Pattern-reversal visual evoked potentials in phenylketonuric children

Pattern-reversal visual evoked potentials (PR-VEPs) and EEG were recorded in 14 phenylketonuric (PKU) children on a low-phenylalanine (phe) diet; the data obtained were correlated with metabolic parameters, namely, the actual phe plasma level, the mean phe plasma level in the last year, an the beginning of the diet. PR-VEPs seem to be more sensitive than EEG in detecting neurophysiological derangements in these subjects; in fact PR-VEPs were pathological in six patients while EEG detected three; no significant alterations were found in the neurophysiological tests among the children with good metabolic control, and only one child was abnormal among the six on an early dietetic regimen; in contrast, six of the nine subjects presenting with high mean phe plasma levels (>10 mg/100 ml) and five of the eight whose diet started after the 2nd month of life showed pathological PR-VEPs.     

Pattern-reversal visual evoked potentials in Down's syndrome

We examined pattern-reversal visual evoked potentials (PRVEPs) in 36 adult patients with Down's syndrome, and analyzed the effects of the opthalmological abnormalities on results of PRVEPs. The P100 latency was significantly delayed in 24 eyes of 16 patients. The P100 latency was significantly longer and its amplitude was significantly smaller (P < 0.001) in Down's syndrome patients than in age-matched normal controls. In 9 patients without any ophthalmological abnormalities, P100 latency showed no significant difference from that in normal controls, but three of them showed a significant delay of P100. Their P100 amplitudes were significantly smaller than those in normal controls. Therefore, we considered that the ophthalmological abnormalities are one of the main factors causing PRVEPs abnormalities in Down's syndrome patients, but some unknown factors should be also responsible.     

Pattern-reversal visual evoked potentials: latency changes with gender and age

Pattern-reversal visual evoked potentials were studied in 123 volunteers with ages ranging from 20 to 77 years. The major positive component (P100) showed a shorter mean latency but a higher mean amplitude for females than males. The age-dependent increase in mean P100 latency was observed in the female group but not in the male group. The present data suggest that gender is more important than age in affecting the P100 latency.     

Pattern-reversal visual evoked potentials in the hereditary ataxias and spinal degenerations

Pattern-reversal visual evoked potentials (PRVEP) were evaluated in 24 patients from 18 separate families with various forms of hereditary ataxia and spinal degeneration. Abnormally delayed latencies were found in 3 of 5 patients with classic Friedreich's ataxia, 1 patient with dominant spastic paraparesis, and 1 patient with recessive dentatorubrospinal degeneration. Fifteen other patients with several different types of dominant and recessive hereditary ataxias had normal PRVEP latencies, including 1 patient with bilateral optic atrophy. Testing of PRVEP will be useful in the clinical delineation of the genetic ataxias and spinal degenerations, and, when interpreted with caution, should be an additional variable evaluated in the differentiation of these disorders from multiple sclerosis.     

Pattern-reversal visual evoked potentials in patients with newly diagnosed epilepsy

PURPOSE: The possible occurrence of evoked potential (EP) abnormalities in patients with newly diagnosed epilepsy has been little investigated. The main purpose of the present study was to investigate possible changes in pattern-reversal visual evoked potential (P-VEP) responses in newly diagnosed epilepsy patients. METHODS: By using P-VEPs, latency values of the N75 and P100 together with amplitude values of P100 were recorded in newly diagnosed idiopathic epilepsy patients. The patients comprised two groups; nonphotosensitive (non-PS), and photosensitive (PS) patients. RESULTS: Shortened N75 and normal P100 latencies of the P-VEP with higher than normal P100 amplitudes were detected in PS patients. In non-PS patients, N75 latencies of the P-VEPs were unaffected; however, P100 latencies were prolonged, and P100 amplitudes were unchanged. CONCLUSIONS: P-VEPs are different from those of controls in previously untreated idiopathic epilepsy patients. Results also indicate different P-VEP features in patients with and without photoparoxysmal responses. The changes might be the result of a disorder of one or more neurotransmitters or subtle morphologic damage such as microdysgenesis.     

