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Results for “Evoked Potentials, Visual”

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PubMed2004

Characteristics of first and second order kernels of visually evoked potentials elicited by pseudorandom stimulation.

The characteristics of the first and the second order kernels of the visually evoked potentials (VEPs) elicited by pseudorandom binary sequence (PRBS) stimuli were investigated. VEPs were recorded from six eyes of four normal volunteers. The effects of stimulus luminance on the latency and amplitude of the first and the second order kernels were determined. The temporal interactions of transient VEPs elicited by single and double pulse stimuli were compared with the first and the second order kernels of the PRBS-VEPs. The correlation coefficient between the logarithm of the stimuli luminance (log I) and VEP amplitude of the first order kernels was 0.45 (p < 0.05), and that between log I and P1 latency was -0.62 (p < 0.005). The second order kernels were not equal to the temporal interactions of the responses. However, the latency of the negative peak of the fourth slice was similar to the temporal interaction to double pulse stimulation with an inter-stimulus interval of 40 ms. An inhibitory component at 40 ms following the first stimulus was detected in the analysis of both PRBS-VEPs second order kernel and transient VEPs. This function may help to increase the frequency of critical flicker fusion in normal subjects.

Adult↗

PubMed1991

Visual evoked potentials and background EEG activity in migraine.

To investigate whether quantification of the background EEG during a visual evoked potential (VEP) study is of value for the diagnosis of migraine we studied 8 unmedicated migraineurs between attacks, and 10 age-matched controls. Three paradigms were used: the first two concerned pattern-reversal VEPs with different analysis times (500 and 1500 ms), and in the third paradigm the pattern did not reverse. Power spectra were calculated for individual responses, and the delta, theta, alpha and beta areas of the averaged spectra were noted as indicators of background reactivity. Alpha and beta powers were consistently but not significantly higher in the migraine group. The difference was too small to be of value as a diagnostic test. Alpha power was (not significantly) lower in the presence of photic stimulation than in its absence. As this was the case in both groups photic stimulation does not explain the higher alpha powers in the migraine group. We conclude that EEG background activity during the VEP does not distinguish reliably between migraineurs and controls.

Adult↗

PubMed1990

Multiple sclerosis: symptom equivalent to delayed visual evoked potential latency.

An investigation on the correlation between ability to read TV subtitles and the duration of visual evoked potential (VEP) latency in 14 patients with definite multiple sclerosis (MS), indicated that VEP latency in patients unable to read the TV subtitles was significantly delayed in comparison to that of patients who mastered this task.

Adult↗

PubMed1990

Visual evoked potential monitoring of optic nerve function during surgery.

A study was made with intra-operative flash--visual evoked potentials (VEP) monitored using a fibre-optic/contact lens photo stimulator in 57 patients undergoing intra-orbital surgical procedures with potential risk to the optic nerve. The VEPs recorded under enflurane and nitrous oxide anaesthesia did not differ significantly in latency or amplitude from the pre-operative recordings. Transient abolition of the VEP was seen under many circumstances and did not correlate with the outcome of surgery, but absence of a previously normal VEP for more than four minutes during surgical manipulation within the orbit did show a correlation with post operative impairment of vision. The technique provides early warning to the surgeon of threats to the integrity of the optic nerve.

Adolescent↗

PubMed1996

Recent developments in an animal model of visual evoked potential augmenting/reducing and sensation seeking behavior.

The early research on an animal (cat) model and biological marker (visual evoked potential augmenting and reducing) of sensation seeking behavior is briefly described. Recent findings with selectively bred lines of rats show that (1) the relationship between sensation seeking behavior and augmenting vs. reducing is also present in the rat; (2) augmenting and reducing is a cortical, not a subcortical, phenomenon, and (3) augmenting/reducing and related sensation seeking behaviors are heritable traits. This paper also discusses evidence for the relative contributions of genetic and environmental factors in determining the sensation seeking trait.

Animals↗

PubMed2002

The multifocal visual evoked potential and cone-isolating stimuli: implications for L- to M-cone ratios and normalization.

