Pattern ERGs and VEP topography evoked by lateral eccentric pattern reversal stimulation

In ten healthy subjects we recorded simultaneously pattern-ERGs and multichannel VEPs evoked by checkerboard reversal stimuli presented in the center, and at three different locations on the nasal and temporal retina. In the near periphery significantly larger pattern-ERG amplitudes were found for the nasal retina. Farther out in the periphery this effect reversed, and stimuli presented to the temporal retina yielded larger pattern-ERG amplitudes. Component latencies showed also differences with larger latencies for nasal than temporal retinal stimuli in the near periphery. In addition, pattern-ERG amplitudes increased with check size while peak latencies decreased. Retinal stimulus location had a significant influence on the VEP topography reflected by potential distributions lateralized over occipital scalp areas contralateral to the hemiretina stimulated. There were no differences between VEP activity evoked by nasal or temporal retinal stimuli. The results relate to differences in local retinal organization reflected by the distribution of photoreceptors and other neural elements across the retina as well as to functional differences in visual information processing between different retinal areas.     

Contribution of pattern reversal foveal and half-field stimulation to analysis of VEP abnormalities in multiple sclerosis

Multichannel pattern reversal visual evoked potentials (PRVEPs) from full-field (FF), half-field (HF) and foveal (central-field, CF) stimulation were recorded in 112 mildly disabled multiple sclerosis (MS) patients with the aim of evaluating the contribution of HF and CF stimulation in this disease. CF stimulation was marginally more sensitive in detecting abnormalities (75% of patients) than FF stimulation (71% of patients). However, more importantly the two techniques were found to be complementary with the maximum number of abnormalities (79% of patients) resulting from a combination of the results. Abnormal FF responses were further evaluated by HF responses. P100 latency prolongation indicative of conduction delay was the most common finding but one-third of abnormalities consisted of disturbances of wave form relating to conduction block predominantly in macular fibres. Furthermore 34% of patients had an absent or indeterminate response to CF stimulation thus providing electrophysiological confirmation of the preferential involvement of macular fibres in MS. Although electrophysiological abnormalities were localised to the optic nerve in the majority of cases, some patients also had evidence of retrochiasmatic and chiasmatic lesions. In the majority of cases CF stimulation proved to be a useful alternative to HF stimulation in evaluating FF responses with abnormal wave forms. The study also suggested that an important factor determining whether a central scotoma will disturb the morphology of the FF VEP in the midline recording channel is the position of the macular representation in the occipital cortex. It is concluded that with multichannel recording and the additional use of CF and HF stimulation it is possible to increase the yield of PRVEP abnormalities found in MS and to define their nature with considerably greater precision.     

Developmental changes in the human visual system as reflected by the latency of the pattern reversal VEP

Pattern reversal visually evoked potentials (VEPs) were recorded from 439 infants and young children ranging in age from 1 month to 5 years in response to large and small checks. Qualitative analysis of the VEP wave form showed that the first major positive component, P1, is consistently present at all ages, while the frequency of occurrence of later positive components is more variable. The proportion of infants showing late positive components increases with age; by 1 year, the frequency of occurrence of late components for large checks is more adult-like than for small checks. The latency of P1 was analyzed quantitatively. Results showed that P1 latency decreases rapidly during the first year of life for both large and small checks and that the time course of the latency change differs as a function of check size. VEPs to large checks attain adult-like P1 latency values by about 1 year of age, while the P1 latency of VEPs to small checks has still not reached adult levels by 5 years of age. Data from 12 infants tested longitudinally between 1 and 7 months of age using both checkerboards and square wave gratings show no difference in P1 latency between checkerboards and gratings comprised of large (30-240 min) pattern elements, but for patterns with small (7.5 and 15 min) elements, P1 latency to checks is significantly longer than P1 latency to stripes. These results are explained on the basis of the difference in the fundamental spatial frequency between checks and stripes.     

