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Results for “Evoked Potentials, Visual”

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PubMed2000

Influence of colors on habituation of visual evoked potentials in patients with migraine with aura and in healthy volunteers.

OBJECTIVE: To investigate whether colored glasses influence the habituation of visual evoked potentials. BACKGROUND: We have previously shown that during pattern-reversal stimulations lasting 2 minutes the amplitude of the visual evoked potential increases in migraine with and without aura between attacks, whereas it decreases in healthy volunteers. Red light was found to increase visually evoked EEG fast activity only in children with migraine with aura. Wearing rose-tinted glasses for 4 months decreased attack frequency in parallel with a reduction of the visually evoked EEG fast activity. METHODS: We compared the change in amplitude of the visual evoked potential using five different tinted glasses in 12 patients with migraine with aura and in 10 healthy volunteers. During continuous stimulation at 3.1 Hz, five blocks of 50 responses were sequentially averaged using red, yellow, green, blue, and grey glasses and without glasses in a random order and analyzed in terms of latencies and N1-P1 amplitudes. Amplitude changes were calculated for each block by comparison with the first block in every condition and analyzed statistically using Zerbe's method. RESULTS: In healthy volunteers, the visual evoked potential amplitude increased with red glasses compared to without glasses (P = .05) or with green glasses (P = .03). In patients with migraine with aura, no significant difference was detected using colored glasses. Our findings in healthy volunteers are in line with earlier reports of increased excitability of the human visual cortex when exposed to red light. The lack of such a pattern in patients with migraine with aura suggests that the visual cortex is interictally hypoexcitable rather than hyperexcitable, which is consistent with studies of transcranial magnetic stimulation.

Adult↗

PubMed2000

A comparative evaluation of Humphrey perimetry and the multi-channel pattern visual evoked potentials.

PURPOSES: To compare the multi-channel pattern visual evoked potentials to Humphrey perimetry in the assessment of central visual function in primary open angle glaucoma. METHODS: The multi-channel checkerboard reversal PVEPs waves to full-field and half-field stimulus of 25 normal persons and 74 patients with primary open angle glaucoma were recorded and analyzed, All patients were examined using Humphrey Field Analyzer. The area of visual field corresponding to the area of retina stimulated during multi-channel PVEPs testing were analysed, straight-line correlation and regression analyses of the various multi-channel PVEPs parameters and the total dB losses were performed. RESULTS: The multi-channel PVEPs demonstrated a low detection rate compared with Humphrey perimetry in the early glaucoma, absolute latency and field loss were correlated in the late stage of glaucoma, and absolute amplitude and field loss were not correlated. CONCLUSIONS: In relation to signalling "early" loss the multi-channel PVEPs was inferior to Humphrey perimetry, in late loss of primary open angle glaucoma, multi-channel PVEPs can provide a valuable, objective complement to Humphrey perimetry.

Adolescent↗

PubMed1997

The use of visual evoked potentials to follow-up prisoners of war after release from detention camps.

Visual evoked potentials were examined in released prisoners of war (POWs) in order to evaluate the extent of neurological impairment after imprisonment in Serbian detention camps. On two occasions visual evoked potentials were determined in a group of 11 released prisoners of war (POWs): 157 days and 379 days after release from detention camp. During the first examination no significant differences were found in VEP parameters between the right and left eye. However, during the second examination significant differences were found in the latencies of waves P100 and N145, statistically significantly prolonged latencies of the P100 wave and significantly greater amplitudes of waves P50 and N75. The results can be regarded as progression of the VEP changes in the released POWs. It is hypothesized that these changes are a result of a demyelination process, caused by the altered immunological status of the POWs during posttraumatic stress syndrome.

Adult↗

PubMedDate not supplied

L-Leucine prevents ammonia-induced changes in glutamate receptors in the brain and in visual evoked potentials in the rabbit.

