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PubMed1992

[Morphologic aspects of the maturation of the sensory areas of the cerebral cortex exemplified by the visual cortex of the rabbit].

When the cerebral cortex commences its earliest functional tasks, the cellular layers and the basic organisation pattern of cell processes have already developed. In the rabbit visual cortex it could be shown that the functional differentiation runs parallel to an increase in number and growth of cell processes. Those tissue compartments where the newly formed branches of the dendritic trees of cortical neurons come into contact with the axons arising from other cerebral regions, grow between two and six times larger depending on the cortical layer where their volume fractions are measured. Cell processes grow and increase in number most rapidly between the second and the fourth postnatal weeks. Myelination of fast conducting axons takes longer and attains an adult level about three month after birth. Then the visual cortex of the rabbit may be regarded as mature with regard to both structure and function.

Animals↗
PubMed1975

Receptive fields of single cells and topography in mouse visual cortex.

The visual cortex was studied in the mouse (C57 Black/6J strain) be recording from single units, and a topographic map of the visual field was constructed. Forty-five percent of the neurons in striate cortex responded best to oriented line stimuli moving over their receptive fields; they were classified as simple (17%), complex (25%) and hypercomplex (3%). Of all preferred orientations horizontal was most common. Fifty-five percent of recpetive fields were circularly symmetric: these were on-center (25%), off-center (7%) and homogeneous on-off in type (23%). Optimal stimulus velocities were much higher than those reported in the cat, mostly varying between 20 degrees and 300 degrees/sec. The field of vision common to the two eyes projected to more than one-third of the striate cortex. Although the contralateral eye provided the dominating influence on cells in this binocular area, more than two-thirds of cells could also be driven through the ipsilateral eye. The topography of area 17 was similar to that found in other mammals: the upper visual field projected posteriorly, the most nasal part mapped onto the lateral border. Here the projection did not end at the vertical meridian passing through the animal's long axis, but proceeded for at least 10 degrees into the ipsilateral hemifield of vision, so that at least 20 degrees of visual field were represented in both hemispheres. The magnification in area 17 was rather uniform throughout the visual field. In an area lateral to area 17 (18a) the fields were projected in condensed mirror image fashion with respect to the arrangement of area 17. Medial to area 17 a third visual area (area 18) was again related to 17 as a condensed mirror image.

Animals↗
PubMed2006

The development of direction selectivity in ferret visual cortex requires early visual experience.

Development of the selective response properties that define columns in sensory cortex is thought to begin early in cortical maturation, without the need for experience. We investigated the development of direction selectivity in ferret visual cortex using optical imaging and electrophysiological techniques and found an exception to this view. Unlike orientation selectivity and ocular dominance, direction selectivity was not detected at eye opening. Direction selectivity emerged several days later and strengthened to adult levels over the following 2 weeks. Visual experience was essential for this process, as shown by the absence of direction selectivity in dark-reared ferrets. The impairment persisted in dark-reared ferrets that were given experience after this period, despite the recovery of response amplitude, preference and bandwidth for stimulus orientation, spatial and temporal frequency, and contrast. Visual experience in early postnatal life plays a necessary and unique role in the development of cortical direction selectivity.

Action Potentials↗
PubMed1995

Expression of DMAP-45R in the rat visual cortex is modulated by visual experience.

Effects of visual experience upon expression of a developmentally regulated microtubule-associated protein (MAP) were studied in the visual cortex of monocularly deprived rats. The antibody Drosophila MAP-45 (DMAP-45) recognizes proteins in the developing ventral nerve cord of Drosophila and in rat brain. Monocular deprivation from day 12, before eye opening, to day 80 reduced the number of DMAP-45 immunoreactive layer V pyramidal cell apical dendrites in the monocular segment (Oc1M) of the visual cortex contralateral to the deprived eye. No significant visual deprivation effects were seen in the binocular segment (Oc1B). Immunoreactivity was restored to control levels in Oc1M of rats in which the monocular sutures were removed at day 75, subsequently allowing 5 days of exposure to light. These results indicate potential involvement of this MAP in experience-dependent structural plasticity.

Animals↗
PubMed2004

A computational model for the development of multiple maps in primary visual cortex.

Primary visual cortex contains multiple maps of features of the visual scene, including visual field position, orientation, direction, ocular dominance and spatial frequency. The complex relationships between these maps provide clues to the strategies the cortex uses for representing and processing information. Here we simulate the combined development of all these map systems using a computational model, the elastic net. We show that this model robustly produces combined maps of these four variables that bear a close resemblance to experimental maps. In addition we show that the experimentally observed effects of monocular deprivation and single-orientation rearing can be reproduced in this model, and we make some testable predictions. These results provide strong support for the hypothesis that cortical representations attempt to optimize a trade-off between coverage and continuity.

