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PubMed2003

Blockade of cyclic AMP-dependent protein kinase does not prevent the reverse ocular dominance shift in kitten visual cortex.

Monocular deprivation (MD) during the critical period for the development of visual cortex causes a loss of binocular response of neurons and a shift to the open eye, a normal ocular dominance (OD) shift. However, when MD is combined with chronic inactivation of the visual cortex by muscimol, the OD distribution of the neurons shifts to the deprived eye (reverse OD shift). We have previously shown that the normal OD shift is abolished by chronic infusion of the protein kinase A (PKA) inhibitor, 8-chloroadenosine-3', 5'-cyclic monophosphorothioate, Rp-isomer (Rp-8-Cl-cAMPS), into kitten visual cortex. In this study, we investigated the effect of this inhibitor on the reverse OD shift. Combination of MD and muscimol infusion into the visual cortex of 6-wk-old kittens caused a reverse OD shift that was comparable to that seen in previous studies. However, a reverse OD shift was also seen with concurrent infusion of the PKA inhibitor with muscimol. The strongest OD shift was observed in layer IV regardless of the presence or absence of the PKA inhibitor. This suggests that the dissociation of pre- and postsynaptic activities, which occurs mainly at thalamocortical synapses, induces the reverse OD shift and that inhibition of PKA does not prevent it. Presumably, an inhibition of PKA has no effect in silent cortex. We conclude that 1) an activation of PKA is not required for the induction of the reverse OD shift, and 2) the intracellular signaling mechanism underlying MD-induced OD plasticity differs between normal and reverse OD shifts.

Animals↗

PubMed2005

Columnar organization of the mammalian visual cortex and its vulnerability following lesion in adult cats.

It is well known that in the mammalian visual cortex the neurons, sharing similar response properties, are grouped together into functional units, known as cortical columns. The orientation and ocular dominance columnar organization is a fundamental element for both the anatomical and physiological features of the visual cortex. Nonetheless, little is known about the functional restoration of matured columnar columns following injury. In the present study, the visual cortex of adult cats was studied electrophysiologically, whereas the primary goal of the study was to reveal the functional stability of the columns, disconnected from the main visual input. Experiments were performed on the primary visual cortex (area 17) of 13 anaesthetized and paralyzed adult cats. The columnar distortion was produced by surgical incision perpendicular to the cortical columns. The single unit activity was recorded from 1186 visual cells (experimental groups) in areas proximal and distal to the lesion and, compared to data, received from intact visual cortex (control group). The results indicate that most of the visually responsive cells were found to be selective to specific orientation in all experimental groups (75-100%) similar to the normal control group (78%). Moreover, the distribution of orientation-specific cells was very similar in all experimental and control groups (p > 0.05), as well as in both recording areas (p > 0.05). The percentage of binocular cells was significantly lower in all experimental groups (23-49%) in comparison to the control (80%). However, the distribution of the binocular cells revealed the significant similarity between the experimental and control groups (p > 0.05). An additional finding of the study is that the visual responsiveness of cells was significantly reduced in all experimental groups: only 28-49% of cells were found to be responsive following injury, as compared to 86% in normal control group (p < 0.001). The distribution of cells has also been analysed in accordance with their directional specificity and it has been found that the majority of cells in the experimental groups were found to be bias and non-specific to light stimuli (52-84%) as compared normal controls (21%) (p < 0.001). It has been concluded that, despite the fact that no improvement in visual function was found, the inherent structure of the disrupted cortical columns in the visual cortex was generally preserved. Therefore, the disruption of the columnar connection does not lead to remarkable distortion of the connectivity pattern on the whole, though it does reduce the responsiveness level there. It was concluded that the columnar structure for both orientation and ocular dominance is characterized by high stability, which enables visual processing with minimal brain connections.

Animals↗

PubMed1984

Direct connections of rat visual cortex with sensory, motor, and association cortices.

