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PubMed2001

The representation of erroneously perceived stimuli in the primary visual cortex.

In order to attain a correct interpretation of an ambiguous visual stimulus, the brain may have to elaborate on the sensory evidence. Are the neurons that carry the sensory evidence also involved in generating an interpretation? To address this question, we studied the activity of neurons in the primary visual cortex of macaque monkeys involved in a task in which they have to trace a curve mentally, without moving their eyes. On a percentage of trials, the monkeys made errors and traced the wrong curve. Here, we show that these errors are predicted by activity in area V1. Thus, neurons in the primary visual cortex do not only represent sensory events, but also the way in which they are interpreted by the monkey.

Action Potentials↗
PubMed1995

Development of basal forebrain projections to visual cortex: DiI studies in rat.

We performed experiments using retrograde and anterograde labeling with DiI to examine the development of basal forebrain (BFB) projections to the visual cortex in postnatal rats. DiI placed in occipital cortex led to retrograde labeling of BFB neurons as early as postnatal day 0 (P0); labeled cells were found mainly in the diagonal band complex but also in the medial septum, globus pallidus, and substantia innominata. The retrogradely labeled BFB cells displayed remarkably well-developed dendritic arbors, even in younger animals, and showed increases in soma size, dendritic arbors, and dendritic spines over the first 2 postnatal weeks. DiI placements in the diagonal band led to anterogradely labeled axons in cortex. At early ages (P0-P1), labeled axons were largely confined to white matter. With increasing age, greater numbers of labeled axons were seen in the white matter and in deep cortical layers, and labeled axons extended into superficial layers. The leading edge of labeled fibers reached layer V of visual cortex by P2 and layer IV by P4 and were found throughout the cortical layers by P6. Numbers and densities of labeled axons in visual cortex were greater in older animals, at least through P14. The time of ingrowth of labeled BFB axons into visual cortex indicates that these afferents grow into particular cortical layers after those layers have differentiated from the cortical plate. These data indicate that basal forebrain projections arrive in occipital cortex after cortical lamination is well underway and after the entry of primary thalamocortical projections.

Animals↗
PubMed1994

Identification of cDNA clones expressed selectively during the critical period for visual cortex development by subtractive hybridization.

We have used the method of subtractive hybridization to isolate cDNA clones of mRNAs expressed in abundance in the visual cortex of 30-day-old kittens but absent or in lower abundance in the adult cat visual cortex. Of 12,000 colonies screened, 200 clones which hybridized to the subtracted probe were isolated and characterized. Northern blots confirmed the specificity of the vast majority of the isolated clones. 120 of the 200 clones were sequenced and the EMBL and GenBank (release 76) database were searched for known identities using FASTA and BLAST programs. Twenty-seven of these sequenced clones were identifiable. The identities showed that these sequences code for proteins involved in a variety of cellular processes. These include cell-cell interaction (TAPA-1, contactin, tachykinin receptor, phospholipase A2), cellular remodeling (C1q beta isoform, heat shock protein), neurofilament assembly (alpha tubulin and alpha internexin), neurotransmitter release (VAMP-2, amphiphysin, carboxypeptidase E, scg 10 and proton channel), energy metabolism (mitochondrial hinge protein, ADP/ATP transporter, cytochrome oxidase subunits), RNA processing (helix destabilizing protein, ribonucleoprotein) and protein synthesis (eIF-4A initiation factor, ribosomal protein S27). The results show that gene expression in the kitten visual cortex differs rather little from that of the adult visual cortex since over 98% of the sequences appear common. The relatively rare kitten-specific sequences are likely to form the basis for the critical period plasticity in this system.

Aging↗
PubMed1992

Oscillatory Neuronal Responses in the Visual Cortex of the Awake Macaque Monkey.

An important step in early visual processing is the segmentation of scenes. Features constituting individual objects have to be grouped together and segregated from those of other figures or the background. It has been proposed that this grouping could be achieved by synchronizing the fine temporal structure of responses from neurons excited by an individual figure. In the cat visual cortex evidence has been obtained that responses of feature-selective neurons have a distinctive oscillatory structure and can synchronize both within and across cortical areas, the synchronization depending on stimulus configuration. Here we investigate the generality of oscillatory responses and their synchronization and specifically whether these phenomena occur in extrastriate areas of the visual cortex of the awake behaving primate. We find in the caudal superior temporal sulcus of the macaque monkey (Macaca fascicularis) that adjacent neurons can synchronize their responses, in which case their discharges exhibit an oscillatory temporal structure. During such periods of local synchrony spatially separated cell groups can also synchronize their responses if activated with a single stimulus. These findings resemble those described previously for the cat visual cortex, except that in the awake monkey the oscillatory episodes tend to be of shorter duration and exhibit more variability of oscillation frequency.

