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PubMed1988

Development of the kitten visual cortex depends on the relationship between the plane of eye movements and visual inputs.

1. Previous experiments have demonstrated that eye movements, acting through the extraocular muscle (EOM) proprioceptive afferents, are necessary for the development of orientation selectivity in the cells of the kitten visual cortex. New experiments were carried out to study the effect of the plane of eye movements on the preferred orientation acquired by the visual cortical cells. 2. Dark-reared (DR) kittens were operated on at 5-6 weeks of age. In the first series of experiments, 4 out of the 6 EOMs were removed bilaterally in such a way that both eyes could only move in a single plane, either vertical or horizontal. In the second series of experiments, the same operation was performed on one eye which was also sutured shut and, on the other side, the EOM were deafferented by intracranial section of the ophthalmic branch of Vth nerve and the eye left open. 3. 1-4 days after surgery the kittens were given 6 h of visual experience and 12 h later were prepared for visual cell recording in Area 17. 4. In kittens of the first series: orientation selectivity developed in the majority (60-65%) of visual cells, most of which encoded horizontal orientations when the eyes had moved in the vertical plane and vertical orientations when the eyes had moved in the horizontal plane. These results show that the plane of eye movements during early visual experience influences the distribution of preferred orientations with an orthogonal relation. Ocular dominance histograms were "strabismic like". 5. In kittens of the second series: orientation selectivity developed in 40-50% of cells, about half of which were tuned for the orientation orthogonal to the direction of movement of the occluded eye, as in experiment I. The seeing, deafferented eye, presumably would have sent normal visual inputs centrally, corresponding to displacements on the retina in every direction since the ocular motility of that eye had not been disturbed. However, proprioceptive information about its movements was suppressed. As only some of the EOMs of the occluded eye were still present and connected, the conclusion is that the observed influence of the plane of eye movements acts through the proprioceptive afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2000

Optical recording of spatiotemporal activation of rat somatosensory and visual cortex in vitro.

A comparative analysis of spatiotemporal activation patterns of somatosensory and visual cortex was carried out in slice preparations using optical recording with voltage-sensitive dyes. Activity propagation velocities were found to be similar in both areas in all layers. Vertical propagation velocity is higher than horizontal propagation velocities. Differences between the two sensory areas exist in terms of horizontal activity spread, that is similar in extragranular layers but smaller in somatosensory than in visual cortex in layer IV. These results imply that despite the extensive similarities in the organization of sensory cortical areas, systematic areal variations in the horizontal cortical plane are present that may reflect adaptations needed for the processing of the corresponding sensory modality.

Animals↗

PubMed1999

Modulation of long-term synaptic depression in visual cortex by acetylcholine and norepinephrine.

In a slice preparation of rat visual cortex, we discovered that paired-pulse stimulation (PPS) elicits a form of homosynaptic long-term depression (LTD) in the superficial layers when carbachol (CCh) or norepinephrine (NE) is applied concurrently. PPS by itself, or CCh and NE in the absence of synaptic stimulation, produced no lasting change. The LTD induced by PPS in the presence of NE or CCh is of comparable magnitude with that obtained with prolonged low-frequency stimulation (LFS) but requires far fewer stimulation pulses (40 vs 900). The cholinergic facilitation of LTD was blocked by atropine and pirenzepine, suggesting involvement of M1 receptors. The noradrenergic facilitation of LTD was blocked by urapidil and was mimicked by methoxamine, suggesting involvement of alpha1 receptors. beta receptor agonists and antagonists were without effect. Induction of LTD by PPS was inhibited by NMDA receptor blockers (completely in the case of NE; partially in the case of CCh), suggesting that one action of the modulators is to control the gain of NMDA receptor-dependent homosynaptic LTD in visual cortex. We propose that this is a mechanism by which cholinergic and noradrenergic inputs to the neocortex modulate naturally occurring receptive field plasticity.

Acetylcholine↗

PubMed1977

Effects of early experience upon orientation sensitivity and binocularity of neurons in visual cortex of cats.

The class of neurons within the visual cortex of normal adult cats that has the smallest receptive fields (less than or equal to 2.25 degrees2) and that responds only to low rates of stimulus motion (less than or equal to 50 degrees / sec) responds preferentially to lines oriented about either the horizontal axis (+/-22.5 degrees) or the vertical axis (+/-22.5 degrees). In animals reared without exposure to patterned visual stimulation, many of these cells display orientation preferences but are activated monocularly. In contrast, in normal animals, neurons that have larger receptive fields or that respond to higher rates of stimulus motion do not exhibit a similar bias in the distribution of their orientation preferences. Cells of this type, studied in animals reared without exposure to patterned visual stimuli, are activated binocularly but do not display orientation preferences.

