Visual Evoked Potentials Components Research Articles

Cortical sources of the early components of the visual evoked potential

This study aimed to characterize the neural generators of the early components of the visual evoked potential (VEP) to isoluminant checkerboard stimuli. Multichannel scalp recordings, retinotopic mapping and dipole modeling techniques were used to estimate the locations of the cortical sources giving rise to the early C1, P1, and N1 components. Dipole locations were matched to anatomical brain regions visualized in structural magnetic resonance imaging (MRI) and to functional MRI (fMRI) activations elicited by the same stimuli. These converging methods confirmed previous reports that the C1 component (onset latency 55 msec; peak latency 90-92 msec) was generated in the primary visual area (striate cortex; area 17). The early phase of the P1 component (onset latency 72-80 msec; peak latency 98-110 msec) was localized to sources in dorsal extrastriate cortex of the middle occipital gyrus, while the late phase of the P1 component (onset latency 110-120 msec; peak latency 136-146 msec) was localized to ventral extrastriate cortex of the fusiform gyrus. Among the N1 subcomponents, the posterior N150 could be accounted for by the same dipolar source as the early P1, while the anterior N155 was localized to a deep source in the parietal lobe. These findings clarify the anatomical origin of these VEP components, which have been studied extensively in relation to visual-perceptual processes.

The effect of sulfur dioxide inhalation on visual evoked potentials, antioxidant status, and lipid peroxidation in alloxan-induced diabetic rats.

The aim of the study was to investigate the effect of 10 ppm sulfur dioxide (SO(2)) exposure on visual evoked potentials (VEPs), thiobarbituric acid reactive substances (TBARS), and the activities of Cu,Zn superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) in diabetes mellitus. Forty healthy male albino rats, aged 3 months, were divided into four equal groups: control (C), sulfur dioxide + control (CSO(2)), diabetic (D), and sulfur dioxide + diabetic (DSO(2)) groups. Experimental diabetes mellitus was induced by IV injection of alloxane monohydrate in a dose of 50 mg/kg body weight. Ten ppm sulfur dioxide was administered to the animals of sulfur dioxide-exposed groups in an exposure chamber for 1 h/day x 7 days/week x 6 weeks while control and diabetic groups were exposed to filtered air in the same condition. SO(2) exposure, though markedly decreasing retina CAT and GSH-Px activities, significantly increased retina Cu,Zn-SOD activity in the diabetic and nondiabetic groups. In contrast to SO(2)-related increase in the activity of Cu,Zn-SOD, decrease in GSH-Px activity was observed in the brain of those groups. Brain CAT activity was unaltered. SO(2) exposure caused the significant elevation in brain TBARS levels of CSO(2) and DSO(2) groups, whereas only in the retina TBARS level of the CSO(2) group. SO(2) exposure caused the significant prolongations of P(1), N(1), P(2), and P(3) components of VEPs in the nondiabetic and all components of VEPs in the diabetic groups. SO(2) exposure also resulted in significant amplitude reductions in both experimental groups.

「見えない」のに「見える」？！ 視野闘争下の視覚誘発電位による注意機能の研究

In order to reveal cognitive processing of sensory information in binocular rivalry, visual evoked potentials (VEP) were recorded using pattern reversal stimulus to received side and the other side of visual field. VEP components were observed by evoking stimulus to non-received side of visual field. Results show that the processed information projected to visual cortex does not always generate subjective visual experience.

Electrophysiological evidence for an early attentional mechanism in visual processing in humans

The effect of sustained spatial attention on a task-irrelevant grating displayed in the left visual field was studied by steady-state and transient visual evoked potentials (VEP). For the steady-state experiment, the task irrelevant grating was phase-reversed at different temporal frequencies. In the transient experiment the grating was reversed abruptly at low temporal frequency. In both conditions a target requiring visual attention was presented either in the left or in the right visual field, directing attention either to the left or to the right. VEPs amplitude enhancement by attention was observed on steady-state VEPs and on P100 and N140 transient VEPs components, confirming previous observations. Moreover, VEPs in the attended condition had shorter latency than VEPs in the unattended condition. The difference was about 15 ms with steady-state; with transient recording the lag was 7 ms for N60 and 10 ms for P100. The latency change of the N60 component, suggests that the modulation of attention on visual processing might be earlier than previously thought. A control experiment to assess the influence of eye movements on the test was also performed.

