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I Bodis-Wollner

Publications and source records attributed to I Bodis-Wollner.

At least 73 records · Page 4Linked to original sources
PubMed1989

Electrophysiological evidence for interhemispheric transmission of visual information in man.

1. Electrophysiological evidence is presented of interactions between two stimuli (sinusoidal gratings of equal spatial frequency but different contrast, phase-reversed sinusoidally at different temporal frequencies) located on opposite side of, and within a few degrees from, the vertical meridian. 2. These interactions are revealed by a depression of the cortical visual evoked potential (VEP) evoked by the grating of lower contrast in the presence of the grating of higher contrast. They are similar to, albeit weaker than, those obtained with superimposed asynchronously modulated gratings. 3. The VEP reduction occurs also if the stimuli are presented dichoptically. 4. It does not occur if the gratings are located one above the other either on the same or on opposite sides of the vertical meridian. 5. The strength of the VEP reduction depends on the relative contrast of the two gratings and vanishes for spatial frequencies beyond 4 cycles/deg and temporal frequencies of the high-contrast grating beyond 10 Hz. 6. The results are in agreement with data on visual callosal connections in animals and confirm previous psychophysical findings (Berardi & Fiorentini, 1987) indicating the particular properties of the interhemispheric cross-talk between symmetric regions of the visual field astride the vertical meridian in man.

Brain↗
PubMed1989

Electrophysiological and psychophysical testing of vision in glaucoma.

Electrophysiological testing in patients with early glaucoma and in glaucoma suspects reveals defects of central or foveal vision. Most studies suggest that glaucomatous eyes are best separated from normal eyes by use of stimuli with a spatial frequency below the peak of the human contrast sensitivity curve and a relatively high temporal frequency. The stimulus-dependent abnormalities in glaucoma are generally consistent with contrast sensitivity data The stimulus-dependent visual changes are related to the physiology of parallel processing in the primate retinogeniculate pathway.

Aged↗
PubMed1988

Systemic 1-methyl,4-phenyl,1-2-3-6-tetrahydropyridine (MPTP) administration decreases retinal dopamine content in primates.

Following MPTP administration, 4 Cynomolgus monkeys developed a parkinsonian syndrome, accompanied by specific changes of both pattern visual evoked potential and electroretinogram. Retinal dopamine and dihydroxyphenylacetic acid contents were measured in the 4 MPTP-treated monkeys and in 3 normal monkeys. Dopamine and dihydroxyphenylacetic acid levels were significantly lower in the retinas of the MPTP-treated animals (p less than 0.001), suggesting that dopamine has a specific function in the visual system of primates.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1988

Signs of early damage in glaucomatous monkey eyes: low spatial frequency losses in the pattern ERG and VEP.

Experimental glaucoma was created in one eye of three cynomolgus monkeys by argon laser application to the mid-trabecular meshwork. Simultaneous pattern electroretinograms (PERG) and pattern visual evoked potentials (PVEP) were measured in both control and glaucoma eyes to spatial frequencies of 0.5, 1.25, 2.5, and 3.5 cpd which were counterphase modulated at 6 Hz. The transient flash electroretinogram was also measured. While normal flash electroretinograms were recorded in all eyes both before and after the unilateral production of elevated intraocular pressure (IOP), reductions in PERG and PVEP amplitude were seen in the eyes with glaucoma as early as two weeks following a sustained increase of IOP, despite the absence of cupping of the optic nervehead judged by ophthalmoscopic examination and analysis of photograph by two observers. Optic nervehead abnormalities occurred subsequently. In glaucomatous monkey eyes, the earliest PERG and PVEP changes were most evident with lower spatial frequencies of stimulation. Our data suggest that the optimal stimulus parameters for the detection of early glaucoma are low spatial frequency patterns presented at a rapid rate of temporal modulation.

Animals↗
PubMed1988

Spatial frequency-dependent abnormalities of the pattern electroretinogram and visual evoked potentials in a parkinsonian monkey model.

