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

Pattern-electroretinograms (P-ERGs) and visual evoked potentials (VEPs) were simulataneously 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 effects 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.     

Age-related changes in pattern visual evoked potentials: differential effects of luminance,contrast and check size

We recorded visual evoked potentials (VEPs) to checkerboard pattern-reversal stimulation in 109 normal subjects (51 males and 59 females; aged 19–84 years) in order to study the aging effect on the multiple channels of the visual system in humans. Transient VEPs to 3 check sizes (15′, 30′ and 50′) were obtained by monocular stimulation. Two test conditions were employed: (1) a high luminance (180 cd/m²) and a low luminance (11 cd/m²) both with a fixed contrast (90%), and (2) a high contrast (85%) and a low contrast (10%) both at a fixed luminance (57 cd/m²). The major features of our results included: (1) the presence of a curvilinear relationship between P100 latency and age for all conditions, while the P100 amplitude did not show any such aging effect, (2) the age-latency function was similar between the two luminance conditions, while it was different between the two contrast conditions, and (3) the differential age effect on the P100 latency caused by changes in contrast depended on the check size. These results suggest that age-related changes in the human visual system are not uniform, but rather are different in the specific functional subdivisions. It is thus hypothesized that aging may differentially influence the separate channels of the human visual system.     

Clinical relevance of phase of steady-state VEPs to P100 latency of transient VEPs

Pattern visual evoked potentials (VEPs) to transient and steady-state stimulation were recorded in 10 normal subjects at 4 levels of luminance (180, 57, 22 and 11 cd/m²). VEPs were also recorded in 5 patients with optic neuropathy at a fixed luminance (180 cd/m²). The relationship between P100 latency of transient VEPs (T-VEPs) and the phase of steady-state VEPs (S-VEPs) was analyzed. As luminance decreased in normal subjects, P100 latency was prolonged and the phase lag increased. A significant linear relationship between the P100 latency and phase was found. Patients showed both the prolonged P100 latency and the delayed phase. The simple linear regression line of the phase-P100 latency function of normal subjects closely matched the patients' values. These results suggest that changes in the phase may be equivalent to changes in the P100 latency. S-VEPs, therefore, may be clinically useful in assessing visual function.     

Suppression of F-VEP during isoflurane-induced EEG suppression

We recorded visual evoked potentials (VEPs) to flash stimuli in moderately deep anaesthesia when EEG showed burst suppression pattern. Flash VEPs could consistently be recorded in all 8 test subjects during bursts but not during suppressions. We conclude that during isoflurane-induced EEG suppression VEPs to flash stimuli are also suppressed. This effect should be taken into account in evoked potential testing during anaesthesia.     

Multichannel visual evoked potentials in migraine

Multichannel recordings of visual evoked potentials (VEPs) have proved to be useful in the evaluation of visual field defects. We studied the topographic distribution of transient VEPs in 15 migraine patients (8 with visual aura and 7 without) and 15 age-matched controls during the migraine-free interval. All the subjects included in the study had normal visual fields. VEPs were recorded from 9 electrodes placed on the posterior scalp. Stimuli were full-field and hemifield reversing square wave grating patterns of medium spatial frequency (4 c/deg). The groups did not show significant differences in latencies and amplitudes of the major components (N70, P100) recorded from the midline. However, migraine patients with visual hemianopic aura showed definite asymmetries in the VEP amplitude distribution. Significantly reduced, absent or polarity-invered VEP responses were recorded ipsilateral to the side of the prodromic visual symptoms. Direct comparison of affected and unaffected hemispheres by partial field stimulation confirmed these findings. According to the VEP cortical generator theory, these abnormalities suggest a functional anomaly consistent with the clinical syndrome and detectable also in the migraine-free interval. None of the migraine patients without aura or the controls showed VEP amplitude asymmetries. We conclude that multichannel VEP recordings may discriminate between different subtypes of migraine and contribute important physiopathological information to the study of this disease.     

Reliability and upper normal variability limits of pattern reversal visual evoked potential parameters.

Twenty healthy volunteers aged 21-48 years (10 males, 10 females) were submitted to pattern reversal visual evoked potentials with 15' and 30' checks. The recordings were repeated after 7 days to assess reliability and upper normal variability limits of the following parameters: latencies of N70, P100, N140 and peak-to peak amplitudes of N70-P100, P100-N140. Reliability was tested with intraclass correlation coefficient, which was excellent or good for all parameters. Test-retest variability limits were computed with = 0.01 for absolute latency differences and relative amplitude differences.     