Each division of rat visual cortex, areas 17, 18a, and 18b, has connections with sensory, motor, and association cortices. These corticocortical connections were sampled using anterograde autoradiographic and retrograde horseradish peroxidase labeling techniques. Area 17 is connected via reciprocal pathways with each division of visual cortex, the posterior one-third of motor area 8, association area 7, and posteroventral area 36 of temporal cortex. It also receives projections from perirhinal areas 13 and 35. Area 18a has reciprocal connections with areas 17 and 18b, a patch in posterior somatosensory area 3, and dorsal auditory area 41. Like area 17, area 18a receives afferents from and projects to the posterior one-third of motor area 8. The connections of area 18a with association cortices are extensive; these regions include parietal areas 7, 39, 40, and 14, posteroventral and dorsal area 36, and perirhinal cortex. Area 18b is connected with areas 17 and 18a, a patch in medial area 3, and dorsal area 41. There are reciprocal projections between area 18b and posterior area 8. As for association cortex, area 18b projects to frontal area 11, area 7, posteroventral and dorsal area 36, and perirhinal cortex. In addition, area 18b receives input from and projects efferents to the dorsal claustrum. Most of the interconnections among areas 17, 18a, and 18b originate from neurons in layers II, III, and V and end in terminal fields in layers I-III and V. In contrast, projections of other sensory, motor, and association cortices to visual cortex originate mainly from neurons in layer V and to a lesser extent from layer II. The reciprocal pathways from visual cortex terminate predominantly in the supragranular layers. In conclusion, these corticocortical pathways provide the basis for cortical visuosensory and visuomotor integration that may aid the rat in the coordination of visually guided behaviors.

Animals↗

PubMed2006

Visual cortex activation in kinesthetic guidance of reaching.

The purpose of this research was to determine the cortical circuit involved in encoding and controlling kinesthetically guided reaching movements. We used (15)O-butanol positron emission tomography in ten blindfolded able-bodied volunteers in a factorial experiment in which arm (left/right) used to encode target location and to reach back to the remembered location and hemispace of target location (left/right side of midsagittal plane) varied systematically. During encoding of a target the experimenter guided the hand to touch the index fingertip to an external target and then returned the hand to the start location. After a short delay the subject voluntarily moved the same hand back to the remembered target location. SPM99 analysis of the PET data contrasting left versus right hand reaching showed increased (P < 0.05, corrected) neural activity in the sensorimotor cortex, premotor cortex and posterior parietal lobule (PPL) contralateral to the moving hand. Additional neural activation was observed in prefrontal cortex and visual association areas of occipital and parietal lobes contralateral and ipsilateral to the reaching hand. There was no statistically significant effect of target location in left versus right hemispace nor was there an interaction of hand and hemispace effects. Structural equation modeling showed that parietal lobe visual association areas contributed to kinesthetic processing by both hands but occipital lobe visual areas contributed only during dominant hand kinesthetic processing. This visual processing may also involve visualization of kinesthetically guided target location and use of the same network employed to guide reaches to visual targets when reaching to kinesthetic targets. The present work clearly demonstrates a network for kinesthetic processing that includes higher visual processing areas in the PPL for both upper limbs and processing in occipital lobe visual areas for the dominant limb.

Adult↗

PubMed1985

Reinstatement of binocular depth perception by amphetamine and visual experience after visual cortex ablation.

In adult cats with bilateral visual cortex ablation the complete deficit in binocular depth perception, as measured on a visual cliff, was reversed by 4 doses of amphetamine. The amphetamine-induced recovery endured after the amphetamine treatment was discontinued. This enduring recovery of function was not obtained if the animals were housed in the dark during drug intoxication. Therefore, both amphetamine intoxication and visual experience are simultaneously required for recovery of binocular depth perception after visual cortex ablation.

Animals↗

PubMed2007

Experience-driven axon retraction without binocular imbalance in developing visual cortex.

