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Results for “Evoked Potentials, Visual”

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PubMed1980

Auditory and visual evoked potentials to irrelevant stimuli during conditioning to a visual stimulus.

Amplitude changes of evoked responses to irrelevant auditory (click) and visual (optic tract stimulation) stimuli were examined during appetitive conditioning to a flashing light. Four female cats, with chronically implanted electrodes along the visual and auditory pathways, were conditioned with pairings of a flashing light and food reinforcement. The results showed that, as conditioning progressed, the auditory evoked potentials were attenuated while the visual evoked potentials did not change significantly. The data seem to indicate possible differences in the neural processing of irrelevant information.

Animals↗
PubMed1995

Short latency visual evoked potentials to flashes from light-emitting diodes.

Short latency visual evoked potentials (SVEPs) have been described in response to high-intensity, strobe flashes. High-intensity flashes can now be generated from goggle-mounted light emitting diodes (LEDs) and the SVEPs to such flashes have been shown to be reproducible across subjects, avoiding photic spread to the examination room and acoustical artifacts from the strobe stimulator. In this study, SVEPs from multichannel records are described in terms of normative latencies and amplitudes, as well as scalp distributions, to explore their generators. Potentials were recorded from 10 young male subjects, from 16 scalp locations, in response to flashes from goggle-mounted LEDs. Flashes were presented to each eye in turn, as well as binocularly. The latencies, scalp distributions and intersubject variabilities of the LED evoked SVEPs were similar to those obtained with strobe flashes. SVEP components were divided into 3 groups, according to their latency and the electrodes at which they were recorded with the largest amplitudes: periocular (under 40 msec latency), fronto-central (40-55 msec) and parieto-occipital (55-80 msec latency). The scalp distributions observed in this study suggest subcortical generators along the visual pathway, beginning at the retina. The use of goggle-mounted LEDs should promote routine evaluation of the integrity of the visual pathway between retina and cortex using SVEPs.

Adult↗
PubMed1996

Chromatic and achromatic visual evoked potentials in Parkinson's disease.

Chromatic and achromatic visual evoked potentials (VEP) were evaluated in 39 patients with idiopathic Parkinson's disease (PD) (age 64.0 +/- 8.6 years) and 43 healthy controls (age 62.8 +/- 8.7 years). The following pattern-reversal checkerboard stimuli were performed: (1) achromatic with luminance contrast 86% (achr.hk.) (2) achromatic with luminance contrast 20% (achr.lk.); (3) chromatic isoluminant blue-yellow (by.); (4) chromatic isoluminant red-green (rg.). The mean latencies N70, P100, and N135 of chromatic and achromatic VEP were significantly delayed in patients with PD as compared to controls. The highest rate (41.0%) of pathological findings could be demonstrated by achromatic stimulation (luminance contrast 86%). Isolated abnormalities of chromatic VEP (in combination with normal achromatic VEP) were found in 5 (12.8%) patients. The delay of VEP-latencies was significantly correlated with the severity of motor symptoms in PD patients. We conclude that VEP are valuable tools to demonstrate a dysfunction of the visual system in PD. Although chromatic VEP are less sensitive than achromatic VEP, the combination of both will increase the diagnostic yield. Therefore, there seems to exist a variety of individual characters of visual impairment in PD.

Adult↗
PubMed1990

Pattern reversal visual evoked potentials (VEP-PR) in migraine subjects with visual aura.

Twenty patients with migraine with visual aura, aged 19 to 55 years (2 men and 18 women) were studied by the method of Visual Evoked Potentials (VEP). The control group consisted of an equal number of healthy subjects, comparable for age and sex. The most important finding in our study is that migraine patients with visual prodromata have a significantly longer P100 latency than the subjects of control group. These modifications of the VEP-PR could indicate, as other investigators have pointed out, that there are some special metabolic conditions and abnormalities of neuromediators during and between attacks.

Adult↗
PubMed1999

Visual evoked potentials and heart rate during white noise stimulation.

Visual evoked potentials (VEPs) were recorded in 12 adult participants as a function of the temporal frequency of a phase-reversed checkerboard, with or without a simultaneously presented white noise. During the VEP recordings also the pulse rate was measured. VEP amplitude changed as function of temporal frequency, but it was not affected by noise. Pulse rate was stable during the session without noise, but it increased during the white noise stimulation at high temporal frequencies. Heart acceleration might be associated to conditions when processing at low levels of visual sensitivity (high temporal frequencies) is furthermore disturbed by interfering stimulation (noise).

