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PubMed1975

Neural plasticity in visual cortex of adult cats after exposure to visual patterns.

Over a period of 2 weeks, adult cats were twice a day exposed for 1 hour to a visual environment consisting only of vertical stripes and for the rest of the time were kept in darkness. Subsequent investigation of the striate cortex showed a decrease in the number of neurons sensitive to orientations around the vertical relative to those sensitive to horizontal orientations. This indicates that plasticity of functional properties of the cortical neuronal network still exists in adult animals.

Animals↗

PubMed1980

Visually induced self-motion sensation adapts rapidly to left-right visual reversal.

After 1 to 3 hours of active movement while wearing vision-reversing goggles, 9 of 12 (stationary) human subjects viewing a moving stripe display experienced a self-rotation illusion in the same direction as seen stripe motion, rather than in the opposite (normal) direction. This result indicates that the neural pathways which process visual self-rotation cues can undergo rapid adaptive modification.

Functional Laterality↗

PubMed2006

Contrast-response functions for multifocal visual evoked potentials: a test of a model relating V1 activity to multifocal visual evoked potentials activity.

The multifocal visual evoked potential (mfVEP) is largely generated in V1. To relate the electrical activity recorded from humans to recordings from single cells in nonhuman primate (V1) cortex, contrast-response functions for the human mfVEP were compared to predictions from a model of V1 activity (D. J. Heeger, A. C. Huk, W. S. Geisler, & D. G. Albrecht, 2000) based upon single-cell recordings from monkey V1 (e.g., D. G. Albrecht, 1995; D. G. Albrecht, W. S. Geisler, R. A. Frazor, & A. M. Crane, 2002; D. G. Albrecht & D. B. Hamilton, 1982; W. S. Geisler & D. G. Albrecht, 1997). A second purpose was to fully articulate the assumptions of this model to better understand the implications of this comparison. Finally, as the third purpose, one of these assumptions was tested. Monocular mfVEPs were obtained from normal subjects with a contrast-reversing dartboard pattern. The display contained 16 sectors each with a checkerboard. Both the sectors and the checks were scaled approximately for cortical magnification. In Experiment 1, there were 64 checks per sector. The contrast-response functions were fitted well up to 40% contrast by the theoretical population curve for V1 neurons; there was a systematic deviation for higher contrasts. The model, as articulated here, predicts that the contrast-response function should be the same and independent of the size of the elements in the display. Varying the size of the elements by varying the viewing distance in Experiment 2 produced similar results to those in Experiment 1. In Experiment 3, the viewing distance and sector size were held constant, but the size of the elements (and therefore the number of checks per sector) was varied. Changing check size by a factor of 16 had relatively little effect on the contrast-response function. In general, the mfVEP results were consistent with the model based upon the V1 neuron population. However, two aspects of the results require further exploration. First, there was a systematic deviation from the model's contrast-response function for higher contrasts. This deviation suggests that one or more of the model's assumptions may be violated. Second, the latency of the mfVEP changed far less than expected based upon single-cell data.

Adult↗

PubMed2002

Spatial and temporal characteristics of visual motion perception involving V5 visual cortex.

The anatomical substrates of the perception of motion have not yet been established in a detailed way on an individual level. The aim of this study was to develop a systematic procedure for mapping the visual cortex using Transcranial Magnetic Stimulation (TMS). The results showed that such an individual and detailed map of the spatial and temporal characteristics of motion perception can be constructed using TMS.

Adult↗

PubMed1995

Visual alterations in de novo Parkinson's disease: pattern electroretinogram latencies are more delayed and more reversible by levodopa than are visual evoked potentials.

There are increased latencies of pattern-reversal visual evoked potentials (VEPs) and electroretinograms (PERGs) in Parkinson's disease (PD) patients who have not received therapy. This study aimed to evaluate whether these delays are present in the early stage of PD and whether they are dopamine-sensitive. The results show that both PERG P50 and VEP P100 latencies are increased (p < 0.0001) in a group of patients with de novo PD (13 subjects; 13.3 +/- 5.6 months' mean disease duration) before therapy in comparison with an age-matched control group (eight subjects). A larger latency increase (9.9% at the 47% contrast level and 7.8% at the 96% contrast level) was present in PERG recordings than in VEPs (6.2% at the 47% contrast level and 3.9% at the 96% contrast level). Levodopa therapy produced recovery of both PERG and VEP latency increases at both contrast levels, but only the PERG recovery at 47% of contrast was statistically significant. Before therapy, five eyes from PD patients showed no reproducible PERG at the 47% contrast level although the simultaneously recorded VEP was present. Both potentials were recordable in the same eyes at the 96% contrast level. During therapy, four of those five eyes showed a clear PERG even at the 47% contrast level. We conclude that, using an adequate midspatial frequency, both VEPs and PERGs are delayed even in the early stage of PD, and that PERGs are more sensitive if low contrast (47%) is used. The larger alterations, as well as the larger recovery during levodopa therapy, seem to correlate the PERG response more than the VEP response to dopaminergic transmission.