Refinement of the neural circuit during brain maturation is regulated by experience-driven neural activity. In the mammalian visual cortex, monocular visual deprivation (MD) in the early postnatal life causes a significant loss of cortical responses to a deprived eye and the retraction of input axons serving the deprived eye. A competitive interaction between inputs serving both eyes has been supposed to underlie the effects of MD because the loss of cortical response is much weaker when both eyes are deprived of vision. Also, the input axons do not retract after binocular deprivation. Here, we report that uncorrelated activity between presynaptic and postsynaptic neurons can solely lead to the retraction of geniculocortical axons in the absence of activity imbalance between two inputs. We analyzed the morphology of geniculocortical axons in a pharmacologically inhibited visual cortex of animals with normal vision and of binocularly deprived animals. In the normal vision animals, the axonal arbors in the inhibited cortex showed robust retraction. On the other hand, the arbors in binocularly deprived animals remained mostly intact. These results suggest that a homosynaptic associative mechanism, rather than a heterosynaptic competition between inputs, may play an important role in experience-driven axon retraction.

Animals↗

PubMed2001

Suppression of perception in migraine: evidence for reduced inhibition in the visual cortex.

BACKGROUND: Results from transcranial magnetic stimulation (TMS) studies of visual cortex have confirmed visual cortical hyperexcitability in patients with migraine. It has been speculated that this may be due to deficient intracortical inhibitory tone. However, the TMS induction of phosphenes relies on the reporting of a subjective experience, and may thus be subject to bias. METHODS: Seven migraineurs with visual aura and seven sex- and age-matched controls were studied. Fifty-four different three-letter combinations were briefly displayed and followed by a magnetic pulse at 40, 70, 100, 130, 160, and 190 msec. Subjects were required to report as many letters as they thought they had recognized. RESULTS: In the migraine group, the mean proportion of correctly identified letters was significantly higher at 100 msec, as was the proportion of trials with two or three letters correctly reported. The time window in which perceptual suppression could be introduced was narrower in migraineurs compared to controls. CONCLUSION: These findings suggest that inhibitory systems are activated to a lesser extent by TMS pulses in patients. This observation is in agreement with the hypothesized deficiency of intracortical inhibition of the visual cortex, at least in migraineurs with aura.

Adolescent↗

PubMed2004

Age-dependent expression of collapsin response mediator proteins (CRMPs) in cat visual cortex.

The functional properties and anatomical organization of the mammalian visual cortex are immature at birth and develop gradually during the first postnatal weeks. There is a 'critical period' where the cortex is plastic and susceptible to changes in visual input. Knowledge of proteins with a high expression during this period has great importance for the understanding of activity-driven maturation of the brain. The collapsin response mediator protein family consists of five cytosolic phosphoproteins (CRMP1-5) that are involved in neuronal differentiation during the development of the nervous system. They have been implicated in axon guidance and growth cone collapse through their action in the signalling pathway of collapsin/semaphorin. We examined the distribution of the CRMPs throughout the visual cortex of kitten and adult cat by in situ hybridization. While CRMP3 could not be detected in cat forebrain, the other CRMPs showed a higher expression in the immature brain compared to the adult state. Western blotting allowed the quantification of the observed age-dependent differences in the expression of CRMP2, 4 and 5. Moreover, for CRMP2 and 5 we observed a number of development-dependent post-translational modifications. We thus conclude that CRMPs might be important during the normal postnatal development of the visual cortex possibly for the fine-tuning of the specific connections in the brain.

Aging↗

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↗

PubMed1992

Effect of dark rearing on the volume of visual cortex (areas 17 and 18) and number of visual cortical cells in young kittens.

