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At least 19 recordsLinked to original sources
PubMedDate not supplied

Brainstem auditory evoked potential, visual evoked potential and nerve conduction velocity and their relation with HbA1c and beta 2 microglobulin in children with insulin dependent diabetes mellitus.

Brain stem auditory evoked response (BAER), visual evoked response (VER) and nerve conduction velocities (NCV) were studied in 18 insulin-dependent diabetic children between the ages of 3.5 and 16 years (mean 9.0 +/- 3.2 years). The results were compared with those of age-matched controls. The VER latencies of the diabetic children in the right eye and left eye were significantly prolonged when compared with the control group. NCV of n. peroneus and the latency of sensorial n. medianus were significantly impaired when compared with the control group. Although the latencies of waves III, IV and V of the right ear and the interpeak latencies of I-III, I-V, III-V of both ears were prolonged, the comparison with the control group was not significant. The beta 2 microglobulin levels of the diabetic patients were significantly higher than those of the control group. There was a positive correlation between the beta 2 microglobulin and the BAER interpeak latencies of wave III-V in both ears (r: 0.51 p < 0.01). There was also a positive correlation between NCVs of n. peroneus and n. medianus (motor and sensorial) with beta 2 microglobulin (r: 0.52 p < 0.01) and between VER latencies (r: 0.52 p < 0.01) of both eyes separately. In our study the prolonged latencies of VER and BAER were detected in the absence of clinical abnormalities in visual and hearing systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Electrocortical signs of word categorization in saccade-related brain potentials and visual evoked potentials.

Visual evoked potentials (VEPs) elicited by foveal presentation of words were compared to brain potentials evoked by the same words in a condition where subjects had to make a saccadic eye movement in order to perceive the words (saccade-related brain potentials, SRPs). Subjects had to categorize the words responding with a button press to stimuli belonging to the target (infrequent, P = 0.2) category. The VEP and SRP waveforms showed divergences in the early (up to 250 ms) components, but a marked similarity between the late components. Principal Component Analysis also revealed the same relationship between the two types of brain responses. Peak latency of the late SRP components measured from saccade offset showed an apparent processing advantage over the corresponding late components of VEPs. The N3 component, indexing semantic processing of visual patterns, peaked between 310 and 375 ms in the SRPs, while in the VEPs it appeared between 410 and 470 ms. The P4 component, associated with final stimulus evaluation, showed a similar latency benefit in favour of SRPs (420-500 ms vs 530-590 ms in VEPs). The mean reaction time was 74 ms shorter in the eye movement condition (measured from saccade offset) than in the VEP condition (703 vs 777 ms). The question of what kind of processes may contribute to the differences in mean RTs and to the latencies of the late components between the two conditions are discussed. We suggest that the late components (P3, N3 and P4) of the VEP and the SRP, respectively, index identical brain processes.

Adult↗
PubMed1994

Effect of dopamine and acetylcholine on the visual evoked potential.

Visual evoked potentials were measured on patients with Parkinson's disease and Alzheimer's disease and normal controls to assess the function of dopamine and acetylcholine in the visual system. Dopamine is a neurotransmitter known to be present in the retina of primates and is found to be severely depleted in the substantia nigra of patients with Parkinson's disease. Acetylcholine is also known to be present in the retina, visual cortex, and superior colliculus and is found to be grossly reduced in patients with Alzheimer's disease. Stimuli were designed to preferentially activate functionally separate pathways in the visual system described as magnocellular and parvocellular. The four stimuli were a diffuse flash; an achromatic, 73' check counterphasing at 6 Hz at a contrast of 30%; an achromatic 10' check counterphasing at 2 Hz at a contrast of 85%; and an isoluminant red/green grating of 4 cpd presented using an on and off cosine ramp of 200 ms. The results indicate that an acetylcholine deficit produces a delay to the flash P2 component of the visual evoked potential. No change was detected when other stimuli were used.

Acetylcholine↗
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↗
PubMed1989

Age-related changes in the first order Weiner kernel visual evoked potential.

Visual evoked potentials were obtained from 112 subjects (215 eyes) aged 5 to 79 years with fast random stimuli. The stimulus (the presence or absence of the initiation of a reversal) and response (voltage measurements) were used in calculating the first order Wiener kernels to obtain the visual evoked potentials. Five check sizes were used to stimulate each eye. The implicit time of the major negative wave showed a significant increase with age for each check size used. Regression lines for the implicit time vs age data for male subjects were significantly different from those of females. The y-intercepts were lower and the slope of the regression lines were consistently steeper for males. Thus the rate of increase in implicit time was higher in males. The relationship of the amplitude of the major wave to age did not appear to be linear. The data suggested that a second-order polynomial curve might be an appropriate representation of the relationship.