Visual evoked potentials in the vicinity of the optic tract during stereotactic pallidotomy

We recorded visual evoked responses in eight patients with Parkinson's disease, using a depth electrode either at or below the stereotactic target in the ventral part of the globus pallidus internus (GPi), which is located immediately dorsal to the optic tract. Simultaneously, scalp visual evoked potentials (VEPs) were also recorded from a mid-occipital electrode with a mid-frontal reference electrode. A black-and-white checkerboard pattern was phase reversed at 1 Hz; check size was 50 min of arc. Pallidal VEPs to full field stimulation showed an initial positive deflection, with a latency of about 50 ms (P50), followed by a negativity with a mean latency of 80 ms (N80). The mean onset latency of P50 was about 30 ms. P50 and N80 were limited to the ventralmost of the GPi and the ansa lenticularis. Left half field stimulation evoked responses in the right ansa lenticularis region while right half field stimulation did not, and vice versa. These potentials thus seemed to originate posterior to the optic chiasm. The scalp VEPs showed typical triphasic wave forms consisting of N75, P100 and N145. The location of the recording electrode in the ansa lenticularis region did not modify the scalp VEP. These results suggest that P50 and N80 are near-field potentials reflecting the compound action potentials from the optic tract. Therefore, N75 of the scalp VEPs may represent an initial response of the striate cortex but not of the lateral geniculate nucleus.     

Neuronal generators of the visual evoked potentials: intracerebral recording in awake humans

Flash and pattern reversal visual evoked potentials were recorded in awake patients undergoing stereotactic procedures for severe dyskinetic disorders resistant to medical treatment. The nucleus ventralis lateralis thalami was reached via an occipital approach. VEPs were recorded on the scalp at the entracce of the intracerebral electrode, and serially from sites at different depths. A polarity reversal of the surface recorded wave form took place as the intracerebral electrode was advanced beneath the surface cortical layers. As concerns F-VEPs, most of the scalp activity mirrored the potentials recorded down to the depth of 70-65 mm from the thalamus. The largest amplitude of intracerebral F-VEPs was obtained from recording sites at 50–70 mm from the thalamus, i.e., in the depth of the calcarine fissure. A negative wave, peaking around 47–50 msec, became evident in recording sites at 30–40 mm from the thalamus but vanished as the electrode was advanced farther. In only one patient could we record a small negative wave, peaking at 33 msec, in the vicinity of the corpus geniculatum externum. Furthermore, the oscillatory activity recorded from the scalp appeared to be generated in the cortical layers. PR-VEPs also underwent polarity reversal as the electrode traversed the cortex. PR-VEPs disappeared more superficially than F-VEPs. No PR-evoked activity could be recorded in the vicinity of the corpus geniculatum externum.We conclude that slow and fast components of VEPs recorded from the scalp are entirely generated in cortical layers.     

Visual evoked potentials and event related potentials in congenitally deaf subjects

The purpose was to test parameters of visual evoked potentials (VEPs) and of event-related potentials (ERPs) in deaf subjects to verify visual and cognitive CNS functions in a handicapped group of the population. Three types of visual stimuli (with dominating parvocellular or magnocellular system activation or with cognitive tasks) were used in the study. Six deaf persons (4 women, 2 men, mean age 17 years) and 6 persons with normal hearing (sex- and age-matched) were included in this pilot study. In all types of stimulation, latencies and amplitudes of main VEPs and ERPs components were evaluated. No significant latency differences were found. However, significantly reduced amplitudes were found in the occipital area for responses to motion and cognitive stimuli which might be interpreted as a part of functional reorganization of the extrastriate and cognitive cortical areas of deaf subjects.     

Visual event-related potentials evoked by using a virtual reality display

This study aimed at investigating whether a virtual reality display (VRD) is an appropriate tool for evoking visual event-related potentials (VEPs). VEPs evoked by VRD stimuli were highly similar in form to VEPs evoked by using a computer monitor, both having two dominant peaks, labeled P100 and N200. Monitor and VRD N200 latencies and amplitudes were highly correlated. However, peak latencies were longer and the peaks were broader when stimuli were presented on the VRD. Besides, VRD P100 amplitude was smaller, and an N75 peak could be seen usually only on monitor VEPs.     

