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PubMed1983

The distribution of displaced ganglion cells in the retina of the pigeon.

Displaced ganglion cells in the pigeon's retina, at the inner margin of the inner nuclear layer, were labelled by retrograde axonal transport of horseradish peroxidase (HRP). Large HRP injections were made in order to fill all the retinal projection sites in the thalamus and midbrain. The distribution of labelled cells was studied in retinal whole mounts incubated with tetramethyl benzidine (TMB) substrate for HRP. A maximum of 5,300 HRP labelled displaced ganglion cells was found. They were concentrated in a band of retina centred on the horizontal meridian, with high density areas (of about 110 cells/mm2) near the area centralis and in the mid-temporal retina. This is a different distribution to that of ganglion and inner nuclear layer cells; these are concentrated in the area centralis and red field. The orientation of retinal maps was checked by ophthalmoscopic measurements of the angle of the pecten to the horizontal in alert pigeons; this was found to be approximately 70 degrees. The array of displaced ganglion cells, studied by nearest neighbour distributions, was irregular and nearly random, which is consistent with a system of low spatial acuity. In the central retina only the cell bodies and not the dendrites of small displaced ganglion cells (7.5 microns diameter) were labelled; towards the periphery large displaced ganglion cells (16 microns diameter) with 2-5 radially arranged primary dendrites were found.

Animals↗

PubMed1983

The distribution of centrifugal terminals in the pigeon retina.

The terminals of the centrifugal fibres of the pigeon retina have been labelled by anterograde axonal transport or diffusion of horseradish peroxidase, and their distribution studied in whole amounts of the retina. Centrifugal terminal arborisations are concentrated in a band near the projection of the horizontal meridian on the retina. Within this band there are high density areas next to the area centralis and in the mid-temporal retina. The arborisations are largely absent from the red field and are nearly randomly arrayed. Their distribution resembles that of the displaced ganglion cells but not of other retinal neurons. We estimate that approximately 7,000 centrifugal terminal arborisations are present in each retina. Approximately two-thirds of these are convergent, with branches ending in large terminals clustered around a single cell in the amacrine sublayer; often penetrating up to 10 microns into the inner nuclear layer. The remainder are divergent endings which innervate a larger area of retina with widely spaced small terminals about 1 micron in diameter. Possible synaptic contacts between centrifugal terminals and displaced ganglion cells are occasionally seen; these contacts and the similarity in distribution suggest a link between the centrifugal and accessory optic systems.

Animals↗

PubMed1982

Visual receptive field properties of cells innervated through the corpus callosum in the cat.

The present experiment examined the receptive field (R.F.) properties of cortical cells which receive part of their input from the contralateral hemisphere via the corpus callosum. Two groups of cats were used to recording unit activity: a normal control group, and an experimental group consisting of cats which had their optic chiasmas split across the midline prior to the recording sessions. Acute recordings were carried out in the conventional manner using tungsten microelectrodes and N2O: O2 anaesthesia. The recording site was the 17-18 border. The stimulus consisted of a thin bar generated on an oscilloscope screen by a computer. The bar, whose orientation was varied automatically from 0 degrees to 345 degrees in 15 degrees steps, was swept across the screen at constant speed orthogonal to the orientation. Various R.F. properties were studied using both quantitative and qualitative criteria. Thus, in the normal cat, simple, complex and hypercomplex type R.F.'s were found, whereas no callosally activated cell was of the simple type. The ocular dominance distribution found in the split chiasma cat was skewed towards the ipsilateral eye, although a fairly large number of cells could be driven with the two eyes. The R.F.'s of the callosally activated neurons were all situated close to the vertical neurons were all situated close to the vertical meridian, which they sometimes straddled. Both in the normal and in the chiasma sectioned cats, the complex cells had larger R.F.'s than the other cell types. However, the R.F.'s determined through the ipsilateral eye was essentially of the same dimensions as those obtained through the indirect interhemispheric pathway, and this irrespective of cell type. Orientation specificity was similar for the two eyes in the split chiasma cats as it was for the normal cats although in the former the orientation tuning curve was narrower for the callosal pathway than for the more direct thalamo-cortical pathway. The results are interpreted within the context of the different functions ascribed to the corpus callosum in vision.

Animals↗

PubMed1983

Effects on binocular activation of cells in visual cortex of the cat following the transection of the optic tract.