The effect of L-leucine on glutamate receptors in the brain and on visual evoked potentials was studied in hyperammonemic rabbits. Hyperammonemia was induced by the iv infusion of 2.1 mmol NH4Cl/h over 3 hr. Hyperammonemia was followed by a 116% increase in the specific binding of 3H-glutamate to synaptic membranes prepared from the hippocampus. This increase was due to both an increase in the affinity and in the density of the glutamate receptor. The simultaneous infusion of L-leucine (6.7 mmol/hr) completely prevented the ammonia-induced increase in the specific glutamate binding, whereas L-valine and D-leucine had no effect. Hyperammonemia was also associated with typical, reproducible, and reversible changes in visual evoked potentials. The amplitudes of the first negative and the second positive peak decreased, whereas the latencies of these peaks remained unchanged. The simultaneous infusion of L-leucine completely prevented these changes. These findings indicate (1) that L-leucine prevents ammonia-induced changes in the glutamatergic excitatory neurotransmitter system and (2) that pharmacologic doses of L-leucine modulate the effects of hyperammonemia on central neurotransmission as assessed by visual evoked potentials. A causal relationship between the effects of L-leucine on ammonia-induced changes in glutamate receptors and in visual evoked potentials cannot be inferred with confidence. These findings provide a potential alternative explanation for the apparent beneficial effects of infusions of branched-chain amino acids on hepatic encephalography in patients with chronic liver disease.

Ammonia↗

PubMed2005

Comparison of visual evoked potentials, automated perimetry and frequency-doubling perimetry in early detection of glaucomatous visual field loss.

The present study compares frequency-doubling perimetry (FDP), automated perimetry (AP) and visual evoked potentials (VEP) for their ability to diagnose early glaucoma. In present study 224 patients of Clinic for Eye Diseases, Clinical Hospital "Sestre Milosrdnice" that had diagnosis of open angle glaucoma and glaucomatous visual field loss proven by automated static perimetry on only one eye were performing all three tests. Visual evoked potentials, automated perimetry and frequency-doubling perimetry were performed four times in each patient with six months period in between testing. Significant difference was proven between frequency-doubling perimetry and automated perimetry in favor for FDP in early detection of glaucomatous field loss. There was no significant difference between FDP and VEP neither between VEP and AP measurements. The results of this study indicate that frequency-doubling perimetry is significantly better method for early detection of glaucomatous visual field loss than automated static perimetry.

Automation↗

PubMed1983

The effect of selective attention on pattern-specific visual evoked potentials.

In a complex choice reaction time experiment, patterned stimuli without luminance change were presented, and pattern-specific visual evoked potentials to lower half-field stimulation were recorded. Two experimental conditions were used. The first was the between-field selection, where square patterns were presented in either the lower or the upper half of the visual field. In a given stimulus run one of the half-fields was task-relevant, and the subjects' task was to press a microswitch to stimuli of higher duration value (GO stimuli), while they had to ignore shorter ones, i. e. stimuli of lower apparent spatial contrast (NOGO stimuli). They had to ignore the stimuli appearing in the irrelevant half-field (IRR stimuli). In order to ensure proper fixation, the subjects had to press another microswitch at the onset of a dim light at the fixation point (CRT stimuli). Our second experimental condition was the within-field selection, where the GO, NOGO, and IRR stimuli appeared in the lower half of the visual field. GO and NOGO were square patterns while IRR stimuli were constructed of circles, or vice versa. (The CRT stimuli were the same as in the previous condition.) Three pattern-specific visual evoked potential components were identified, i. e. CI (70 ms latency), CII (100 ms latency), and CIII (170 ms latency). There were marked selective attention effects on both the CI-CII and CII-CIII peak-to-peak amplitudes. In both experimental conditions, responses with the highest amplitude were evoked by the GO type of stimuli, while the IRR stimuli evoked the smallest responses. According to these results, attention effects on the pattern-specific visual evoked potentials in the first 200 ms cannot be attributed to a simple stimulus set kind of selection.

Adolescent↗

PubMed1986

Biofeedback of visual evoked potentials.

The present study investigated the operant conditioning of visual evoked potentials within a latency range between 200 and 600 ms using a visual discrimination task, and scrutinized whether biofeedback-induced potential shifts covaried with behavioral responses (reaction time, RT). It could be demonstrated that subjects were able to modify their ERPs towards more or less positivity according to the instruction given. In addition, in could be shown that a biofeedback-induced greater positivity of the P300-complex was highly correlated with a decrease of reaction time. It is hypothesized that this could be due to a modification of P300-components reflecting information processing.