Evoked potential findings in Behçet's disease. Brain-stem auditory,visual, and somatosensory evoked potentials in 44 patients

We studied 54 patients with Behçet's disease, 41 males and 13 females, mean age 28 years. Forty-four patients had auditory brain-stem evoked potential (BAEP) recordings, 39 had pattern reversal visual evoked potentials (VEP), 27 had median nerve somatosensory evoked potential (SEP) recordings, and 25 tibial nerve SEPs. BAEPs were abnormal in 16 patients (52%) with neurological manifestations and in 4 (31%) without, because of decreased amplitude of wave V, prolonged I–III or III–V interpeak latencies, or uncertain/absent waves III and/or V. Eleven patients (40%) with neurological symptoms and 3 patients (25%) without, had abnormal VEPs. Absent potentials, decreased amplitude, with or without prolonged P100 latency, were found in 75% of the cases, the rest had prolonged P100 latency only. Median SEPs were abnormal in 8 patients (38%) with neurological manifestations. Four patients (21%) had abnormal tibial SEPs. Decreased amplitude with or without mild slowing in central conduction was the predominant SEP abnormality. SEPs were normal in all patients without neurological symptoms. In total, 84% of patients with, and 38% of patients without, neurological symptoms had abnormalities of one or more EP modality.When used cautiously, EP studies in Behçet's disease might be helpful to separate neuro-Behçet from other disorders with similar symptomatology, to disclose subclinical CNS involvement, to evaluate and monitor CNS disease activity, and to provide objective measures of treatment response.     

Use of visually evoked responses in evaluation of visual blurring in brain-damaged patients

Pattern visual evoked potentials were recorded in brain-damaged patients who complained of fluctuation of vision causing visual blurring. Continuous prolonged pattern stimulation revealed marked variability of P100 amplitudes. In contrast, normal subjects and brain-damaged patients who did not complain of visual blurring showed stable P100 amplitudes. Fluctuation of vision thus seems to have an electrophysiological correlate in terms of P100 amplitude lability, which can be objectively assessed by prolonged continuous recording of pattern visual evoked potentials.     

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.     

Serial pattern evoked potential recording in a case of toxic optic neuropathy due to ethambutol

Visual evoked potentials (VEPs) were studied in a patient who developed visual impairment during ethambutol treatment. The ERG and the flash VEP were normal at the time of maximal visual loss, whereas pattern reversal VEPs 2 and 5 months after onset revealed evidence of severe bilateral optic nerve involvement, especially affecting macular fibres. Seven months after onset paramacular PNP complexes with a late positivity (scotomatous response) were recorded after pattern reversal and half-field stimulation, suggesting involvement of fibres subserving central vision. At the time when visual acuity was normal there was still electrophysiological evidence of a mild involvement of the anterior visual pathway. The papillomacular bundle seems to be especially involved in ethambutol eye toxicity.     

The evoked brain activity during hyperbaric exposure

Changes of amplitude-temporal parameters of visual evoked potentials (VEPs) under hyperbaric action testify to reconstruction of the activity of functional brain systems participating in the generation of responses to light stimulation. The revealed EP changes depend both on conditions of hyperbarism and on individual characteristics of subjects. The parameters of VEPs may manifest the estimation of common functional state under prolonged extreme influences.     

视力与视觉诱发电位的相关分析

对104例病人的图形翻转VEP的瞬态波形各参数,以及9例正常或近视学生的稳态曲线功率谱与视力之间的关系进行了多元相关统计分析,旨在探讨VEP的哪些参数可客观地评估视力.结果表明,瞬态VEP的波形参数中以13’格诱发的N_1P_1、P_1N_2的峰峰值及P_(100)潜伏期与视力的相关系数最大,故认为,分析视力时以平均P_(100)波的波幅值和P_(100)波潜伏期作指标较为灵敏;而稳态、VEP能谱曲线则显示,视力与平均相叶能谱或刺激频率点的能谱相关性较大,与二次谐波的相关性则小.     