Effects of angularity of the figures with sharp and round corners on visual evoked potentials

Following a study in which equilateral triangles elicited larger visual evoked potentials (VEPs) than either squares or circles, we examined the effect of single‐line angular figures with a sharp or a round corner at angles of 45°, 90°, 135° or 180°. VEPs were recorded monopolarly at four locations on the midline of scalp for 10 subjects, while the figure was tachiscopically presented to the lower visual field. Subtracted waves were obtained between figure and control (blank) conditions. N1 (peak latency 135–142 ms) and P2 (235–237 ms) waves were identifiable. N1 amplitude tended to decrease as a function of angularity, irrespective of orientation (angle pointing up or down). The effect of the sharpness/roundness of the corner was much smaller than that of its angularity. These findings suggest that the greater VEP response with triangles than with squares and circles may be attributable to the acute angularity of triangles. Related cortical processes and VEP components are also discussed.

Visual evoked potential interhemispheric transfer time in different frequency bands

Objective: Visual evoked potentials (VEP) have been used to estimate interhemispheric transfer time (IHTT). However, the complex wave of VEP is most probably formed by different generators of neural populations that act through different frequency channels. If the main peaks of VEP are established by different types of generators, which can also be connected to each other by a different type of callosal fibres, we would be able to estimate a wide range of various IHTT by measuring the latency between time-locked peaks of narrow band-pass filtered VEP. This research aimed to test this hypothesis. Mmethods: Nine right-handed men were presented with a reversal of a checkerboard pattern as stimuli at RVF or LVF, and EEG was recorded at O1, O2, P3, P4. The grand-averaged VEPs were transformed to the frequency domain by means of the fast Fourier transform to obtain the amplitude frequency characteristics. Band-pass filters were chosen adequately, according to tuning frequencies indicated by clear peaks in the amplitude frequency characteristics. The chosen band pass filters (4–8 Hz, 8–15 Hz, 15–20 Hz, 20–32 Hz) were applied to the VEP of the subjects, and 4 different components of VEPs for each VEP were obtained. The latency of P100 and N160 of unfiltered VEP was measured. In the band-pass digital filter applied VEPs, positive and negative peaks, which are consistent with P100 and N160, were measured for each subject. Latency differences between hemispheres for digitally unfiltered and filtered VEPs were computed to estimate IHTT. Results: In the different frequency bands, different IHTTs were estimated, ranging from 3 ms to 30 ms. Approximately 16 ms for theta band, 11 ms for alpha band, 6 ms for 15–20 Hz and 3 ms for 20–32 Hz bands were found. Conclusions: Our findings support the hypothesis which states that unfiltered VEPs provide us with only a rough estimation of IHTT. Also, they are consistent with anatomical findings that describe callosal fibres of varying dimensions, predicting various velocities between hemispheres.

551 Relationship of phantom phenomena and somatosensory cortical reorganization in amputees

The present study was designed to investigate differences in neural processing of pain-related semantic information in amputees with and without chronic phantom limb pain and healthy controls. One-hundred-and-twenty words (40 neutral, 40 body-related, 40 pain-related) were presented in pseudorandom order to probe group differences in the perception of pain-related information. Visual evoked potentials (VEP) to the words were recorded from 11 scalp locations, EMG was measured at the stump and the contralateral side and bilaterally from the M. corrugator. In addition, heart rate and skin conductance responses were obtained. Both early and late VEP components were altered. Pain-free amputees showed a reduced N100 amplitude compared to phantom limb pain patients and healthy controls whereas the phantom limb pain patients displayed a significantly enhanced late positivity (500–800 msec after word onset). VEP components were unaffected by word type. The peripheral EMG responses were significantly different among the groups: phantom limb pain patients showed larger EMG reactions on the stump than on the contralateral side, whereas pain-free amputees showed the opposite effect. The data suggest an enhanced central and peripheral processing of visual stimuli in phantom limb pain patients.

574 Intellectual peculiarities of boys and girls with different laterality indices

Objective: Visual evoked potentials (VEP) have been used to estimate interhemispheric transfer time (IHTT). However, the complex wave of VEP is most probably formed by different generators of neural populations that act through different frequency channels. If the main peaks of VEP are established by different types of generators, which can also be connected to each other by a different type of callosal fibres, we would be able to estimate a wide range of various IHTT by measuring the latency between time-locked peaks of narrow band-pass filtered VEP. This research aimed to test this hypothesis.Mmethods: Nine right-handed men were presented with a reversal of a checkerboard pattern as stimuli at RVF or LVF, and EEG was recorded at O1, O2, P3, P4. The grand-averaged VEPs were transformed to the frequency domain by means of the fast Fourier transform to obtain the amplitude frequency characteristics. Band-pass filters were chosen adequately, according to tuning frequencies indicated by clear peaks in the amplitude frequency characteristics. The chosen band pass filters (4–8 Hz, 8–15 Hz, 15–20 Hz, 20–32 Hz) were applied to the VEP of the subjects, and 4 different components of VEPs for each VEP were obtained. The latency of P100 and N160 of unfiltered VEP was measured. In the band-pass digital filter applied VEPs, positive and negative peaks, which are consistent with P100 and N160, were measured for each subject. Latency differences between hemispheres for digitally unfiltered and filtered VEPs were computed to estimate IHTT.Results: In the different frequency bands, different IHTTs were estimated, ranging from 3 ms to 30 ms. Approximately 16 ms for theta band, 11 ms for alpha band, 6 ms for 15–20 Hz and 3 ms for 20–32 Hz bands were found.Conclusions: Our findings support the hypothesis which states that unfiltered VEPs provide us with only a rough estimation of IHTT. Also, they are consistent with anatomical findings that describe callosal fibres of varying dimensions, predicting various velocities between hemispheres.