Cells in area 17 of the cortex are generally activated either directly through a retino-thalamic pathway or indirectly via a contralateral hemisphere-callosal pathway. The aim of the present experiment was to evaluate the effects of eliminating this second pathway on the binocular activation of cells in the primary visual cortex. The optic tract was sectioned on one side in 18 cats and unit activity was recorded in the contralateral hemisphere. This hemisphere should receive normal thalamo-cortical inputs but no visual callosal input. These animals were compared to 21 normal cats. Extracellular electrophysiological recordings were carried out in the conventional way using tungsten microelectrodes and N2O anaesthesia. Results indicated that the proportion of binocular cells found in the cortex of tract sectioned animals was lower than that found in normal animals. However, this decrease in binocularity could be essentially attributed to cells having receptive fields situated to within 4 degrees of the vertical meridian of the visual field. These results are interpreted as being congruent with the demonstrated anatomo-physiological projections of the callosal system.

Animals↗

PubMed1983

Oblique effects, vertical effects and meridional amblyopia in monkeys.

Orientation anisotropies were investigated for monkeys with normal visual acuity and for monkeys with experimentally induced amblyopia. It was found that the majority of control monkeys showed a normal oblique effect if any existing refractive errors were carefully corrected, but a few of the control monkeys had a meridional amblyopia, i.e., an orientation anisotropy in which the grating orientation for the greatest and lowest contrast sensitivities were correlated with the principal meridians of an astigmatic refractive error even when the refractive error was corrected. For monkeys with strabismic amblyopia caused by a surgically induced divergent strabismus, the orientation anisotropies showed a vertical effect in which contrast sensitivity was lower for vertically oriented gratings than for horizontally oriented gratings. However, monkeys with the same degree of amblyopia resulting from experimental procedures that did not involve a misalignment of the visual axes showed orientation anisotropies that corresponded to the usual oblique effect.

Amblyopia↗

PubMed1987

Reticulo-spinal neurons participating in the control of synergic eye and head movements during orienting in the cat. I. Behavioral properties.

The activity of 24 reticulo-spinal neurons (RSN) identified by antidromic stimulation at the C1-C2 level has been recorded intra-axonally in the pons of alert head-fixed cats during spontaneous gaze shifts and orienting towards novel targets. Relationship of neuronal discharge to saccadic eye movements, positions of fixation and EMG of dorsal neck muscles were analysed. The present report describes behavioral properties of a group of 14 RSN showing similar types of correlations with motor parameters during eye-head synergies. These "eye-neck" RSN (EN-RSN) generate bursts in synchrony with phasic components of ipsilateral neck EMG and leading ipsiversive saccades by a variable lead time. Bursts are followed by a prolonged discharge whose frequency decays even when eccentric eye position is maintained constant and accompanied by sustained neck muscle activity. The firing rate of EN-RSNs depends on eye position: they are silent with saccades in their ON-direction when the eyes are deviated towards the contralateral half of the oculomotor range and the ipsilateral neck muscles are relaxed. When the eyes cross the vertical meridian, the frequency of phasic and tonic components related to eye-head synergies increase proportionally to ipsilateral eye position. Ten of the 14 EN-RSNs, located in the pontine reticular formation, received monosynaptic input from the contralateral superior colliculus. Two were labeled by intra-axonal injection of HRP which revealed extensive branching in the abducens, facial, medial and lateral vestibular, prepositus and intercalatus nuclei and in the caudal pontine and bulbar reticular formation. It is concluded that the caudal pontine tegmentum, including the region just anterior to the abducens nucleus, contains RSNs whose signals seem appropriate to control phasic neck muscle activity and which also project to structures related to ocular and facial movements. Comparisons with the perisaccadic activity of tectal neurons projecting in the predorsal bundle reveals a profound transformation of the descending signal at the level of EN-RSNs which represent first order relay neurons of the tecto-reticulo-spinal pathway.

Action Potentials↗

PubMed1988

Topographic relations between ocular dominance and orientation columns in the cat striate cortex.

In the visual cortex of four adult cats ocular dominance and orientation columns were visualized with (3H)proline and (14C)deoxyglucose autoradiography. The two columnar systems were reconstructed from serial horizontal sections or from flat-mount preparations and graphically superimposed. They share a number of characteristic features: In both systems the columns have a tendency to form regularly spaced parallel bands whose main trajectory is perpendicular to the border between areas 17 and 18. These bands frequently bifurcate or terminate in blind endings. The resulting irregularities are much more pronounced in the ocular dominance than in the orientation system. The periodicity of the columnar patterns was assessed along trajectories perpendicular to the main orientation of the bands and differed in the two columnar systems. The spacing of the ocular dominance stripes was significantly narrower than the spacing of orientation bands. The mean periodicity of a particular columnar system was virtually identical in the two hemispheres of the same animal but it differed substantially in different animals. However, the spacing of orientation columns covaried with that of the ocular dominance columns, the ratios of the mean spacings of the two columnar systems being similar in the four cats. The superposition of the two columnar systems revealed no obvious topographic relation between any of the organizational details such as the location of bifurcations, blind endings and intersections. We suggest the following conclusions: 1. The developmental processes generating the two columnar systems seem to obey the same algorithms but they act independently of each other. 2. The space constants of the two systems are rigorously specified and appear to depend on a common variable. 3. The main orientation of the bands in both columnar systems is related to a) the representation of the vertical meridian, b) the anisotropy of the cortical magnification factor, and c) the tangential spread of intracortical connections.