Brain Mapping↗
PubMed1988

Split chiasm developmentally induced in kittens: plasticity of interhemispheric transfer in visual cortex cells.

Visual callosal transfer during development was studied in order to reveal plasticity-related compensation for the absence of direct contralateral inputs. The optic chiasm was midsagittally sectioned in 6-8 weeks old kittens (OCK) and for comparison, in adult cats (OCA). Unit recording was made during adulthood in the border area between visual cortex areas 17 and 18, namely the callosal projection zone. The proportion of cells showing interhemispheric transfer in the OCK group, as indicated by the presence of visual input from the contralateral eye was 10.5%; in the OCA cats their proportion was 4.0%. Moreover, 2.3% of the cells showed a pure transfer of input from the contralateral eye in the OCK, although none was seen in the OCA cats. Thus, during the developmental period, a plasticity induced process, albeit limited, takes place in the enhancement of interhemispheric transfer of visual information.

Animals↗
PubMed1993

Activity-dependent expression of the transcription factor Zif268 reveals ocular dominance columns in monkey visual cortex.

The visualization of neuronal populations activated by sensory stimulation has been approached using a number of different methodologies. Recent developments in our understanding of transcription factors have provided a new window for observing neural activity. We have found that the transcription factor Zif268 is expressed throughout the visual cortex of the monkey at high basal levels and that monocular visual deprivation produces dramatic changes in its levels revealing ocular dominance columns in striate cortex with as little as 2 h of selective exposure. These results show that immunodetection for Zif268 may be used for labelling activated neuronal populations in the monkey with several key advantages over prior techniques.

Animals↗
PubMedDate not supplied

Role of GABA(A)-mediated inhibition in controlling the responses of regular spiking cells in turtle visual cortex.

The visual cortex of freshwater turtles contains pyramidal cells, which have a regular spiking (RS) firing pattern, and several categories of aspiny, inhibitory interneurons. The interneurons show diverse firing patterns, including the fast spiking (FS) pattern. Postsynaptic potentials (PSPs) evoked in FS cells by visual stimulation of the retina reach their peak amplitudes as much as 200 ms before PSPs in RS cells (Mancilla et al., 1998). FS cells could, consequently, control the amplitudes of light-evoked PSPs in RS cells by producing disynaptic, feedforward inhibitory postsynaptic potentials (IPSPs) that overlap in time with geniculocortical excitatory postsynaptic potentials (EPSPs). Since FS cells receive recurrent, excitatory inputs from RS cells, they could also control the amplitudes of light-evoked PSPs in RS cells via polysynaptic, feedback inhibition. The in vitro geniculocortical preparation of Pseudemys scripta was used to characterize the temporal relationships of EPSPs and IPSPs produced in RS cells by electrical activation of geniculate afferents and by diffuse light flashes presented to the retina. GABA(A) receptor-mediated inhibition was blocked using extracellular application of bicuculline (3.5 mM) or intracellular perfusion of picrotoxin (1 microM) in individual RS cells. Electrical stimulation of thalamic afferents produced compound PSPs. Blockade of GABA(A) receptor-mediated IPSPs with either bicuculline or picrotoxin provided evidence for both early and late IPSPs in RS cells. Analysis of the apparent reversal potentials of light-evoked PSPs indicated the existence of early IPSPs during the first 140-300 ms following light onset. Light responses of cells perfused with picrotoxin diverged from control light responses at about 300 ms after light onset and had maximum amplitudes that were significantly different from control light responses. These experiments indicate that the responses of RS cells to both electrical and natural stimulation of geniculate afferents are controlled by both early and late IPSPs, consistent with activation of both feedforward and feedback pathways.

Animals↗
PubMed2001

Effect of the glycine modulatory site of the N-methyl-D-aspartate receptor on synaptic responses in kitten visual cortex.

In visual cortical slices taken from kittens, the administration of D-serine, an agonist of the N-methyl-D-aspartate receptor complex, significantly enhanced synaptically evoked responses using field potential recordings in lower layer II/III. Expression of normally appearing long-term potentiation (LTP) took place in the presence of the agonist during high-frequency stimulation (HFS). The administration of an antagonist of this receptor, 7-chloro-kynurenic acid (7-Cl KY) alone had no appreciable effect on low-frequency synaptic transmission while HFS failed to induce LTP. Combined administration of D-serine and 7-Cl KY resulted in no alteration of low-frequency synaptic transmission, although expression of LTP was normally obtained. These results suggest that in visual cortex of kittens, the availability of this glycine binding site of the NMDA receptor is necessary for the expression of LTP.

Animals↗
PubMed2004

Imaging cortical correlates of illusion in early visual cortex.