Influence of L-DOPA/carbidopa on pattern reversal VEP: behavioural difference in primary and secondary parkinsonism

Data obtained from a total of 246 monocular VEPs performed on 46 patients, 35 with Parkinson's disease and 11 with arteriosclerotic parkinsonism, classed in the first 3 stages on the Hohen and Yahr disability scale, are reported. Our data show a delay of mean P100 latency in the primary parkinsonian group during the period of washout from L-DOPA therapy as well as in the secondary parkinsonian group. But the interocular mean difference in VEP P100 results significantly increased in primary parkinsonism only. A more important different behaviour between primary and secondary parkinsonism concerns a possible reduction of VEP delay related to L-DOPA/carbidopa treatment. An improvement of P100 delay can be noticed after acute and after chronic DOPA therapy in primary parkinsonism only. The above data confirm previous reports concerning VEP delays in Parkinson's disease, suggesting monitoring of different pharmacological sensitivity in idiopathic and arteriosclerotic parkinsonian patients as a useful method.     

Stimulus rate-induced VEP attenuation in preterm infants.

The effect of the stimulus rate on the single flash VEP amplitude and latency (N1) was studied in 26 mechanically ventilated, preterm infants during the first days of life. Significant decreases in VEP amplitude and increases in latency were observed within a series of 3 single flash VEPs recorded with stimulus rates of 1/4 Hz. After a recovery period of 30 sec between series, the amplitude had attained baseline level, whereas the latency delayed progressively. The underlying cause of this rate effect is speculative, as individual degrees of VEP attenuation were not statistically related to gestational age, clinical state or cerebral oxygen delivery.     

Coloured pattern displacement and VEP amplitude.

The results of this experiment confirm that evoked potential amplitude is linear with checkerboard pattern displacement. We have also found that this linear relationship holds for red, green and blue patterns. The hypothesis that there would be no significant differences between the amplitude of the evoked potential to colour/'black' stimulation and a white/'black' stimulus of equivalent luminance has been substituted. Differences were found between colours. The mean level for the blue pattern was lower than that for the red and the green patterns. We have further confirmed the relationship between luminance and the latency of the evoked potential. Differences in latency were found between all conditions in this study, suggesting that more accurate methods of measuring luminance are required in studies using colour pattern displacement if latency measurements are the main focus of the study.     

Cortical and subcortical components of the pattern VEP

Studies in the past have shown that wavelength related VEPs can be recorded from both cortical and noncortical sites. Elements of pattern-specific VEPs for both transient and pattern-reversal stimuli are also obtained from these sites. From the noncortical montage consistent responses are obtained with a major component at about 100 msec, which has been found for both the wavelength related and pattern related VEP. In contrast, the cortical VEP to both types of stimuli include two major components, at around 100 and 200 msec. In pattern reversal these components react quite differently to changes in spatial frequency. The component around 100 msec reacts strongly to a wide range of spatial frequencies when recorded from either cortical or noncortical sites. In contrast, the component around 200 msec, obtained with cortical recording, reacts very strongly to high spatial frequencies and very weakly to low spatial frequencies. This finding corresponds to recent results of single-cell studies in the macaque LGN and striate cortex.     

Presenile dementia--the use of the flash and pattern VEP in diagnosis

Flash, pattern reversal and pattern onset-offset VEPs were recorded in 17 patients with a clinical diagnosis of presenile dementia. The results were compared with those from two control groups--17 normal volunteers of equivalent ages and 17 patients from the same psychiatric hospital with affective disorders but no clinical evidence of dementia. The flash P2 component was found to be significantly delayed in the group of patients with dementia, but the latency of the P1 component and pattern VEP components were all within normal limits. This unusual finding presents a useful index for the diagnosis of presenile dementia.     

Critical flicker frequencies in MS patients with normal or abnormal pattern VEP

Critical flicker frequencies (CFF) were compared with the latencies of visual pattern reversal evoked potentials (VEP) in 2 groups of MS patients to evaluate the value of CFF in electrophysiological diagnostics of demyelination of the optic tract. A microprocessor-based device was constructed to obtain CFF thresholds with a 2-alternative forced-choice method. VEP latency was more frequently pathological than CFF, but CFF was abnormal in 2 optic neuritis patients with normal VEP. The frequency of pathological CFF and VEP was different in the patient group with a long history of MS compared with the new cases; in the freshly diagnosed group, CFF had a better diagnostic yield compared to the patients with a longer history.     