Multifocal visual evoked potentials (mfVEP) were recorded with a pattern-reversing display that modulated only the long wavelength-sensitive (L) cones or only the middle wavelength-sensitive (M) cones. Outside the central 5.8 degrees (radius), the ratio of the amplitudes of the mfVEP responses to L- and M-cone modulation varied across the six subjects, ranging from 1.1 to 1.7. The responses from the central 1 degrees (radius) showed a substantially lower ratio, ranging from 0.8 to 1.1 (average of 0.9). The variation among individuals outside the central fovea is probably due to differences in the ratio of the L/M cone input to both magno- and parvocellular pathways. The substantially lower ratios for the central responses is consistent with an L/M cone ratio closer to 1.0 in the central 1 degrees and/or an adjustment in the gain of the L- versus M-cone contributions to the central parvocellular pathways. Taking into consideration evidence from other techniques, we believe it is unlikely that most individuals have a L/M cone ratio of 1.0 in the fovea. Instead, it appears that there is a change in gain before the mfVEP is generated in area 17.

Adolescent↗

PubMed1986

Effect of L-dopa on visual evoked potential in patients with Parkinson's disease.

In 47 patients with Parkinson's disease, we studied the visual evoked potential (VEP) using the pattern-reversal checkerboard (CBVEP) and the grating (GVEP) stimuli before and after 3 months of L-dopa therapy. The P100 latency in both CBVEP and GVEP was prolonged before L-dopa therapy, usually commensurate with the degree of motor disability. Clinical improvement of the parkinsonian state after L-dopa therapy was associated with shortening of the P100 latency in CBVEP, but not significantly in GVEP.

Aged↗

PubMedDate not supplied

120 Hz oscillations in the flash visual evoked potential are strictly phase-locked and limited to the first 100 ms.

Flash stimulation elicits a visual evoked potential (VEP) as part of the electroencephalogram (EEG). This VEP is known to contain strong oscillatory activity around 120 Hz, which ceases 100 ms after the flash. It was unclear so far whether this time limit represents an averaging artifact due to loss of intertrial phase coherence or indicates a veridical cessation. Here we present results obtained from single-trial analysis of the EEG. These show that the oscillations exhibit virtually perfect phase locking and do in fact cease around 100 ms after the stimulus. Thus, the cessation of oscillatory activity in the VEP is not due to increasing intertrial phase jitter. Comparison with simultaneous retinal recordings exclude the possibility of direct crosstalk from the retina, but suggest that the oscillations are propagated from the retina to the cortex with a time lag of 48 ms.

Cerebral Cortex↗

PubMed2004

Visual evoked potentials in multiple sclerosis patients treated with interferon beta-1a.

AIM: To study pattern-reversal visual evoked potentials (VEP) in patients with relapsing-remitting multiple sclerosis on interferon beta-1a treatment. METHODS: In a randomized, prospective, non-blinded, placebo-uncontrolled study, VEP were studied in 9 patients (18 eyes) with relapsing-remitting multiple sclerosis treated with interferon. Three of them have had an episode of unilateral optic neuritis. VEP were first recorded before interferon treatment and then followed up for 12 months, at 3-month intervals, in the time when patients were receiving interferon, 11 microg twice weekly. All patients did not appear regularly at 3-months intervals follow-up, except for 6-month follow-up. P100 latency and P100 amplitude in responses to full field, right and left half-field stimulation were evaluated. RESULTS: For the group of 18 eyes, there was no statistically significant difference in P100 latency and P100 amplitude before and after 6 months of treatment. In individual cases P100 latency was delayed in 3 eyes of 3 patients with a history of optic neuritis before treatment. At follow-up, P100 latency remained delayed in 3 eyes with a history of optic neuritis. Further, in 3 eyes of two patients who have had normal P100 latency before treatment, P100 latency became delayed. Overall, P100 latency was at follow-up delayed in 6 eyes of 5 patients. CONCLUSION: Interferon beta-1a therapy (22 microg per week) administered for 12 months during 1998/99 in Croatia showed no statistically significant VEP changes in the group of relapsing-remitting multiple sclerosis patients. However, VEP may reveal evidence for asymptomatic deterioration.

Adult↗

PubMed2005

[The picture of visual evoked potentials in type 1 diabetes mellitus].