Journal Article↗
PubMed1986

A transient pyramidal tract projection from the visual cortex in the hamster and its removal by selective collateral elimination.

During the early postnatal development of the neocortex in rats there is an axonal projection from the occipital cortex (which includes the visual cortex) to the spinal cord which is subsequently completely removed through a process of selective collateral elimination. In order to determine whether a similar phenomenon occurs during the development of the hamster cortex, we have injected the retrogradely transported fluorescent dye Fast Blue (FB) into the pyramidal decussation of hamsters at various ages. In adult hamsters such an injection results in a band of labeled neurons confined to layer V and to about the rostral two-thirds of the neocortex; no labeled cells are seen in the occipital cortex. However, a similar FB injection made during the first postnatal week results after a 4-day survival in a continuous band of FB-labeled layer V neurons spread throughout the tangential extent of the neocortex, including the occipital cortex. A similar continuous band of FB labeled layer V neurons is seen throughout the tangential extent of the neocortex including the occipital region in hamsters injected during the first postnatal week but allowed to survive until the fourth week (i.e., after the restriction of the widespread neonatal pattern has occurred). Injections of the anterograde tracer wheat germ agglutinin conjugated to horseradish peroxidase made into the occipital cortex, or for comparison, into more rostral cortical regions in hamsters ranging in age from neonates to adults, reveal that the extension of pyramidal tract axons is staggered along the anterioposterior axis of the cortex such that axons originating from the posterior regions lag behind those arising from more rostral areas. The transient occipital projection appears to reach a maximum around the end of the first postnatal week: a large number of labeled occipital axons is seen in the medullary pyramidal tract, and some of these can be followed through the pyramidal decussation and into the dorsal funiculus of the spinal cord. Injections into the occipital cortex on P16 label only a few fibers in the medullary pyramidal tract, and none is labeled in hamsters injected as adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Model studies of the mechanisms of tuning of visual cortex neurons to incomplete cross-shaped figures.

Numerical simulation modeling of the receptive fields of visual cortex neurons able to detect cross-shaped figures with masked central or peripheral areas was performed. Receptive field models of two types were considered: those with antagonistic and cooperative interactions between the center and the periphery. Model neurons with receptive fields with reciprocal (antagonistic) interactions produced greater responses to peripheral or central crosses than to complete crosses. Studies using the model showed that the basis of this type of tuning could be provided by a disinhibition mechanism: blockade of the inhibitory zones in the center or periphery of the receptive field by activation of a lateral disinhibitory zone. A model with cooperative interactions between the center and periphery of the receptive field was also studied, in which responses to complete crosses were summed from the responses to the peripheral and central parts. Tuning of these model receptive fields was comparable to the sensitivity of real visual cortex neurons to the shape, size, and orientation of figures. The properties of model receptive fields (configuration, localization, and weightings of the various zones) allowing simulation of the properties of cat visual cortex field 17 neurons sensitive to the orientation and configuration of incomplete cross-shaped figures were identified.

Models, Neurological↗
PubMed1994

The corpus callosum provides a massive transitory input to the visual cortex of cat and rat during early postnatal development.

Studies of corpus callosum development in cat revealed that the callosum must be intact during postnatal month 1 if normal visual development is to occur [11-20,25]. The use of DiI, a lipophilic carbocyanine dye that is an in vitro membrane tracer, permits a detailed search for morphological evidence to account for these functional results because many cells can be simultaneously labeled in their entirety. To search for morphological evidence, the corpus callosum was labeled in vitro with DiI in tissue from cats aged 2-277 days old [21]. To determine whether there was consistent callosal development in mammals, similar studies were carried out in tissue from rats aged 0 days old through adult [22]. Hemispheres were coronally sectioned 1-24 months later. Sections were reconstructed in photomontages to show the overall distribution of corpus callosum projections, as well as provide details about the locations of individual corpus callosum axons and their presumed terminals. The distribution of corpus callosum projections, examined in visual cortex of cat and rat, changed significantly during development. During early postnatal development, callosal axons extended throughout visual cortex to layer I. Numerous varicosities on callosal axons were located en passant and at axon terminals in layer I. In the following weeks, the density of callosal projections was reduced in all cortical areas, although many axons still extended to layer I. By postnatal month 2 the callosal axons were predominantly near the borders between adjacent cortical areas. Thus, for several postnatal weeks, many elaborately formed transitory corpus callosum axons are distributed throughout visual cortex. The transitory callosal axons appear to have terminals in layers I-VI. If some of these terminals were to for synapses, the corpus callosum could provide an extensive input to layers I-VI throughout visual cortex while the majority of cortical microcircuitry is being established.