Animals↗

PubMed2005

Lack of experience-mediated differences in the immunohistochemical expression of blood-brain barrier markers (EBA and GluT-1) during the postnatal development of the rat visual cortex.

The development of the cortical vascular tree depends on functional development. External inputs are an essential requirement in the modeling of the visual cortex, mainly during the critical period, when congruous blood supply is needed. The blood brain barrier (BBB) function regulates the passage of substances between the blood and the brain parenchyma, which is one of the main differential features of central nervous system (CNS) microvessels. The endothelial barrier antigen (EBA) has been reported as a specific marker for the BBB physiological function in rats. We studied the postnatal development of EBA expression in the visual cortex of rats reared under opposite paradigms of visual experience, e.g., standard laboratory conditions, dark rearing, and enriched environment at 14, 21, 28, 35, 42, 49, 56, and 63 days postnatal (dpn). Parallel sections were immunohistochemically processed for endothelial barrier antigen (EBA) and glucose transporter-1 (GluT-1). Total vasculature was quantified by Lycopersicon esculentum (LEA) lectin histochemistry. No differences in EBA expression were found between groups, although quantitative differences were recorded paralleling differences in vascular density. Paradoxically, there was no expression in certain cortical vessels which were GluT-1 immunopositive and positivity was consistent in non-barrier areas such as the pineal gland. These findings were completely independent of age or experimental conditions. Therefore, the role of the EBA antigen in the BBB remains unclear: it has been undeniably linked to vascular permeability, but its presence in non-barrier vessels suggests another vascular function. Although visual experience modifies vascular density in the visual cortex, it has not been shown to have an influence on the maturation of the BBB function.

Age Factors↗

PubMed1999

Dark rearing blocks the developmental down-regulation of brain-derived neurotrophic factor messenger RNA expression in layers IV and V of the rat visual cortex.

In this study, we describe the distribution of brain-derived neurotrophic factor messenger RNA in the binocular primary visual cortex of the rat during postnatal development, starting at postnatal day (P) 13. High-resolution non-isotopic in situ hybridization combined with Nissl staining were used to quantify the number of cells expressing brain-derived neurotrophic factor messenger RNA. At P13, most of the cells express brain-derived neurotrophic factor messenger RNA. After eye opening (P14-P15), the relative number of brain-derived neurotrophic factor messenger RNA-positive cells decreases by a factor of two in layer IV, i.e. that receiving the visual input, and in layer V. To verify the hypothesis that light could trigger this decrease, pups were kept in complete darkness from birth. At P22, pups reared in the dark were killed and the visual cortex processed for in situ hybridization and northern blotting. The results obtained in dark-reared animals prove that light deprivation can: (i) decrease the general levels of brain-derived neurotrophic factor messenger RNA, and (ii) increase the relative number of brain-derived neurotrophic factor messenger RNA-positive cells in layers IV and V with respect to control rats. Exposure to light for five days after the period of darkness restored the number of brain-derived neurotrophic factor messenger RNA-positive cells. We conclude that the expression of brain-derived neurotrophic factor messenger RNA in the rat primary visual cortex is regulated during development and that this process is under the control of visual input.

Animals↗

PubMed2005

Early modulation of visual cortex by sound: an MEG study.

Sound can alter visual perception. This has been recently demonstrated by a strong illusion in which a single flash is perceived as multiple flashes when accompanied by multiple brief sounds. While psychophysical findings on this sound-induced flash illusion indicate that the modulations of visual percept by sound occur at a perceptual processing level, it remains unclear at what level of perceptual processing these interactions occur and what mechanisms mediate them. Here we investigated these questions using MEG. We found modulation of activity in occipital and parietal scalp locations, when comparing illusion trials with visual-alone and auditory-alone trials. This modulation occurred as early as 35-65 ms from the onset of the visual stimulus. Activity was also modulated in the occipital and parietal areas as well as anterior areas at a later ( approximately 150 ms post-stimulus) onset. No significant interactions were observed in occipital and parietal areas in trials in which illusion was not perceived. These results indicate that the auditory alteration of visual perception as reflected by the illusion is associated with modulation of activity in visual cortex. The early onset of these modulations suggests that a feed-forward or lateral circuitry is at least partially involved in these interactions.

