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PubMed1994

Differences in the pattern visual evoked potential between pregnant and non-pregnant women.

It has been proposed that latencies of some components of the pattern-reversal visual evoked potential (PRVEP) are shorter in women than in men because of differences in levels of circulating sex steroids. Pregnancy is a time when serum levels of oestrogen and progestogen are considerably greater than in the non-pregnant state. Whole and half field PRVEP latencies and amplitudes have been compared in 16 pregnant and 38 healthy non-pregnant women. The mean P100 latencies for all responses were shorter in the pregnant women, with statistically significant differences for the left eye whole field latency (P < 0.05) and the left eye right and left half field latencies (P < 0.005 and P < 0.05, respectively) and the right eye right half field latency (P < 0.05). The latencies in women in the pregnant group showed a negative correlation with gestation, which reached statistical significance for the REWF (r = -0.55, P < 0.05). These observed differences in PRVEP latencies in pregnant and non-pregnant women and the association between latency and gestation are likely to be due to differences in circulating sex steroids, and this effect may be the principal reason for latency differences between the sexes.

Adolescent↗
PubMed1988

Separate brain potential characteristics in children with reading disability and attention deficit disorder: relevance-independent effects.

The effects of reading disability (RD) and attention deficit disorder (ADD) on event-related potentials (ERPs) were investigated in 52 boys between 8 and 12 years of age. There were four groups: 25 children without RD divided into two groups (17 without ADD and 8 with ADD) and 27 children with RD divided into two groups (11 without ADD and 16 with ADD). The children participated in three tasks ("games") designed to assess selective attention to the color black (vs white), to any of two letters (vs. two patterns), and to any of 12 letters (vs. 12 patterns). ERPs were recorded over the left and right occipital, central, and frontal hemispheres. Children with RD as compared to those without RD were characterized by the following ERPs: (1) a smaller amplitude positive wave at about 240 msec (P240) over the left central hemisphere: (2) a smaller amplitude positive wave at about 500 msec (P500) over the right central hemisphere: (3) a larger P500 over the right central hemisphere: (3) a larger P500 over both left and right occipital hemispheres: and (4) smaller within-subject-and-condition variability of ERP waveform. These effects did not differ significantly for the three games and, therefore, were not specific to letter processing per se. The effects of RD did not interact with the effects of ADD for the most part. The ERPs clearly indicated these two disorders, in part, involve different underlying brain processes.

Arousal↗
PubMedDate not supplied

Rat and human visual-evoked potentials recorded under comparable conditions: a preliminary analysis to address the issue of predicting human neurotoxic effects from rat data.

Pattern-onset visual-evoked potentials (VEPs) were recorded from rats and humans in order to perform cross-species comparison of neuronal functional properties reflected by the early VEP components. The spatial frequency of a sinusoidal test grating was varied in Experiment 1. For both species, amplitude of the first positive VEP component was larger at low spatial frequency and decreased as spatial frequency increased. The immediately succeeding negative component was small at low spatial frequency and was of maximal amplitude at moderate spatial frequency. The effects of stationary pattern adaptation on these components were investigated in Experiment 2. Subjects viewed either a blank field or the test grating prior to recording VEPs. For both species, adaptation had no effect on the positive component but strongly attenuated the negative component. Experiment 3, in which only humans were tested, indicated that the negative component was of cortical origin. Only cortical neurons are known to be orientation selective, and the effect of adaptation diminished as the orientation difference between the adaptation and test gratings increased. These results suggest that the early positive and negative components arise from parallel visual pathways, and that the rat components may reflect visual processes qualitatively similar to those of humans.

Adaptation, Physiological↗
PubMed1988

Asymmetries in ON and OFF visual pathways of humans revealed using contrast-evoked cortical potentials.