The aim of this study was to assess frequency of abnormal visual evoked potentials in type 1 diabetic patients and the correlation between patients' age, duration of the disease, metabolic control and coexisting clinical complications on the abnormal recordings. The investigation was carried out in a group of 50 diabetic patients, aged from 16 to 55 years. The VEP recordings were performed four times, each time using a pattern made up of elements of another size (18, 36, 72 and 144 angular minutes). With this method the abnormal VEP were recorded in 26% of the cases and it was possible to find 10% patients who had more than one abnormal test. In VEP recorded with stimulation with a single size pattern, abnormal results were recorded from 8% to 14% of the cases. The pathological VEP were recorded as elongation of P100 latency in 86% type 1 diabetic patients, and as significant difference between the latencies from both eyes in 14% cases. There was no statistically significant correlation between the age, duration of the disease, coexisting clinical complications or metabolic compensation and the abnormal recordings.

Adolescent↗

PubMed2005

[The picture of visual evoked potentials in type 2 diabetes mellitus].

The aim of this study was to assess frequency of abnormal visual evoked potentials in type 2 diabetic patients and the correlation between patients' age, duration of the disease, metabolic control and coexisting clinical complications on the abnormal recordings. 41 diabetic patients, aged 35 to 62 years were examined. The VEP recordings were performed four times, each time using a pattern made up of elements of another size (18, 36, 72 and 144 angular minutes). With this method the abnormal VEP were recorded in 22% of the cases. The abnormal VEP recordings with a single size pattern were in 8% to 14% of the cases. The P100 latency increased in 33% of the pathological recordings and in about 66% of the cases there was a significant difference between the latencies from both eyes. There was no statistically significant correlation between the age, duration of the disease, coexisting clinical complications or metabolic compensation and the abnormal recordings.

Adult↗

PubMed2006

[Research for De-noising in the detection of chromatic visual evoked potential based on wavelet].

The signal analysis technology based on wavelet was used to detect the chromatic visual evoked potential (VEP). The method was based on wavelet transform modulus maxima reconstruction. The test signal was decomposed using the dyadic discrete time wavelet transform "Mallat" algorithm, and the modulus maxima distribution of each scale was obtained. Signal was de-noised as the Lipschitz coefficient. The POCS method was used to reconstruction the original signal. The news method proved not only good for de-noising but also for decreasing the times of test by the simulation result.

Color↗

PubMed1990

[Retinal periphlebitis and multiple sclerosis. Incidence, cerebrospinal fluid and results of visual evoked potentials].

In a retrospective study 323 patients with multiple sclerosis were screened for the incidence of retinal periphlebitis. The results of lumbar puncture and the visual evoked potentials were related to the eye disease. Retinal periphlebitis was seen in 19 patients (5.9%). Of the patients with retinal periphlebitis, 79% developed the eye pathology within the first 10 years of multiple sclerosis. The cerebrospinal fluid and visual evoked potentials were no different than the results in a control group of multiple sclerosis patients without periphlebitis. Multiple sclerosis should always be considered as one of the potential underlying diseases in retinal periphlebitis since it is found in 30% before or at the same time as the first neurological symptoms of multiple sclerosis.

Adult↗

PubMedDate not supplied

Pattern visual evoked potential mapping in Alzheimer's disease: correlations with visuospatial impairment.

We evaluated pattern visual evoked potentials (PVEPs) in patients with Alzheimer's disease (AD) and correlated the neurophysiological results with visuospatial performances in order to understand better the underlying causes of visual disturbances. Latencies and topographical distribution of PVEP components were evaluated in 20 AD patients who underwent an extensive battery of neuropsychological tests. Mean latencies of N70 and P100 were normal in AD patients, while mean latencies of N140 and P200 were significantly increased in comparison with age-matched healthy controls. The topographical distribution of PVEP components did not show any significant difference between the two groups. Visuospatial impairment was detected in 8 patients (40%). Statistically significant positive correlations were observed between P200 amplitude (posterior right hemisphere mean z score) and performance in visuospatial tests. Our data are consistent with a sparing of foveal retinocortical pathways and with the selective dysfunction of either corticocortical connections between the striate cortex and the visual associative structures or of right temporo-parieto-occipital visual analyzers.