Animals↗

PubMed1988

The ipsilateral field representation in the striate cortex of the opossum.

Reference axes for the visuotopic study of the opossum's striate cortex were estimated from corresponding binocular response fields using multi-unit recording. These central binocular axes (CBA) were derived from experimental data based on the concept that corresponding receptive fields for each eye should be mostly in register under natural conditions. Vertical reference meridians, orthogonal to these axes, define a contralateral and an ipsilateral field for each eye with respect to the recording site. An ipsilateral field representation was observed for both eyes in the striate cortex at the transition zone with peristriate. Maximal values for the center and border of ipsilateral receptive fields were, respectively, 8 and 20 degrees for the contralateral eye and 6 and 14 degrees for the ipsilateral eye. An equivalent ipsilateral field representation was found in animals that had the anterior commissure cut prior to the recording session. This suggests that the ipsilateral field of both eyes may be represented in the striate cortex via the ipsilateral optic tract. Additionally, it was observed that the region of higher ganglion cell density in the retina shows a flattened distribution and that the CBA intersects the retina at the temporal aspect of this region.

Animals↗

PubMed1989

The callosal projection in cat visual cortex as revealed by a combination of retrograde tracing and intracellular injection.

The neuronal composition of callosally projecting cells in cat visual cortex was determined with a combination of retrograde labelling and intracellular injection. Fluorescent tracers were stereotaxically injected into the proximity of the area 17/18 border, corresponding to the representation of the visual vertical meridian. In fixed slice preparations of homotopic regions of the contralateral hemisphere retrogradely labelled cells were filled with Lucifer Yellow. Of more than a hundred injected cells a morphological variety of pyramidal cells, located in cortical layers II-IV and VI, constituted the prevalent cell class in the contralateral projection. A minor proportion of spiny stellate cells was encountered in layer IV. Despite the presence of a contralaterally projecting smooth stellate cell, presumed to be a basket cell, it is concluded that the efferents to contralateral visual cortex predominantly arise from pyramidal and spiny stellate cells. Thus, in agreement with findings from anterograde degeneration studies, the interhemispheric pathway most likely conveys a direct excitatory input to postsynaptic target cells.

Animals↗

PubMed1989

Dark adaptation and increment threshold in rhesus monkey and man.

Dark adaptation and increment thresholds were determined for a trained rhesus monkey and a human observer under identical conditions. The measurements were made with a 1.5' diameter, 100 ms target at 10 degrees and 40 degrees eccentricity along the temporal horizontal meridian. Qualitatively, the results are similar for the two species: Both rhesus monkey and man have photopic and scotopic branches, which cross at approximately the same time in the dark and at approximately the same background luminance.

Adaptation, Physiological↗

PubMed1988

Callosal projections between areas 17 in the adult tree shrew (Tupaia belangeri).

In the primary visual cortex (area 17) of the tree shrew (Tupaia belangeri) neurons projecting to the contralateral area 17 via the corpus callosum were identified by horseradish peroxidase histochemistry (HRP, WGA-HRP). The distribution of homotopic and heterotopic connections was studied. We found that a narrow stripe of area 17 close to the dorsal area 17/18 border - which corresponds to the visual field along the vertical meridian - is connected via homotopic callosal projections. The adjacent dorsal part of area 17, which largely corresponds to the binocular visual field, is connected via homotopic as well as heterotopic projections. Heterotopic projections originate in the cortical stripe along the area 17/18 border and their contralateral targets are displaced medially. Callosal neurons are located mostly in supragranular but also occur in infragranular layers. The supragranular neurons in general are pyramidal cells. In addition to these findings, we confirmed earlier reports on ipsilateral projections of the primary visual area to the dLGN, the claustrum, area 18 and other visual areas.

Animals↗

PubMed1985

Internal representations and operations in the visual comparison of transformed patterns: effects of pattern point-inversion, position symmetry, and separation.