Positive- and negative-contrast stimuli yield the perceptions of brightness and darkness, respectively, and are processed separately by ON and OFF neural pathways. The properties of these morphologically and pharmacologically distinct subsystems were measured in humans by recording visual evoked potentials (VEPs). These electrical responses from the visual cortex were elicited by novel positive- and negative-contrast stimuli, designed to emphasize, selectively, contributions from ON and OFF pathways. Results revealed differential processing of the two types of contrast information, suggesting asymmetries in ON and OFF subsystems; OFF subsystems have finer spatial tuning and greater contrast gain than ON subsystems. These VEPs may be useful in diagnosing neurological disorders that involve primarily one subsystem.

Adult↗
PubMed1992

Electroretinograms (ERGs) and visual-evoked potentials (VEPs) elicited by pattern displacement.

The relation between the amplitude of visual responses to a checkerboard stimulus and the degree of lateral displacement of the checks was examined across different check sizes with simultaneously recorded electroretinograms (ERGs) and visual-evoked potentials (VEPs). The amplitudes of both the b-wave and the after-potential of the ERG increase linearly with pattern displacement. However, the major components of the VEP (N70 and P100) were smaller than expected from linearity for both small checks with small displacements (thresholding) and for large checks with large displacements (saturation). These results suggest that the ERG is proportional to the number of receptors stimulated, but the VEP reflects neural processes influenced by the spatial structure of the stimulus.

Adult↗
PubMed1993

Episodic multiregional cortical coherence at multiple frequencies during visual task performance.

The way in which the brain integrates fragmentary neural events at multiple locations to produce unified perceptual experience and behaviour is called the binding problem. Binding has been proposed to involve correlated activity at different cortical sites during perceptuomotor behaviour, particularly by synchronization of narrow-band oscillations in the gamma-frequency range (30-80 Hz). In the rabbit olfactory system, inhalation induces increased gamma-correlation between sites in olfactory bulb and cortex. In the cat visual system, coherent visual stimuli increase gamma-correlation between sites in both the same and different visual cortical areas. In monkeys, some groups have found that gamma-oscillations transiently synchronize within striate cortex, superior temporal sulcus and somatosensorimotor cortex. Others have reported that visual stimuli produce increased broad-band power, but not gamma-oscillations, in several visual cortical areas. But the absence of narrow-band oscillations in itself does not disprove interregional synchronization, which may be a broad-band phenomenon. We now describe episodes of increased broad-band coherence among local field potentials from sensory, motor and higher-order cortical sites of macaque monkeys performing a visual discrimination task. Widely distributed sites become coherent without involving other intervening sites. Spatially selective multiregional cortical binding, in the form of broad-band synchronization, may thus play a role in primate perceptuomotor behaviour.

Animals↗
PubMed1992

Cortical potentials evoked by short wavelength patterned light.

Pattern-evoked cortical potentials (PECPs) were recorded in response to the onset of blue and black, square wave gratings superimposed on a bright orange background. Several lines of evidence, including spectral sensitivity and the absence of response in a tritanopic subject, indicate that the measured cortical potentials reflect input from S cones. Spatial and temporal tuning of this response are comparable to psychophysical measures of the S-pathway. In agreement with previous studies of achromatic and chromatic spatial processing, a comparison of the response to patterns of different complexity indicates that spatial processing in the S-pathway can be described by linear systems analysis. An oblique effect for the S-pathway is demonstrated. Additional findings which bear on the nature of postreceptoral processing in the S-pathway are considered. Included are measurements from a patient with diabetic retinopathy. This study underscores the potential importance of the S-pathway for spatial information processing.

Adult↗
PubMed1990

Multiple sources of P3b associated with different types of information.