Adult↗

PubMed1997

Pattern reversal visual evoked potentials in eyes with macular holes and their fellow eyes.

PURPOSE: To investigate whether the pattern reversal visual evoked potential can be useful in the diagnosis and management of macular hole patients. METHODS: The pattern reversal visual evoked potential was measured in 66 patients with a macular hole and in 43 healthy control subjects. Check sizes of 34', 17' and 10' were applied. RESULTS: Results showed that, for the check sizes of 34', 17' and 10', eyes with a macular hole had significantly prolonged N80 and P100 latencies and a significantly reduced P100 amplitude as compared to their fellow eyes. Furthermore, for the 10' check size, the fellow eyes appeared to have a significantly reduced P100 amplitude in comparison with the control eyes, whereas N80 and P100 latencies of the fellow eyes of the macular hole patients were not prolonged. CONCLUSION: Significant pattern reversal visual evoked potential alterations were shown in eyes with macular holes and fellow eyes for small check sizes.

Aged↗

PubMed2001

[Determination of +Gz tolerance end-point by steady state visual evoked potential].

OBJECTIVE: To study the possibility of applying steady-state visual evoked potential (SSVEP) to detect the end-point of +Gz tolerance. METHOD: When a subject was exposed to +Gz acceleration on a human centrifuge, the SSVEP signals (evoked by LED lamps triggered by 8 Hz pulse train) were recorded. The characters of SSVEP in frequency domain were extracted by adaptive filtering, and a modified T2circ statistic was used to determine the visual obstruct objectively. RESULT: SSVEP had strong relationship with visual obstruct of the subjects during +Gz exposure. CONCLUSION: SSVEP might be used as an objective criterion for determination of end-point of +Gz tolerance and an index of the degree of symptoms as well. But, multi-parameter method seemed still necessary to get reliable estimations.

Acceleration↗

PubMed1985

The value of visual evoked potential as a screening test in neurofibromatosis.

Pattern reversal visual evoked potential (VEP) test was performed in 30 asymptomatic patients with neurofibromatosis (NF). All patients had normal visual acuity, visual fields, and ophthalmoscopic examination results. Pattern reversal VEP was abnormal in eight patients (26%). Seven of these patients had computed tomographic scans with reformated orbital views. Orbital computed tomographic scans were abnormal in six patients and in each case showed enlargement of the optic nerve on the side of VEP abnormality. Our data indicate that pattern reversal VEP is a valuable screening test in asymptomatic patients with NF. Because of the high incidence of VEP abnormality in such patients, VEP abnormality must be interpreted cautiously when a patient with NF is suspected of having other diseases or disorders that potentially affect the visual pathways.

Adolescent↗

PubMed1995

The changes of pattern reversal visual evoked potentials in normal infants.

PURPOSE: To study pattern reversal visual evoked potential (PVEPs) and determine the developmental character and mature time of visual function in normal infants at different months of age. METHODS: PVEPs were recorded from 115 normal infants at 3, 6, 9, 12 months age. P1 latency for different checks (1 degree 40', 25', 6') was analyzed and compared to those of normal adults. Changes of N1, N2 latency of PVEPs were also examined. RESULTS: P1 latency for all checks (1 degree 40', 25', 6') was significantly longer at 3 months than at 6 months of age (P < 0.05), but no significant differences can be seen after 6 months of age for larger (1 degree 40') and intermediate (25') checks (P > 0.05). P1 latency for larger checks (1 degree 40') reached adult level after 3 months of age, but not for the intermediate check (25'), while P1 latency for small check (6') presented the character of fluctuation. CONCLUSION: The visual system continued to develop after birth and appeared a certain regularity. Our results showed that P1 latency for larger check (1 degree 40') reached adult levels after 3 months of age. But P1 latency for intermediate check still has not reached adult levels after 3 months of age. To determine the age at which adult levels are finally reached, infants of 12 months and older must be tested. The reason why P1 latency for smaller check (6') presented the character of fluctuation should be the temporal tuning function developing much more slowly.

Child Development↗

PubMed1984

Power spectral analysis of visual evoked potentials in multiple sclerosis.