Age of Onset↗

PubMed2003

Study of visual evoked potentials in the assessment of the central optic pathways in leprosy patients.

We evaluated the possible involvement of central optic pathways (COP) in leprosy patients with visual evoked potentials, an easy, sensitive and reliable noninvasive method for evaluation of COP. In 37 patients with lepromatous leprosy and in 37 age-matched controls, we measured reversal pattern visual evoked potentials (RP-VEP) and nerve conduction parameters. The mean latency value of positive peak P100 in leprosy patients was significantly delayed compared to that of controls (patients, 108.02+/-9.61 ms in left eye and 108.23+/-8.51 ms in right eye; controls, 96.22+/-4.20 ms in left eye and 95.75+/-4.03 ms in right eye; p<0.05). Abnormally delayed P100 latency was recorded in 5 of 37 leprosy patients (13.5%). The mean amplitude of P100 latency in leprosy patients was smaller than that of controls (patients, 8.7+/-5.6 micro V in left eye and 9.5+/-4.8 micro V in right eye; controls, 10.7+/-4.6 micro V in left eye and 10.5+/-5.1 micro V in right eye), but this difference was not significant. No correlation was observed between abnormalities of RP-VEP and sensorimotor nerve conduction parameters. This study suggests that involvement of COP may develop in patients with lepromatous leprosy. RP-VEP measurement, which can be easily and rapidly performed in an EMG laboratory using standard equipment, can show these alterations.

Adult↗

PubMed1996

The scotopic electroretinogram to blue flashes and pattern reversal visual evoked potentials in insulin dependent diabetes.

Pattern reversal visual evoked responses (PR-VEPs), the electroretinogram (ERG) to blue flashes of light in dark adaptation, the steady state ERG to 40 Hz flicker, and alterations in pupil diameter following dark adaptation were studied in 56 juvenile onset diabetics, 34 of whom had no ophthalmoscopic or photographic evidence of diabetic retinopathy (DR-group). The remaining 22 had mild background retinopathy (DR+group). Normal data was obtained from 24 subjects matched for age and sex with diabetics. Skin electrodes were used for all recordings. The scotopic 'b' wave of the ERG was significantly lower in amplitude in the DR- diabetics and it was even more reduced in the DR+group. The PR-VEP was significantly delayed in diabetics but there was no difference between the two groups. The steady state ERG was not significantly different between normals and diabetics. These findings indicate that retinal and more central abnormalities develop early in diabetics. Detection of objective electrophysiological abnormalities may be used to identify persons at risk of developing retinopathy and to monitor the effects of treatment.

Adolescent↗

PubMed1995

[The visual evoked potentials of non-amblyopic eyes in children with amblyopia].

We investigated the characteristics of visual evoked potentials (VEPs) of the eyes with normal visual acuity in 84 children of whom 20 were normal, 28 of anisometropic amblyopia, 8 of anisometropic amblyopia already cured, 8 pairs of monozygotic and 6 pairs of dizygotic twins with amblyopia. The results showed that although the fellow eye of an amblyopic eye or the cured amblyopic eye had normal visual acuity, the VEPs presented abnormal, the marked abnormality being the prolongation of the latency of P100 peak. No significant difference was found in VEPs between the eye with normal visual acuity and the eye with amblyopia in the monozygotic twins with the same genetic background (P > 0.05). This study demonstrated that possibly the clinical examinations of visual acuity and VEPs reflect different visual information processes, and the "normal" eyes of amblyopes are not normal.

Amblyopia↗

PubMed1992

Electroretinograms (ERGs) and visual-evoked potentials (VEPs) elicited by pattern displacement.

The relation between the amplitude of visual responses to a checkerboard stimulus and the degree of lateral displacement of the checks was examined across different check sizes with simultaneously recorded electroretinograms (ERGs) and visual-evoked potentials (VEPs). The amplitudes of both the b-wave and the after-potential of the ERG increase linearly with pattern displacement. However, the major components of the VEP (N70 and P100) were smaller than expected from linearity for both small checks with small displacements (thresholding) and for large checks with large displacements (saturation). These results suggest that the ERG is proportional to the number of receptors stimulated, but the VEP reflects neural processes influenced by the spatial structure of the stimulus.

Adult↗