This experiment investigated how the P3a, P3b, and Slow Wave components of the event-related brain potential (ERP) respond to manipulations of the nature, timing, and extent of information delivery. There were two experiments in which the total amount of task information was distributed between pairs of successive stimuli (S1 and S2) within each trail. The task was to predict the relation between S1 and S2. In Experiment 1, the S1 could resolve no, partial, or all uncertainty with respect to the prediction outcome (correct or incorrect). Each S1 delivered three types of information: 1) outcome information--which resolved the subjects' uncertainty about the correctness of their prediction; 2) procedural information--which resolved uncertainty about how much outcome information would be delivered by S1; and 3) memory information--the identity of S1, which had to be stored for subsequent comparison with S2. In Experiment 2, the activity of these components was contrasted in two conditions in which the S1 delivered either memory information alone or both memory and procedural information. P3a and Slow Wave were sensitive only to outcome information. P3b was sensitive to all three types of information, and its scalp topography varied as a function of the type of information. The topographic variations indicate that P3b is not a unitary phenomenon but rather is a composite of activity arising from multiple intracranial sources of bioelectric activity.

Adult↗
PubMed1992

Visual evoked electrical and magnetic response to half-field stimulation using pattern reversal stimulation.

The visual evoked magnetic response to half-field stimulation using pattern reversal was studied using a d.c. SQUID coupled to a second order gradiometer. The main component of the magnetic response consisted of a positive wave at around 100 ms (P100M). At the time this component was present the response to half-field stimulation consisted of an outgoing magnetic field contralateral and extending to the midline. When the left half field was stimulated the outgoing field was over the posterior right visual cortex and when the right half field was stimulated it was over the left anterior visual cortex. These findings would correctly identify a source located in the contralateral visual cortex. The orientation of the dipoles was not that previously assumed to explain the paradoxical lateralization of the visual evoked potential. The results are discussed in terms of both electrical and magnetic models of the calcarine fissure.

Adult↗
PubMed1992

Colour, contrast and the visual evoked potential.

Visual evoked potentials exhibit interesting morphological changes when they are elicited by checkerboards of different spatial and chromatic contrast, counterphasing in the foveal and lower macula field. The characteristic, positive wave of the phase-reversal visual evoked potential, for example, is preceded by an increasingly prominent negative peak as luminance contrast progressively increases above 10% and, at isoluminance, the response to red and green checkerboards becomes a predominantly monophasic negative wave. To study the nature of the morphological change we synthesized these waveforms with a computer simulation consisting of Gaussian components. The amplitudes of positive and negative components were altered until the synthesized response was closely similar to the recorded data. These Gaussian components have response characteristics which are identified with those of magnocellular and parvocellular neurones.

Color Perception↗
PubMed1983

Effects of exposure to lines of one or two orientations on different cell types in striate cortex of cat.

We raised cats using goggles to control early visual exposure (stripe-rearing). Four conditions were used: (a), both eyes exposed to 0 degrees lines, (b), both eyes exposed to 90 degree lines, (c), one eye exposed to 45 degree lines, the other to 135 degree lines, (d), one eye exposed to 0 degree lines, the other to 90 degree lines. At the completion of the rearing, we recorded extracellularly from single cells in striate cortex (area 17) of these animals; circular statistics were used to analyse the distribution of the orientation preferences of neurones recorded. Exposure to either one or two stimulus orientations produced a significant bias in the distribution of the orientation preferences of cells recorded. We found no more non-selective cells in cats exposed to one orientation (15%) than in cats exposed to two orientations (14%). We found about the same mean proportion of binocular cells in cats exposed to one orientation (27%) as in cats exposed to two orientations (24%). Cells were comparable in orientation selectivity in cats exposed to one orientation (mean half-width at half-height = 37 degrees) and in cats exposed to two orientations (mean half-width at half-height = 34 degrees). The effects of the rearing depended upon the receptive field properties of the cells. For cells with narrow receptive fields and low cut-off velocities, the rearing produced no bias in the distribution of the orientation preferences; for all other groups of cells the rearing produced a bias toward the exposed orientation. In addition, the cells with narrow receptive fields and low cut-off velocities were more finely tuned for orientation than the remaining cells. We conclude that there are cell types in the striate cortex of the cat which differ in their susceptibility to the effects of stripe-rearing; these cell types can be discriminated on the basis of their physiological characteristics. We can compare these cell types with morphologically identified cell types that also differ in their susceptibility to the effects of stripe-rearing.

