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PubMed1980

The distribution of interhemispheric projections in area 18 of the cat: coincidence with discontinuities of the representation of the visual field in the second visual area (V2).

In normal adult cats three regions with callosal projections from the contralateral visual areas 17, 18, and 19 have been identified at the lateral border of area 18 by degeneration techniques (Sanides, 1978). The visuotopic distribution of these callosal patches has now been investigated by combining anatomical with physiological techniques. The centers of the receptive fields recorded in the callosal patches are located on or close to the vertical meridian in the contralateral hemifield reaching eccentricities of about 15 deg. Some of these fields are of extraordinary size crossing the vertical meridian and covering large areas of the ipsilateral hemifield. On the other hand, receptive fields recorded from the acallosal parts of lateral area 18 may reach eccentricities of more than 50 deg. Thus, the callosal patches of lateral area 18 are wedged in between parts of lateral area 18 which represent the periphery of the contralateral hemifield. It is concluded that the retinotopic arrangement at lateral area 18 (the second visual area) distinguishes this area fundamentally from area 17, the primary visual area.

Animals↗

PubMed1986

Hemifield pattern-reversal visual evoked potentials (VEPs) in retrochiasmal lesions with homonymous visual field defect.

This study was designed to examine the clinical significance and the reliability of hemifield pattern reversal VEPs in the assessment of homonymous visual field defects due to retrochiasmal lesions. 13 patients with traumatic, neoplastic or ischemic lesions of the cerebral parenchyma, and 18 normal subjects were studied. The results show that amplitude asymmetries over 4 microV (between responses evoked by right and left hemifield stimulation, recorded ipsilaterally to the stimulated hemifield) are clinically relevant for hemianopic visual field defect. Significant correlations were found between the VEP features and the site of the damage: lesions of the occipital cortex were generally found to cause more pronounced bioelectrical abnormalities than those due to lesions affecting the visual pathways, with cortical sparing.

Adolescent↗

PubMed1983

Maturational sequence of the visual system: serial measurements of visual evoked potential and electroretinogram in the healthy neonatal lamb.

The value of measurements of visual evoked potential (VEP) for neurological assessment of the adult is widely accepted. Its use for neonatal evaluation following birth asphyxia has been limited by our knowledge of developmental changes occurring in the newborn brain. VEPs and electroretinograms (ERGs) were simultaneously recorded from five healthy newborn lambs from birth until 30 days of life. Newborn age was then compared with amplitude (height of the signal) and latency (time from stimulus to a specific wave deflection) measurements from these neuroelectrical signals. Latencies to A wave (photoreceptor activity) and B wave (bipolar and ganglion cells) of the ERG declined in a small but significant manner, while the latency interval from A to B wave did not change with age. Latency to wave N1 of the VEP remained stable while latency to P2 declined from birth to 30 days. The ERG and VEP signals exhibited linear increases in amplitude as the lambs became older. We conclude from these observations that ganglion and bipolar cells (B wave of the ERG) within the retina and primary nerve tracts (N1 of the VEP) along the visual system are mature at birth. In contrast, photoreceptor activity within the retina (A wave of the ERG) and nerve conduction through the visual cortex (P2 of the VEP) exhibit changes which are consistent with ongoing maturation of these more specialized areas through the early newborn period.

Animals↗

PubMed1987

Visual resolution and sensitivity in a nocturnal primate (galago) measured with visual evoked potentials.

Visual resolution and contrast sensitivity were examined in anesthetized, paralyzed galagos using visual evoked potentials (VEPs) resulting from stimulation with phase-reversed sinewave gratings. Spatial frequency vs contrast response functions were band-pass with peak sensitivity at 0.2-0.4 c/deg and a high frequency cut-off between 1.6 and 3 c/deg. Peak contrast sensitivities (estimated from extrapolation of contrast response functions) varied across animals from 10 to 170. Variation of the stimulus modulation rate showed that best responses occurred at 1 Hz with an upper limit of 6-16 Hz. As in other primates, an oblique effect was seen in 6 of 8 animals. The contrast sensitivity function (CSF) determined from cortical VEPs agrees well with the CSFs of cells in the lateral geniculate nucleus, but peak sensitivity and spatial frequency are slightly lower than found for the behavioral CSF. Overall visual performance resembled closely that of another nocturnal species, the cat.

Animals↗

PubMed1988

Visual split brain and monocular deprivation in kittens: differentiation between the effects of disuse and of binocular competition in visual cortex cells.

To differentiate between the resulting effect of disuse, developmentally induced by deprivation, and the binocular competition effect on cortical cells, visual split brain was performed concurrently with monocular deprivation in kittens. In the experienced hemisphere of the split brain deprived cats (ipsilaterally to the non-deprived eye), there were twice as many visually responsive cortical cells than found in their inexperienced hemisphere (ipsilaterally to the deprived eye); however, these cells were equal in number to that found in the split brain controls. In the monocularly deprived control cats a relation of 3.2 was found between cells driven by the non-deprived and the deprived eye. Visual disuse, therefore, resulting from monocular deprivation, affects cortical cells under complete absence of binocular competition but is greatly enhanced by the latter.