Adolescent↗
PubMed1997

Neurophysiologic correlates of implicit face memory in intracranial visual evoked potentials.

Visual evoked potentials were recorded in the amygdala, hippocampus, mid- and inferotemporal cortex, orbitofrontal cortex, and lateral frontal cortex of seven epileptic patients while they were engaged in a difficult task requiring the discrimination between repeated and nonrepeated faces. The explicit recognition of previously seen faces was at chance levels, as measured by the accuracy of push-button responses. Nevertheless, all subjects showed clear-cut differential evoked responses to repeated versus nonrepeated faces, indicating implicit encoding of the distinction between the two types of stimuli. Differential responses were more frequent in neocortical recording sites (especially in the mid- and inferotemporal leads) than in limbic recording sites such as the amygdala and hippocampus. The authors conclude that implicit encoding processes are modulated by neocortical visual association areas of the temporal lobes.

Adult↗
PubMed1987

Different scalp localization of pattern onset and reversal visual evoked potentials.

Visual evoked potentials were recorded monopolarly from seven electrodes on a horizontal line from T3 to T4 and bipolarly in one channel from left of the midline to right of the midline. Stimulation of the right and left half-fields was performed with a checkerboard generator of 10 degrees x 13.5 degrees and checks of various sizes at high contrast. The results may be summarized as follows: 1. Source-sink analysis for lateral half-field pattern onset with small checks shows C1, peaking about 80 msec, to have a source on the scalp contralateral to the half-field stimulated with a sink on the midline. 2. To half-field pattern reversal, bipolar recording across the scalp midline indicates an early phase reversal peaking about 80 msec followed by another phase reversal peaking at about P100 latency. Source-sink analysis indicates the first reversal has a contralateral source, while the second has a source on the scalp midline or ipsilateral to the field stimulated. 3. Pattern reversal results vary with check size, with a smaller check size increasing the amplitude of the first phase reversal and decreasing the amplitude of the second.

Evoked Potentials, Visual↗
PubMed1999

Early visual processing during binocular rivalry studied with visual evoked potentials.

Visual evoked potentials (VEPs) were recorded to probes presented to the dominant and suppressed eyes in a binocular rivalry paradigm. Probes presented to the suppressed eye interrupted the current dominance phase and produced a P300-like deflection (400-700 ms). Probes delivered to the dominant eye increased the duration of the current dominance phase. VEPs to these probes included an endogenous component that overlapped the early exogenous components. The early endogenous component (rivalry-related potential, RRP) started as early as 70 ms and had a broad centroparietooccipital distribution.

Adult↗
PubMed1986

The effect of grating contrast on the human visually evoked potential.

Visually evoked potentials (VEPs) were recorded from the human occiput at the appearance of sinusoidal gratings. Grating spatial frequency was 4 c/deg, at which both the early and late negative waves, N1 and N2 were present in VEP. Increasing grating contrast from a near-threshold value, 0.006, to the value of 0.3, the maximum in the linear range of the device, resulted in a peak-latency shortening and an amplitude increase of both N1 and N2. While the latencies changed in parallel, the amplitudes did not. The N1 amplitude increased almost linearly with log contrast in the whole range tested. The amplitude of N2 was large at the lowest contrast level, increased by a factor of about 2 and saturated at the contrast of 0.05. The results suggest a greater contrast sensitivity of the generator of N2 than of the generator of N1 and support the assumption that these generators belong to structures with different properties and functions.

Electroencephalography↗
PubMedDate not supplied

Spatial frequency response functions obtained from cat visual evoked potentials.

