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PubMed1986

Orientation selectivity of synaptic potentials in neurons of cat primary visual cortex.

Neurons of the visual cortex of the cat were penetrated with intracellular electrodes and postsynaptic potentials evoked by visual stimuli recorded. By alternately polarizing the cell with steady current injected through the recording electrode, IPSPs and EPSPs could be recorded and analyzed independently. Hyperpolarizing current suppressed IPSPs and enhanced EPSPs by moving the membrane potential toward the IPSP equilibrium potential. Depolarizing the cell toward the EPSP equilibrium potential enhanced IPSP. The responses to electrical stimulation of the LGN, where EPSPs and IPSPs could be distinguished easily by virtue of their characteristic latencies and shapes, were used to set the current injection to the appropriate level to view the two types of synaptic potential. EPSPs were found to be well oriented in that maximal depolarizing responses could be evoked at only one stimulus orientation; rotating the stimulus orientation in either direction produced a fall in the EPSP response. IPSPs were also well tuned to orientation, and invariably the preferred orientations of EPSPs and IPSPs in any one cell were identical. In addition, no systematic difference in the width of tuning of the two types of potential was seen. This result has been obtained from penetrations of over 30 cortical cells, including those with simple and complex receptive fields. It is concluded that orientation of cortical receptive fields is neither created nor sharpened by inhibition between neurons with different orientation preference. The function of inhibition evoked simultaneously with excitation by optimally oriented stimuli has yet to be determined, though it is likely to be the mechanism underlying other cortical receptive field properties, such as direction selectivity and end-stopping.

Animals↗
PubMed1984

Specificity of intrinsic connections in primate primary visual cortex.

Several recent studies have suggested a patchy system of intrinsic lateral connections in area 17 of the macaque monkey. To see whether this pattern bore any relationship to the cytochrome oxidase blobs we made multiple tiny injections of horseradish peroxidase into layers 2 and 3 of area 17, small enough so that some of the injections (or their cores) were entirely inside a single blob, or entirely outside. When the injection centers were entirely in blobs, the label in layers 2 and 3 was transported preferentially to nearby blobs, avoiding nonblob areas. When the injections were in nonblob areas, the label was found predominantly in surrounding nonblob areas, avoiding the blobs. Besides this lateral transport, label was also present in the layers below 2 and 3: the label in layers 4 and 6 was very restricted, occupying roughly the diameter of the injection core and presumably representing axons of cell bodies at the injection site; in layer 5 diffusely labeled patches observed the same blob/nonblob segregation seen above layer 4.

Animals↗
PubMed1984

[Demonstration of an effect of (3H)-L-proline on the number of dendritic spines on stellate cells of the primary visual cortex in Macaca during the critical period].

A morphometric study in cortical layer IVC of Macaca area 17 was performed during the critical period. A 20% increase in the number of dendritic spines was observed in neurons with horizontal dendritic tree in the cortical sublayer IVC alpha after an intraocular injection of (3H)-L-proline. A neuroactive role of this amino acid is discussed.

Animals↗
PubMed1989

Nuclear terminations of corticoreticular fiber systems in rats.

Corticoreticular fiber systems were examined in adult albino and hooded rats using anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) and anterograde degeneration. WGA-HRP injections were made stereotactically into the medial prefrontal cortex, the medial agranular cortex, the anterior cingulate cortex, the face motor cortex, the forelimb motor cortex, the trunk-hindlimb motor cortex, the face somatosensory cortex, the primary auditory cortex, the secondary visual cortex and the primary visual cortex. With exception of the cingulate cortex (which is relatively inaccessible to lesioning methods) and the primary visual cortex, electrocautery lesions were made into these same cortical areas. The precise locations of cortical injection/lesion sites were corroborated on the basis of cortical cytoarchitectonic criteria, patterns of retrograde and anterograde thalamic labeling, and patterns of anterograde labeling in non-reticular brainstem nuclei such as the red nucleus, trigeminal nuclei and dorsal column nuclei. The heaviest corticoreticular projections arise from the medial agranular cortex. The medial prefrontal cortex also gives rise to consistently strong corticoreticular projections. The anterior cingulate cortex sends robust corticoreticular projections to the upper brainstem but relatively weak projections to the lower brainstem. With respect to the primary motor cortex, the face area gives rise to the densest corticoreticular projections, rivaling those emanating from the medial agranular cortex. The trunk-hindlimb area gives rise to substantial corticoreticular projections, but those originating from the forelimb area are modest and directed chiefly to midbrain and medullary levels. The face area of the somatosensory cortex gives rise to rather weak corticoreticular projections, while those arising from the primary auditory cortex are fewer still. Descending projections from the secondary visual cortex are sparse, with labeled terminals occurring in a few pontine and medullary reticular nuclei. Only one brainstem reticular nucleus (nucleus cuneiformis) was found to receive projections from the primary visual cortex, and this input was extremely sparse. Corticoreticular projections to the upper brainstem terminate predominantly ipsilateral to the cortical injection site, whereas medullary corticoreticular projections distribute bilaterally. Corticoreticular fibers from the medial agranular, face motor and trunk-hindlimb motor cortex terminate heavily in somatomotor brainstem reticular nuclei such as the pontis oralis, the pontis caudalis and the gigantocellularis.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1991

Relation of cortical cell orientation selectivity to alignment of receptive fields of the geniculocortical afferents that arborize within a single orientation column in ferret visual cortex.