Animals↗

PubMed1987

Effects of altered visual input upon the development of the visual and somatosensory representations in the hamster's superior colliculus.

The right superior colliculus and right eye were ablated in hamsters within 12 h of birth and the visual and somatosensory representations in the remaining (left) superior colliculus were evaluated using standard single unit recording and receptive field mapping techniques when the animals reached adulthood (at least 3 months of age). In a number of the hamsters used for recording, injections of [3H]leucine were made into the left eye 6-10 days prior to the terminal experiment. This was done to insure that the neonatal lesions did, in fact, produce the extensive recrossing of retinal fibers demonstrated by others who have employed this preparation. All of the hamsters which received [3H]leucine injections prior to the recording experiment exhibited a markedly expanded ipsilateral retinocollicular projection and retinal axons which recrossed the midline at the level of the tectum. The recording experiments showed further that this projection resulted in a visual map which was generally mirror symmetric to that in normal hamsters. There were, however, numerous irregularities and discontinuities in this representation and, in a few hamsters, it appeared almost completely disorganized. There were also a number of abnormalities in the somatosensory representation in the deep tectal laminae of the neonatally brain damaged hamsters. There was a substantial increase in the number of cells with receptive fields that extended onto the ipsilateral side of the body, neurons with split receptive fields were recorded and there were changes in the magnification of different portions of the body surface. These alterations did not, however, change the organization of the somatosensory map in a manner which brought it into alignment with the visual representation in the superficial laminae. Nevertheless, additional recording experiments in animals subjected to enucleation of both eyes and ablation of the superficial laminae of one superior colliculus did indicate that the existence of the aberrant retinal projection was a necessary condition for the somatosensory abnormalities which we observed. Additional anterograde and retrograde tracing experiments demonstrated only one abnormality in the organization of the somatosensory afferent input to the remaining colliculus. In 75% of the brain damaged hamsters, there was a weak crossed projection from the sensorimotor cortex that was never observed in normal animals. Ablation of this cortex at the time of the recording experiment did not, however, reduce the incidence of abnormal somatosensory receptive fields in these hamsters.

Afferent Pathways↗

PubMedDate not supplied

Effects of superior colliculus inhibition on three-dimensional visual motion processing in the lateral suprasylvian visual area of the cat.

PURPOSE: To determine whether visual inputs from the tectothalamocortical pathway influence three-dimensional motion processing within the lateral suprasylvian (LS) area of the cat. METHODS: Tungsten microelectrodes were used for recording visual-evoked potentials (VEPs) from the LS area of 4 cats. Random dot stereograms were used as visual stimuli. Three-dimensional, motion-triggered VEPs were recorded from the LS area. Each motion sequence consisted of an abrupt onset of motion disparity with a 2 degrees amplitude followed by an abrupt offset and a stationary phase of 900 ms. The velocity of the motion disparity was varied in eight steps from 10 degrees to 400 degrees per second. The onset of motion disparity was used as the trigger for recording the VEPs. Single or multiple injections (two to three) of muscimol were made mainly into the rostral superior colliculus (SC). The amplitudes of the VEPs before and after the muscimol injection were compared. RESULTS: A large negative wave ( N1) with an implicit time of 92.7 +/- 13.5 ms (mean +/- SD, n = 98) was recorded consistently. The amplitude of N1 was significantly larger on stereovision of motion disparity than on either binocular vision of two-dimensional lateral motion or monocular vision, indicating that N1 contains neurons sensitive to motion disparity. The amplitude of N1 was not altered by muscimol injection into the SC at velocities < or =50 degrees/s. On the other hand, the amplitude of N1 was reduced to 66-71% of that observed before muscimol injection at velocities > or =75 degrees/s. CONCLUSIONS: These findings suggest that the LS area processes three-dimensional motion inputs via two parallel pathways, the geniculostriate pathway and the tectothalamocortical pathway, at velocities of motion disparity > or =75 degrees/s, while the three-dimensional motion inputs project to the LS area only via the geniculostriate pathway at velocities of motion disparity < or = 50 degrees/s.

Animals↗

PubMed1996

Voltage-clamp measurement of visually-evoked conductances with whole-cell patch recordings in primary visual cortex.

Whole cell patch recordings have been realized in the primary visual cortex of the anesthetized and paralyzed cat, in order to better characterize input resistance and time constant of visual cortical cells in vivo. Measurements of conductance changes evoked by visual stimulation were derived from voltage clamp recordings achieved in continuous mode at two or more different subthreshold holding potentials. They show that the magnitude of the conductance increase can reach up to 300% of the mean conductance at rest. The observation of similar changes for the preferred and antagonist responses, when flashing ON and OFF, a test stimulus in pure ON and OFF subfields supports the hypothesis of a role for shunting inhibition in the spatial organization of simple receptive fields.