Power spectral analysis (PSA) was performed on the visual evoked potentials (VEPs) to counterphased checkerboard stimuli from 98 eyes in 49 patients with multiple sclerosis (MS) and 54 eyes of 27 normal volunteers. Attenuation of high frequency components of the transient visual evoked potential was found in 53% of MS patients and 4% of controls. Loss of high frequency components was poorly correlated with prolonged latency (r = 0.346). The consideration of both PSA and latency of the VEP increased the percentage of MS patients exhibiting visual pathway conduction abnormalities from 61% to 86%. The use of PSA in the diagnosis of MS is useful in increasing detection especially in cases where deformed waveforms preclude a reliable estimation of latency.

Adult↗

PubMed2006

Use of multifocal visual evoked potential tests in the objective evaluation of the visual field in pediatric epilepsy surgery.

OBJECT: To evaluate objectively the visual fields of patients with pediatric epilepsy who are uncooperative with perimetry and in whom postoperative visual field deficits are expected, the authors investigated the usefulness of the multifocal visual evoked potential (VEP) method. METHODS: Normal waves in multifocal VEP were determined in 21 healthy children (21 eyes) 6 to 15 years of age (mean 11.4 years). Responses from eight sites in each child were divided into four quadrants (superior and inferior temporal and superior and inferior nasal). In each quadrant, two response waves were grouped and averaged. The peak latency and amplitude at approximately 100 msec were used for assessment. In three cases involving patients with epilepsy, multifocal VEP measurements were also recorded and compared with the peak latency and amplitude in the healthy children. In these children, no significant differences were observed in the peak latency of amplitude among four quadrants using one-way analysis of variance. In each patient, multifocal VEP tests showed abnormal waves in the quadrant corresponding to the lesion demonstrated in neuroradiological images. This result was useful in the treatment of choice and the postoperative evaluation. CONCLUSIONS: Multifocal VEP tests can be useful in evaluating the visual field of children objectively. They can also be valuable in assessing preoperative visual field defects and revealing changes in the visual field after treatment.

Adolescent↗

PubMed1992

Differences in pattern visual evoked potential (PVEP) between hemodialysis and peritoneal dialysis patients.

The visual evoked potential was recorded in peritoneal and hemodialysis patients as compared to normal controls. By using the appropriate visual stimulus we were able to disclose specific VEP abnormalities for each of the two dialysis groups. The dissociation found between the latency of N70 and P100 in peritoneal dialysis patients suggests a possible postsynaptic visual abnormality not described previously. The correlation between the high serum aluminum and the P100 latency of peritoneal dialysis patients requires further investigation.

Adult↗

PubMed1996

Visual evoked potentials with crossed asymmetry in incomplete congenital stationary night blindness.

PURPOSE: To investigate a proposed postretinal defect in patients with the incomplete form of congenital stationary night blindness (CSNB2) and to compare visual evoked potential (VEP) results with those found in various forms of albinism. METHODS: Visual evoked potentials were performed in 10 patients with a diagnosis of CSNB2, 10 subjects with albinism, and 17 normal subjects. Visual evoked potentials were elicited monocularly with diffuse flash stimulation. Scalp electrodes were placed over each hemisphere and referred to the forehead. Interhemispheric bipolar recordings were derived, and the correlation coefficient (CC) was calculated for various segments of the interhemispheric responses. RESULTS: A crossed visual evoked potential asymmetry pattern could be demonstrated in 9 of 10 patients with CSNB2. All subjects with albinism and none of the normal subjects showed the crossed asymmetry pattern. Statistical comparison of the CC computed for various segments of the interhemispheric response shows that the pattern of inversion in CSNB2 is more prominent in the 25 to 100 msec range (median CC, -0.37) and in the 175 to 250 msec range (CC, -0.27). In subjects with albinism, all segments show a negative CC (range, -0.46 to -0.60). In normal subjects, all segments are positively correlated (range, 0.36 to 0.66). CONCLUSIONS: Crossed visual evoked potential asymmetry was found in patients with CSNB2; therefore, excessive decussation, as demonstrated by this testing procedure, should not be considered as pathognomonic for albinism.

