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PubMed1989

Patterns of connections in rat visual cortex.

The definition of visual areas is one of the central problems in visual cortex research. Rodent extrastriate cortex offers a striking example of the complexity of this issue, in that different parcelation schemes identify within it from 2 to as many as 13 separate visual areas. In the experiments reported here, patterns of connections within rat visual cortex were studied in an effort to better define its organizational layout. The experimental paradigm used consisted of the following steps: first, the pattern of callosal connections was revealed in vivo with the fluorescent tracer bisbenzimide. Then, using the callosal pattern as a landmark, single injections of WGA-HRP were placed at various sites in striate and extrastriate cortex. Subsequently, the relation between the tangential distribution of ipsilateral corticocortical connections, the callosal connections, and the borders of striate cortex were examined in the flattened cortex preparation. The experiments revealed widespread, patchy connections within rat visual cortex. These connections appeared to reflect 3 organizational trends. First, neighboring sites were more extensively connected than distant ones. Second, extrastriate sites receiving common striate cortex inputs tended to be interconnected. Finally, projections from opposite poles in striate cortex tended to form interdigitating patterns of connections in regions of overlap. Altogether these trends suggest that the extrastriate band adjoining striate cortex has a single, global map organization. However, within the global map, a clear modular organization was evident, which appeared to correspond to the multiple visuotopic representations reported for this region. Based on its location, and some organizational similarities. it is suggested that the global map may constitute the rat homolog of area V2 in cat and monkey.

Animals↗
PubMed1990

Change in the pattern of behavioural specialization of neurons in the motor cortex of the rabbit following lesion of the visual cortex.

In order to find out whether damage of the visual cortex (area 17) of the brain results in a functional reorganization of the motor cortex, experiments were carried out with freely moving rabbits performing a food acquisition task in an experimental cage. Two rabbits served as controls, while in three rabbits the visual cortex was bilaterally damaged. Analysis of the activity of 575 neurons in the control and operated rabbits after the recovery of the original instrumental food acquisition behaviour revealed a marked difference in the behavioural specialization of the neurons in the motor cortex of two operated rabbits compared with the control animals. Although the same types of units as in the control rabbits could be found in the operated rabbits (M neurons activated in relation to body and limb movements, S neurons activated in relation to food seizure and L neurons activated in relation to learned food acquisition task), the number of S units was about half of that in the controls and the number of L units about double. The relative number of activations of the neurons in the operated rabbits was significantly less frequent during the food seizure and more frequent during the learned behaviour. This difference indicates a change in the pattern of behavioural specialization of the neurons in the motor cortex due to the damage of the visual cortex. In this reorganization, the motor cortex became more like (but not identical to) visual and limbic cortices that normally contain noticeably more L neurons than the motor cortex. The number of neurons activated in relation to the behaviour in the operated rabbits, as compared with the control animals, was smaller in the upper and larger in the lower layers of the motor cortex. This may indicate recruitment of new neurons from the lower cortical layers.

Animals↗
PubMed1978

Physiological consequences for the cat's visual cortex of effectively restricting early visual experience with oriented contours.

1. The early visual experience of nine cats was restricted to viewing horizontal or vertical lines inside opaque goggles. 2. When the kittens were 3-4 mo old, extracellular recordings were made in the primary visual cortex. To obtain a representative sample of cortical cells, units were studied at regularly spaced intervals along the course of electrode penetrations traveling oblique to the cortical surface. An automated assessment of preferred orientation using a computer-driven optical display was employed, and during the recording session the experimenters did not know which orientation(s) each animal had viewed in early life. 3. In the cats that viewed horizontal lines with one eye and vertical lines with the other during rearing, two major findings of previous workers (14) were confirmed. First, a majority of units were not selective for orientation. Second, units with preferred orientations near vertical tended to be activated exclusively by the eye that had viewed vertical, and likewise for horizontal. 4. In cats that viewed lines of the same orientation with both eyes during rearing, a substantially smaller proportion of units were selective for orientation; the preferred orientations of these units also tended to match the orientation to which the cats had been exposed. 5. Portions of some electrode penetrations showed an orderly arrangement of cells according to preferred orientation similar to that seen in normal cats, but with regions over which only nonselective cells were found. Many penetrations appeared less orderly. 6. The results are consistent with a role for early visual experience in maintaining the responsiveness and innate selectivity of cortical neurons, although they cannot entirely rule out the possibility that experience may alter or determine the preferred orientation of some cells.

Animals↗
PubMed1988

Temporal sequence of neurotransmitter expression by developing neurons of fetal monkey visual cortex.