The surface area, total volume, and total number of neurons of areas 17 and 18 in one hemisphere of dark-reared (DR), dark-reared and light-exposed (DRL), and normally reared (NR) kittens were studied at the age of 6 weeks. The thickness of the visual cortex was lower by 13% and 11% (area 17) and by 17% and 16% (area 18) in DR and DRL groups, respectively, when compared with similar cortical areas in NR kittens. The surface area values of area 17 were nearly the same in DR and DRL kittens, both being, however, 37% smaller than in NR animals. The surface area of area 18 was significantly smaller than that of area 17 in each group, and was also lower in DR (by 27%) and DRL (by 21%) groups when compared with the NR group. As a consequence of dark rearing, the numerical density of cortical neurons in area 17 amounted to about double of the value observed in normally reared kittens and was also significantly higher in area 18. The numerical density of nerve cells of DRL kittens fell between the DR and NR groups. The total cortical volume of area 17 was similar in DR and DRL groups but it was by 46% (DR) and by 44% (DRL) smaller than in NR kittens. In each experimental group, the total volume of area 18 was significantly smaller than that of area 17. The cortical volume of area 18 was also smaller than in the NR group by 39% and 34% in DR and DRL groups, respectively. In DR and NR kittens, the total numbers of neurons in areas 17 (DR = 26.4 million, NR = 25.7 million) and 18 (DR = 8.5 million, NR = 9.0 million) were essentially similar. In the DRL groups a significantly smaller number of cortical neurons was found both in area 17 (21.5 million) and in area 18 (6.8 million). It is concluded that, in spite of considerable differences in the cortical thickness, surface area, numerical density, and total cortical volume, the absolute numbers of neurons in area 17 and 18 of visually deprived (DR) and NR kittens do not differ at 6 weeks of age. The main deficit in cortical organization following dark rearing, therefore, appears to be confined mainly to the neuropil, as a result of an underdevelopment of neuronal processes and of depressed synaptic organization.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2005

Differential behavior of simple and complex cells in visual cortex during a brief IOP elevation.

PURPOSE: To study and compare responses of different types of cortical neurons in the primary visual cortex in cats to grating stimuli before and during brief elevation of intraocular pressure (IOP). METHODS: Single-unit electrophysiological recordings were performed in anesthetized and paralyzed cats. The IOP was elevated by injecting saline into the anterior chamber of the cat's eyes through a syringe needle. The IOP was elevated to a level at which the retinal perfusion pressure (arterial pressure minus IOP) was maintained at approximately 30 mmHg for a period of 4 minutes. The responses of simple and complex cells in the primary visual cortex to visually drifting sinusoidal gratings were measured before and during the elevation of IOP. RESULTS: The response amplitude of all the cortical cells in the primary visual cortex declined during a brief elevation of IOP. The decrease in the response of simple cells was always more significant than that of complex cells. The differential decrease between the two major types of cells was independent of the cell's receptive field location and cortical depth. There was a mild tendency for cells with higher preferred spatial frequencies to be more sensitive than those with lower frequencies. The preferred orientation and direction of most cortical cells remained roughly unchanged though their orientation and direction biases decreased. An increase in the animal's blood pressure, which returned the retinal perfusion pressure to a normal level, compensated for the decreased response induced by the elevation of IOP. CONCLUSIONS: The differential effects of a brief elevation of IOP on the response of simple and complex cells in the visual cortex are general and may originate from the retina through the lateral geniculate nucleus (LGN), where different effects of elevation of IOP are exerted on X- and Y-type retinal ganglion cells. The results may suggest differential behavior of neurons tin the parvo and magno pathways of the primate.

Animals↗

PubMed1997

Blockade of serotonin-2C receptors by mesulergine reduces ocular dominance plasticity in kitten visual cortex.