Acoustic Stimulation↗
PubMedDate not supplied

[Hemispheric asymmetry of visual evoked potentials during human recognition of facial emotional expressions].

Visual evoked potentials (VEP) in standard 16 EEG derivations were recorded in 26 young men and 20 women during recognition of facial emotional expressions and geometric figures. The stimuli were presented on a computer screen in the center of the visual field or randomly in the right or left vision hemifields. Peak VEP latency and mean amplitude in 50-ms epochs were measured; spatiotemporal VEP dynamics was analyzed in a series of topographic maps. The right hemisphere was shown to be more important in processing emotional faces. The character of the asymmetry was dynamic: at earlier stages of emotion processing the electrical activity was higher in the right inferior temporal region compared to the left symmetrical site. Later on the activity was higher in the right frontal and central areas. The dynamic mapping of "face-selective" component N180 of VEPs revealed the onset of activation over the right frontal areas that was followed by the fast activation of symmetrical left zones. Notably, this dynamics didn't correlate with the hemifield of stimuli exposition. The degree of asymmetry was lower during presentation of figures, especially in the inferior temporal and frontal regions. The prominent asymmetry of information processes in the inferior temporal and frontal areas was suggested to be specific for recognition of facial expression.

Adolescent↗
PubMed1979

Visual evoked potentials and the visuogram in multiple sclerosis.

Visual evoked potential (VEP) latency to a sinusoidal grating pattern was measured in each eye of 103 patients with multiple sclerosis (MS) and compared with results in a control group of 56 patients hospitalized for other neurological conditions. Of the 50 patients classified as having definite MS, 90% showed prolonged latency (over 131 msec) in one or both eyes. In each eye of 24 of the MS patients, psychophysical measurement of the detectability of grating patterns was obtained. This test was abnormal in 11 of 13 patients with definite MS, 3 of 4 with probable MS, and 5 of 7 with possible MS. There was no concordance between prolonged VEP latency and visual impairment as revealed by the psychophysical test. Apparently pathways determining VEP latency and spatial contrast detection may be unequally affected in MS.

Evoked Potentials↗
PubMed1984

Schizophrenia and spectral analysis of the visual evoked potential.

Power spectral analysis was performed on the visual evoked potentials (VEPs) recorded in response to flashes of different intensity in both unmedicated schizophrenic and normal subjects. At occipital locations (O1, O2), schizophrenics showed less power than normals in the 10-14 Hz frequency range. In the 18-22 Hz range, schizophrenics showed under-activation in the left hemisphere and over-activation in the right. At temporal locations (T3, T4), schizophrenics showed abnormal (left greater than right) hemisphere patterns of activation in 10-14 Hz and 18-22 Hz ranges. There were no group differences in relationships between power and intensity changes at vertex (Cz). The results suggest abnormal cortical-subcortical interactions during analysis of visual information in schizophrenia.

Adult↗
PubMed1978

Visual evoked potentials during hypothermia and prolonged circulatory arrest.

Visual evoked potentials were recorded in eight children during hypothermia and circulatory arrest. The potentials were lost in all children recorded in late arrest. The evoked potential is a more sensitive indicator of CNS stress as provoked by combined hypothermia and hypoxia than is the EEG. EEG activity persisted in six of the eight children in this series even during circulatory arrest. The EEG had been seen to do the same in more than half of a larger series of children recorded at that stage. The results suggest that evoked potentials may be a sensitive indicator of early impairment of cerebral function and may demonstrate useful change sooner than the EEG. The examination may be useful in following children with illnesses producing hypoxia or anoxia. The N1 component was as easily and as frequently identifiable as the P2 component. Under the stress of this procedure, the latency of the P2 component became more variable than the N1 peak. The results suggest the N1 component may be as useful and perhaps more useful than the P2 wave in following the effect of some CNS stresses in children.

Cardiac Surgical Procedures↗
PubMed2006

[Intraoperative monitoring of visual evoked potentials].