Pattern-reversal visual evoked potentials in patients with chronic renal insufficiency

Visual evoked potentials (VEPs) were recorded from 88 patients with chronic renal insufficiency twice at a 6 month interval. In dialysed patients statistically significant decreases in amplitudes and prolongations of VEP peak latencies were found. Azotaemic non-dialysed patients showed related, but smaller, changes in their VEPs. In patients after kidney transplantation the VEP amplitudes were normal but peak latencies were prolonged. No systematic significant relationship between the VEPs and creatinine and urea levels in the blood could be shown.     

Pattern-reversal visual evoked potentials recorded in children with generalized epilepsy

Visual potentials evoked by pattern reversal (PRVEPs) were studied in 64 normal subjects (age range 7 to 15 years) and in 15 patients with primary generalized epilepsy (age range 8 to 13 years), 10 of whom were without anticonvulsant medication. Most of them were studied during sodium valproate (VPR) therapy and some during carbamazepine (CBZ) medication. A Quadristim set (Alvar) was used to present checkerboard patterns on a TV monitor, to amplify the EEG signals and to average and plot the evoked potentials. The potentials were elicited by binocular full-field 2/s checkerboard reversals, recorded from an electrode 4 cm above the inion, and analyzed for latency, amplitude and waveform. Our PRVEP measurements examined peak latency of positive P2 (or P100) component and trough-to-peak amplitude on N1P2 wave complex. The degree of similarity between pairs of PRVEP plots were determined by Pearson correlation coefficient r for an analysis time of 150 ms. In most of our patients, no pronounced influence of the disease itself on the parameters and waveform of the normal PRVEP pattern was demonstrated if anticonvulsant drugs were not taken. In patients who were under complete seizure control, the anticonvulsant did not change the PRVEP morphology as well. The PRVEP abnormality was most pronounced in patients who were taking anticonvulsant medication, but whose seizures were poorly controlled. This pattern distortion can be revealed by the correlation coefficient, but not by other PRVEP parameters. Therefore, this coefficient may be useful as a sensitive and objective measure both of PRVEP distortion and PRVEP improvement. Our results give further evidence that nondemyelinating disorders, but with synaptic transmission defects, can produce measurable changes in PRVEP morphology.     

Pattern-reversal visual evoked potentials in infants: gender differences during early visual maturation

This paper investigates gender differences in the peak latency and amplitude of the P1 component of the pattern-reversal visual evoked potential (pattern-reversal VEP) recorded in healthy term infants. Pattern-reversal VEPs in response to a series of high contrast black and white checks (check widths 120', 60', 30', 24', 12', 6') were recorded in 50 infants (20 males, 30 females) at 50 weeks post-conceptional age (PCA) and in 49 infants (22 males, 27 females) at 66 weeks PCA. Peak latency of the major component, P1, was considerably shorter in female compared with male infants. Differences in head circumference do not entirely account for the gender differences in peak latency reported here. A gender difference in P1 amplitude was not detected. These findings stress the importance of considering gender norms as well as age-matched norms when utilizing the pattern-reversal VEP in clinical investigations. Studies including a wider range of ages are clearly necessary in order to establish whether the earlier peak latencies in female infants represents a difference in the onset or rate of visual maturation.     

Pattern-reversal visual evoked potentials in children with migraine: a correlation analysis

Visual potentials evoked by pattern reversal (PRVEPs) were studied in 64 normal children (age range 7 to 15 years) and in 20 age-matched patients with common and complicated migraine (age range 6 to 16 years). Most of them were studied before and during prophylactic therapy. A Quadristim set (Alvar) was used to present checkerboard patterns on a TV monitor, to amplify the EEG signals and to average and plot the evoked potentials. The potentials were elicited by binocular full-field 2/s checkerboard reversal, recorded from an electrode 4 cm above the inion, and analyzed for latency, amplitude and waveform morphology. The degree of similarity between pairs of PRVEPs was determined by the correlation coefficient. In all our patients no pronounced influence of the disease itself was demonstrated on the PRVEP latencies and amplitudes, but in most of them the correlation coefficients were significantly different from that showing the measure of normal PRVEP variations. Prophylactic medication influenced non-significant increase of the coefficient. This increase seems to be related to recovery from medication in terms of attack frequency. No significant difference in PRVEP results of common and complicated migraine was noticed. The PRVEP distortion can be revealed by the correlation coefficient but not by other PRVEP parameters. Therefore, this parameter may be useful as a sensitive measure of both PRVEP distortion and PRVEP improvement. Our results give further evidence that non-demyelinating disorders, but with ischemic damage and abnormalities in neurotransmitters, can produce measurable changes in PRVEP morphology.     