Aged↗

PubMed1979

Is Fourier analysis performed by the visual system or by the visual investigator.

A numerical Fourier transform was made of the pincushion grid illusion and the spectral components orthogonal to the illusory lines were isolated. Their inverse transform creates a picture of the illusion. The spatial-frequency response of cortical, simple receptive field neurons similarly filters the grid. A complete set of these neurons thus approximates a two-dimensional Fourier analyzer. One cannot conclude, however, that the brain actually uses frequency-domain information to interpret visual images.

Animals↗

PubMed1975

[Interhemispheric relations of the cat visual cortex following unilateral polarization of the secondary visual area].

In 40 anesthetized cats, evoked potentials following light flashes during unilateral polarization of the secondary cortical visual area with DC anode (2-10 mcA) were studied in symmetrical centers of the 17th and 18th fields. Four phases of interhemisphere interrelationships between the 18th field's symmetrical centers were shown: 1 -- extracallosal phase of synergic depression; 2 -- callosal phase of dominant interrelationships; 3 -- callosal phase of synergic depression; 4 -- callosal-extracallosal phase of dominant interrelationships. In symmetrical centers of the 17th field, the only 1 extracallosal phase of synergic depression was observed during which the transcallosal modulation of nervous processes occurred. The data obtained are interpreted from the standpoint of the role of dominanta in interhemisphere interrelationships.

Animals↗

PubMedDate not supplied

[Possibilities of the use of visual evoked potentials in the evaluation of visual acuity in congenital myopia in children].

Studies of visual evoked potentials (EP) to chess field reversion in 80 children (147 eyes) aged 5 to 16 with congenital myopia have demonstrated significant deviations from the reference values of the P100 component to all the stimuli. The clinical groups with various changes in the fundus oculi were found to differ by the P100 component amplitude when chess fields with cells 112 and 56 angular min in size were shown. The number of discrepancies between the clinical vision acuity and its assessment from the threshold EP grew from 19% when no changes in the fundus oculi were seen to 54 and 61% when myopic and non-myopic changes were detectable in the fundus oculi. These data evidence that EP amplitude to chess field reversion better reflects the status of the retino-cortical route than the central vision acuity.

Adolescent↗

PubMed1990

[Trial on the objective evaluation of visual acuity and its maturation by the method of evoked visual potentials].

We have developed a method to estimate foveal visual acuity (VA) through analysis of VEPs. It consists in determining the smallest check size in a pattern reversal that elicits a significant cortical response. The VEP is regarded as significant if the P 100 amplitude reaches a pre-established level in the signal to noise ratio. A valid criterion to determine normal VEP-VA emerges from the testing of 84 emmetropic and ametropic eyes: within our stimulation and recording conditions, a significant VEP response to the reversal of seven minutes checks corresponds to normal foveal acuity. This criterion has also proved pertinent to discriminate between normal VAs of 20/20 and decreased VAs (20/40 or less) with four other groups of subjects: 14 adult eyes whose VAs of 20/20 are decreased through Bangerter occlusives, 32 emmetropic and ametropic eyes belonging to five-years-olds children, 28 emmetropic and ametropic eyes of twelve-years-olds. In order to guarantee the validity of our results we carried out a double-blind study with ophthalmologists. The relevance of the method we suggest is related to that of the method which consists in extrapolating the regression line between VEP amplitudes and the pattern element sizes. At least we have aimed at establishing VEP norms for the maturation of VA. We have collected data from the following subjects: 5 infants tested monthly between 1 and 6 months, 31 infants ranging in age from 1 to 16 months, 10 five-year-old children, 13 twelve-year-olds, and 11 subjects aged 20. Within our stimulation and recording conditions a significant evoked response to the reversal of seven minute checks can be observed from 8 months onward. With an eight-month-old infant this response to the reversal of seven minute checks cannot be identified to the same response with an adult. There are two major differences: the latency of the major positive component is longer, and the structure of the evoked response consists of fewer components.