Our success rate of intraoperative monitoring of visual evoked potential (VEP) had been approximately 30% in the past. In order to improve recording rate of intraoperative VEP, we developed a new stimulating device using high power light emitting diodes. Electroretinogram was simultaneously recorded to understand whether flash stimulation reached the retina. In addition, total venous anesthesia with propofol was used to avoid the adverse effect of inhalation anesthesia. We report the results after introduction of these improvements. Intraoperative monitoring of VEP was attempted in 35 cases. We evaluated success rate of VEP recording, correlation between VEP findings and postoperative visual function, and reasons why recording was not successful. Stable and reproducible waveforms were obtained in 59 sides (84%). Two cases, whose VEP deteriorated intraoperatively, developed postoperative visual disturbance: In 11 sides (16%), stable waveforms were not obtained. There were two main causes. In 8 sides out of 11, the cause was attributed to pre-existing severe visual disturbance. In these 8 sides, VEP in the awake state was not recordable or was recordable, but with very low amplitudes under 1 microV. In the other 3 sides, the cause was attributed to movement of a stimulating device by reflecting the fronto-temporal scalp flap. In conclusion, the successful recording rate was increased to 84% from approximately 30%, after introduction of various trials. We need further improvement in recording intraoperative VEP to establish a reliable intraoperative monitoring method for VEP.

Aged↗
PubMed1987

Effects of age and sex on pattern electroretinograms and visual evoked potentials.

Pattern-electroretinograms (P-ERGs) and visual evoked potentials (VEPs) were simultaneously recorded in 112 normal individuals aged 20-75. Two-sized checks subtending 15' and 31' were used as stimuli. A weighted regression analysis was used to determine which of the variables, sex or age, was significant. The latency of the a and b wave of the P-ERGs showed a progressive increase with age but no difference between sexes. The effect was statistically significant for both 15' and 31' checks. There was no statistically significant aging effect for VEPs elicited by 31' checks. Aging, however, affected N70, P100, and the interpeak interval between b wave to N70 and b wave to P100 for responses to 15' checks. Shorter VEP latencies were noted in females for both 15' and 31' checks. The simultaneous recording of P-ERGs and VEPs has demonstrated that aging is a major variable at the retinal level. The effects on the a and b waves are mostly due to optic changes with aging and only partially to aging changes in the neuronal retinal circuitry. The effect of aging on VEPs is different for different size stimuli. The cause is a random neuronal cell loss in the visual pathways from the optic nerve to the visual cortex as the individual ages. The difference in VEP data between sexes may be related to anatomical size and hormonal influences.

Adult↗
PubMed2006

Age-associated changes of flash visual evoked potentials in dogs.

Age-associated changes of visual evoked potentials by flash stimulation (flash VEP) were evaluated in 53 beagle dogs aged from 1- to 15-year-old. Among the components of flash VEP consisted of 3 positive (P1, P2 and P3) and 2 negative (N1 and N2) peaks by 150 msec, the latency of P2 and the later peaks (N2 and P3) were significantly delayed with aging. Both amplitudes of the P2-N2 and N2-P3 also showed a significant correlation with aging. The flash VEP is considered to be an available and useful technique to evaluate not only for visual pathway, but also some disturbance of neurological functions, like as those reported in demented human.

Age Factors↗
PubMedDate not supplied

[Experimental visual evoked potentials. Interstimuli interval and cortical excitability].

The excitability of the visual system was studied in ten adult chronic cats. Visual evoked potentials were recorded, using decreasing interstimulus intervals. A decrease of the excitability of the visual system is observed when interstimulus intervals are less than 800 milliseconds. Clinical applications with regard to visual evoked potential recording on comatose patients are suggested.

Animals↗
PubMed1984

Monocular pattern-shift visual evoked potentials in hemispheric strokes.

Monocular pattern-shift visual evoked potentials were obtained in (i) 33 patients with unilateral non-hemorrhagic hemispheric infarction (age 50-79 years; 23 males, 10 females), (ii) 21 age- and sex-matched patient controls (control group or CGI) with no remote or recent stroke, normal neurological examination and similar incidence of diabetes mellitus, hypertension and heart disease, and (iii) 21 age- and sex-matched healthy elderly community volunteers (CGII). Subjects with history of glaucoma, cataracts, other media opacities or symptomatic retinal lesions were not considered or included in any of the 3 study groups. In addition, all subjects in each of the 3 groups had a normal ocular and fundoscopic examination. The mean interocular P100 latency difference in the stroke group was significantly greater than that in CGI or II (P less than 0.01). The mean interocular P100 amplitude ratio (small P100/large P100) in the stroke subjects was significantly different from that of CGI or II (P less than 0.02). The mean P100 latency on ocular stimulation ipsilateral to the side of infarction was significantly longer than that of either left or right ocular stimulation in CGI or II (P less than 0.01). The mean P100 latency on ocular stimulation contralateral to the side of infarction was similarly but less significantly longer than that on left or right ocular stimulation in CGI or II (P less than 0.05). Evidence of anterior visual pathway dysfunction was thus elicited in the stroke population using the technique.