The developing fetal monkey visual cortex was studied immunocytochemically from 110-155 days post-conception in order to localize cell populations immunoreactive (ir) for gamma-aminobutyric acid, Substance P, cholecystokinin-octapeptide, somatostatin, neuropeptide Y, and proenkephalin A peptide (BAM-18). The area 17/18 border and all cortical laminae identified in the adult visual cortex were discernible from the youngest age examined. All ir-cell populations studied were present at each fetal age. However, despite a relatively adult-like cytoarchitecture, all ir-cell populations studied displayed patterns of immunostaining which were unlike those described in adult visual cortex, and showed significant changes in laminar distribution, morphology, and numbers over the time course of gestation examined. Despite the differences in the patterns of immunostaining between the fetal and adult visual cortex, ir-cell populations intrinsic to the developing visual cortex exhibited adult-like combinations of co-localized transmitters and peptides. The developing monkey cortex also contains ir-cell populations, particularly BAM-18-ir cells, which have not been detected immunocytochemically in the adult monkey cortex. Differences between the fetal and the adult ir-cell populations might be accounted for by cell death, morphological transformation, secondary migration or changes in gene expression for neurotransmitters and neuropeptides.

Animals↗
PubMed1989

Horizontal organization of orientation-sensitive cells in primate visual cortex.

In the visual cortex of the monkey the horizontal organization of the preferred orientations of orientation-selective cells follows two opposing rules: (1) neighbors tend to have similar orientation preferences, and (2) many different orientations are observed in a local region. We have described a classification for orientation maps based on the types of topological singularities and the spacing of these singularities relative to the cytochrome oxidase blobs. Using the orientation drift rate as a measure we have compared simulated orientation maps to published records of horizontal electrode recordings.

Animals↗
PubMed1991

Calcium binding proteins and neuropeptides as molecular markers of GABAergic interneurons in the cat visual cortex.

In the cat visual cortex, almost all parvalbumin-positive cells are GABAergic, and about 80% of the calbindin D-28K-positive neurons are also GABA-immunoreactive. About 37% of the GABAergic neurons contain parvalbumin and a smaller fraction (about 18%) contains calbindin. Furthermore, parvalbumin and calbindin are localized in two separate neuronal populations in the cat visual cortex, suggesting that two GABAergic populations can be distinguished, one containing parvalbumin and one containing calbindin. Double staining for parvalbumin and neuropeptides (CCK, SRIF and NPY), revealed no double-labeled cells, with the exception of a few SRIF- and parvalbumin-positive neurons. These results show that cortical GABAergic cells can be differentiated on basis of their calcium binding protein and neuropeptide immunoreactivity.

Animals↗
PubMed1979

Mapping the representation of the visual field by electrical stimulation of human visual cortex.

Electrical stimulation of human visual cortex produces punctuate phosphenes in the visual field. This phenomenon, which is being explored as the basis for a visual prosthesis for the blind, also provides the first electrophysiological information about the retinocortical map in man. Stimulation of points clustered on the surface of the visual cortex produces phosphenes clustered in visual space. However, adjacent surface electrodes located on opposite sides of a sulcus can produce widely separated phosphenes, because the intervening cortex is buried and inaccessible to stimulation. Such electrodes can also produce multiple phosphenes by simultaneously stimulating both banks of the sulcus. Electrodes which are widely spaced on the brain can produce phosphenes close together in visual space providing they stimulate cortex corresponding to overlapping maps in areas 17 and 18. Analysis of the phosphene map indicates that successive stimulation of points further from the tip of the occipital pole produces phosphenes progressively more distant from the fixation point. Successive stimulation of points along the orthogonal dorsoventral dimension produces a progressive change in phosphene bearing. These results confirm the general view of cortical organization derived from field defect studies in man, and from anatomical and electrophysiological studies in monkeys, and provide a new tool for more detailed study of retinotopic projections in man.

Adult↗
PubMed1975

[Responses of squirrel visual cortex neurons to patterned visual stimuli].

The responses of visual cortical neurons to patterned visual stimuli were studied in squirrel Sciurus vulgaris. The direction selective, orientation-selective and non-selective neurons were observed. Most direction-selective and non-selective neurons were sensitive to high speeds of stimulus movement--hundreds deg/s. The direction-selective neurons exhibited their selectivity at such high speeds in spite of the short time of the stimulus movement through the receptive field. Orientation-selective neurons (with simple or complex receptive fields) were sensitive to lower speeds of the stimulus movement (tens deg/s). Some mechanisms of the properties described are discussed.

Animals↗
PubMed1976

Influence of association cortex on penicillin discharges in the primary visual cortex.