Effects of Prenatal Substance Exposure: Altered Maturation of Visual Evoked Potentials

We investigated the effects of prenatal substance use on visual evoked potentials (VEPs). Seventy-four children were tested at birth and 1 month of age with binocular flash VEPs and at 4, 8, and 18 months of age with binocular pattern VEPs. Regressions were run by trimester to assess the independent effects of substance exposure. Variables included in the regression model were alcohol, marijuana, tobacco, other drug use for each trimester, maternal age, education, income, race, marital status, infant sex, birthweight, and Dubowitz score. Changes in specific components of the binocular VEP were both substance- and trimester-specific. First trimester alcohol use was associated with prolonged P 1 wave latencies at 1 month of age. Prolonged P 1 wave latencies at birth and 18 months were associated with tobacco use during each of the three trimesters, at 1 and 18 months with third trimester marijuana use, and at 1 and 18 months with first trimester other illicit drug use. Although these women were moderate substance users during pregnancy, their offspring exhibited maturational changes in components of the VEP in the absence of neonatal behavioral disturbances.

Symmetry detection and orientation perception: Electrocortical responses to stimuli with real and implicit axes of orientation

The present study was designed to investigate the electrocortical correlates of visual anisotropy with particular reference to the anisotropics reported for symmetrical patterns. On the basis of earlier studies of visual evoked potentials (VEPs) to lines of differing orientation, it was predicted that VEP parameters would differ according to the orientation of the axis of symmetry of a stimulus pattern. It was further predicted that a direct comparison of explicit orientation (by line presentation) and implicit orientation (via patterns symmetrical about axes differing in orientation) would yield data consistent with the notion that symmetry detection is a special case of orientation detection. The present findings indicated that for components of VEP waveforms up to 500 ms from stimulus onset, amplitude was generally greater for patterns with a vertical axis of symmetry than for patterns with a horizontal axis of symmetry, while patterns with positive and negative oblique axes evoked VEPs with the lowest amplitude components. In addition, it was found that the early VEP components exhibited latency differences for different axes of symmetry, with shortest latencies occurring for figures with vertical symmetry. The data are discussed, within the context of theories that suggest symmetry detection is an acquired process dependent on the development of cell populations responsible for particular stimulus orientations.

Fast visual evoked potential input into human area V5.

Studies of the human visual cortex have demonstrated that an area for motion processing (V5) is located in the lateral occipito-temporal cortex. To study the timing of arrival of signals in V5 we recorded multi-channel visual evoked potentials (VEPs) to checkerboard stimuli. We then applied dipole source analysis which was computed on a grand average of 10 subjects, and on five individual subjects, respectively. We demonstrate an early VEP component with onset before 30 ms and with a peak around 45 ms, located in the vicinity of V5. This early component was independent of a second activity, which started around 50 ms and peaked around 70 ms, and was located within the striate cortex (V1). These results provide further evidence for a very fast input to V5 before activation of V1.

Contrast dependency of motion-onset and pattern-reversal VEPs: Interaction of stimulus type, recording site and response component

We compared the contrast dependency (from 0.4 to 98%) of the visual evoked potential (VEP) to motion onset and to pattern reversal at an occipital and lateral recording site using sinewave grating stimuli of 0.9 c/deg, drifting at 4.9 deg/sec. Two differing VEP components were identified: a positive component, peaking at around 130 msec, dominating the occipital derivation, enhanced in pattern-reversal stimulation, exhibiting a high-threshold, late-saturating contrast response characteristic with a half-amplitude contrast above 7%; and a negative component at around 180 msec, dominating the lateral derivation, enhanced in motion-onset stimulation, exhibiting a low-threshold, saturating contrast characteristic with a half-amplitude contrast below 4%. The results suggest: (1) The negative component (N180) represents motion mechanisms, located more laterally, while the positive component (P100–P130) represents form-processing mechanisms, located near the V1/V2 areas. (2) A pattern-reversal stimulus triggers both form-processing and motion mechanisms that can be discriminated by latency. In an occipital derivation, the clinical reversal VEP P100 will be little contaminated by motion responses.