Adolescent↗

PubMed1988

Somatosensory and visual evoked potentials in insulin-dependent diabetics with mild peripheral neuropathy.

Using somatosensory and visual evoked potential techniques we have looked for evidence of central neuropathy in a group of insulin-dependent diabetics with mild peripheral neuropathy. The N9, N13, and N20 components of the somatosensory evoked potential were significantly (P less than 0.001) delayed in the diabetic group compared with the control subjects. There was a small but non-significant increase in the interpeak N13-9 and N20-13 latencies in the diabetic group. The visual evoked potential (P100) showed a small but insignificant delay. The delay in cerebral evoked potentials was mostly attributable to peripheral neuropathic damage and no firm evidence was obtained in favour of central diabetic neuropathy.

Adult↗

PubMed1999

Functional correlates with left-right asymmetry of visual evoked potentials in stroke patients: modeling and experimental results.

OBJECTIVE: To determine the correlation between a clinical measure of function in patients after first stroke and left-right scalp amplitude of visual evoked potentials using a theoretical model of the head. DESIGN: A random sample of first-stroke patients underwent routine function measurement and investigation of left-right scalp potential asymmetry. Results of the encephalographic tests were compared with those of a healthy subject. To examine the effect of the conductivity in the damaged area on the potential asymmetry, numerical calculations were performed on a model, with four concentric circular compartments representing the brain, cerebrospinal fluid layer, skull, and scalp. The damaged region was modeled as a circular section. SETTING: Neurologic rehabilitation ward of a major rehabilitation hospital and university-affiliated biomedical engineering laboratory. PATIENTS: Four men aged 58 to 71 years, 3 with brain thrombosis and 1 with hemorrhagic stroke. The patients were admitted for rehabilitation an average of 3 weeks after the stroke and stayed for an average of 137 days. Damage was confined to the right brain in all cases; three of the patients had neglect syndrome and/or sensory disturbances. A healthy subject without stroke was also examined. MEASURES: Function was measured with the Functional Independence Measure (FIM) at 48 to 72 hours from admission and during the last week before discharge. Functional gain was calculated by subtracting the FIM admission score from the discharge score. Left-right scalp visual evoked potential amplitude was studied with flash stimuli according to the 10-20 international system and a theoretical model of the head based on two-dimensional computed tomography images; the volume conductor equation was solved numerically using the finite volume method. Left-right potential asymmetry and the damaged-region-to-brain-area ratio were calculated and correlated with the FIM values by linear regression analysis. Negative asymmetry indicates that the activity in the right damaged hemisphere is lower than in the undamaged one. RESULTS: A negative correlation was noted between the FIM score on admission and the left-right scalp potential amplitude asymmetry, and between the FIM gain and the damaged-region-to-brain-area ratio obtained from the computed tomography image. Asymmetry was negative in the thrombotic patients and positive in the hemorrhagic one. The healthy subject showed nonsignificant asymmetry. CONCLUSION: A relationship might exist between the left-right asymmetry of the scalp visual evoked potential and both the damaged-region-to-brain-area ratio and the functional outcome of rehabilitation in poststroke patients. The modeling study shows that the left-right asymmetry is most likely the result of changes in the conductivity at the damaged area, which, in turn, are probably associated with patient functional status and evolution. Further validation in larger groups of patients and normal subjects is needed before these parameters can serve as useful indices for clinical purposes.

Aged↗

PubMed1988

Visual evoked potentials in the investigation of "blindsight".

We recorded long-latency visual evoked potentials in four patients with homonymous hemianopias, one of whom had clinical evidence of "blindsight." Stimuli consisted of different words that appeared randomly and at a constant angle to either side of the center of a TV screen, and subjects responded to one previously specified word (the "target") by finger extension. Target stimuli in the intact hemifield elicited a well-formed P3 response in all subjects, whereas stimuli in the blind field produced no such response except in the subject with blindsight. In addition, the earlier potentials in this subject were larger with stimulation of the blind hemifield than the intact field. By contrast, a P100 response was present only with stimulation of the intact field in this subject. These results indicate that cognitive processing of visual stimuli can occur even when subjective awareness of such stimuli is absent, and suggest that such processing occurs independently of the geniculostriate pathway.

Adult↗