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PubMedDate not supplied

Topographical analysis of motion-triggered visual-evoked potentials in man.

PURPOSE: The middle temporal (MT) area of the cortex of the monkey is involved in visual motion analysis. Previous studies using brain-imaging techniques have shown that the area around the anterior occipital cortex in man is homologous to the area MT of the monkey. In this study, we investigated the cortical components of motion-triggered visual evoked potentials and their topography in the visual cortex of man. METHODS: Visual evoked potentials to the onset of a visual motion stimulus (m-VEPs) were recorded from 5 normal subjects aged 25 to 34 years. A random dot pattern was used as the stimulus for the m-VEPs. The dots moved horizontally to the right and then to the left alternately for 500 milliseconds with interstimulus intervals of 1500 milliseconds. The speed of motion was varied in five steps from 5-25 degrees/s. Fifteen electrodes were placed on the occiput around O(z) at 5-cm intervals. Color contour maps showing the distribution of voltage over the 15 electrodes at latencies ranging from 0-200 milliseconds with a 20-millisecond interval were made for each subject. These were coregistered with three-dimensional magnetic resonance images of the same brain to specify the topography of the main components of the m-VEPs in relation to the sulcal and gyral pattern of the visual cortex. RESULTS: We consistently observed a positive wave with a peak latency of about 100 milliseconds (P100) and a negative wave with a peak latency of about 150 milliseconds (N150) for all subjects. Topographical analysis showed that P100 was dominant in a relatively wide area caudal to O(z), whereas N150 was dominant in a relatively small area posterior to the right anterior occipital sulcus, which included the area corresponding to the area MT in man. CONCLUSIONS: These findings suggest that N150 represents the activity of the area MT in the human visual cortex related to motion perception.

Adult↗
PubMed1995

Effect of the cholinesterase-inhibiting substance galanthamine on evoked visual potentials in rats.

We studied the effect of intravenous injection of the cholinesterase inhibitor galanthamine (GAL) in doses from 0.025 to 5.0 mg/kg on electrically evoked field potentials in rat visual cortex. In all the experiments the amplitude of late components of evoked potentials was significantly reduced, while early components remained unaffected. These findings indicate that cortical cells are inhibited by acetylcholine (ACh). Furthermore, combined application of a muscarinic receptor blocker (atropine) and GAL reliably suppressed the effects of galanthamine. These observations suggest that ACh-induced inhibition may be mediated by activation of GABAergic interneurones that possess muscarinic receptors.

Animals↗
PubMed2005

Effects of exercise on visual evoked potentials.

The aim of this study was to investigate the effects of acute or habitual exercise on visual evoked potentials (VEP). The study group consisted of 9 female and 7 male volleyball players and the control group contained 9 female and 7 male students who were not involved in any sportive activity. The N75, P100, and N145 latency and amplitudes were measured before and after exercise. Intragroup comparison was made to evaluate the acute effects and intergroup comparison for the chronic effects of exercise. Significant differences were noted between athletes and the sedentary subjects in terms of pre-exercise left-N145 latencies and amplitudes and left -P100 amplitudes. Right-eye N145 latencies of inactive female subjects obtained before and after exercise were also statistically different. The results suggest that acute and habitual exercise affects the VEP responses independent from the body temperature and other physiological parameters. Small sized pre-exercise P100 amplitudes in the athletes can be attributed to the effect of rapid visual-activity-demanding sports on the central nervous system. Visual evoked potentials maybe used as neurophysiological criteria in defining the performance of an athlete.

Adult↗
PubMed1987

The use of the visual evoked potential (VEP) in delineating a state of subclinical encephalopathy. A comparison with the number connection test (NCT).

Visual evoked potential determinations and the number connection test were performed for 49 patients with stable chronic liver disease and portal hypertension but without clinical evidence of hepatic encephalopathy. The latencies of the evoked potential components N2, P2 and N3 were significantly prolonged compared to the controls. Seven patients had a prolonged N2, 10 had a prolonged P2, and 14 patients had a prolonged N3 latency. Only five of these patients had increased theta activity of the electroencephalogram. When age norms were applied, the number connection test was significantly prolonged only in the 16-36-years age group. It is concluded that the visual evoked potential identifies a group of patients with neurophysiological abnormalities and may be useful in identifying those at risk of developing overt encephalopathy.