Pattern-reversal visual evoked potentials in rabbits are resistant to occlusion of the carotid artery

Contrast (pattern-reversal) visual evoked potentials (VEPs) were examined in the awake rabbit to test the possibility that carotid occlusion would disrupt sensory transmission in the visual pathways. Rabbits were operated to ligate one carotid and to chronically transplant another one into a skin flap. VEPs to checkerboard stimuli reversing with a rate of 2/s were recorded from the visual cortex. No significant changes in latency, amplitude and waveshape of VEPs were noted after 3-30 min of carotid occlusion. Apparently, blood flow from the basilar system can be easily shunted via the circle of Willis to the territory of the internal carotid.     

The effect of eccentricity and colour on negativity in pattern onset visual evoked potentials

The effects of stimulus size, eccentricity and colour on the amplitudes of N100 and N130 were investigated in pattern onset VEPs. For black-and-white pattern stimulation, the first set of stimuli was derived from a full dartboard pattern. Central stimulation of various extents was produced by patterns with reduced number of outer rings and for eccentric stimuli a number of central rings were removed from the full pattern. It was found that amplitude of N100 was maximal in VEPs to central stimuli and that it was greatly reduced when eccentric stimulation was applied. The amplitude of N130 showed no significant change in relation to the type of stimulus. When checkerboard stimuli of identical configuration were used for black-and-white pattern stimulation instead of dartboards, systematic changes in peak latencies of N100 were observed in relation to check size. In VEPs to centrally presented small checks the emergence of an early negative peak preceding N100 was recorded at 75 msec. In VEPs to coarse checkerboards presented centrally N100 was often observed with a delayed peak latency of 110 msec. Changes in N130 were not regular when checkerboards with different check sizes were presented centrally. For eccentric checkerboard stimulation, both negative peaks N100 and N130 were revealed. Their peak latencies were similar to those observed in the case of dartboard paracentral stimulation. In VEPs to patterns projected through red or blue filters, regular changes were observed in both negative peaks. Introduction of the red filter led to enhancement of the N100 amplitude in VEPs to dartboard and to checkerboards with fine checks, but it caused no effect on N100 in the VEPs to coarse checkerboards. Introduction of the blue filter led to a decrease in the N100 amplitude in VEPs to dartboard and fine checkerboards and to a slight increase of N100 in VEPs to coarse checkerboards. Changes in N130 were observed only when the blue filter was introduced and they corresponded to those which take place when the level of illumination changes from photopic to mesopic.     

Pattern-reversal visual evoked potentials in normal 7- to 15-year-old twins: a correlation analysis

Pattern-reversal visual evoked potentials (PRVEPs) were tested in 11 sets of monozygotic (MZ) twins and 22 sets of dizygotic (DZ) twins matched on age, sex and educational level. They ranged in age from 7 to 15 years. The PRVEPs of MZ twins exhibited a significantly greater degree of similarity than those of DZ twins. The peak latencies and amplitudes of PRVEP components obtained from MZ twin pairs were significantly correlated. The correlation coefficients for the peak latencies of the P2 (or P100) component were the only ones to differ significantly between the DZ twins of the same sex and DZ twins of opposite sexes. These coefficients, obtained using PRVEPs, were much greater than those obtained with flash visual evoked potentials.     

Pattern-reversal auditory evoked potential

The late auditory evoked potential (AEP) was studied in response to an alternatingly frequency-modulated complex tone. This 'pattern-reversal' AEP was found to be a heartier response than the more conventional tone-burst evoked potential, albeit longer in latency.     

Pattern-reversal visual evoked potential: Method of analysis and results in multiple sclerosis

A detailed method of analysis of the pattern-reversal visual evoked potential is presented. This method takes into account a number of parameters in addition to the latency of the major surface-positive component (P2) and has been tested in a group of 50 normal subjects and in 98 patients with established or suspected multiple sclerosis (MS). It was found that this more detailed form of analysis improved the detection rate of abnormal responses in the MS subjects particularly in those classified in the suspected category. The potential value of this form of analysis, particularly in clinical neurophysiology laboratories where the recording of visual evoked potentials is the only technique employed in the investigation of patients with suspected MS, is discussed.     