A scheme for visual pattern recognition is described. It is supposed, amongst other things, that patterns are internally represented by the visual system in terms of local features, spatial-order relations between local features, and global spatial relations specifying approximate pattern position with respect to the point of fixation. It is further supposed that there are two distinct types of internal operation that may be applied to the components of internal representations in the process of pattern comparison: typically a discrete spatial-order-reversal operation and a continuous position-shift operation. Some general predictions of the scheme are tested against data obtained in an experiment using random-dot patterns that were subjected to rigid transformations and presented at various locations along the horizontal meridian. Patterns were presented sequentially, in pairs, to subjects in a "same-different" comparison task. Pattern pairs were to be responded to as "same" if they were identical or related by point-inversion (planar rotation through 180 degrees) or responded to as "different". Extending earlier findings, the present results showed that "same"-detection performance for identical and point-inverted patterns depended differentially on the distance between the patterns and the symmetry of the pattern positions about the point of fixation in a manner consistent with the predictions of the scheme.

Adult↗

PubMed1985

A two dimensional model for saccade generation.

A model for the generation of oblique saccades is constructed by extending and modifying the one dimensional local feedback model. It is proposed that the visual system stores target location in inertial coordinates, but that the feedback loop which guides saccades works in retinotopic coordinates. To achieve straight trajectories for centripetal and centrifugal saccades in all meridians, a comparator computes motor error as a vector and uses the vectorial error signal to drive two orthogonally-acting burst generators. The generation of straight saccade trajectories when the extraocular muscles are of unequal strengths requires the introduction of a burst-tonic cell input to motor neurons. The model accounts for the results of two-site stimulation of the superior colliculus and frontal eye fields by allowing simultaneous activation of more than one comparator. The postulated existence of multiple comparators suggests that motor error may be computed topographically.

Animals↗

PubMed1983

Two spatio-temporal filters in human vision. 2. Selective modification in amblyopia, albinism, and hemianopia.

We have used the psychophysical methods described in the first paper of this series (Holliday and Ruddock, 1983) to determine selected spatial and temporal response characteristics of the ST1 and ST2 filters for subjects suffering visual defects. Data are given for 19 amblyopes, an albino and a hemianope, and comparison data are also given for a number of subjects with normal vision. The ST1 spatial responses for both the "normal" and "amblyopic" eyes of 12 convergent strabismic amblyopes are displaced to low spatial frequencies compared to the normal curve, which implies that there is a loss of fine spatial tuning. In all but one subject, the curve for the "amblyopic" eye peaks at a spatial frequency lower than that for the "normal" eye, thus the former deviates further from the normal pattern than the latter. The ST1 spatial responses of 6 refractive amblyopes are also displaced to the low frequency side of the normal curve, although on average the shift is smaller than in the case of the strabismic amblyopes. For each subject, the response curve of the "amblyopic" eye peaks at a lower spatial frequency than does that for the "normal" eye. ST1 spatial responses were measured for targets located up to 30 degrees off-axis along the horizontal meridian and sample data are given for one strabismic and one refractive amblyope and for two normal subjects. It is concluded from these data that the changes in the spatial responses associated with amblyopia do not simply reflect eccentric fixation of the target. The ST2 spatial response was measured for the "normal" and "amblyopic" eyes of 9 amblyopes (7 strabismic and 2 refractive). There is no significant difference between the average amblyopic response and that of normal subjects, and only in one case does the response for an "amblyopic" eye peak at a frequency lower than the peak frequency for normal vision. The ST2 temporal response for 9 amblyopes shows no systematic deviations from the normal response. For the albino, both the ST1 and ST2 spatial responses peak at around 0.3 cycles deg-1, and both curves are displaced considerably to the low spatial frequency side of the normal ST2 spatial response. The albino's ST2 temporal response is essentially normal. Measurements for the hemianope's "blind" hemifield under conditions appropriate to the isolation of the ST1 and ST2 spatial responses reveal no tuning curves. The ST2 temporal response for the "blind" hemifield, however, is of large amplitude, with a peak at 2 Hz, well below the normal frequency response peak. It is argued that the loss of fine spatial tuning which occurs in the ST1, but not the ST2, spatial responses of the amblyopes is consistent with the sequential organisation of these two filter classes proposed by Holliday and Ruddock (1983). Further, for the only two subjects whose ST2 spatial response curves are displaced to abnormally low frequencies (the albino and a strabismic amblyope) the ST1 spatial response is shifted to low spatial frequencies compared to the normal ST2 curve...

Albinism↗

PubMed1976

[A description of a method for objective perimetry (author's transl)].