Acoustic Stimulation↗

PubMed1984

Enhanced binocular interaction in the visual cortex of normal kittens subjected to intracortical norepinephrine perfusion.

It was previously proposed that norepinephrine (NE)-containing nerve terminals in visual cortex are important for the maintenance of cortical plasticity. Observations at that time indicated that local microperfusion of exogenous NE for 1 week directly into kitten visual cortex, with no alteration of the visual environment, resulted in an unexpected bias in ocular dominance toward the contralateral eye. The proportion of binocular cells, however, remained close to normal. In the present study, we examined this contralateral bias in visual cortical neurons addressing the following two issues: the time needed for change in ocular dominance to occur, and its dependence on visually evoked activity. We found no bias in ocular dominance toward the contralateral eye when the continuous local perfusion of 48 microM NE lasted for 3 days. Such change became obvious after 1 week. However, if the animal was placed in the dark during the period of NE perfusion, no change whatsoever in ocular dominance was observed. These results suggest that NE itself does not affect ocular dominance circuitry directly, since both high levels of NE and an extended period of visually evoked activity are necessary for the observed change in ocular dominance to occur. We conclude that the present results are consistent with the previously proposed role for NE in the modulation of visual cortical plasticity.

Animals↗

PubMed1992

Binocularity and excitability loss in visual cortex cells of corpus callosum transected kittens and cats.

The contribution of the corpus callosum to binocularity of visual cortex cells and to their responsiveness was studied in cats. Electrophysiological recordings of the responses of single cells to visual stimulation was performed in the callosal projection zone, visual cortex area 17-18 boundary in callosotomized cats. Callosotomy was carried out by transection of the visual segment of the corpus callosum in 6-7-week-old kittens and in acute and chronic adult cats (postoperative recovery time: 11 days-39 months). While in our normal cats the common proportion of binocularly driven cells (79.8%) was found (66.3% in the sham controls), a remarkable diminution (29.7%) was found in the callosotomized kittens, in the acute (39.7%) and in the chronic (50.6%)-operated cats. We have also found a change in the amount of binocularity as function of postoperative recovery time. While the proportion of binocular cells was conceivable (60.7%) in the short- and intermediate-term callosotomized cats (postoperative time: 0.3-5.5 months), it was diminished (36.9%) in the long-term (6.5-39 months) chronic cats. As to the responsiveness level, it was found that visual responsive cells constituted 88% of the cells in the normal and 80.3% in the sham controls. In comparison, they constituted 69.2% in the acute, 54.4% in the chronic and 52.8% in the callosotomized kittens. Furthermore, callosal transection had produced a symmetric effect in the two hemispheres, regarding binocularity and responsiveness. It has been thus concluded that the corpus callosum is essential for the mediation of binocular functions between the two hemispheres; in addition, cortical excitability has been also found to depend on callosal integrity.

Animals↗

PubMed1977

Response recovery cycles in the visual cortex and superior colliculus following conditioning "ON" and "OFF" stimulation in the rabbit.

The responsiveness of visual cortex (VC) and superior colliculus (SC) was simultaneously compared following conditioning "ON" or "OFF" stimulation, in the rabbit. Average evoked responses were recorded simultaneously from the visual cortex ans superior colliculus. "ON" or "OFF" steps constituted the conditioning stimuli whereas the test stimulus consisted of optic nerve stimulation. All evoked responses exhibited a reversal of their polarity when the electrode was moved in the dorsoventral direction (Negative-Positive in the SC, Positive-Negative in the VC). This assured the somato-dentritic origin of the potentials. The results showed that responsiveness in both structures was significantly higher following an "OFF" simulus than after an "ON" step. Collicular responsiveness was higher than in the VC when the same conditioning stimulus was applied. The spatial distribution of the source of "OFF" responses was circumscribed to the ventral part of the superficial layer of the superior colliculus. These results suggest specific properties associated with the brightening and dimming systems.

Animals↗

PubMed1990

Anticonvulsant effects of zonisamide and phenytoin on seizure activity of the feline visual cortex.