The pattern visual evoked potential (PVEP) and pattern electroretinogram (PERG) were studied in 5 cynomolgus monkeys before and during the development of a parkinsonian syndrome induced by MPTP. The stimuli were vertical bars of four spatial frequencies (0.5, 1.2, 2.5 and 3.5 cycles/degree (cpd) modulated at temporal rates of 1, 4, 6, and 8 Hz. Following MPTP administration, all monkeys developed parkinsonian signs accompanied by changes in the amplitude and latency of the PVEP and PERG. Sinemet L-dopat carbi olopa administration produced temporary recovery of both PVEP and PERG. Two of the monkeys were followed for a prolonged period: 30-40 days after MPTP, the parkinsonian signs showed partial recovery; the PVEP latency and amplitude to 2.5 and 3.5 cpd stimuli and the latency to 1.2 cpd showed improvement but remained abnormal. The latencies of PERGs were normal, but the amplitudes were significantly reduced when stimuli of 2.5 and 3.5 cpd were used. Both PVEP and PERG to 0.5 cpd stimuli returned to normal. No further modifications were seen in the recordings performed 6 months and 1 year later. This study demonstrates (1) that spatial frequency-dependent electrophysiological abnormalities occur in the MPTP-treated monkey, a result previously found in human Parkinson's disease, and (2) that dopamine has a specific function in neurotransmission in the visual system of primates.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1988

Cortical contrast gain control in human spatial vision.

1. We evaluated human visual cortical contrast gain using visual evoked potential (VEP) measurements. The steady-state VEP was elicited by 7.5 Hz contrast modulation of a 6 cycles/deg sinusoidal grating. The stimulus may be regarded as the sum of a steady grating (C) and a counterphase grating of the same spatial frequency (delta C). The counterphase grating is modulated sinusoidally in time. 2. The VEP was measured to combinations of different modulation contrasts (delta C) and different mean levels of grating contrast (C) which produced stimuli with contrast modulation depths (delta C/C) ranging from 0.0625 to 1.0 ('on-off'). 3. The VEP signals were Fourier analysed and the amplitude and phase of the first (7.5 Hz) and second (15 Hz) harmonic frequency components were examined. The monocular VEP to a contrast-modulated grating contains significant first and second harmonic frequency components. 4. The amplitude and phase of the monocular VEP was plotted as a function of delta C for each mean level of contrast explored. The amplitudes of both the first and second harmonic frequency components grow with increasing delta C. However, the slope of each function depends on the mean contrast (C): with higher levels of C, the slope of the function is more shallow. Furthermore, at each level of C the amplitude of the first harmonic frequency saturates at a lower delta C than does the second harmonic frequency component. VEP amplitude is therefore not determined by the absolute contrast change (delta C) alone. The VEP phase of the first harmonic frequency shows less dependence on either modulation or on mean contrast; the phase of the second harmonic frequency component is strongly dependent on mean contrast (C) but not on delta C. 5. When the second harmonic amplitude component of the VEP response (R) is expressed as Ractual/Rmax, where Rmax is the response to C = delta C (i.e. 'on-off'), all second harmonic VEP functions can be well fitted with a power function. This is not the case for the function of the first harmonic amplitude data. 6. A dichoptic VEP was obtained by presenting the steady and counterphase gratings to opposite eyes. The dichoptic VEP, in distinction to the monocular VEP, contains only a second harmonic frequency component. The amplitude of the second harmonic frequency component grows with increasing delta C, similar to the function seen for the monocular VEP.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1987

Electrophysiological evidence that early glaucoma affects foveal vision.