Adult↗

PubMed1990

[Experimental studies of the role of the adrenergic system in the development of bioelectric response of the retina and visual cortex. IV. Visual evoked potentials in rabbits after administration of alpha and beta receptor agonists and blockaders].

The influence of noradrenaline, dihydroergotamine, isoprenaline and propranolol on the VEP in rabbit was examined. The records of VEP showed a lowering of the amplitude of the A and B waves after compounds stimulating and restraining the adrenergic alpha and beta receptors. The C wave increased after dihydroergotoxine, isoprenaline and propranolol; it was lowered after noradrenaline. On the basis of the obtained results the author discusses the role of the adrenergic system in formation of the bioelectric response of the visual cortex.

Animals↗

PubMedDate not supplied

[Visual evoked potentials in the evaluation of visual acuity in infants].

Vision acuity was assessed by visual evoked potentials (VEP) in response to low-frequency chess pattern reversion in 31 full-term healthy babies aged 6 to 28 weeks. The mean vision acuity of babies aged 6 to 9 weeks was 0.5 +/- 0.01, of those aged 16 to 18 weeks 0.1 +/- 0.01; in babies aged 24 to 26 weeks vision acuity was at least 0.14, but still lower than in normal-sighted adults. The authors emphasize the advantages of low-frequency chess pattern reversion in assessment of vision acuity from VEP in babies.

Adult↗

PubMed1994

Spatial distribution of the inhibition elicited by the offset of a visual cue on manual reaction time to a visual target.

Simple reaction time (RT) to a peripheral visual target (S2) is shortened when a non-informative cue (S1) is flashed at the S2 location 100-150 ms before target onset (early facilitation). Afterwards, RTs to targets appearing at the S1 location are lengthened (inhibition of return). In the present investigation we studied the spatial distribution of the inhibition elicited by the offset of S1. Twelve subjects were asked not to respond to S1 which appeared on a horizontal meridian located 5.5 degrees above the fixation point (FP), but to respond, by pressing a key, to a target (S2) occurring at 5.5 degrees to the left or to the right. S1 could appear at one of 9 locations along this meridian (5.5, 3.5, 1.5, and 0.5 degrees to the left, 0.0 and 0.5, 1.5, 3.5, and 5.5 degrees to the right) and S2 occurred only at the most eccentric positions. Each trial began with the presentation of FP. Five-hundred ms later, S1 appeared and remained on for 700 ms. One hundred or 800 ms after S1 offset, S2 appeared in the same or in the opposite hemifield. We found that the offset of S1 elicits an inhibition (OFF-inhibition) which has the following features: a) it is maximal at cue's position; b) it spreads to other positions in the cued hemifield, and c) it decreases when the time interval between S1 offset and S2 onset increases from 100 to 800 ms.

Adult↗

PubMed1977

[Interaction of fibers from the retina and visual region of the cortex in several subcortical visual formations of rats].

The medial nucleus of the optic tract, the ventral lateral geniculate nucleus and the superior colliculus have been studied using the light (Nissl, Golgi, Viktorov) and electron microscopic methods in normal rats and in rats which survived for different periods after enucleation or occipital cortical lesions. Data were obtained on differences in terminal patterns of the afferent pathways. The study of the neuronal and synaptic organization of subcortical visual centers showed the distinctions and correlation between the complexity of neuronal and synaptic organization. Three types of interrelations between the optic and cortical pathways on the efferent neurons of the investigated structures are suggested.

Animals↗

PubMed2004

Regulation of the CREB signaling cascade in the visual cortex by visual experience and neuronal activity.

The cAMP-responsive element (CRE) regulatory pathway has been studied as a model of signal-regulated transcription and is critical for some forms of learning and adaptation. In cell culture systems, the extracellular-regulated kinase (ERK) and ribosomal S6 kinase (RSK) couple synaptic signals to CRE-mediated gene expression by modulating CRE-binding protein (CREB) phosphorylation. However, it is not known whether sensory experience regulates gene expression in the brain by this mechanism. In this study, we ask: Are activated forms of ERK, RSK, and CREB colocalized in the cortex and are they coordinately regulated by synaptic signals? We find that these three signaling components are regulated in distinct ways. First, cells that show CRE-lacZ reporter expression, primarily excitatory neurons, do not colocalize with cells containing phospho-ERK. Second, while phosphorylation of ERK and RSK are modulated by visual experience, phosphorylation of CREB at serines 133, 142, or 143 is detected constitutively and is unaffected by experience. This finding suggests that neural activity might not regulate CREB phosphorylation in vivo. To test this hypothesis, we blocked action potentials by injection of tetrodotoxin and found no effect on CREB phosphorylation. These in vivo data show that, in contrast to cell culture systems, cortical synaptic activity controls CRE-mediated gene expression without affecting CREB phosphorylation, possibly by modification of RSK and CREB-associated coregulators.