An infrared-sensitive TV Camera has been fitted into a projection perimeter, which allows to control fixation independent of the particular background illumination. The consensual pupil light reflex, triggered by the test light of the perimeter, is measured and registered with a special TV processor designed for this purpose. The method was tested for its efficiency on four healthy volunteers. The course of sensory and pupillomotor thresholds were measured on the 135 degree meridian of the visual field. Determinations were conducted in the photopic range of 10 asb background illumination with two test points of 27' and 7'. A difference of 10 dB was found between the sensory and pupillomotor thresholds.

Adult↗

PubMed1979

Visual reaction time as a function of locus, area, and complexity of stimulus.

Reaction time (RT) of normal subjects to square-wave gratings of two different frequencies were related to locus of presentation, area, and stimulus complexity. Each frequency was presented to either side of the horizontal meridian (half size stimulus) or both sides stimultaneously (full size stimulus). The two different frequencies were also flashed simultaneously to both hemifields (compound stimulus). Stimulus position affected RT with the 1 c/deg stimulus, RT being faster for the lower hemifield. With presentation on both sides of the horizontal median simultaneously or of the two spatial frequencies, the resulting RT was equal to that of the faster component. Implications of the results for the functional organization of the visual system are discussed.

Female↗

PubMed1990

Morphological classification and retinal distribution of large ganglion cells in the retina of Bufo marinus.

The retrograde transport of horseradish peroxidase (HRP) and cobaltic-lysine complex (CLC) was used to morphologically characterize large ganglion cells (GCs) and to determine their distribution in retinal wholemounts and in sectioned material in the retina of Bufo marinus. Large GCs, amounting to about 0.5% of total GC population, were defined to be those with very large dendritic field sizes varying between 0.1 mm2 to 0.6 mm2 and cell soma sizes of between 100 microns 2 to 400 microns 2. These cells were subdivided into 3 major groups, Types I, II and III, on the basis of their dendritic field sizes, aborization patterns and the strata of dendritic branching within the inner plexiform layer (IPL). The majority of large neurons (about 90%) were classified as Type I GCs with symmetrical dendritic arbor. These cells had either bistratified branching in the scleral and vitreal sublamina of the IPL (65% of Type I Cells) or unistratified branching in the scleral (26%) or in the vitreal (9%) sublamina. Their dendritic field sizes increased linearly from the retinal centre from 0.13 mm +/- 0.02 mm2 (mean and S.D.) to 0.58 +/- 0.11 mm2 in the retinal periphery. Type II GCs (about 9% of large GC population) were characterized by an asymmetrical dendritic aborization directed towards the ciliary margin with unistratified branching in the scleral sublamina of the IPL. The mean dendritic field sizes of these cells were 0.26 +/- 0.09 mm2. Type III GCs, the least frequent (about 1%) category of large GCs had sparsely branching, elongated dendritic branching aligned approximately parallel with the nasotemporal axis of the retina. The unistratified dendritic branches of these neurons were located in the vitreal sublamina of the IPL with a mean dendritic field size of 0.42 +/- 0.11 mm2. The dendritic field sizes of Types II and III GCs did not increase with retinal eccentricity. Type I GCs were distributed unevenly across the retina, the density being greatest in the visual streak, along the nasotemporal meridian of the retina. The dendritic field sizes of these cells increased towards the retinal periphery, resulting in a constant dendritic field coverage factor across the retina. Each retinal point was covered by the dendritic fields of 4-5 adjacent GCs. In contrast, Types II and III GCs had only discontinuous dendritic coverage. The identification of morphological types of large GCs with previously described functional classes of GCs in the anuran retina is discussed.

Animals↗

PubMed1992

Extended-wear of high oxygen-permeable quantum contact lenses.

This study was performed to investigate the effects of extended-wear of rigid aspherical high gas-permeable contact lenses on the cornea. In the study 32 subjects (62 eyes) were followed over a period of 3 to 24 months. A high gas-permeable contact lens (Dk 92), made of fluoro-silicone-acrylate copolymer, was used. Vision remained constant during the studied period. The corneal thickness decreased significantly (p less than 0.05) during the first six months. Significant changes (p less than 0.05) were found after three months in the corneal curvature, especially in the vertical meridian. No further topographical changes were noted in the period between three and six months of extended-wear. Complications, like acute red eye syndrome and bacterial infections, which may be encountered in soft lens extended-wear, were not noticed. At the end of the study 20 subjects (38 eyes, 61%) were still on extended-wear, 9 subjects (18 eyes, 29%) changed to daily wear and 3 subjects (six eyes, 10%) became unavailable for follow-up. Extended-wear of rigid aspherical high gas-permeable contact lenses may be considered as an acceptable alternative for soft lens extended-wear.

Adult↗