We have investigated the role of serotonin-2C (5-HT2C) receptors in modulation of ocular dominance plasticity in kitten visual cortex. A small quantity of the 5-HT2C receptor blocker, mesulergine, was infused into the visual cortex of one hemisphere of 5- to 7-week-old kittens using osmotic minipumps, while the control hemisphere received vehicle solution. At the same time, one eyelid of the experimental animals was sutured shut. The ocular dominance distributions in the visual cortex (area 17) were assessed using extracellular recording methods after 1 week of combined mesulergine infusion and monocular deprivation. We found that the majority of the neurons remained binocularly responsive in the mesulergine-treated hemisphere, while most of the neurons recorded were either unresponsive or only weakly responsive to the deprived eye in the control hemisphere. Local infusion of mesulergine into the kitten visual cortex thus reduced the shift of ocular dominance that normally occurs in animals of these ages following monocular deprivation. The blocking effect seems to be distance-dependent and therefore dose-dependent: the farther away the recording sites were from the injection site, the fewer binocularly responsive cells were found. These results are relevant to previous findings indicating transient overexpression of 5-HT2C receptor in visual cortex of kittens at these ages. The data suggest that the 5-HT2C receptor system may be involved in the formation and modification of ocular dominance columns in the developing visual cortex.

Animals↗

PubMed1986

Why spatial frequency processing in the visual cortex?

The nature of redundancy in visual images is discussed and the methods of removing statistical redundancies are considered. It is demonstrated that local spatial frequency analysis is a highly successful method and it is thus argued that this determines the choice of representation of the visual image by the simple cells of the visual cortex.

Humans↗

PubMed2005

Study on long-term potentiation in developing rat visual cortex during the critical period of plasticity.

PURPOSE: To study the property of LTP in layers II -IV of the rats visual cortex at different postnatal days induced by pairing low-frequency stimulation at layer IV with post synaptic depolarization in order to explore the synaptic and cellular mechanism of experience-dependent plasticity in the visual cortex. METHODS: Postsynaptic currents (PSCs) of layers II -IV in visual cortex slices of Wistar rats aged P0-29 d were recorded by patch-clamp whole cell recording method. Long-term potentiation (LTP) was induced by low-frequency stimulation (LFS) at 1Hz for 60-90 s. Each pulse of the LFS paired with depolarization of post-synaptic neurons to -20 mV.100 microM APV, a kind of competitive N-methyl-d-aspartate (NMDA) receptor antagonist, was both applied to some slices to test the property of LTP. RESULTS: 1. The LTP incidence was very low before PlOd (5/34), and increased rapidly to the top at P15-24 d (17/28), then decreased sharply to 1/5 at P25-29 d, coinciding well with the critical period of plasticity of rat visual cortex. The LTP incidence of P15-29 d (after eye opening, 18/33) was significantly higher than that of P0-14 d (before eye opening, 12/43, P < 0.05). 2. Compared with non-APV applied group (30/76), LTP incidence of APV applied group (4/33) was significantly decreased (P < 0.01). There were 4 LV-IV horizontal synapses. APV application could not block the LTP induction. CONCLUSIONS: 1. LTP was a reflection of naturally occurring, experience-dependent plasticity in rat visual cortex. The patterned visual stimuli received after eye opening might be an activation factor of the synaptic plasticity. 2. LTP of visual cortex induced by LFS in layer IV paired with postsynaptic depolarization was NMDA receptor dependent during the critical period of visual plasticity. However, there were LTP existed in IV-IV horizontal synapses which could not be blocked by 100microM APV.

Animals↗

PubMed1999

Monocular deprivation decreases brain-derived neurotrophic factor immunoreactivity in the rat visual cortex.