Action Potentials↗

PubMed2004

The complexity of the visual cells and visual pathways of the sturgeon.

The visual cells in the retinae of the sturgeon were studied by scanning electron microscopy and transmission electron microscopy. Our investigations revealed the presence of rods, two types of single cones, one type of double cone (two nonidentical cone components adhered together), and one type of twin cone (two identical cone components adhered together). In some of the cones, large glycogen bodies were present in the inner segments and all cones contained oil droplets. Such cone morphology was very similar to that described in the retinae of higher vertebrates, for example the chicken. DiI tracing of retinofugal pathways following uniocular injection demonstrated their bilateral localization and extensive termination in the diencephalon and mesencephalon of both sides. Fibers also crossed over from one side to another through commissures, including the posterior commissure. The complexity of the pathway surpassed that of the teleosts and further indicated the evolutionary importance of this fish.

Animals↗

PubMed2006

Myelin deficiencies visualized in vivo: visually evoked potentials and T2-weighted magnetic resonance images of shiverer mutant and wild-type mice.

Visually evoked potentials (VEPs) and micro magnetic resonance imaging (micro MRI) are widely used as noninvasive techniques for diagnosis of central nervous system (CNS) diseases, especially myelin diseases, such as multiple sclerosis. Here we use these techniques in tandem to validate the in vivo data in mouse models. We used the shiverer mutant mouse, which has little or no CNS myelin, as a test model. These data show that shiverer (MBP(shi)/MBP(shi)) has a VEP latency that is 30% longer than that of its wild-type sibling. Surprisingly, the heterozygous (MBP(shi)/+) mouse, with apparently normal myelin, nevertheless has a 7% increase in its VEP latency vs. wild type. The micro MRIs of the same animals show that myelinated white matter is hypointense compared with gray matter as a result of the shorter T2 in myelinated regions of the CNS. T2-weighted images of wild-type and heterozygous shiverer mice show regions of hypointensity corresponding to the major myelinated tracts, including the optic nerve and the optic tract of the CNS, whereas shiverer mice have no regions of low intensity and therefore no detectable myelinated areas. In shiverer mice, micro MRI can discern hypomyelination throughout the brain, including the optic tract, and these changes correlate with longer VEP latencies. In addition, VEPs can also detect changes in the molecular make up of myelin that are not discernible with histology or micro MR. These data show the potential of using micro MRI in combination with VEPs to follow changes in both the quality and the quantity of myelin in vivo. These combined methods would be useful for longitudinal studies and therapy testing.

Animals↗

PubMed1986

Pattern disappearance visually evoked cortical potential in the diseases of visual pathway.

Visually evoked cortical potentials in response to pattern-appearance, -disappearance, and -reversal stimuli were studied in normal subjects and in patients suffering from optic neuritis. It was found in normal subjects that pattern disappearance VECPs were as reliable as the pattern reversal ones. On the other hand, the appearance response showed interindividual differences which made its evaluation rather difficult. The same was true in the records of the patients. Both the mean peak latencies of the disappearance responses and those of the pattern reversal ones were prolonged significantly in optic neuritis, compared with those obtained from normal subjects. We concluded that the peak latencies of the disappearance response could be more confidently used than those of the appearance response for diagnosing optic neuritis.

Adult↗

PubMed1985

Abolition of visual cortical direction selectivity affects visual behavior in cats.

We reared cats in an environment illuminated stroboscopically at 8 Hz, and studied their ability to detect and discriminate the direction of motion of sinusoidal gratings. Normal cats, like humans, could discriminate the direction of a grating's motion at contrasts that are just barely visible. Strobe-reared cats could detect the grating at contrasts similar to those required by normal cats, but required contrasts that were about 10 times threshold to identify the direction of motion. We subsequently studied the activity of single units in the striate cortex in these cats, and found that directional motion selectivity--normally a prominent feature of striate cortical neurons--was almost absent; other cortical receptive field properties were roughly normal. These results suggest that directionally selective neurons are involved in visual discriminations based on the direction of motion.

Animals↗