Visual evoked potentials (VEPs) were obtained from the surface of the cat visual cortex in response to contrast reversing sinusoidal gratings. Gratings of different spatial frequency were presented either separately, using signal averaging to increase the signal-to-noise ratio, or as a spatial frequency sweep, in which spatial frequency was sequentially increased every 5 sec during a 40 sec trial (3.99 Hz) or every 3 sec during a 24 sec trial (6.65 Hz). The second harmonic amplitude- and phase-spatial frequency functions derived from averaging or from sweep trials were similar, indicating that the swept stimulus method can be used to provide a rapid and reliable measure of the VEP-spatial frequency function. Intravenous administration of physostigmine, an acetylcholinesterase inhibitor, evoked a spatial frequency-dependent change in VEP amplitude. At 3.99 Hz, responses to low spatial frequencies were enhanced to a greater extent than were responses to high spatial frequency stimuli. At 6.65 Hz, responses to mid-range spatial frequencies were enhanced to a greater extent than were responses to low and high spatial frequency stimuli. VEP phase at both 3.99 and 6.65 Hz was advanced to a greater degree at the higher spatial frequencies. These results indicate that the swept spatial frequency method may be useful in studying spatial frequency-dependent pharmacological effects on the VEP and support the possibility that pharmacological disruption of the cholinergic visual system can produce such changes.

Analysis of Variance↗
PubMed2006

Studies of human visual pathophysiology with visual evoked potentials.

Visual evoked potentials (VEPs) offer reproducible and quantitative data on the function of the visual pathways and the visual cortex. Pattern reversal VEPs to full-field stimulation are best suited to evaluate anterior visual pathways while hemi-field stimulation is most effective in the assessment of post-chiasmal function. However, visual information is processed simultaneously via multiple parallel channels and each channel constitutes a set of sequential processes. We outline the major parallel pathways of the visual system from the retina to the primary visual cortex and higher visual areas via lateral geniculate nucleus that receive visual input. There is no best method of stimulus selection, rather visual stimuli and VEPs' recording should be tailored to answer specific clinical and/or research questions. Newly developed techniques that can assess the functions of extrastriate as well as striate cortices are discussed. Finally, an algorithm of sequential steps to evaluate the various levels of visual processing is proposed and its clinical use revisited.

Brain Diseases↗
PubMed2006

Visual function with acupuncture tested by visual evoked potential.

Visual evoked potential (VEP) testing is used frequently and is an important ophthalmologic physiological test to examine visual functions objectively. The VEP is a complicated waveform consisting of negative waveform named N75 and N135, and positive waveform named P100. Delayed P100 latency and greatly attenuated amplitude on VEP are known characteristics for diagnosing optic nerve disease. Acupuncture has been used to treat wide clinical symptoms with minimal side effects. The confirmation of the efficacy of acupuncture generally relies on subjective symptoms. There is not much scientific evidence supporting the acupuncture treatments for eye diseases up to today. However, the VEP test can evaluate objectively and numerically the efficacy of the treatment by the acupuncture. We analyzed 19 healthy subjects (38 eyes). The P100 latencies in the group of less than 101.7 msec (total average) before acupuncture stimulations were not different than those after treatment (98.2 +/- 3.0 msec, 98.2 +/- 4.0 msec, respectively, p = 0.88, n = 17), but the latencies in those subjects with longer or equal to 101.7 msec were statistically different after acupuncture (104.6 +/- 2.8 msec, 101.9 +/- 3.7 msec, respectively, p = 0.006, n = 21). These results show that the acupuncture stimulation contributes to the P100 latencies of pattern reversal (PR)-VEP to some subjects who have delayed latencies, and this electrophysiological method is a valuable technique in monitoring the effectiveness of acupuncture therapy in the improvements of visual functions. The purpose of this study is to evaluate the physiological effects by acupuncture stimulations using PR-VEP in normal subjects.

Acupuncture Therapy↗
PubMed1983

Cataract, pattern stimulation and visually evoked potentials.

Visually evoked potentials on pattern stimulation are lowered by cataracts via scatter, absorption and defocusing. These effects have to be known before pattern stimulation can be fruitfully applied in patients when a lowered vision cannot or can hardly be explained by the cataract. It was remarkable that pattern responses were relatively good as compared to visual acuity. With a pattern of 80' check size and 80% contrast all patients with a visual acuity of more than 0.1 had recognizable responses; this holds also true with 40' check size and 40% contrast in all patients with a visual acuity of more than 0.3. Reversely, with 10' check size and 10% contrast only half of the normal subjects had detectable responses.

Cataract↗
PubMedDate not supplied

[The evaluation of central visual fatigue in computer terminal users by visual evoked potentials].