Animals↗

PubMed1984

Effects of telencephalic ablation on visual unit, sustained potential shift, and EEGs recorded from the toad tectum in response to a visual stimulus.

Extracellular recordings were made of visual unit activity, sustained potential shifts (SPSs), and electroencephalographic activity (EEGs) from the optic tectum and of EEGs from the telencephalon of immobilized toads (Bufo bufo). Moving visual stimuli were presented, and the bioelectric responses were monitored both before and after ligature of the telencephalon. The operation reduced the neuronal spike frequency and the amplitude of the tectal SPS and EEG responses. EEGs were still recorded from the tectum and even the isolated telencephalon. The results are discussed in relation to possible adaptive functions of SPS and EEG changes, the genesis of the EEG, and the role of the telencephalon in visually guided prey-catching behavior.

Animals↗

PubMed1996

A note on the concept of the visual field in neurology, psychology, and visual neuroscience.

Some current confusions in visual neuroscience and psychology over the use of the terms 'visual field', 'field of vision', 'stimulus field', and topographic 'brain maps' are reviewed. These are often used as synonyms, whereas they refer to quite different things. A plea is made that visual scientists should use these terms correctly to avoid conceptual and engineering confusion.

Brain↗

PubMed1990

Binocular advantage and visual processing in dyslexic and control children as measured by visual evoked potentials.

The role of visual processing in dyslexia continues to stir controversy. Previous research using early components of visual evoked potentials (VEP's) has revealed differences in visual processing between dyslexics and controls. VEP's have successfully indexed binocular advantage. Intrasensory functioning could conceivably be deficient in dyslexics. This study recorded VEP's in response to contrast-reversing checkerboards binocularly and monocularly from dyslexic and control children. The overall monocular and binocular amplitudes of the major positive peaks (P100) were greater for controls than dyslexics; however, contrary to the original hypothesis, the magnitude of binocular advantage was higher for dyslexics than for the control children. Stimulus factors had an effect, but did not interact with reading ability.

Analysis of Variance↗

PubMed2004

Induced visual illusions and gamma oscillations in human primary visual cortex.

Using magnetoencephalography, we studied the spatiotemporal properties of cortical responses in terms of event-related synchronization and event-related desynchronization to a range of stripe patterns in subjects with no neurological disorders. These stripes are known for their tendency to induce a range of abnormal sensations, such as illusions, nausea, dizziness, headache and attacks of pattern-sensitive epilepsy. The optimal stimulus must have specific physical properties, and maximum abnormalities occur at specific spatial frequency and contrast. Despite individual differences in the severity of discomfort experienced, psychophysical studies have shown that most observers experience some degree of visual anomaly on viewing such patterns. In a separate experiment, subjects reported the incidence of illusions and discomfort to each pattern. We found maximal cortical power in the gamma range (30-60 Hz) confined to the region of the primary visual cortex in response to patterns of 2-4 cycles per degree, peaking at 3 cycles per degree. This coincides with the peak of mean illusions and discomfort, also maximal for patterns of 2-4 cycles per degree. We show that gamma band activity in V1 is a narrow band function of spatial frequency. We hypothesize that the intrinsic properties of gamma oscillations may underlie visual discomfort and play a role in the onset of seizures.

Adult↗

PubMed2001

Two functional channels from primary visual cortex to dorsal visual cortical areas.

Relationships between the M and P retino-geniculo-cortical visual pathways and "dorsal" visual areas were investigated by measuring the sources of local excitatory input to individual neurons in layer 4B of primary visual cortex. We found that contributions of the M and P pathways to layer 4B neurons are dependent on cell type. Spiny stellate neurons receive strong M input through layer 4Calpha and no significant P input through layer 4Cbeta. In contrast, pyramidal neurons in layer 4B receive strong input from both layers 4Calpha and 4Cbeta. These observations, along with evidence that direct input from layer 4B to area MT arises predominantly from spiny stellates, suggest that these different cell types constitute two functionally specialized subsystems.

Animals↗

PubMed1984

Visual fatigue and visual evoked potentials in multiple sclerosis, glaucoma, ocular hypertension and Parkinson's disease.

Visual evoked potential (VEP) abnormality is widely used as an objective indication of visual pathophysiology in the diagnosis of multiple sclerosis. One major limitation of this test is that VEP abnormality is not specific to multiple sclerosis. In an attempt to explore ways of making the VEP test more specific, changes were measured in VEPs caused by superimposing upon the VEP stimulus either a flicker or a moving pattern. The rationale was to test for visual fatigueability, since it is known that some demyelinated axons fatigue rapidly. Of 10 patients with multiple sclerosis, 90% showed VEP fatigue, while none fatigued in the groups of 10 patients with glaucoma and 10 with Parkinson's disease. Fatigue is, however, not completely specific for multiple sclerosis, since three of 10 patients with ocular hypertension showed VEP fatigue.