Animals↗
PubMed1985

The luminance origin of the pattern electroretinogram in man.

Electroretinograms (e.r.g.s) and visually evoked potentials (v.e.p.s) to pattern stimuli were recorded simultaneously from healthy subjects. The stimuli were produced by a configuration in which the luminance of two sets of spatial elements (checks) could be modulated independently. Experiments were designed to distinguish between contrast responses and non-linear luminance responses. In the first of two basic experiments, the luminance of only one set of checks was modulated, at a constant level in every trial. The other set was not modulated, but its luminance was set at various levels. Under these conditions the local luminance stimulation was kept equal for every trial whereas the contrast stimulation varied. Therefore, local luminance responses in these experiments were expected to be constant and contrast responses were expected to vary. The e.r.g.s were identical for all luminance settings of the unmodulated checks, suggesting that luminance rather than contrast determines the response. The v.e.p.s showed, on the contrary, the behaviour expected for contrast responses. In the second basic experiment the local luminance stimulation was also kept constant, but the phase difference between the modulations of the two sets of checks was varied between 0 deg (pure luminance stimulation) and 180 deg (pattern reversal). In this type of experiment the second harmonic responses to local luminance modulation are expected to decrease to a minimum as phase difference goes from 0 to 90 deg and increase again as phase difference goes to 180 deg. Contrast responses are expected to increase monotonically from zero to maximal at phase difference shifts from 0 deg (no contrast stimulation) to 180 deg (contrast reversal). The e.r.g.s decreased to a minimum at 90 deg phase difference and increase again with phase difference going to 180 deg. At 0 and 180 deg the same value was recorded. Consequently, the e.r.g. behaviour suggests a luminance origin of the responses. The v.e.p.s monotonically increased as phase difference went from 0 to 180 deg, thus suggesting a contrast origin of the responses. Two additional control experiments were performed. The first experiment compared the responses to homogeneous field red/green exchange and pattern red/green exchange, with the luminances of the red and green sources matched by heterochromatic flicker photometry. The exchange of luminance-matched red and green checks (pattern reversal) did not produce different e.r.g. responses from those recorded in response to homogeneous field red/green exchange. The v.e.p. showed a significant increase for the pattern stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Color Perception↗
PubMedDate not supplied

VEP acuity, FPL acuity, and visual behavior of visually impaired children.

Forced-choice preferential-looking (FPL) and pattern-visual-evoked potential (VEP) acuity tests were conducted with 42 children with bilateral moderate to severe visual impairment (age, 4 months to 9 years). Within this group of children, FPL acuity testing was more successful than VEP acuity testing (98% versus 64%). Mean FPL acuity was better than mean VEP acuity (20/155 vs 20/290, P less than .002). For the children who completed both FPL and VEP acuity tests, an acuity difference score (FPL minus VEP) was derived, and compared to difference scores based on normative data. Significant differences were found between visually impaired (VI) and control difference scores (P less than .001). Difference scores of VI were larger than and opposite in sign to the control scores. Rating scores of visual behaviors supported the concurrent validity of the FPL acuities (P = .01), but not the VEP acuities.

Child↗
PubMed1987

Visual acuity prediction using the visual evoked response.

A technique is described for predicting visual acuity in adult humans by using the visually evoked response (VER). This involves using a pattern-reversal checkerboard with a small check size (5.5. min arc) as the stimulus, and measuring the peak-to-trough amplitude of the VER wave arising from it. The technique is therefore both rapid and convenient. The pattern-reversal rate was varied in order to assess the influence of the temporal modulation on the VER waves. The results suggest that a rapid pattern reversal rate produces a VER which displays a reduced association with spatial processing.

Adult↗