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.     

Scotopic multifocal visual evoked potentials

ObjectiveTo investigate the scope of scotopic multifocal visual evoked potentials (mfVEP_S) for the assessment of scotopic visual fields.MethodsPattern-reversal mfVEP for photopic (mfVEP_P) and scotopic conditions (mfVEP_S; 0.003 cd/m²) were recorded from 36 visual field locations of a circular checkerboard pattern (25° radius) in 9 participants with normal vision. MfVEP_P were recorded with a conventional central fixation cross, mfVEP_S were recorded (i) with (mfVEP_S+) and (ii) without (mfVEP_S?) an additional fixation aid. Latency shifts were determined using cross-correlations, mfVEP magnitudes were analysed in an eccentricity dependent manner using signal-to-noise ratios (SNRs).ResultsIn comparison to mfVEP_P, mfVEP_S? and mfVEP_S+ were delayed by 101 ms and 97 ms, respectively, and had smaller signal-to-noise-ratios. Both mfVEP_S were reduced down to noise level in the center and also severely reduced for the most peripheral stimulus eccentricity used. The visual-field-coverage for the paracentral eccentricities of mfVEP_S+ and mfVEP_S? was 76% and 65% [4°–9°], respectively, and 79% and 66% [9°–16°].ConclusionsMfVEP_S were delayed compared to mfVEP_P and demonstrated the expected central response drop-out typical for scotopic vision.SignificanceMfVEP_S may hold promise of an objective, spatially resolved visual field test which motivates testing it in patients with diseases affecting scotopic vision.     

Further investigation of visual evoked potentials elicited by lateralized stimuli: effects of stimulus eccentricity and reference site

Visual evoked potentials (VEPs) to small lateralized flashes were recorded from the parietal midline, homotopic lateral central and occipital electrodes, and from left and right mastoid processes, all referred to a balanced non-cephalic reference. Two stimulus eccentricities, 4 degrees and 10 degrees, were employed, and a comparison made between the non-cephalic and linked mastoid references. P120 (measured at lateral occipital sites only) peaked earlier and was of smaller amplitude at the electrode contralateral to the visual field of stimulus exposure. N160 peaked earlier at central than occipital sites, was larger from electrodes over the contralateral hemisphere, and at the occipital sites only, peaked earlier in the electrode contralateral to the visual field of stimulus exposure. These effects were virtually unaffected by the eccentricity manipulation and it is concluded that light scatter across the visual midline is unlikely to be responsible for the observed pattern of ipsilateral-contralateral VEP asymmetries. The mastoids were found to detect significant stimulus-locked activity in the same latency range as the occipital N160 component. However, comparison of the non-cephalic and linked mastoid references revealed only non-specific effects, and no sign of any change in the pattern of ipsilateral-contralateral VEP asymmetries, or the magnitude of the associated latency differences. It is concluded that these effects may be of value in the study of callosal transfer.     

Pattern-reversal visual evoked potential in a case of nitrous oxide abuse and recovery

Pattern reversal visual evoked potentials were recorded in a dentist who had abused nitrous oxide while he showed neurologic impairment and during recovery. The latency of the major positive peak (P100) remained constant during both phases. However, the amplitude of this peak was markedly reduced during the stage of neurologic involvement, and increased during recovery after withdrawal. The clinical significance of this is discussed.     

The relationship between visual seizures and visual evoked potentials

We have studied a patient (pt) in status epilepticus with visual seizures (szs) arising focally from the right occipital area and have recorded the visual evoked potential (VEP) to three different stimuli under three different conditions (during, between and with no szs). The pt experienced "sparkling" in the contralateral visual field as the sz and the intensity of the "sparkling" was directly related to the frequency of the ictal activity recorded on the EEG. During the szs the VEPs could still be recorded, but the amplitude of the P100 was higher on the contralateral side with pattern reversal (PR) stimuli, and with flashes (FL) the positive peak after the P100 was less evident on the ipsilateral side. Latencies to these latter two positivities were generally shorter than in normals, with much greater standard deviations ipsilaterally with FL and contralaterally with PR, especially during the actual szs. The relationship between VEP generation and visual sz phenomena is discussed.