Adult↗

PubMed1983

Effect of eye rotation on visual-field map onto superior colliculus and visual cortex.

We used multiunit recording to assess the effect of rotating one eye approximately 90 degrees at about the time of normal eye opening. Rotation of the eye did not alter the topography of the retinal maps onto visual cortex or superior colliculus. The intorted eye drove cells at most recording points in the contralateral visual cortex and superior colliculus. In its ipsilateral colliculus the intorted eye drove cells at about 10% of the recording points; that is, the temporal retina of this eye was quite ineffective in driving collicular cells. In its ipsilateral cortex the intorted eye drove cells at about 30% of the recording sites. The unoperated eye drove cells at all locations in both colliculus and cortex on both sides of the brain. The effects of extorsion were studied only in the superior colliculus. Extorsion and intorsion produced similar results except that extorsion produced a less severe deficit in the ability of the temporal retina to drive cells in its ipsilateral colliculus. Cutting all the extraocular muscles without eye rotation was studied only in the colliculus and produced results similar to those produced by intorsion and extorsion. However, the temporal retina of the operated eye was more effective after muscle cut alone than after intorsion or extorsion. Forcing the animal to use the rotated right eye alone on alternate days during the first 3 mo of life did not decrease the deficits. Almost all recording sites in the right colliculus were driven only by the unoperated left eye. If the left eye was sutured when the right eye was rotated, only the right eye drove cells in the left colliculus, but the two eyes were about equally effective in the right colliculus; however, rather few sites in the right colliculus were binocularly driven. We conclude that both extraocular muscle section and eye rotation reduce the effectiveness of the uncrossed input from the operated eye to the superior colliculus and visual cortex. The effects on the superior colliculus are, however, greater.

Animals↗

PubMed1989

Relations between visual acuity, refraction and the pattern reversal visual-evoked cortical potential in aphakia.

The investigations included 20 aphakic patients. Relations were established between visual acuity, refraction and the pattern reversal visual-evoked cortical potentials (PRVECP). Close correlations were found between the three values. The optimum correction for obtaining best visual acuity, the skiascopic value, and the correction value for obtaining the largest PRVECP amplitude at minimum peak time differ by an average of 0.5 dptr.

Aged↗

PubMed1997

Visual electrophysiology in Parkinson's disease: PERG, VEP and visual P300.

A retinal dopaminergic deficiency underlies some visual changes in Parkinson's disease (PD), in particular those elicited by stimuli near the peak of the human and monkey spatial contrast sensitivity. The correspondence of retinal changes and VEP alterations is not perfect: they do not seem to rely on identical mechanisms. It seems that additional pathology beyond the retina affects visual responses, including VEPs. The relevance of "distal" primary VEP changes to higher cognitive visual abnormalities in PD is not established at present.

Animals↗

PubMed2003

Pattern reversal visual evoked potentials as a measure of visual pathway pathology in multiple sclerosis.

BACKGROUND: Pattern reversal visual evoked potentials (PRVEPs) have a well-documented role in diagnosis of multiple sclerosis (MS), but their value as a visual function surrogate remains controversial. METHODS: We evaluated PRVEP in 37 patients with MS who were participating in a long-term follow-up study following a phase III trial of interferon beta-1a (Avonex). Patients were examined to determine the Kurtzke Extended Disability Status Score (EDSS), multiple sclerosis functional composite (MSFC), contrast letter acuity (CLA), and had cranial MRI scans to determine whole brain atrophy (BPF). PRVEP was evaluated for P100 latency, amplitude, and waveform morphology. Two summary scores were created: for Score A, abnormal latencies, morphologies, and amplitudes of each individual eye were added; for Score B, abnormal latencies, morphologies, and amplitude ratio between eyes was determined. Sixteen patients in this group also had PRVEP at the time they enrolled in the clinical trial, eight years previously. RESULTS: At the follow-up exam, over 75% of patients had abnormal PVEP parameters while visual acuity (VA) was abnormal only in 59%. Increased PRVEP latency over the eight-year period correlated with deterioration assessed by EDSS (P = 0.006), BPF (P = 0.0001), and MSFC (P = 0.0041). Score A was significantly correlated with EDSS, BPF, CLA, cognitive function, and quality of life assessed with the Sickness Impact profile. No correlation was seen with the MSFC. CONCLUSIONS: The results indicate that PRVEP measures MS-related pathology, and can provide not only diagnostic but also prognostic information during evaluation of MS patients.

Evoked Potentials, Visual↗