The effects of renal hemodialysis on pattern reversal evoked potentials

PREP P100 latency was significantly prolonged in patients maintained on renal hemodialysis. P100 latency also failed to show changes related to time past dialysis. PREPs may be of use in evaluating the progression of uremic induced dysfunction.     

Normal checkerboard pattern reversal evoked potentials in parkinsonism

The utility of checkerboard pattern reversal visual evoked potentials in the evaluation of Parkinson disease (Pd) was studied in 25 patients and controls without eye pathology. The results did not reveal differences in potential latency but the amplitude appeared slightly larger in PD than controls. Major intraocular differences were observed only in Pd patients with glaucoma, cataracts or retinal degeneration. The commonly employed high contrast and luminance, checkerboard pattern reversal technique did not appear useful in the evaluation of Pd. Selection of proper stimulus parameters may be critical in detecting VEP abnormality in Pd.     

The visual evoked response to pattern reversal in 'normal' 6-11-year-old children

The visual evoked response to a 7 mm (40') check using a pattern reversal stimulus was measured in 73 normal children, aged 6-11. Full pattern displacement for the right and left eye and 1/4 and 1/2 pattern displacement for the right eye were studied. The amplitudes of the N65-P95 and P95-N125 wave, together with the P95 latency, were measured. Analysis of the data showed that there was no clear relationship between the mean amplitude or latency of the evoked response and age. However, significant changes were found between linear displacement and linear age for the N65-P95 wave and there was a complex interaction for the same wave between age, sex and eye. There was a significant difference in latencies between right and left eye between the boys and the girls, with the boys having longer latencies. There are thus both age- and sex-related differences in the amplitude and latency of the N65-P95 wave in 6-11 year-old children.     

Developmental changes of pattern reversal visual evoked potentials

Analysis of developmental changes in pattern reversal visual evoked potentials (PVEPs) was performed on 141 normal children ranging in age from 1 month to 19 years 4 months. The stimulus was a black and white checkerboard pattern on a television screen, and the check edge subtended 50 min of retinal arc. The major positive peak (P2) was observed in all subjects, and the incidence of other peaks tended to increase with age. The P2 latency decreased rapidly during the first six months of life and reached a constant value after the age of 2 years. The P2 latency with monocular stimulation was significantly longer than that with binocular stimulation in most age groups. Developmental changes of the N1-P2 or P2-N2 amplitudes were unclear, and the standard deviation of the amplitude in each age was too large for clinical application. The P2 latency with binocular stimulation was shorter for females than for males only at the age of 8-11 years.     

True checkerboard pattern reversal with light-emitting diodes.

The use of rectangular red light-emitting diodes permits construction of a true checkerboard pattern-reversal stimulator, which given evoked responses comparable in amplitude and wave form to those obtainable by a TV pattern generator. The device interfaces easily with commercial avergers and allows the incorporation of several features that may increase the sensitivity of visual evoked responses in screening for multiple sclerosis.     

The refractory period of the visual evoked potential produced by pattern reversal in multiple sclerosis

Refractoriness of the visual evoked potential to pattern-reversal stimulation has been studied using a light-emitting diode stimulator, the effect on a test P100 of a conditioning pattern reversal being determined for conditioning-test intervals of 20 ms, 50 ms and 100 ms. In 20 normal subjects, the latency of the test P100 was increased by a mean of 9.8% (SD 5.0%) with the 20-ms interval, 5.8% (SD 6.6%) with the 50-ms interval, and 2.8% (SD 4.7%) with the 100-ms interval. Patients with clinically definite multiple sclerosis were divided into 3 groups based on the latency of P100 in the conventional VEP: within 2 SD of the normal mean (7 patients), plus 3-6 SD (7 patients), and greater than 10 SD (7 patients), representing normal, mildly abnormal and grossly abnormal latencies, respectively. Only 4 patients had "abnormal" results in the conditioning-test paradigm, 2 of whom were in the "grossly abnormal" group and 1 in each of the other two groups. The prolongation in latency tended to be greater the longer the control P100. The conditioning-test paradigm did not reveal evidence of a significantly prolonged refractory period of demyelinated axons in the optic nerve, and did not assist in the identification of changes "typical of demyelination" in patients with normal or mildly abnormal control P100s. It is concluded that testing the refractoriness of the VEP may not enhance the diagnostic yield of the VEP in multiple sclerosis.     

