliberate alteration of the visual evoked potential should be considered in patients suspicious of hysteria or malingering.

Adult↗
PubMed1995

Pattern reversal visual evoked potentials in patients with hemineglect syndrome.

To investigate basic visual information processing in patients with hemineglect syndrome, pattern reversal visual evoked potentials (VEPs) were recorded in 21 brain-injured patients (10 with neglect symptoms) and 6 healthy subjects. The stimulus was a checkerboard which varied in check size or temporal frequency, presented to the left or right visual field. VEPs recorded in neglect patients to stimuli presented in the subjectively neglected left visual field were comparable in amplitude to those recorded to stimuli presented in the normal right visual field. For stimuli presented centrally, there was no difference in VEPs between neglect patients and brain-damaged patients without neglect. These results support neuropsychological theories that state that the neglect syndrome is more closely related to deficits at post-sensory levels than to impairments in basic visual processing. Some evidence, however, suggests that the nature of the interaction between the two visual hemi-fields may also be altered in neglect patients.

Aged↗
PubMed1981

Binocular stimulation reveals cortical components of the human visual evoked potential.

Dynamic random dot correlograms (RDCs) produced by a rear-projection television system elicited visual evoked potentials (VEPs) in a sample of 10 observers corrected to emmetropia. When the observers viewed the RDCs binocularly through stereo wave length filters, characteristic wave forms were recorded. Four components were reliably recorded at the onset and the offset of the correlated state of the RDCs. These components differ with statistical significance (P less than 0.05) from each other. These RDC VEPs provide a practical technique to evaluate the integrity of binocular and, by inference, cortical processes.

Adult↗
PubMed1984

Cortical visual evoked potentials during the sleep wakefulness cycle of the freely moving cat. Characterization and statistical comparisons.

Visual evoked potentials (VEPs) were obtained during the stages of wakefulness (W), slow sleep (SS) and paradoxical sleep (PS) by means of a light-emitting diode chronically implanted in the frontal sinus of the freely moving cat. Statistical analysis of the variables: latencies, latency intervals and amplitudes, between each of the mentioned stages shows that, for the first components, variations occurred only in the first interval of latency during SS vs. W. Lengthening of VEP latencies and increase of VEP amplitudes were observed for all secondary components in the comparisons between both SS and W, and SS and PS. PS-VEPs vs. W-VEPs showed shortening of latencies and decrease of amplitudes of all secondary components of the former case. The results confirm that in the freely moving cat, the secondary VEP response is more intensely affected by sleep than the primary VEP response, but indicate that there are different mechanisms in the generation of the VEP during SS and PS.

Animals↗
PubMed1986

Anticholinesterase agents affect contrast gain of the cat cortical visual evoked potential.

The effects of the anticholinesterase agents physostigmine, pyridostigmine, diisopropylfluorophosphate and soman on the cortical visual evoked potential (VEP) were examined using phase reversed sine wave gratings of varying contrasts. All 4 agents decreased the slope (gain) of the response vs log contrast function while the intercept with the noise level (threshold, an indicator of contrast sensitivity) was unaffected. These results suggest that anticholinesterases modify the VEP by changing a contrast gain control mechanism.

Acetylcholine↗
PubMed2001

Identification of the stimulated hemiretina in primary school children and adults based on left and right hemifield pattern reversal visual evoked potentials--a comparative study.

OBJECTIVES: The analysis of left and right hemifield pattern-reversal visual evoked potentials (PVEPs) in children and the identification of the stimulated hemiretina testing different identification procedures previously applied to adults. METHODS: Lateral hemifield PVEPs were recorded in 40 children (6-11 years) and 27 adults (25-40 years) from, at least, 19 standard electrodes. Two procedures were tested for the determination of the stimulated hemifield: firstly, the evaluation of the values of instantaneous frequency at the occipital electrodes at P100 latency (determined by the global field power), and secondly, the application of a generalised dynamic neural network (GDNN) using the PVEP time course at selected electrode positions as the external input. RESULTS: P100 latency as well as P100 amplitude over the contralateral occiput in children were significantly greater than in adults. Contrary to the behaviour in adults, instantaneous frequency is not a robust identifier of left and right hemiretina stimulation in children. The best identification performances were achieved when using group trained GDNNs with the bipolar difference signals of electrodes P3/P4 or T5/T6 as the external input. CONCLUSIONS: The PVEPs at electrodes P3/P4 and T5/T6 contain essential information for the determination of the stimulated hemifield. This should be further considered during the development of on-line procedures for automatic PVEP detection in future studies.

Adult↗
PubMed2001

Motion adaptation in chromatic motion-onset visual evoked potentials.