Neurotrophins play a crucial role in the development and activity-dependent plasticity of the visual cortex [Berardi N. et al. (1994) Proc. natn. Acad. Sci. U.S.A. 91, 684-688; Bonhoeffer T. (1996) Curr. Opin. Neurobiol. 6, 119-126; Cellerino A. and Maffei L. (1996) Prog. Neurobiol. 49, 53-71; Domenici L. et al. (1994) NeuroReport 5, 2041-2044; Galuske R. A. W. et al (1996) Eur. J. Neurosci. 8, 1554-1559; Katz L. C. and Shatz C. J. (1996) Science 274, 1133-1138; Maffei L. et al. (1992) J. Neurosci. 12, 4651-4662; Pizzorusso T. and Maffei L. (1996) Curr. Opin. Neurol. 9, 122-125; Thoenen H. (1995) Science 270, 593-598]. As a possible mechanism of action, it has been postulated that the activity-dependent expression of neurotrophins by cortical cells could regulate synapse stabilization during the first period of postnatal life (critical period). Indeed, brain-derived neurotrophic factor messenger RNA expression in the visual cortex is regulated by neuronal activity as well as during development [Castrén E. et al. (1992) Proc. natn. Acad. Sci. U.S.A. 89, 9444-9448]. Moreover, we showed that monocular deprivation decreases brain-derived neurotrophic factor messenger RNA levels in the visual cortex receiving input from the deprived eye [Bozzi Y. et al. (1995) Neuroscience 69, 1133-1144]. What is missing, however, is the demonstration that brain-derived neurotrophic factor protein expression follows that of brain-derived neurotrophic factor messenger RNA. The aim of the present study is to fill this important gap in order to support the hypothesis that brain-derived neurotrophic factor is fundamental in the plasticity of the visual cortex. We found that brain-derived neurotrophic factor immunoreactivity peaks during the critical period and that it is preferentially localized in layers II-III and V-VI. We also demonstrated that monocular deprivation determines a decrease of brain-derived neurotrophic factor immunoreactivity exclusively in the visual cortex contralateral to the deprived eye. Our results support the proposed role for brain-derived neurotrophic factor in the development and activity-dependent plasticity of the visual cortex [Cabelli R. J. et al. (1995) Science 267, 1662-1666].

Aging↗

PubMed1994

Summation and division by neurons in primate visual cortex.

Recordings from monkey primary visual cortex (V1) were used to test a model for the visually driven responses of simple cells. According to the model, simple cells compute a linear sum of the responses of lateral geniculate nucleus (LGN) neurons. In addition, each simple cell's linear response is divided by the pooled activity of a large number of other simple cells. The cell membrane performs both operations; synaptic currents are summed and then divided by the total membrane conductance. Current and conductance are decoupled (by a complementary arrangement of excitation and inhibition) so that current depends only on the LGN inputs and conductance depends only on the cortical inputs. Closed form expressions were derived for fitting and interpreting physiological data. The model accurately predicted responses to drifting grating stimuli of various contrasts, orientations, and spatiotemporal frequencies.

Animals↗

PubMed1975

Laminar thermocoagulation of the visual cortex in the rat. II. Visual pattern discrimination.

Hooded rats were trained on a series of four visual discrimination tasks in a Y-maze, and subjected to a variety of posterior cortical lesions. In 17 animals this consisted of an extensive aspiration lesion contralateral to a more superficial lesion made by laminar thermocoagulation and centered over the striate area. After operation the animals were tested on the same problem series. The behavioral deficit in this group varied with the extent and depth of the thermal lesion, and six animals with very superficial thermal lesions displayed an isolated difficulty in solving an encircled triangle problem. This deficit seemed to be referable to widespread involvement of supragranular cortex, and specifically of layer I of area striata which receives an input from the nonspecific thalamocortical afferents. The possible influence of various interlaminar projections upon underlying vertically-oriented cell columns as a mechanism for the mediation of 'selective attention' was discussed.

Animals↗

PubMed1995

Interocular transfer of receptive field expansion in cat visual cortex.

Receptive fields in primary visual cortex have been shown to be capable of rapid expansion and contraction when exposed to an artificial scotoma, a masked segment of the visual field. To distinguish cortical from thalamic contributions to receptive field mutability, we tested interocular transfer of the effect in binocular cortical receptive fields, presenting the conditioning stimulus to the field in one eye and measuring size changes in the receptive field of the other eye. The expansion of the receptive fields in the non-conditioned eye was comparable to that in the conditioned eye. This result suggests that the expansion is due to mechanisms intrinsic to the cortex.

Animals↗