Adult↗
PubMed1992

The neurophysiologic significance of frontal negativity in pattern-reversal visual-evoked potentials.

To demonstrate that the frontal negative potential (N100) does exist in response to pattern-reversal visual stimulation and its independence of the dipole source from the major occipital positive potential (P100), modifications of P100 and N100 with changes in the check size, contrast, and luminance of the stimulus pattern were studied in healthy subjects. Eight different check sizes (10-90 min of arc), eight different contrast levels (10-85%), and six different luminance levels (11-180 cd/m2) were used. Changing the stimulus conditions modified the latencies and amplitudes of P100 and N100 in different ways. P100 latency had a band pass spatial tuning function against check size; N100 latency did not. P100 was sensitive to changes in contrast and luminance; N100 was less dependent on these parameters. These findings suggest the existence of different physiologic properties for N100. Consequently, frontal negativity is considered to be independent of P100.

Adult↗
PubMed1988

[Visual evoked potentials and water deprivation of rats during intrahypothalamic application of substance P].

Visually evoked potentials (VEP) were recorded in the visual cortex, the dorsal geniculate nucleus and the lateral hypothalamus of satiated and water-deprived rats with and without additional drinking sounds to strengthen motivation and were compared with those during substance-P-injections. Differences in VEP and corresponding spatial and temporal interrelationships of these areas were found by using the method of coincidence of single VEP. Variations of drinking behaviour, weight loss and motor activity were recorded. The findings are discussed with regard to SP and its function as a "regulid peptide".

Animals↗
PubMed1988

Visual-evoked potentials in cats, using a light-emitting diode stimulator.

Visual-evoked potentials (VEP) were studied in 8 healthy adult cats anesthetized with xylazine HCl and ketamine HCl. Monocular visual stimulation was accomplished by a 3 x 5 matrix of light-emitting diodes. Subcutaneous needle electrodes placed in the scalp at various locations and a contact lens electrode on the cornea were used to record cortical and electroretinographic activities, respectively. Multiple electrode pairings and unilateral optic nerve transsection were used to distinguish between retinal and postretinal potentials recorded from scalp electrodes. The VEP was a robust polyphasic cortical potential, with peak latencies between 0 and 110 ms. Using the light-emitting diode method of stimulation, a VEP was recorded which was not contaminated by volume-conducted retinal activity.

Animals↗
PubMed1980

Human intelligence and power spectral analysis of visual evoked potentials.

The relationship between intelligence and power spectra of visual evoked potential was investigated using 8 normal and 8 mentally retarded children as subjects. The results showed the power spectrum of mentally retarded has a peak at 4 to 6 Hz, whereas that of normal has two apparent peaks at 4 and 12 Hz. It appears the peak at 12 Hz reflects the difference of intelligence.

Adolescent↗
PubMed2001

Effects of grating spatial orientation on visual evoked potentials and contrast sensitivity in multiple sclerosis.

Previous studies suggest a delay of pattern visual evoked potentials (PVEPs) in multiple sclerosis (MS) depending on grating orientation. We examined a group of 14 patients with definite MS recording PVEPs to vertical and horizontal grating and analysing latency and amplitude of P60, N70 and P100 waves. We evaluated contrast sensitivity (CS) to dark and bright bars of several spatial frequencies (SF). The aim was to evaluate the diagnostic value of evoked responses and CS in revealing involvement of cortical structures. PVEPs to 1 degrees cycle/degree (c/d) vertical bars were abnormal in 25% for P60, in 32% for N70 and in 36%, for P100; in 25%, 36% and 42% respectively at 4 c/d; as regards horizontal bars at 1 c/d we found alterations of P60, N70 and P100 in 11%, 19% and 27% respectively; at 4 c/d in 19%, 27%) and 35%. CS resulted more abnormal for vertical grating, with a maximum impairment for 3.7 c/d SF. We may conclude that the use of vertical grating in clinical routine is more reliable both for PVEPs and CS testing; in addition CS can be abnormal even with normal PVEPs: this could mean an early impairment of CS and provide useful indications about a subclinical involvement of visual cortex.