Animals↗
PubMed1999

Using multi-stimulus VEP source localization to obtain a retinotopic map of human primary visual cortex.

OBJECTIVE: The goal of this study was to acquire a detailed spatial and temporal map of primary visual cortex using a novel VEP stimulus and analysis technique. METHODS: A multi-stimulus array spanning the central 18 degrees of the visual field was used where each of 60 checkerboard stimulus 'patches' was simultaneously modulated with an independent binary m-sequence (Sutter, 1992). VEPs corresponding to each patch were recorded from 3 subjects using a dense posterior electrode array. For each stimulus patch, single dipole source localization was conducted to determine the location, magnitude, and time-function of the underlying neural activation. To reduce ambiguity in the solution, a common time-function was assumed for stimulus patches at the same visual eccentricity (defining an annulus). The analysis was conducted independently for each annulus composed of 4-12 patches. RESULTS: The loci of the dipole solutions followed a smooth retinotopic pattern across annuli consistent with the classical organization of primary visual cortex. Specifically, each dipole was found contralateral to the corresponding stimulus patch and field inversion was observed for all subjects. CONCLUSIONS: Using this technique, the most detailed spatial and temporal retinotopic map of primary visual cortex to date has been obtained.

Adult↗
PubMed1991

The length summation properties of layer VI cells in the visual cortex and hypercomplex cell end zone inhibition.

Layer VI of the visual cortex has been considered to be dominated by cells with very long receptive fields, typically summing to 8 degrees or more. We have re-examined this issue in a series of experiments in which the length tuning profiles of layer VI cells in the cat visual cortex have been quantitatively determined. Responses were assessed to optimally oriented bars of light of varying length drifted over the receptive field. The lengths were varied on a randomised interleaved sequence. Although our data confirm the presence of long field cells in layer VI, only 24% of a population of 119 cells had fields greater than 6 degrees in length. Fields greater than 8 degrees were only seen in 17% of cells. 61% of the population of cells had fields showing summation to 4 degrees or less with a mean length of 2.8 degrees (+/-0.15 sem). In this "short field" group, 18% had fields of 1 degrees or less. We observed 7 cells with rapid initial spatial summation up to 1 degree, followed by clear end zone inhibition. It has been recently suggested on the basis of localised inactivation experiments, that layer VI cells with long (greater than 8 degrees) fields may provide the drive to inhibitory interneurones in layer IV generating hypercomplex cell end zone inhibition. This observation is difficult to equate with evidence indicating that hypercomplex cell end zone inhibition reflects a mechanism showing maximal summation at lengths in the region of 2.8 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Is there a role of visual cortex in spatial hearing?

The integration of auditory and visual spatial information is an important prerequisite for accurate orientation in the environment. However, while visual spatial information is based on retinal coordinates, the auditory system receives information on sound location in relation to the head. Thus, any deviation of the eyes from a central position results in a divergence between the retinal visual and the head-centred auditory coordinates. It has been suggested that this divergence is compensated for by a neural coordinate transformation, using a signal of eye-in-head position. Using functional magnetic resonance imaging, we investigated which cortical areas of the human brain participate in such auditory-visual coordinate transformations. Sounds were produced with different interaural level differences, leading to left, right or central intracranial percepts, while subjects directed their gaze to visual targets presented to the left, to the right or straight ahead. When gaze was to the left or right, we found the primary visual cortex (V1/V2) activated in both hemispheres. The occipital activation did not occur with sound lateralization per se, but was found exclusively in combination with eccentric eye positions. This result suggests a relation of neural processing in the visual cortex and the transformation of auditory spatial coordinates responsible for maintaining the perceptual alignment of audition and vision with changes in gaze direction.