The acute anticonvulsant effects of zonisamide (ZNS) and phenytoin (PHT) on seizure activity produced by electrical stimulation of the feline visual cortex were studied. The intravenous administration of ZNS 60 mg/kg reduced kindled generalized seizures into partial seizures, with marked reduction in the afterdischarge duration. ZNS also suppressed focal seizure activity of the visual cortex and produced a dose-related increase in the afterdischarge threshold. The anticonvulsant effect of ZNS (60 mg/kg) was comparable to that of PHT (15 mg/kg) and was observed in the absence of neurological toxicity and background EEG changes. The present findings demonstrated that ZNS possesses potent anticonvulsant action against focal seizure and its secondary generalization from the visual cortex.

Animals↗

PubMed1977

Responses of single neurons to electrical stimulation of the surface of the visual cortex.

We have recorded from single neurons in the visual cortex of the cat while stimulating the cortical surface with the same type of electrodes and the same parameters of stimulation which have produced phosphenes in conscious man. Parameters of stimulation which will permit excitation of single cortical neurons with little risk of producing afterdischarges are described. The patterns of excitation of single neurons during surface stimulation and the effects of stimulation on neuroglial cells have also been studied. Surface stimulation also produced marked alterations in cortical excitability as tested with visually presented stimuli. Mechanisms by which single neurons are excited by surface stimulation are also considered.

Action Potentials↗

PubMed1999

Effect of the group II metabotropic glutamate agonist, 2R,4R-APDC, varies with age, layer, and visual experience in the visual cortex.

Group II metabotropic glutamate receptors (mGluR 2/3) are distributed differentially across the layers of cat visual cortex, and this distribution varies with age. At 3-4 wk, mGluR 2/3 receptor immunoreactivity is present in all layers. By 6-8 wk of age, it is still present in extragranular layers (2, 3, 5, and 6) but has disappeared from layer 4, and dark-rearing postpones the disappearance of Group II receptors from layer 4. We examined the physiological effects of Group II activation, to see if these effects varied similarly. The responses of single neurons in cat primary visual cortex were recorded to visual stimulation, then the effect of iontophoresis of 2R,4R-4 aminopyrrolidine-2, 4-decarboxylate (2R,4R-APDC), a Group II specific agonist, was observed in animals between 3 wk and adulthood. The effect of 2R, 4R-APDC was generally suppressive, reducing both the visual response and spontaneous activity of single neurons. The developmental changes were in agreement with the immunohistochemical results: 2R, 4R-APDC had effects on cells in all layers in animals of 3-4 wk but not in layer 4 of animals >6 wk old. Moreover, the effect of 2R, 4R-APDC was reduced in the cortex of older animals (>22 wk). Dark-rearing animals to 47-54 days maintained the effects of 2R, 4R-APDC in layer 4. The disappearance of Group II mGluRs from layer 4 between 3 and 6 wk of age is correlated with the segregation of ocular dominance columns in that layer, raising the possibility that mGluRs 2/3 are involved in this process.

Aging↗

PubMed2000

Attentional activation of the visual thalamic reticular nucleus depends on 'top-down' inputs from the primary visual cortex via corticogeniculate pathways.

This study is concerned with corticothalamic neural mechanisms underlying attentional phenomena. Previous results from this laboratory demonstrated that the visual sector of the GABAergic thalamic reticular nucleus is activated by attention in rats. Here it is demonstrated that Fos-detected activation of the visual reticular sector in rats, induced by attentive exploration of a novel-complex environment, is dependent on 'top-down' cortical inputs from the primary visual cortex, on the basis (a) that activation of the visual reticular sector is drastically diminished after ibotenate lesions mostly restricted to layer 6 of the primary visual cortex, which gives origin to the corticogeniculate pathway that innervates both the visual reticular sector and the dorsal lateral geniculate nucleus; and (b) the lesions did not induce retrograde degeneration nor diminution of Fos label in the geniculate. The results are consistent with the previously proposed hypothesis that a focus of attention in V1 generates a column of increased thalamocortical transmission in LGN by means of monosynaptic glutamatergic corticogeniculate inputs, and decreased transmission of surrounding regions by disynaptic cortico-reticulo-geniculate (ultimately GABAergic) inputs. The results also suggest that attentional modulation of thalamocortical transmission is a main function of corticothalamic pathways to sensory relay nuclei.

Action Potentials↗

PubMed1996

Subthreshold facilitation and suppression in primary visual cortex revealed by intrinsic signal imaging.