Adult↗
PubMed1994

The timing of visual evoked potential activity in human area V4.

Studies of human occipital visual cortex have demonstrated functional specializations for colour and for motion, with a pivotal area for colour processing (area V4) being located in the fusiform gyrus. To study the timing of arrival of signals in area V4 we have recorded multi-channel visual evoked potentials (VEPS) to colour and grey 'Mondrian' stimuli, spatio-temporal dipole source analysis being computed on two independent group averages of five and six subjects respectively. Three active brain regions were identified, which we interpret to correspond to areas V1, V2 and V4; they showed sequential but overlapping activity in time with no difference in magnitude between colour and grey stimulated VEPs. Source analysis of the difference potentials, colour minus grey, isolated source activity resulting from colour stimulation and located it in the region of area V4. Activity in area V4 started at 100 ms and peaked at 135 ms after the onset of the visual stimulus.

Adult↗
PubMed2000

Steady-state visual evoked potentials and travelling waves.

OBJECTIVE: The amplitude and phase of the steady-state visual evoked potential (SSVEP) is sensitive to cognition and attention but the underlying mechanism is not well understood. This study examines stimulus evoked changes in the SSVEP phase topography and the putative role of travelling waves. METHODS: Eighteen subjects viewed a central-field checkerboard and full-field flicker stimulus temporally modulated at the peak alpha rhythm frequency. EEG was recorded from 10 midline scalp sites and the bipolar SSVEP obtained from differences between adjacent electrodes. RESULTS: The SSVEP phase comprised either progressive variations consistent with travelling waves or a phase reversal consistent with standing waves. The checkerboard pattern elicited travelling wave patterns in 14 subjects with estimated phase velocities ranging from 7 to 11 m/s after correcting for folded cortex. The flicker stimulus elicited phase reversals in 9 subjects, suggesting standing waves. Six subjects demonstrated a phase topography specific to the stimulus with travelling wave patterns associated with the checkerboard and standing wave patterns associated with the flicker. CONCLUSIONS: These differences suggest the emergence of travelling and standing waves under different spatial configurations of visual input to the cortex and that wave phenomena contribute to the spatiotemporal dynamics of the SSVEP.

Adult↗
PubMed2003

Refractive state of tree shrew eyes measured with cortical visual evoked potentials.

PURPOSE: To determine the refractive state of tree shrew eyes using visual evoked potentials (VEP's) recorded from primary visual cortex and compare the values with those obtained with streak retinoscopy and with an autorefractor. METHODS: VEP's were recorded in seven normal tree shrews and three animals in which approximately 5 D of myopia (relative to control eye) was induced by monocular -5 D lens wear. While the animals were awake, refractive correction was measured with an autorefractor before and after cycloplegia (1% atropine and 2.5% phenylepherine). When anesthetized, cycloplegic refractive correction was measured with streak retinoscopy. Then VEP's were produced with square-wave counterphased (1 Hz) high-contrast checkerboard patterns near the animals' high spatial frequency cutoff. Spherical lenses (2 D steps) were placed before the eye, and the VEP (average of 128 sweeps) was measured to determine the lens that produced the largest first positive peak (P1). RESULTS: VEP's were obtained over a broad range of trial lenses. Tuning was narrower when check sizes were small. In normal and control eyes, the P1 amplitude was largest, on average, for a trial lens of (mean +/- SD) -0.6 +/- 1.6 D (corrected for working distance but not vertex distance). The mean streak retinoscopy value (spherical equivalent at the corneal plane) was 7.0 +/- 0.8 D, and mean autorefractor values were 4.0 +/- 1.1 D (cycloplegic) and 3.7 +/- 1.2 D (noncycloplegic). In the eyes that compensated for a -5 D lens, the largest P1 values occurred with lenses with a power of -6.3 +/- 3.2 D. Thus, the VEP measure showed a similar treated vs. control eye difference as did streak retinoscopy (treated eyes, 4.7 +/- 0.4 D myopic) and the autorefractor (treated eyes, 4.8 +/- 0.5 D myopic). CONCLUSIONS: Normal tree shrew eyes are approximately emmetropic. The hyperopic values obtained with streak retinoscopy and the autorefractor are consistent with the presence of a "small-eye artifact" in tree shrews. Eyes that have compensated for a -5 D lens are myopic by approximately the value of the lens.