High test–retest reliability of checkerboard reversal visual evoked potentials (VEP) over 8 months

ObjectiveThe inter-individual variation in the shape of a visual evoked potential (VEP) is large even for simple stimuli. We compared the inter-individual variation in VEP waveform to the intra-individual stability.MethodsWe recorded VEP with checkerboard stimulation in 10 women aged 19–29 years in two sessions. We determined the latencies and the peak-to-peak amplitude of N75 and P100. As a new approach in VEP research, we regressed VEP waveforms pairwise onto each other and calculated a t-value between all sessions. The maximal t-value was taken to indicate recognition for all 19 comparisons performed with one session. The recognition rate was cross-validated in a generalized linear regression model (GLM).ResultsThe number of sessions correctly matched to the correct subject was 19 of 20 (true positives) leading to a sensitivity of 95.0% with confidence interval [75.1% 99.9%] for the method. The number of true negatives was 359 of 360 leading to a specificity of 99.7% [98.5% 100.0%].ConclusionsThe VEP waveform shows high intra-individual stability compared to the inter-individual variation in healthy women.SignificanceWith a new statistical approach the effect of external factors on the VEP waveform can now be contrasted against the normal variability over time in longitudinal studies.     

Amplitude asymmetry of hemifield pattern reversal VEPs in healthy subjects.

The amplitudes of transient and steady-state visual evoked potentials (VEPs) were measured during hemifield stimulation of the left eye in 10 healthy adults. Pattern reversal of a checkerboard was produced at 4 stimulation frequencies: 1, 5, 10 and 15 Hz. The amplitudes of pattern VEPs were evaluated using the paired t test to determine significant differences between right and left hemifields. The transient VEP amplitudes from midoccipital, midparietal, ipsilateral occipital and contralateral occipital electrodes were significantly greater with right hemifield stimulation. The steady-state VEP amplitudes from the midoccipital electrode during 15 Hz stimulation were significantly greater with right hemifield stimulation. Our neurophysiological data may be compatible with neuroanatomical asymmetries of the occipital lobes in humans.     

Cyclic alternating pattern in infants with congenital hypothyroidism

Congenital hypothyroidism is defined as thyroid hormone deficiency present at birth which is crucial for brain development. Recently, the cyclic alternating pattern, a rhythm present in electroencephalography recordings in non-Rapid eye movement sleep, has been related to brain development and cognition in different pediatric conditions. Therefore, we evaluated the cyclic alternating pattern rate in infants with congenital hypothyroidism, thyroxine supplementation, and healthy controls. The parameters of the cyclic alternating pattern were evaluated in 19 healthy infants (10 female, mean age 25.5?±?15.5?months) and 21 infants diagnosed with congenital hypothyroidism (19 female, mean age 24.3?±?19.0?months). We considered the transient electro-cortical activations (phase A of the cycle) in non-Rapid eye movement sleep and the subdivisions of the A phase in: A1, A2 and A3, based on their frequency content. All subjects were subjected to polysomnography recording in a standard laboratory setting. Sleep data were stored computer following the International 10–20 System. Data showed that congenital hypothyroidism infants exhibited higher frequency of central apnea, hypopnea, and arousals in comparison to controls. Particularly, central apnea index decreased with age in the control group but not in congenital hypothyroidism group. Regarding to cyclic alternating pattern measurements, congenital hypothyroidism infants exhibit a higher frequency in the percentage of A3 subtype (electroencephalographic desynchrony) and conversely a lower percentage of A1 subtype (electroencephalographic synchrony), than healthy infants. An important finding of this study is the positive correlation between A1 mean duration and age, which is bigger in control group than in congenital hypothyroidism group (time duration in control group (0.52?s/month) versus congenital hypothyroidism group (0.1?s/month). Infants with congenital hypothyroidism showed an increase of A3 subtype, of central apnea, and of arousals. The reduction of percentage and mean duration of A1 subtype could be a valuable indicator of sleep development in patients with congenital hypothyroidism and healthy infants.