Brain potentials associated with pattern displacement and saccadic eye movements in humans and rhesus monkeys

Visual evoked potentials (VEPs) to the onset of motion of visual patterns and brain responses associated with saccadic eye movements (SRPs) were compared in human subjects and in rhesus monkeys. Three different velocities of pattern motion were employed. In humans, brain responses were recorded from six scalp areas. In monkeys, transcortical recordings were obtained from chronically implanted electrodes in the occipital, temporo-parietal, and frontal areas. In humans there was a clear difference in VEPs to the pattern motion between the anterior (Fz, Cz) and posterior (Pz, Oz) scalp regions. The earliest component was a positive peak at 85 ms at Oz followed by a negativity around 110 ms. In the fronto-central leads the VEP was characterized by a negativity at 145 ms and a subsequent broad positive component around 250 ms. SRP responses differed in the early components from the VEPs to pattern motion but a good correspondence was found in the morphology of the late components of the two types of brain potentials. Furthermore, flashed-on VEPs and SRPs elicited a late positivity of more pronounced amplitude than VEPs to pattern displacement. In monkeys similar findings were found: an early negative component of the pattern-displacement VEP could not be observed in the SRP responses over the visual cortex while the late portion of the SRP waveform was greater than the late positivity of the VEP to motion-onset.     

The effect of binocular stimulation on each component of transient and steady-state VEPs

We recorded the monocular and binocular VEPs to the alternation of sinusoidal gratings in order to evaluate the binocular interaction in each component of transient and steady-state VEPs in 13 normal subjects. Three spatial frequencies (1.3, 2.6 and 5.3 c/deg) with a 90% contrast were used as visual stimuli. The latencies and amplitudes of N70 and P100 of the transient VEPs were measured. The steady-state VEPs were Fourier analyzed, and both the phase and amplitude of the second (2F) and fourth (4F) harmonic responses were obtained. Binocular interaction was influenced by spatial frequency such that a binocular summation or even an inhibition occurred. For the transient VEPs, a binocular summation was more pronounced in the amplitude of N70 than in that of P100 at all spatial frequencies. There were no significant effects of binocular stimulation on latencies of N70 or P100. However, the latencies of N70 and P100 showed different spatial frequency characteristics. For the steady-state VEPs, the amplitude of 2F revealed a binocular summation that was more pronounced at 5.3 c/deg, whereas the 4F amplitude showed binocular inhibition at 2.6 and 5.3 c/deg. The 2F phase showed binocular inhibition at all spatial frequencies, whereas no such inhibition was observed in the 4F phase. These results suggest that individual components of transient and steady-state VEPs are physiologically distinct and may therefore be generated from different neuronal populations in striate cortex.     

A polysensory pathway to the forebrain of the pigeon: the ascending projections of the nucleus dorsolateralis posterior thalami (DLP).

Visual evoked potentials (VEPs) in the associative neostriatum caudolaterale (NCL) have shorter latencies than those recorded in other visual forebrain areas. Therefore visual input into NCL probably stems from a subtelencephalic relay. Tracing experiments revealed a projection of the nucleus dorsolateralis posterior thalami (DLP) into those portions of NCL in which visual, auditory, and somatosensory afferents from intratelencephalic parasensory areas terminate. Since VEPs in NCL are abolished after DLP-lesions, this structure has to be the critical relay. However, DLP also projects to other associative forebrain areas and parts of the basal ganglia. Previous experiments had furthermore revealed that DLP-neurons integrate visual, auditory, and somatosensory inputs. Thus, the DLP-projection onto various associative forebrain areas represents a true polysensory thalamotelencephalic system.     

Mapped distribution of pattern reversal VEPs to central field and lateral half-field stimuli of different spatial frequencies

Visual evoked potentials (VEPs) to pattern reversal vertical bar stimuli of 3 different sizes (1, 2, 4 c/deg) were recorded from 19 scalp derivations in 50 controls. The stimuli were presented on a full-field (FF) screen of 24° visual angle, and on left and right half-fields (HF) of 12° radius. In 15 controls partial HF stimuli were presented on the central 3 and 6° and as hemiannular stimuli of 12° with occlusion of the central 3 and 6°.An antero-posterior polarity reversal of the N1-P1-N2 sequence was observed for FF VEPs. A tangential polarity reversal was observed for HF VEPs. Also with central or hemiannular stimuli polarity reversals of all VEP components were observed within the scalp.Variants of VEP distribution, absence of prominence of some of the ipsi- or contralateral VEP components were observed in 8–40% of controls.The FF and HF VEP distribution, and the variant VEP asymmetries were partly dependent on the pattern spatial frequency.