Animals↗
PubMed1980

[Visual evoked potentials in cerebrovascular disorders. Method and results].

Investigation of visual evoked potentials (VEP) by means of checkerboard inversion gives values with good reproducibility and low standard deviation for the latencies and amplitudes of VEP. In patients with scanty symptoms of cerebrovascular disease and without visual field defects, we found either differences of VEP amplitudes from side to another of over 25% (in relation to the larger value) or very small absolute values of the amplitudes (smaller than 3 mu V) as pathological values compared to control subjects. The latencies were normal. The method of investigation described helps towards objective analysis of functional disturbances in patients with cerebrovascular diseases.

Cerebrovascular Disorders↗
PubMed1980

Visual evoked potentials elicited by circular grating.

In the belief that it would prove a more effective stimulus for eliciting visual evoked potentials, a circular grating was designed so that the relationship between its bar width and visual acuity was held constant, and, therefore, the bars were equally well resolved across the visual field. Visual evoked potentials elicited by the onset presentation of the pattern were evaluated but found to be excessively variable owing to summation of different waveforms generated by equivalent stimulation of different parts of the visual field.

Adult↗
PubMed1983

Visual evoked potentials and long latency event-related potentials in chronic renal failure.

We studied auditory event-related potentials elicited in a target detection paradigm (P300) and pattern shift visual evoked potentials (PVEPs) in 22 patients with chronic renal failure and no clinical evidence of cognitive or visual impairment. Thirteen patients were maintained on chronic hemodialysis, and 9 patients were receiving a low-protein diet. Thirty-three percent of patients receiving the low-protein diet and 58% of the dialysis patients had abnormal P300 latencies. Most patients tested had abnormal PVEP. Four hemodialysis patients had elevated serum parathyroid hormone (PTH) levels, and 9 had normal or slightly elevated values. P300 and PVEP latencies were abnormal in both groups. These observations indicate that elevated PTH levels are not solely responsible for the abnormalities in all patients. P300 and PVEP may be valuable in evaluating neuronal dysfunction in the patient with chronic renal failure.

Adult↗
PubMed1984

Visual evoked potentials in the diagnosis of multiple sclerosis.

A three-year collaborative study was done on 96 patients presenting with signs of neurological dysfunction suggestive of multiple sclerosis. All were tested using Visual Evoked Potentials, with the final diagnosis not known to the tester. Patients with bilateral Visual Evoked Potential P1 wave conduction delays were more likely to have a subsequent diagnosis of MS, than those with unilateral delays, or normal VEPs. The average delay between the onset of the first symptom, and a definitive diagnosis of MS was 3.5 years. The most frequent initial symptom was paresthesias of the lower extremities, followed by blurred vision. This study suggests that the presence of Visual Evoked Potential abnormalities may be useful in the longitudinal diagnostic evaluation of patients with a presumptive diagnosis of multiple sclerosis.

Adult↗
PubMed1993

Visual evoked potential changes in patients with tropical pancreatic diabetes.

Visual impairment is an important complication of diabetes. There are conflicting reports on Visual Evoked Potential (VEP) changes in diabetes. P100 latency of VEP was evaluated in twenty patients with Tropical Pancreatic Diabetes (TPD) and compared with that of age and sex matched controls. There was no statistically significant difference in the P100 latency between the two groups. There was no correlation between the P100 latency and the severity of diabetes or presence of defective vision or retinopathy. The defective vision in diabetes is likely to be due to ocular causes rather than due to a defect in the central visual pathways.

Adult↗