Acoustic Stimulation↗
PubMed1993

Memory for spatial locations, motor responses, and objects: triple dissociation among the hippocampus, caudate nucleus, and extrastriate visual cortex.

Based on behavioral procedures aimed at measuring working or data-based memory for spatial location, response, and visual object information, it is shown that there is a triple dissociation among the hippocampus, caudate nucleus, and extrastriate visual cortex in mediating spatial location, response, and visual object information, respectively. The hippocampus appears to subserve only spatial location, the caudate nucleus only response, and the extrastriate visual cortex only visual object information. The results support the neurobiological foundation of the attribute memory model.

Animals↗
PubMed1993

A correlational model for the development of disparity selectivity in visual cortex that depends on prenatal and postnatal phases.

Neurons in the visual cortex require correlated binocular activity during a critical period early in life to develop normal response properties. We present a model for how the disparity selectivity of cortical neurons might arise during development. The model is based on Hebbian mechanisms for plasticity at synapses between geniculocortical neurons and cortical cells. The model is driven by correlated activity in retinal ganglion cells within each eye before birth and additionally between eyes after birth. With no correlations present between the eyes, the cortical model developed only monocular cells. Adding a small amount of correlation between eyes at the beginning of development produced cortical neurons that were entirely binocular and tuned to zero disparity. However, if an initial phase of purely same-eye correlations was followed by a second phase of development that included correlations between eyes, the cortical model became populated with both monocular and binocular cells. Moreover, in the two-phase model, binocular cells tended to be selective for zero disparity, whereas the more monocular cells tended to have nonzero disparity. This relationship between ocular dominance and disparity has been observed in the visual cortex of the cat by other workers. Differences in the relative timing of the two developmental phases could account for the higher proportion of monocular cells found in the visual cortices of other animals.

Aging↗
PubMed1997

Perineuronal sulfated proteoglycans and cell surface glycoproteins in the visual cortex of adult and newborn cats.

Sections of the visual cortex of newborn (1-4 weeks after birth) and adult cats were stained with cationic iron colloid, aldehyde fuchsin or lectins (lectin Vicia villosa, soybean and Wisteria floribunda agglutinins). Many neurons in the adult cat visual cortex contained perineuronal sulfated proteoglycans detectable with cationic iron colloid and aldehyde fuchsin, or cell surface glycoproteins reactive to lectins. Double staining indicated that some of the lectin-labeled neurons were not stained with cationic iron colloid, and also that some of the cationic iron colloid-stained neurons were not labeled with lectins. The perineuronal sulfated proteoglycans and cell surface glycoproteins developed 3 weeks after birth. In the newborn cats 1-2 weeks after birth, no neurons were reactive to cationic iron colloid, aldehyde fuchsin or lectins. In the newborn cats 3-4 weeks after birth, it was clearly observed that the cytoplasm of the glial cells closely associated with the neurons containing the perineuronal sulfated proteoglycans showed an intense reaction to cationic iron colloid and aldehyde fuchsin, and that the Golgi complexes of the neurons with cell surface glycoproteins were intensely labeled with lectins. These findings suggest that the perineuronal sulfated proteoglycans are derived from the associated glial cells, and that the cell surface glycoproteins are produced by the associated nerve cells.

Animals↗
PubMed1996

Brain-derived neurotrophic factor reversed experience-dependent synaptic modifications in kitten visual cortex.

During a critical period of early postnatal development the functional architecture of the visual cortex is shaped by experience-dependent circuit selection following a Hebbian mechanism. One consequence is that monocular deprivation (MD) leads to competitive repression of the input from the deprived eye. Recently it has been proposed that this process might involve activity-dependent competition for neurotrophic substances because the synthesis of brain-derived neurotrophic factor (BDNF) is regulated by visual input. Here we investigate the effects of intracortical infusion of BDNF and nerve growth factor (NGF) on MD effects in the visual cortex. Neuronal responses were monitored with optical and single unit recording techniques in the visual cortex of kittens that had been infused intracortically either with BDNF, NGF or cytochrome C while subjected to MD for 1 week during the peak of the critical period. NGF or cytochrome C had no effect on the consequences of MD. After BDNF treatment, by contrast, ocular dominance (OD) shifted towards the deprived eye in a zone extending 2.5-3.5 mm from the infusion cannula, and neurons lost their orientation selectivity. At intermediate distances both eyes activated the cortex equally well and responses were again tuned for orientation; at still larger distances OD was shifted towards the normal eye. Thus, BDNF antagonizes the functional effects of MD and at high concentrations causes paradoxical disconnection of non-deprived afferents and a loss of orientation selectivity.