The pattern electroretinogram (PERG) and visual evoked potential (PVEP) were recorded simultaneously using a 1.1 cpd pattern which was counterphase modulated at 1 Hz. The responses of ocular hypertensive (OHT) eyes (with normal visual fields) and eyes with early glaucoma (with early visual field defects and/or early cupping of the optic nervehead) were compared to age-matched normal observers. All patients (26 eyes) and normal observers (14 eyes) had normal transient flash electroretinograms. Delays were seen in mean PERG latency in both OHT and early glaucoma eyes, while mean PERG amplitude was significantly reduced only in the early glaucoma eyes. The PVEP responses were 'unmeasurable' in 11/26 patient eyes because the waveforms were grossly abnormal in shape, making it impossible to identify the N- and P-components. The data were categorized in this manner: a patient response was considered abnormal if latency or amplitude exceeded normal limits (PERG or PVEP) or if the waveform was 'unmeasurable' due to its shape (PVEP only). Of the 26 patient eyes, we found that 8 eyes had normal PERG and PVEP, 11 eyes had abnormal PERG and PVEP, one eye had an abnormal PERG and a normal PVEP, and 6 eyes (3 patients) had a normal PERG and an abnormal PVEP. These data support the proposition that foveal vision (as assessed by the PVEP) may be affected by early glaucomatous damage. The relationship between the PERG and PVEP also was evaluated using a new measurement which we call the 'latency window'. Using this measurement, 15/26 patient eyes were abnormal-9 of these had 'unmeasurable' PVEPs. This measurement could be useful in classifying 'W'-shaped PVEPs as normal or abnormal.

Adult↗
PubMed1987

Scalp distribution of pattern visual evoked potentials in normal and hemianopic monkeys.

We examined the hemispheric distribution of the pattern visual evoked potential in 3 Cynomolgus monkeys, before and after right optic tractotomy or left occipital lobectomy. The stimuli were vertical gratings of 4 spatial frequencies, presented using counterphase and on-off modulation at 1 and 8 Hz. In the normal monkey, the amplitude and latency of the PVEPs elicited by 1 Hz stimulation were similar across all electrode sites. While no differences were found in the phase of the PVEP elicited by 8 Hz stimulation across the different derivations, PVEP amplitude generally decreased over the lateral electrodes. Once experimental hemianopia was created, PVEPs recorded over the midline and the intact hemisphere were normal. However, partially polarity-inverted PVEPs of smaller amplitude were recorded over the deafferented hemisphere. In addition, the interhemispheric phase difference became more prominent in the PVEP recorded over the deafferented hemisphere as the spatial frequency was increased.

Animals↗
PubMed1987

Delayed visual evoked potentials are independent of pattern orientation in macular disease.

Visual evoked potentials (VEPs) and contrast sensitivity (CS) were studied in patients affected by maculopathy. VEP delays and CS reduction were demonstrated in each affected eye. In distinction to patients affected by multiple sclerosis (MS), in maculopathy patients VEP latency is independent of the orientation of the grating stimulus. It is proposed that stimulating with more than one pattern orientation is useful in the differential diagnostic use of VEPs.

Adult↗
PubMed1987

The effect of blur and contrast on VEP latency: comparison between check and sinusoidal and grating patterns.

Pattern defocusing was used to evaluate the contribution of different spatial frequency components in checks to VEP latency. Latency shifts with increasing blur (-2.5 to +2.5 diopters) were determined for sinusoidal grating and check patterns equated in fundamental spatial frequency. With both check and grating patterns, the effect of blur was greater the higher the spatial frequency. Given an equal fundamental spatial frequency, however, the latency of checks was more effected. This latency difference between check and sine patterns was pronounced at low fundamental spatial frequencies (large pattern) and decreased with higher spatial frequencies (small pattern). Latencies were then compared for patterns which were defocused vs. simply reduced in contrast. Results show that the increase in latency with defocused large checks is due to both fundamental and higher harmonic spatial components but with small checks, to the fundamental spatial frequency alone.

Adolescent↗
PubMed1987

Plasticity of monocular and binocular vision following cerebral blindness: evoked potential evidence.

Using monocular and dynamic random dot correlogram (DRDC) stimuli, sequential visual evoked potentials changes were demonstrated in 2 patients following cerebral blindness. The recovery of binocular vision was delayed in comparison to the recovery of monocular vision. The results are not due to simple acuity impairment or convergence deficiency, and thus provide evidence for the vulnerability of postsynaptic cortical mechanisms of human binocular vision.