The influence of visual association cortex on the pattern of neuronal activity in the lateral geniculate body, during penicillin-induced discharges in visula cortex, was studied. In a majority of those geniculate cells which exhibited a pre-penicillin discharge increment in activity, that increment was abolished or significantly reduced during focal hypothermia of the visual association cortex. The frequency of penicillin discharges in visual cortex was, in most cases, reduced during cooling of association cortex. These findings are briefly discussed in terms of corticothalamic interactions.

Animals↗
PubMed1979

Postnatal dendritic development in the rabbit visual cortex.

Golgi preparations of rabbit visual cortex aged 1-25 days, as well as similar tissues from adults, were examined for the growth of the dendritic arbor, and in particular the development of dendritic spines. The layer 5 pyramidal neurons and layer 4 stellate neuron were chosen as representatives of larger classes of neurons in the visual cortex. It was determined that the growth of the dendritic arbor, determined by counts of total number of dendritic and total dendritic length, is quite similar for pyramidal and stellate neurons. Dendritic spine development, however, is more rapid in pyramidal neurons than in stellate. This disparity in the rate of dendritic spine development is discussed in the light of physiologic studies on the development of receptive field properties in the rabbit visual cortex.

Age Factors↗
PubMed1975

Modification of single neurons in the kitten's visual cortex after brief periods of monocular visual experience.

Kittens were deprived of form vision by suturing the lids of both eyes, except for a brief period (1, 6 or 20 hours) on the 29th day when the right eye was opened. 6 space and 20 hours of monocular vision produced a distinct shift in the ocular dominance of visual cortical neurons towards the experienced eye, and an increase in the proportion of cells with obvious orientation selectivity. These modifications in the visual cortex were enhanced by a period of "consolidation": they were somewhat less obvious if recordings were taken immediately after the exposure but were complete 2 days later. Although remarkably little visual experience was needed for these changes, the results contrast with the effects of rearing in an environment of vertical stripes, where only 1 hour of exposure produces much more striking effects. A normal visual environment may have a less powerful organizing influence on cortical neurons than such an environment containing only one orientation.

Animals↗
PubMed1978

Retinotopic organization of the guinea pig's visual cortex.

Under anaesthesia the right visual cortex of the guinea pig was investigated with 1.5 M potassium citrate-filled glass microelectrodes. Single unit and small unit cluster response showed an organized three-part representation of the contralateral visual field on the animal's visual cortex. The major central division (V1) had the representation of a nasotemporally elongated visual field. This visual field extended for about 110 degrees horizontally and for about 70 degrees vertically. The nasal visual field was represented laterally on the cortex and the lower visual field anteriorly. The visual field representation was not uniformly magnified in V1; the magnification of the nasal field was higher than the rest of the visual field. On either side of V1, the guinea pig's cortex had two additional visually responsive strips. The strip V2L, situated lateral to V1, had a condensed representation of about 40 degrees of the animal's nasal visual field and mirror-imaged the visual field representation of the adjacent V1. The strip V2M, situated medial to V1, had a similar representation of about 40 degrees of the animal's temporal visual field and mirror-imaged the visual field representation of the area V1 adjacent to it. A binocularly responsive zone of cortex was observed on either side of the boundary between the areas V1 and V2L, representing between 10 degrees and 15 degrees of the nasal visual field on each side of the boundary line. Investigation of the retinal ganglion cell distribution of the animal showed a nasotemporally oriented 'visual streak' with a high ganglion cell density per unit area of the retina, near the optic disc. Away from the 'visual streak' the density of the ganglion cells of the retina diminished progressively. The configuration of the 'visual streak' and the general pattern of the ganglion cell distribution in the rest of the retina coincided with the asymmetry in the magnification of representation of the animal's visual field on the cortex.

Animals↗
PubMed1991

Comparison of serotonin 5-HT1 receptors and innervation in the visual cortex of normal and dark-reared cats.

The visual cortical serotoninergic system was compared in normal and dark-reared cats to determine whether visual experience is necessary for its normal development. In vitro receptor binding of [3H]5-HT indicated an increase in 5-HT1 receptor number in dark-reared cats with no change in affinity. This elevation was specific to the visual cortex and no changes were found in the frontal cortex as a result of dark rearing. Autoradiographic histology revealed that in the normal cat visual cortex, 5-HT1 receptors were present in all cortical layers and were slightly more dense in supragranular and infragranular layers. In dark-reared cats, there was a marked elevation in receptor density in supragranular and infragranular layers and little change within layer IV. Immunohistochemical techniques (anti-5-HT) were used to compare serotoninergic innervation in the visual cortex of normal and dark-reared cats. In normal cat visual cortex, serotonin fibers were most dense in the superficial layers (I-III), least dense in layers IV and VI, and intermediate in layer V. No differences were found between normal and dark-reared cats in the laminar distribution or density of serotoninergic innervation. These results indicate that visual experience is necessary for the normal development of the visual cortical serotonin system. The findings that the effects of dark rearing were specific to the visual cortex and that within the visual cortex these effects were specific to supra- and infragranular layers are consistent with a possible role for serotonin in the prolonged physiological plasticity that occurs in the visual cortex of dark-reared cats.