Neurons in the primary visual cortex of higher mammals are arranged in columns, and the neurons in each column respond best to light-dark borders of particular orientations. The basis of cortical cell orientation selectivity is not known. One possible mechanism would be for cortical cells to receive input from several lateral geniculate nucleus (LGN) neurons with receptive fields that are aligned in the visual field (Hubel and Wiesel, 1962). We have investigated the relationship between the arrangement of the receptive fields of geniculocortical afferents and the orientation preferences of cortical cells in the orientation columns to which the afferents provide visual input. Radial microelectrode penetrations were made into primary visual cortex of anesthetized adult sable ferrets. Cortical cells were recorded throughout the depth of the cortex, and their orientation preferences were determined. Cortical cell responses were then eliminated by superfusion of the cortex with either kainic acid (Zahs and Stryker, 1988) or muscimol. After the drug treatment, responses from many single units with distinct receptive fields were recorded. These responses were presumed to be those of geniculocortical afferents, because they had the response properties characteristic of LGN neurons, and because they could be recorded only in cortical layers that receive geniculate input. In 16 of 18 cases, the afferent receptive fields recorded in a single penetration covered an elongated region of visual space. In these penetrations, the best-fit line through the centers of the afferent receptive fields generally paralleled the preferred orientation of cortical cells recorded at the same site in cortex. These results are consistent with the Hubel and Wiesel (1962) model for the construction of oriented visual cortical receptive fields from geniculate inputs with aligned receptive fields.

Afferent Pathways↗
PubMed1982

Thalamic inputs to cytochrome oxidase-rich regions in monkey visual cortex.

In primate primary visual cortex, staining for cytochrome oxidase reveals a regular array of blob-like structures, most prominent in layers II and III but also present in layers V and VI. In an attempt to learn more about the input to these blobs, we injected the lateral geniculate bodies of macaques and squirrel monkeys with [3H]proline or horseradish peroxidase and looked in the cortex for transported label. As expected, label was present in layers IVa, IVc alpha, IVc beta, and VI. In addition, both methods revealed an array of puffs deep in layer III. Seen in tangential sections, the puffs precisely matched the cytochrome blobs. These results indicate a projection from the lateral geniculate body to the blob regions deep in layer II/III, either indirect via layer IV or more likely direct. In area 18 stained for cytochrome oxidase, we also observed complex banding patterns; these were remarkably similar to the pattern found after [3H]proline or horseradish peroxidase injection and were also similar to the pattern produced with 2-deoxyglucose labeling after stimulation with vertical or horizontal stripes; the proline and peroxidase labels probably represent a projection from the pulvinar to area 18.

Animals↗
PubMed1992

Visual projections routed to the auditory pathway in ferrets: receptive fields of visual neurons in primary auditory cortex.

How does cortex that normally processes inputs from one sensory modality respond when provided with input from a different modality? We have addressed such a question with an experimental preparation in which retinal input is routed to the auditory pathway in ferrets. Following neonatal surgical manipulations, a specific population of retinal ganglion cells is induced to innervate the auditory thalamus and provides visual input to cells in auditory cortex (Sur et al., 1988). We have now examined in detail the visual response properties of single cells in primary auditory cortex (A1) of these rewired animals and compared the responses to those in primary visual cortex (V1) of normal animals. Cells in A1 of rewired animals differed from cells in normal V1: they exhibited larger receptive field sizes and poorer visual responsivity, and responded with longer latencies to electrical stimulation of their inputs. However, striking similarities were also found. Like cells in normal V1, A1 cells in rewired animals exhibited orientation and direction selectivity and had simple and complex receptive field organizations. Furthermore, the degree of orientation and directional selectivity as well as the proportions of simple, complex, and nonoriented cells found in A1 and V1 were very similar. These results have significant implications for possible commonalities in intracortical processing circuits between sensory cortices, and for the role of inputs in specifying intracortical circuitry.

Animals↗
PubMed1990

Arrangement of ocular dominance columns in human visual cortex.