Animals↗
PubMed1993

Ageing and monoamine turnover in the lateral geniculate nucleus and visual cortex of the rat.

The effects of ageing on the turnover of dopamine, noradrenaline and serotonin in the lateral geniculate nucleus and the visual cortex were evaluated, using high performance liquid chromatography (HPLC) with electrochemical detection. Compared to adult animals, aged rats showed more changes in the visual cortex than in the lateral geniculate nucleus, with dopamine turnover decreased in both structures and noradrenaline turnover unaltered. Changes in serotonin turnover were witnessed only in the visual cortex. A decrease in the monoamine oxidase-A to -B ratio was also observed with increased age for both the lateral geniculate nucleus and visual cortex.

Aging↗
PubMed1979

[Feedback inhibition in microsegments of the visual cortex].

Interaction between 3-4 neighbouring neurons in the visual cortex of awakening cats was examined using a cross-correlation analysis. In some microsystems neurons revealed a tendency towards synchronized activity indicating a shared excitatory input. In other microsystems asymmetrical interaction was observed: neurons with larger spike amplitudes exhibited excitatory effect on neurons with smaller spike amplitudes (latent period about 5 ms) and neurons with small spike amplitudes inhibited neurons with large spike amplitudes (latent period 1-8 ms, duration of inhibition 30-200 ms). Suggestions were made about the existence of recurrent inhibition and inhibitory interneurons in microsystems of the visual cortex.

Animals↗
PubMed2003

Extracellular GABA concentrations in area 17 of cat visual cortex during topographic map reorganization following binocular central retinal lesioning.

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system of mammals, plays an important role in cortical reorganization following sensory deprivation, by regulating the level of cortical inhibition and gating changes in receptive field size and synaptic efficacy. In cats it has been shown that 2 weeks after the induction of binocular retinal lesions, GABAergic inhibition, as determined by immunocytochemistry, is decreased in the deafferented region of area 17, whereas 3 months post-lesion, normal GABAergic control is restored within the cortical scotoma. In this study we used in vivo microdialysis to investigate the extracellular GABA concentrations 1-2 months post-lesion, in the sensory-deprived and remote, non-deprived region of area 17. Data were collected at those sample times and sites for which the extracellular glutamate concentrations had been determined in a previous investigation to elucidate the role of this excitatory neurotransmitter in cortical reorganization. As for glutamate, we observed significantly increased extracellular GABA concentrations in non-deprived area 17, whereas in deafferented area 17, extracellular GABA concentrations were comparable to those observed in normal, control subjects. These data suggest that 1-2 months post-lesion the deafferented cortex behaves like normal visual cortex, in contrast to remote, non-deprived cortex. Notwithstanding the increase in extracellular GABA concentration of 134%, the parallel increase in glutamate concentration of 269% could give rise to a net increase in excitability in remote area 17. We therefore suggest that LTP-like mechanisms, and thereby cortical reorganization, might still be facilitated, while possible excessive hyperexcitability is balanced by the moderately increased GABAergic control.

Animals↗
PubMed2000

A new cat Fos antibody to localize the immediate early gene c-fos in mammalian visual cortex after sensory stimulation.

We developed a novel antibody against cat Fos by immunizing rabbits with a 26-amino-acid peptide. Immunocytochemistry on visual cortex of cats undergoing different visual manipulations was applied to test the reliability and the efficacy of this antiserum. One hour of light stimulation after an overnight dark adaptation resulted in strongly induced Fos expression in supra- and infragranular layers of cat primary visual cortex. Short-term monocular deprivation changed the Fos expression profile into a columnar immunostaining related to ocular dominance columns. Fos expression has also been analyzed in cats in which visual input was confined to the right hemisphere by sectioning the left optic tract and the corpus callosum. In the right hemisphere, visual stimulation elicited Fos induction, whereas in the contralateral hemisphere a very low Fos signal was observed. The specificity of this newly synthesized antibody was confirmed by Western blotting. To further establish the applicability of this Fos antiserum, we performed immunostaining on monkey and rat visual cortex. This new cat Fos antibody appears to be excellent for study of Fos expression as a marker for mapping neuronal activity in mammalian brain.

Animals↗