Visual evoked potentials, heart rate responses and memory to emotional pictorial stimuli

Although the effects of emotional stimuli on event-related cortical potentials, heart rate, and memory have been extensively studied, the association of these variables in a single study has been neglected. The influence of pleasant, unpleasant, and neutral photographic slides on visual evoked potentials (VEPs), heart rate responses, and free recall, was investigated in 20 normal subjects. VEPs were recorded from Cz and Pz locations, and analyses were performed on both amplitudes and latencies of identifiable endogenous peaks (P2, N2 and P3), and mean amplitude in the 100–200-ms, 400–600-ms, and 600–900-ms latency ranges. An emotional effect was present on VEPs starting from about 282 ms on, as revealed by the N2, P3, and late components. Both pleasant and unpleasant slides yielded larger cortical positivity as compared to neutral ones. Peak latencies did not show any emotional effect. Heart rate data showed a deceleratory response that was larger to unpleasant slides. Free recall of the projected slides showed a better performance for emotional slides compared to neutral ones. VEPs and memory data showed the same pattern: both pleasant and unpleasant slides induced larger positivity in the event-related potentials and were better remembered than neutral slides. Positive correlations were found between the late negative VEPs component (600–900 ms), recorded from Cz, and heart rate deceleration ( r=0.62), and between P3 (at Pz location) and the number of remembered slides ( r=0.53). © 1997 Elsevier Science B.V.

Binocular interaction in normal vision studied by pattern-reversal visual evoked potential (PR-VEPS).

Monocular and binocular visual evoked potentials (VEPs) in response to different check size (15-21-38-84 minutes or arc) were studied in 14 subjects with normal visual acuity and stereopsis. The binocular VEP amplitude is slightly higher than the VEP amplitude on stimulation of the "better eye" and significantly higher than the VEP amplitude on stimulation of the "worse eye"; this effect is observed using small checks and almost exclusively involved N75-P100. Both the N75 and P100 peaks occur earlier after binocular than monocular stimulation. The shortening of the N75 mean latency is significantly greater than that of the P100 mean latency when larger check sizes are used. The mean latency of the N145 potential is not significantly different in monocular and binocular stimulus conditions. The slight summation effect and latency shortening in the binocular VEPs are not consistent with the hypothesis that it is the sum of separate monocular signals originating from the visual cortex that gives rise to the response. The early components of both monocular and binocular VEPs are thought to be of post-synaptic origin (outside layer 4c of area 17), where the inputs become mixed so that most cells receive information from both eyes. The amplitude enhancement of binocular VEPs, which mainly occurs when using small checks, may be related to the increase in the total amount of cortical activity representing the macular region; this may account for binocular superiority in fine spatial resolution. The latency shortening in binocular conditions can be explained by considering that the critical determinant of the latency is the fundamental spatial frequency of the pattern. When coarse patterns are used, their effectiveness in parafoveal stimulation may affect the VEPs, with a significant contribution coming from the more peripheral retina. The enlargement of the visual field when the eyes see simultaneously may therefore further reduce the latency of the response when using the larger checks suitable for eccentric stimulation.

Multi-modal visual evoked potentials in a case of POEMS syndrome

Electrophysiological studies of visual evoked potentials (VEPs) in a case of POEMS (polyneuropathy, organomegaly, endocrinopa-thy, M-protein, and skin changes) syndrome were performed. The subject, a 58-year-old male, had bilateral optic disc swelling. Arden's score showed sensitivity losses at high spatial frequencies. In the short and middle latency VEPs elicited by flash and pattern reversal stimulation, the peak latencies of the major components of the short latency VEPs were within normal range, but those of the middle latency VEPs were delayed. Based on these results, the visual conduction process was normal in this case, but there might be some abnormalities in the cortical processing of the visual integration mechanism.