The arrangement of the ocular dominance columns in the human primary visual cortex was studied by examining cytochrome oxidase activity in autopsy specimens of occipital lobes obtained from two patients who became blind in one eye before death. By artificially flattening the cortex before processing, it was possible to reconstruct the pattern formed by the ocular dominance columns throughout most of the primary visual cortex. The columns form a mosaic of irregular parallel stripes about 500 microns to 1000 microns wide (right eye column plus left eye column measures 1 to 2 mm), oriented at right angles to the boundary of the primary visual cortex. The columns are wider near the boundary of the primary visual cortex and within the representation of the peripheral visual field, the ocular dominance columns of the ipsilateral eye become fragmented until they disappear altogether at the border of the monocular crescent representation. The arrangement of ocular dominance columns in the human visual cortex is very similar to the pattern reported in the macaque monkey, although the columns in humans are wider.

Aged↗
PubMed1991

Specialized vascularization of the primate visual cortex.

We have analyzed blood vessel distribution in the primary and secondary visual cortices of the squirrel monkey in relation to cortical modules, laminae, and cytoarchitectonic areas. Measurements of microvessel length in tangential sections through the primary visual cortex showed that blobs are more richly vascularized than intervening cortical regions. Thus, the mean total length of microvessel profiles per unit was 42% greater within these cortical modules than within adjacent (interblob) areas. Total microvessel length per unit area in another class of module, the stripes in the secondary visual cortex, was 27% greater than in interstripe regions. Microvessel distribution also varied systematically from layer to layer in the primary visual cortex, being greatest in lamina IVc. Finally, the overall microvessel length per unit area in sections of the primary visual cortex was 26% greater than that in the secondary visual cortex. These observations indicate that the modular, laminar, and regional organization of the primate visual cortex is reflected in the underlying distribution of cortical microvessels. These vascular patterns should be discernable in living animals with vascular contrast agents and appropriate imaging techniques.

Animals↗
PubMed1986

Cortical activity blockade prevents ocular dominance plasticity in the kitten visual cortex.

Recordings from single units in kitten primary visual cortex show that a reversible blockade of the discharge activities of cortical neurons and geniculocortical afferent terminals by intracortical infusion of the sodium channel blocker tetrodotoxin (TTX) completely prevented the ocular dominance shift that would normally be seen after monocular deprivation. The blockade of cortical plasticity, like the blockade of discharge activity, was reversible, and plasticity was restored following recovery from the effects of TTX. These results extend previous work suggesting involvement of electrical activity at the level of the cortex in the phenomenon of cortical plasticity by demonstrating an absolute requirement for discharge activities in the primary visual cortex.

Action Potentials↗
PubMed1980

Retinotopic organization of striate and extrastriate visual cortex in the mouse.

Detailed retinotopic maps of primary visual cortex (area 17) and the extrastriate visual regions surrounding it (areas 18a and 18b) have been constructed for the C57BL/6J mouse using standard electrophysiological mapping techniques. Primary visual cortex (area 17), as defined cytoarchitectonically, contains one complete representation of the contralateral visual field, termed V1, in which azimuth and elevation lines are approximately orthogonal. The upper visual field is represented caudally and the nasal field laterally. Binocular cells are encountered in the cortical representation of the nasal 30--40 degrees of the visual field, and there is an expanded representation of the nasal field. Extrastriate visual cortex of the mouse, like that of other mammals, contains multiple representations of the visual field. The cytoarchitectonic region of cortex lateral and rostral to area 17, termed area 18a, contains at least two such representations. The more medial of these, which by convention we have called V2, is a narrow strip surrounding V1 on its lateral and rostral aspects; the vertical meridian lies along a portion of its common border with V1. The visual field representation in V2 is not a mirror image of that in V1; the representation of the horizontal meridian forms the lateral border of V2, and the visual field representation is split so that adjacent points on either side of the horizontal meridian are represented in nonadjacent parts of V2. The other visual field representation within area 18a, which we have termed V3, is a small but apparently complete representation that lies lateral to V2. The visual field representations medial to area 17 correspond to cytoarchitectonic area 18b. Area 18b contains two representations of the temporal visual field that we have labeled Vm-r and Vm-c, and contains little or no representation of the most nasal aspect of the field.

Animals↗
PubMed1990

Remote astrocytic response as demonstrated by glial fibrillary acidic protein immunohistochemistry in the visual cortex of dorsal lateral geniculate nucleus lesioned rats.