Visual evoked potentials (VEPs) were recorded in a group of 20 operators aged 25-45 years during two sessions, before and after a 5-hour work at computer terminals, in order to assess visual system fatigue. The outcomes were referred to the norms established for the age-matched population of 30 subjects not exposed to professional contact with computers. Most of the examined operators suffered various complaints concerning not only the organ of vision but the central nervous system as well. VEPs were elicited by means of monocular stimulation using the reversal checkerboard pattern and recorded simultaneously from the scalp electrodes placed over the right and the left cerebral hemisphere. Only recording acquired after finishing of a working day demonstrated significant statistically abnormalities of the VEPs waveforms, which suggests their transient character. The changes mentioned above included prolongation of peaks P100 and N2 latency with concomitant attenuation of their amplitudes and a decrease of the correlation coefficient values for the recordings from the hemispheres. The preliminary findings presented in this paper seem to justify a conclusion that the non-invasive VEPs method can be considered as the objective indicator of the central visual fatigue induced by the workload at computer terminals.

Accommodation, Ocular↗
PubMedDate not supplied

White noise effects on pattern-reversal visual evoked potentials.

Visual evoked potentials (VEPs) were recorded in 9 subjects from occipital and temporal leads. The stimulus was a checkerboard phase-reversed at the frequency of 1 Hz, binocularly viewed by the subject. VEPs were recorded during white noise stimulation (9 different levels of intensity) and without noise stimulation. P100 latency was not affected by the white noise stimulation, whereas the N75-P100 amplitude turned out to be affected by the simultaneous auditory stimulation with different patterns in relation to the site of the recording. The results are discussed in terms of general activation aroused by the white noise on visual information processing.

Acoustic Stimulation↗
PubMed1990

The effects of visual field size on hemispheric asymmetry of pattern reversal visual evoked potentials.

Visual evoked potentials (VEPs) were recorded in 17 females (10 right-handers and 7 left-handers) and 17 males (10 right-handers and 7 left-handers). The stimulus was a checkerboard pattern phase-reversed at a rate of 1 Hz, binocularly viewed by the subject. Two experimental conditions were tested: field size (the stimulus was enlarged from 1 to 30 degrees of visual angle) and occlusion (the central part of the stimulus was occluded by experimental scotomata of various size--from 1 to 16 degrees). Responses recorded at occipital and temporal leads of the two hemispheres were compared. The P100-N145 amplitude was larger at occipital than at temporal leads, it augmented increasing the size of the stimulus and diminished occluding progressively larger portions of the central field. Hemispheric asymmetries emerged with large field sizes and were not abolished by the presence of experimental scotomata. The hemispheric asymmetry was related to handedness (left-handers had larger amplitudes in the right hemisphere, right-handers in the left hemisphere), but not to sex. Hemispheric asymmetries in VEPs latency were not present. In comparison to males, females showed larger amplitudes and shorter latencies. These results point out that hemispheric asymmetries are found also for the processing of elementary visual stimuli like checkerboards, and they depend both on stimulus parameters (field size) and subject variables (handedness).

Adult↗
PubMed1982

The effects of contrast and length of gratings on the visual evoked potential.

Visual evoked potentials (VEP's) were obtained to grating stimuli modulated in phase at 8 Hz. The amplitude of the VEP was linearly related to the length of a centrally-fixated grating up to a critical length value equivalent to 9-16 grating cycles, for a range of spatial frequencies; thereafter amplitude first decreased then increased with increasing length. VEP amplitude was proportional to log. contrast as well as to length, and the intercept of the regression line with the contrast axis coincided with the psychophysical threshold for gratings of different lengths. More sensitive measurements with low-contrast stimuli around threshold indicated that in this range VEP amplitude is linearly related to contrast, and there is no threshold nonlinearity. The effects of visual field location and adaptation on the VEP to gratings of different lengths and spatial frequencies were also studied. The relationship of these findings to psychophysical, single-cell and transient VEP data is discussed.

Adaptation, Ocular↗
PubMed1979

Contrast sensitivity of the human neonate measured by the visual evoked potential.

Visual evoked potentials (VEPs) were recorded from a total of 97 1- to 10-day-old infants, with phase-reversing sinusoidal grating stimuli. The grating contrast or spatial frequency for which 50% of infants gave a statistically significant VEP was taken as a measure of threshold. This procedure yielded an estimate of neonatal acuity of 0.85 cycles/degree and an optimal contrast threshold of 50%. VEPs from an older infant showed good agreement with behavioral measures of sensitivity on the same individual. Comparison of the neonatal VEP results with behavioral data from 5-week-old infants, suggests little change in visual performance over the first month of life.

Evoked Potentials↗