Animals↗
PubMed1991

Distribution of somatostatin receptors in the cat and monkey visual cortex demonstrated by in vitro receptor autoradiography.

Somatostatin (SRIF, S14) receptors in the cat and monkey visual cortex were visualized by means of in vitro autoradiography with an iodinated agonist of SRIF, [125I-Tyr0,DTrp8]S14. The kinetics, performed on tissue sections, revealed an apparently single, saturable site (KD = 3.92 +/- 0.31 10(-10) M for the cat, and 3.82 +/- 0.28 10(-10) M for the monkey visual cortex) with pharmacological specificity for S14 and [DTrp]-substituted S14. Autoradiography, performed on frontal sections of the cat and monkey visual cortex, revealed a heterogeneous regional and laminar distribution of SRIF receptors. In cat areas 17, 18, and 19, SRIF receptors occur mainly in the supragranular layers, although small interareal and intra-areal differences are observed. The infragranular layers (V-VI) in area 19 contain a significantly higher proportion of SRIF receptors compared to both areas 17 and 18. In the antero- (AMLS) and posteromedial lateral suprasylvian area (PMLS), layers V and VI contain the highest proportion of SRIF receptors. This latter pattern is also observed in the area prostriata medially adjoining area 17 in the splenial sulcus. In the monkey visual cortex, areas 17 and 18 exhibit similar distribution patterns, SRIF receptors being primarily concentrated in layers V and VI. Neither in the cat nor the monkey visual cortex could we observe significant differences in SRIF receptor distribution between different retinotopic subdivisions within one area.

Animals↗
PubMed1991

Dark-rearing delays the loss of NMDA-receptor function in kitten visual cortex.

Some features of the visual cortex develop postnatally in mammals. For example, geniculocortical axons that initially overlap throughout cortical layer IV segregate postnatally into two sets of interleaved eye-specific bands. NMDA (N-methyl-D-aspartate) receptors are necessary for eye-specific axon-segregation in the frog tectum, and as NMDA receptors play a greater part in synaptic transmission in early life and decrease in function during the period of axon segregation, they may be involved in the segregation of geniculocortical axons: they are well placed to do so as they transduce retinally derived signals essential for segregation. Rearing animals in the dark in early life delays segregation and prolongs the critical period for plasticity. We now report that dark-rearing of kittens also delays the loss of NMDA receptor function in the visual cortex, supporting the view that they play an important part in neuronal development and plasticity.

2-Amino-5-phosphonovalerate↗
PubMed1990

Neural systems contributing to acetylcholinesterase histochemical staining in primary visual cortex of the adult rat.

Histochemical studies demonstrate that cortical area 17 (primary visual cortex) of the adult rat displays a characteristic laminar pattern of acetylcholinesterase (AChE) activity. While AChE-positive axons are found throughout the cortical layers, most intense staining occurs in a band that corresponds to layer V and the deep portion of layer IV. The present studies were directed toward determining the neural systems containing this AChE activity. Unilateral electrolytic or excitatory amino acid induced lesions of the basal forebrain result in reductions of AChE staining in ipsilateral visual cortex, particularly in layers IV and V. Electrolytic or scalpel lesions, placed in white matter underlying dorsal and lateral neocortex to interrupt basal forebrain projections to visual cortex, also reduce AChE staining in visual cortex. Lesions in the cingulate bundle and supracallosal stria reduced AChE staining retrosplenial cortex but did not affect staining visual cortex. Placement of electrolytic lesions in the hypothalamus produced no detectable change in the pattern of AChE in visual cortex. Electrolytic lesions in the midbrain tegmentum, placed to interrupt ascending axons from brainstem monoamine neurons, produced no detectable change in the pattern of AChE in visual cortex. Placement of lesions in the dorsal thalamus that include all of the dorsal lateral geniculate nucleus did not alter AChE staining in visual cortex. The results indicate that AChE activity in adult visual cortex is found primarily within afferent axons from the basal forebrain system. These data demonstrate further that the AChE staining characteristic of adult visual cortex is associated with neural systems that are distinctly different from those associated with AChE staining in visual cortex of the infant rat.

Acetylcholinesterase↗