The reaction of astroglia was investigated after unilateral destruction of the dorsal lateral geniculate nucleus in the primary visual cortex of adult albino rats. The destruction of the dorsal lateral geniculate nucleus was performed by stereotaxic injections of ibotenic acid, and the location was verified in Nissl stained sections in each animal. Electron microscopic observations demonstrated the presence of degenerating axon terminals surrounded by hypertrophic astroglial processes mainly in layers III and IV of the ipsilateral primary visual cortex. The ipsilateral (impaired) and contralateral (control) sides of the primary visual cortex showed light microscopically a clearly differing appearance and distribution of glial fibrillary acidic protein (GFAP) immunoreactivity 7 to 11 days after the unilateral injection of ibotenic acid into the dorsal lateral geniculate nucleus. Whereas the control side of the primary visual cortex showed GFAP staining only in the subpial zone of layer I and close to the white matter, all layers of the impaired cortex showed an intense GFAP immunoreactivity. The increase in immunoreactivity was confined to the primary visual cortex. The extent of and increase in immunoreactivity was corroborated by image analysis. These findings were interpreted as a localized hypertrophy of astroglia caused by the anterograde degeneration of geniculocortical terminals. This hypertrophy is accompanied by an increase in GFAP, which may represent the stabilization of the cytoskeleton of newly formed glial processes involved in the rearrangement of the impaired neuropil.

Afferent Pathways↗
PubMed1989

Corticopontine projection in the rat: the distribution of labelled cortical cells after large injections of horseradish peroxidase in the pontine nuclei.

The distribution of cortical cells projecting to the pontine nuclei in rats was studied by making large injections of horseradish peroxidase that filled the basilar pons and measuring the density of labelled cells in each cortical area. All retrogradely labelled cells were layer V pyramidal cells. The highest densities of labelled cells were observed in the motor areas. The lowest densities were in temporal association cortex and perirhinal cortex. Visual cortical areas, including the primary visual cortex, provided a major source of pontine projections. The distribution of corticopontine cells within the primary visual cortex was studied in more detail. In all cases the highest density of labelled cells was observed in the region of cortex that represents the nasal visual field. Control injections into brainstem regions adjacent to the pontine nuclei produced a much lower absolute density of retrogradely labelled cortical cells and the distribution of those cells was different from that observed following pontine injections. We conclude that every area of the rat's cerebral cortex projects to the pontine nuclei and that there are consistent variations in the density of the projections both between and within areas.

Animals↗
PubMed1991

Prosencephalic connections of striate and extrastriate areas of rat visual cortex.

Afferent connections of rat primary visual cortex (area 17 or V1 area) and the rostral and caudal parts of areas 18a and 18b were studied, by placing in each of the areas, small electrophoretic injections of enzyme horseradish peroxidase (HRP) or wheat germ agglutinated-HRP. The results indicate that: 1) each of the areas has a distinct pattern of distribution of afferent neurons in the ipsilateral visual thalamus - area 17 receives its principal thalamic input from the dorsal lateral geniculate nucleus, the caudal parts of areas 18a and 18b receive a major thalamic input from the lateral posterior nucleus and a minor input from the posterior nucleus, while the rostral parts of areas 18a and 18b receive a major input from the posterior nucleus, and a minor projection from the lateral posterior nucleus; 2) the rostral and caudal parts of areas 18a and 18b each receive an associational input from area 17; 3) the rostral parts of areas 18a and 18b each receive associational input from three different extrastriate regions, the caudal part of the same extrastriate area, and the rostral and caudal parts of the other extrastriate area, whereas the caudal parts of areas 18a and 18b receive associational inputs only from one or two extrastriate regions; 4) area 17, area 18b and rostral area 18a each receive a substantial associational input from lamina V of the caudal part of the frontal eye field (FEF) in the motor cortex; however the input from the FEF to caudal area 18a (if present) is very small; 5) The extrastriate areas studied receive associational input from the restrosplenial cingulate area 29d; however, the input from area 29d to area 17 appears to be very small. The distinct patterns of distribution of prosencephalic afferents suggest to us that multiple retinotopically organized areas described previously in the rat cortex (cf Montero 1981; Espinoza and Thomas 1983) represent functionally distinct areas.

Afferent Pathways↗
PubMed1989

Neuropeptide Y-containing neurons are situated predominantly outside cytochrome oxidase puffs in macaque visual cortex.

Layers II/III of the primary visual cortex contain a regular pattern of histochemically detectable cytochrome oxidase (CO)-rich "puffs," which differ from the interpuff regions in their thalamo-cortical and cortico-cortical connectivity, receptive-field properties, and the density of inhibitory GABA-containing synaptic terminals. We used an immunocytochemical method, in combination with cytochrome oxidase histochemistry, to analyze the spatial relationship between neurons that contain neuropeptide Y (NPY) and the CO puffs. Of a total of 606 neurons, only 2.6% of the NPY-containing cells are located in the puffs, whereas the rest are situated in the interpuffs, or at the interface between puffs and interpuffs. The number of NPY-containing neurons in the puffs is substantially less than that expected in an equal volume of the interpuffs (X2 = 13.86; df = 1; P less than 0.001). These observations indicate that columns containing the puffs may differ also from those in the interpuff regions in that they contain a unique array of chemically and morphologically distinct local circuit neurons.

Animals↗