Adult↗
PubMed1987

Visual dysfunction in Parkinson's disease. Loss in spatiotemporal contrast sensitivity.

Flicker sensitivity and spatial contrast sensitivity (CS) were examined in a total of 99 patients with Parkinson's disease (PD). All patients were undergoing treatment with dopaminergic agents. Specific losses in sensitivity observed in PD were (1) a loss in flicker sensitivity which was most pronounced around the peak of the function (8 Hz) and (2) a loss near the peak of the spatial CS curve, often with no noticeable low frequency attenuation. Several PD patients affected by the 'on-off' syndrome were tested in both 'on' and 'off' phases, and the results show that the CS function switches in parallel with motor symptoms of the disease. These data suggest that not only is the visual system affected in PD, but that dopamine may have an essential role in receptive field organization in human vision.

Adult↗
PubMed1987

Effect of L-acetyl carnitine HCl on rat steady-state visual evoked potentials. Comparison with L-carnitine.

L-acetyl carnitine administration increases the amplitude of the steady-state visual evoked potentials (VEPs) obtained with sinusoidal luminance stimulation at 8.4 Hz. This effect was studied with three different doses of L-acetyl carnitine (50, 25, 5 mg/kg) and was compared with the results of injection of similar doses of L-carnitine. The effect is most evident when 50 mg/kg L-acetyl carnitine are administered and has two different time peaks. The second peak of activity showed a dose dependency when 25 mg/kg and 5 mg/kg doses were tested. The effects of L-acetyl carnitine could be depressed by the simultaneous administration of atropine sulfate.

Acetylcarnitine↗
PubMed1987

Effect of levo-acetylcarnitine on P300-like potentials of the normal monkey.

Endogenous components of evoked potentials resembling P300 in human beings were sequentially studied in four cynomolgus monkeys (Macaca fascicularis using an auditory "oddball" paradigm, after classical conditioning training. When robust P300-like signals were obtained, each animal underwent further recording sessions in which a placebo, L-carnitine or L-acetylcarnitine (LAC) was injected. Only LAC induced an amplitude increment of P300 waves in all the animals and a latency decrement in two animals. Furthermore a transient effect with amplitude reduction on the primary cortical auditory evoked potentials (AEP) both to rare and frequent tones was also recorded in all the animals. This effect resembled the AEP amplitude reduction induced by physostigmine administration. The findings suggest an effect of LAC on normal processes accompanying cognition.

Acetylcarnitine↗
PubMed1986

Temporal frequency-dependent VEP changes in Parkinson's disease.

We recorded steady-state (4.19 and 8.41 Hz) VEPs in 17 Parkinson's Disease (PD) patients and 18 control observers using on-off temporal modulation of a 2.3 c/deg sinusoidal grating. With 4.19 Hz, 20 out of 33 PD patient eyes had abnormal VEPs. However, only 8 of 33 eyes were abnormal with 8.41 Hz. "Routine" (counterphase) transient VEPs revealed delayed VEPs for only 7 out of 24 eyes of the patients. These findings suggest an "input" temporal frequency-dependent abnormality in the foveal pathway.

Adult↗
PubMed1986

P300-like potentials in the normal monkey using classical conditioning and an auditory 'oddball' paradigm.

Endogenous components of evoked potentials resembling P300 in humans were sequentially studied in 3 cynomolgus monkeys (Macaca fascicularis) using an auditory 'oddball' paradigm. The two different auditory stimuli were 500 Hz and 4000 Hz tones, designated as the 'frequent' and 'rare' stimuli, respectively. The probability of 'rare' tone presentation was initially 0.2. We further used probabilities of 0.1, 0.3 and 0.5. The 'rare' stimulus was reinforced by electrical stimulation, which followed the onset of the high tone by 700 msec. After 3-5 training sessions, a late positive wave was observed following the 'rare' tone. The latency of this P300-like signal was 314 +/- 16.2 msec, and the amplitude was 23.6 +/- 3.14 microV. The amplitude of this potential was modified by changes in stimulus presentation probability and by withholding reinforcement.

Animals↗