Aged↗
PubMed1988

Spatial frequency-dependent abnormalities of the pattern electroretinogram and visual evoked potentials in a parkinsonian monkey model.

The pattern visual evoked potential (PVEP) and pattern electroretinogram (PERG) were studied in 5 cynomolgus monkeys before and during the development of a parkinsonian syndrome induced by MPTP. The stimuli were vertical bars of four spatial frequencies (0.5, 1.2, 2.5 and 3.5 cycles/degree (cpd) modulated at temporal rates of 1, 4, 6, and 8 Hz. Following MPTP administration, all monkeys developed parkinsonian signs accompanied by changes in the amplitude and latency of the PVEP and PERG. Sinemet L-dopat carbi olopa administration produced temporary recovery of both PVEP and PERG. Two of the monkeys were followed for a prolonged period: 30-40 days after MPTP, the parkinsonian signs showed partial recovery; the PVEP latency and amplitude to 2.5 and 3.5 cpd stimuli and the latency to 1.2 cpd showed improvement but remained abnormal. The latencies of PERGs were normal, but the amplitudes were significantly reduced when stimuli of 2.5 and 3.5 cpd were used. Both PVEP and PERG to 0.5 cpd stimuli returned to normal. No further modifications were seen in the recordings performed 6 months and 1 year later. This study demonstrates (1) that spatial frequency-dependent electrophysiological abnormalities occur in the MPTP-treated monkey, a result previously found in human Parkinson's disease, and (2) that dopamine has a specific function in neurotransmission in the visual system of primates.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2005

Steady state visual evoked potential abnormalities in schizophrenia.

OBJECTIVE: The steady state visual evoked potential (SSVEP) can be used to test the frequency response function of neural circuits. Previous studies have shown reduced SSVEPs to alpha and lower frequencies of stimulation in schizophrenia. We investigated SSVEPs in schizophrenia at frequencies spanning the theta (4Hz) to gamma (40Hz) range. METHODS: The SSVEPs to seven different frequencies of stimulation (4, 8, 17, 20, 23, 30 and 40Hz) were obtained from 18 schizophrenia subjects and 33 healthy control subjects. Power at stimulating frequency (signal power) and power at frequencies above and below the stimulating frequency (noise power) were used to quantify the SSVEP responses. RESULTS: Both groups showed an inverse relationship between power and frequency of stimulation. Schizophrenia subjects showed reduced signal power compared to healthy control subjects at higher frequencies (above 17Hz), but not at 4 and 8Hz at occipital region. Noise power was higher in schizophrenia subjects at frequencies between 4 and 20Hz over occipital region and at 4, 17 and 20Hz over frontal region. CONCLUSIONS: SSVEP signal power at beta and gamma frequencies of stimulation were reduced in schizophrenia. Schizophrenia subjects showed higher levels of EEG noise during photic stimulation at beta and lower frequencies. SIGNIFICANCE: Inability to generate or maintain oscillations in neural networks may contribute to deficits in visual processing in schizophrenia.

Adult↗
PubMed1981

Biochemistry of the augmenting-reducing response in visual evoked potentials.

The augmenting-reducing response in visual evoked potentials (VEP) has between shown to be a useful tool in psychiatric research. A series of studies has been devoted to the search for the biochemical basis of this phenomenon. An augmenter response in VEP is shown to be clearly related to low levels of endorphins, 5-HIAA and homovanillic acid in CSF and to low serum-dopamine-beta-hydroxylase activity, while no significant relationship was found with 4-hydroxy-3-methoxyphenylethylene glycol or tryptophan in CSF or MAO in thrombocytes. The results indicate that an augmenter response in VEP is related to low activity in the serotoninergic, dopaminergic and endophinergic pathways in CNS.

Adult↗