Evidence for a change in neural processing in phantom limb pain patients

The present study was designed to investigate differences in neural processing of pain-related semantic information in amputees with and without chronic phantom limb pain and healthy controls. One-hundred-and-twenty words (40 neutral, 40 body-related, 40 pain-related) were presented in pseudorandom order to probe group differences in the perception of pain-related information. Visual evoked potentials (VEP) to the words were recorded from 11 scalp locations, EMG was measured at the stump and the contralateral side and bilaterally from the M. corrugator. In addition, heart rate and skin conductance responses were obtained. Both early and late VEP components were altered. Pain-free amputees showed a reduced N100 amplitude compared to phantom limb pain patients and healthy controls whereas the phantom limb pain patients displayed a significantly enhanced late positivity (500–800 msec after word onset). VEP components were unaffected by word type. The peripheral EMG responses were significantly different among the groups: phantom limb pain patients showed larger EMG reactions on the stump than on the contralateral side, whereas pain-free amputees showed the opposite effect. The data suggest an enhanced central and peripheral processing of visual stimuli in phantom limb pain patients.

Potentiation instead of habituation characterizes visual evoked potentials in migraine patients between attacks

We have studied habituation of the pattern-reversal visual evoked potential (VEP) in healthy volunteers (n = 16) and in patients suffering from migraine without (n = 27) or with aura (n = 9). Five blocks of 50 responses at a stimulation rate of 3.1 Hz were sequentially averaged and analyzed separately for latencies, peak-to-peak amplitudes of N1-P1 and P1-N2, and the area under the N2 component Latencies of N1, P1, or N2 components were not significantly different between the sequential trial blocks, or between groups. Mean amplitudes of N1-P1 and P1-N2 in the first and subsequent blocks of SO responses were not statistically different among groups. In healthy subjects, there was a decrement of N1-P1 and P1-N2 amplitudes and N2 area on successive averagings. This habituation was maximal in the third and fourth blocks, but tended to disappear in the fifth block. In marked contrast to healthy subjects, migraine patients were characterized by a transient amplitude increment (i.e. potentiation) of VEP components which reached its maximum in the second to fourth blocks. Amplitude changes in sequential blocks were not dependent on attention and differed significantly between healthy subjects and migraineurs, but not between migraine with and without aura. Taken together with previous studies showing deficient habituation of contingent negative variation in migraine, these results indicate a dysfunction of central information processing which might have behavioral and pathogenic correlates.

Identification of early visual evoked potential generators by retinotopic and topographic analyses

AbstractThis study investigated the cortical sources of the early (50‐250 ms) components of the pattern‐onset visual evoked potential (VEP). VEPs were recorded in response to a small circular checkerboard stimulus that was flashed over a range of visual field positions. Temporally and spatially overlapping VEP components were distinguished by differences in retinotopic sensitivity and scalp topography, and by inverse dipole modeling. The C1 component (50‐80 ms) was found to change its polarity and topography systematically as a function of stimulus position in a manner consistent with the retinotopic organization of the striate cortex. The P1 component (comprised of the P75 and P100 subcomponents) had a time course that overlapped the C1 but could be distinguished from the C1 by its differing topography and reduced sensitivity to stimulus position. The P1 generators were localized to the lateral extrastriate cortex. Inverse dipole models were consistent with these striate and extrastriate source locations for the C1 and P1, respectively. The N1 component (120‐180 ms) was found to originate from several spatially distinct generators that differed in their retinotopic organization. © 1995 Wiley‐Liss, Inc.

Prolonged latencies of pattern reversal visual evoked early potentials in Alzheimer disease.

We studied patients with Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis (ALS) with a pattern reversal (checkerboard light diode) visual evoked potential (VEP) paradigm to observe the involvement of the visual system in these primary neurodegenerative diseases. All patients were in the mild or moderate stage of the disease. In Alzheimer disease there was a significant increase of the latency of the P55, N65, P100, and N130 components, as well as an increase of the P55-P100 interpeak latency, compared with matched normals. These alterations indicate dysfunction of both the retinocalcarine pathway and the cortex. Patients with Parkinson disease revealed a significant delay of the N130 component only. Patients with ALS had normal latency values of all VEP components. The P100-N130 amplitude was diminished in all these disease groups compared with age-matched controls.

Delayed late component of visual global field power in probable Alzheimer's disease.

A substantial literature shows that late components of visual evoked potentials (VEPs) are delayed in at least some forms of dementia in the elderly. The late-component delay is selective in that earlier components are not affected. More recent work with better defined clinical groups suggests that the selective late-component delay may be characteristic of Alzheimer's disease (AD) rather than an inevitable feature of dementia in general. To overcome problems in traditional VEP component latency measurement the present study uses reference-free Global Field Power (GFP) analysis to more objectively define VEP components and finds that the GFP peak corresponding to the late P2 component of the flash VEP is delayed in a probable AD group but not in a demented unlikely AD group, relative to age-equivalent healthy controls. The late-component delay is again found to be selective in that the GFP peak corresponding to the earlier P1 component of the flash VEP does not differ between groups. These findings further strengthen the evidence for electrocortical changes in the visual system of AD patients.