The aim of this study was to investigate the influence of motion adaptation on visual evoked potentials (VEPs) elicited by the onset of isoluminant chromatic motion. VEPs were recorded from the occipital cortex of human subjects using a sinusoidal grating stimulus of one cycle per degree which moved at either a velocity of 2 or 10 degrees/s and subtended a field of 7 degrees with a mean luminance of 30 cdm(-2). In the first experiment the effects of adaptation were investigated via the manipulation of the stimulus duty cycle which was varied between 11-90%. The results showed a significant (p < 0.001) reduction in the N2-P2 amplitude of the chromatic response. In contrast, P1-N2 amplitude was not significantly affected by motion adaptation. Subsequent experiments demonstrated that the chromatic motion onset VEP was attenuated not only following adaptation to isoluminant chromatic motion, but also to luminance motion as well. These results indicate that the chromatic motion onset VEP is just as susceptible as its luminance counterpart to motion after effects (MAEs) and as a result it is highly likely that it is a motion specific response. Furthermore, the fact that the VEP shows that there are cross-adaptation effects between motion defined by change in colour and by change in luminance, suggests that the two types of motion stimuli have inputs into a common motion mechanism.

Adaptation, Ocular↗
PubMed1995

Effect of valproate and carbamazepine on visual evoked potentials in epileptic children.

The effects of carbamazepine (CBZ) and sodium valproate (SV) monotherapy on visual evoked potentials (VEP) were studied in 18 epileptic children receiving CBZ and nine epileptic children receiving SV. Pattern reversal VEP were determined before the administration of antiepileptic drugs (AED) and 1 year later during which time the patients had received AED. The VEP amplitude showed no consistent changes after 1 year of CBZ and SV therapy, but VEP P-100 latencies were significantly prolonged after 1 year of CBZ therapy. We conclude that CBZ causes a slowing down of central impulse conduction and that VEP is useful to evaluate the effects of AED within the central nervous system.

Carbamazepine↗
PubMed1998

Visually evoked potentials in 52 children requiring operative repair of craniosynostosis.

We evaluated the prevalence of pathological visually evoked potentials (VEP) before the appearance of papilledema or other signs of elevated intracranial pressure in children suffering from craniosynostosis. In 52 children (19 girls, 33 boys, median age 7.6 months, mean age 7.6 months, range from 3 to 34 months) preoperative VEP were analyzed. In 13 patients, pathological VEP were observed. In all children, both eyes were involved. Only 1 child suffered from papillar anomalies. Latency was pathological in 12 children, whereas the amplitude was suppressed in only 2 children. In all children with preoperative pathological VEP, postoperative controls (n = 4) were improved or normal. Thus, VEP may be the first test for neuronal damage in craniosynostosis.

Child, Preschool↗
PubMed1990

Binocularity in the little owl, Athene noctua. II. Properties of visually evoked potentials from the Wulst in response to monocular and binocular stimulation with sine wave gratings.

Visually evoked potentials (VEPs) have been recorded from the Wulst surface of the little owl, Athene noctua, in response to counterphase-reversal of sinusoidal gratings with different contrast, spatial frequency and mean luminance, presented either monocularly or binocularly. Monocular full-field stimuli presented to either eye evoked VEPs of similar amplitude, waveform and latency. Under binocular viewing, VEPs approximately doubled in amplitude without waveform changes. VEPs with similar characteristics could be obtained in response to stimulation of the contralateral, but not ipsilateral, hemifield. These results suggest that a 50% recrossing occurs in thalamic efferents and that different ipsilateral and contralateral regions converge onto the same Wulst sites. The VEP amplitude progressively decreased with increase of the spatial frequency beyond 2 cycles/degree, and the high spatial frequency cut-off (VEP acuity) was under binocular viewing (8 cycles/degree) higher than under monocular (5 cycles/degree) viewing (200 cd/m2, 45% contrast). The VEP acuity increased with increase in the contrast and decreased with reduction of the mean luminance. The binocular gain in both VEP amplitude and VEP acuity was largest at the lowest luminance levels. Binocular VEP summation occurred in the medium-high contrast range. With decreased contrast, both monocular and binocular VEPs progressively decreased in amplitude and tended to the same contrast threshold. The VEP contrast threshold depended on the spatial frequency (0.6-1.8% in the range 0.12-2 cycles/degree). Binocular VEPs often showed facilitatory interaction (binocular/monocular amplitude ratio greater than 2), but the binocular VEP amplitude did not change either by changing the stimulus orientation (horizontal vs. vertical gratings) or by inducing different retinal disparities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