Neurons in primary visual cortex (area 17) respond vigorously to oriented stimuli within their receptive fields; however, stimuli presented outside the suprathreshold receptive field can also influence their responses. Here we describe a fundamental feature of the spatial interaction between suprathreshold center and subthreshold surround. By optical imaging of intrinsic signals in area 17 in response to a stimulus border, we show that a given stimulus generates activity primarily in iso-orientation domains, which extend for several millimeters across the cortical surface in a manner consistent with the architecture of long-range horizontal connections in area 17. By mapping the receptive fields of single neurons and imaging responses from the same cortex to stimuli that include or exclude the aggregate suprathreshold receptive field, we show that intrinsic signals strongly reveal the subthreshold surround contribution. Optical imaging and single-unit recording both demonstrate that the relative contrast of center and surround stimuli regulates whether surround interactions are facilitative or suppressive: the same surround stimulus facilitates responses when center contrast is low, but suppresses responses when center contrast is high. Such spatial interactions in area 17 are ideally suited to contribute to phenomena commonly regarded as part of "higher-level" visual processing, such as perceptual "popout" and "filling-in."

Animals↗

PubMed2005

Predicting the stream of consciousness from activity in human visual cortex.

Can the rapid stream of conscious experience be predicted from brain activity alone? Recently, spatial patterns of activity in visual cortex have been successfully used to predict feature-specific stimulus representations for both visible and invisible stimuli. However, because these studies examined only the prediction of static and unchanging perceptual states during extended periods of stimulation, it remains unclear whether activity in early visual cortex can also predict the rapidly and spontaneously changing stream of consciousness. Here, we used binocular rivalry to induce frequent spontaneous and stochastic changes in conscious experience without any corresponding changes in sensory stimulation, while measuring brain activity with fMRI. Using information that was present in the multivariate pattern of responses to stimulus features, we could accurately predict, and therefore track, participants' conscious experience from the fMRI signal alone while it underwent many spontaneous changes. Prediction in primary visual cortex primarily reflected eye-based signals, whereas prediction in higher areas reflected the color of the percept. Furthermore, accurate prediction during binocular rivalry could be established with signals recorded during stable monocular viewing, showing that prediction generalized across viewing conditions and did not require or rely on motor responses. It is therefore possible to predict the dynamically changing time course of subjective experience with only brain activity.

Adult↗

PubMed1996

A morphological study of neurons expressing NADPH diaphorase activity in the visual cortex of the golden hamster.

The distribution of the enzyme nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase, which is identical to nitric oxide synthase (NOS), was examined in cortical area 17 and the 17/18a border region in the brain of the golden hamster. The activity of the enzyme was present as a network of processes and in special populations of neurons in the visual cortex. The dense enzyme-positive network exhibited numerous varicosities distributed throughout the cortex. The prominent orientation of the processes in layer I and the white matter are parallel to the surface of the brain, but those in layers II-IV are perpendicular to the surface of the brain. However, the processes in layers V and VI seem to run randomly. The NADPH diaphorase-positive cells could be divided into two classes: heavily stained neurons and lightly stained neurons. For the lightly stained NADPH diaphorase-positive neurons, only the cell bodies could be observed, whereas for the heavily stained neurons, the cell bodies and their varicosity-carrying dendrites and, occasionally, the smooth, thin and weakly stained axons were visible. The heavily stained neurons were morphologically diverse, but no pyramidal or spiny neurons were found. Multipolar and bipolar neurons were located throughout the depth of the cortex, including the white matter, more frequently in layers V and VI. Occasionally, monopolar neurons were found in layer VI. Callosal projecting neurons in the visual cortex were labeled retrogradely with the use of FluoSpheres applied at the opposite visual cortex, but these neurons did not co-localize with the NADPH diaphorase-positive neurons, suggesting that the callosal projecting neurons and NADPH diaphorase-positive neurons belong to two populations of cells in the visual cortex.

Animals↗

PubMed1986

A mathematical model of the primary visual cortex and hypercolumn.

A mathematical model of the primary visual cortex is presented. Basically, the model comprises two features. Firstly, in analogy with the principle of the computerized tomography (CT), it assumes that simple cells in each hypercolumn are not merely detecting line segments in images as features, but rather that they are as a whole representing the local image with a certain representation. Secondly, it assumes that each hypercolumn is performing spatial frequency analyses of local images using that representation, and that the resultant spectra are represented by complex cells. The model is analyzed using numerical simulations and its advantages are discussed from the viewpoint of visual information processing. It is shown that 1) the proposed processing is tolerant to shifts in position of input images, and that 2) spatial frequency filtering operations can be easily performed in the model.

Depth Perception↗