Exploring visual illusions reveals fundamental principles of cortical processing. Illusory motion perception of non-moving stimuli was described almost a century ago by Gestalt psychologists. However, the underlying neuronal mechanisms remain unknown. To explore cortical mechanisms underlying the 'line-motion' illusion, we used real-time optical imaging, which is highly sensitive to subthreshold activity. We examined, in the visual cortex of the anaesthetized cat, responses to five stimuli: a stationary small square and a long bar; a moving square; a drawn-out bar; and the well-known line-motion illusion, a stationary square briefly preceding a long stationary bar presentation. Whereas flashing the bar alone evoked the expected localized, short latency and high amplitude activity patterns, presenting a square 60-100 ms before a bar induced the dynamic activity patterns resembling that of fast movement. The preceding square, even though physically non-moving, created gradually propagating subthreshold cortical activity that must contribute to illusory motion, because it was indistinguishable from cortical representations of real motion in this area. These findings demonstrate the effect of spatio-temporal patterns of subthreshold synaptic potentials on cortical processing and the shaping of perception.

Animals↗
PubMed2002

Neurotrophins and plasticity in the visual cortex.

The visual cortex is one of the favorite models for the study of experience-dependent changes in neuronal structure and function. A number of recent investigations indicate that the neurotrophic factors of the nerve growth factor family (neurotrophins) play a pivotal role in visual cortical plasticity. Neurotrophins and their receptors are present in the cortex during the critical period for plasticity, and neurotrophin levels are regulated by electrical activity. Neurotrophins modulate synaptic transmission and patterns of neuronal connectivity in the cortex. This review summarizes the in vivo and in vitro data that demonstrate the involvement of neurotrophins in visual cortical plasticity and discusses the possible mechanisms of their action.

Animals↗
PubMed1996

Lateral suprasylvian visual cortex is activated earlier than or synchronously with primary visual cortex in the cat.

To explore functional connectivity between area 17 and posteromedial lateral suprasylvian (PMLS) area of the cat cerebral cortex, we carried out cross-correlation analysis of spike trains of neurons recorded simultaneously from both areas of anesthetized, paralyzed cat. Most of correlated pairs had peaks which indicate that PMLS cells were activated earlier than or simultaneously with their partners in area 17, suggesting that 'backward' as well as synchronous activation operates between these cortical areas.

Animals↗
PubMed2006

Receptive-field modification in rat visual cortex induced by paired visual stimulation and single-cell spiking.

Experience-dependent plasticity of visual cortical receptive fields (RFs) involves synaptic modifications in the underlying neural circuits, but the site and mechanism of these modifications remain to be elucidated. Using in vivo whole-cell recordings, we show that pairing visual stimulation at a given retinal location with spiking of a single neuron in developing rat visual cortex induces rapid RF modifications. The time course of the response to the visual stimulus at the paired RF location is altered, with an enhancement of the response preceding the spike time and a reduction following the spike. Such bidirectional modification is consistent with spike timing-dependent plasticity. Response modification also occurs at nearby locations, the direction and magnitude of which are correlated with the change at the paired location. In addition, changes at unpaired locations show a negative correlation with the initial strength of the response, which may facilitate rapid modification of the spatial RF profile.

Animals↗
PubMed2003

Flexible retinotopy: motion-dependent position coding in the visual cortex.

Although the visual cortex is organized retinotopically, it is not clear whether the cortical representation of position necessarily reflects perceived position. Using functional magnetic resonance imaging (fMRI), we show that the retinotopic representation of a stationary object in the cortex was systematically shifted when visual motion was present in the scene. Whereas the object could appear shifted in the direction of the visual motion, the representation of the object in the visual cortex was always shifted in the opposite direction. The results show that the representation of position in the primary visual cortex, as revealed by fMRI, can be dissociated from perceived location.

Attention↗
PubMed1987

The deafferented visual cortex: neuronal activity and visual evoked potentials.

The callosal transfer of information to the visual cortex following its unilateral deafferentation from its geniculate input was studied in both hemispheres. Deafferentation was performed in adult cats by sectioning the optic tract. Action potentials of single cortical cells and visual evoked potentials were recorded from area 17-18 boundary in acute and chronic operated cats. In the deafferented hemisphere, cortical cells were usually visually inactive. However, some recovery of function took place in this hemisphere in the chronic cats, as expressed by the increase in the proportion of S-cells. In the intact hemisphere diminution of responsiveness and reduction of selectivity to the stimulus orientation and direction were found. The responsiveness and selectivity level in the intact hemisphere increased with postoperative time. The ocular dominance distribution in this hemisphere was similar to that of our normal control cats. The characteristics of the visual evoked potentials were in keeping with the hemispheric dominance of the cortical cells found in the experimental cats. It was concluded that a plasticity related mechanism is involved in the recovery of callosal activation of visual cortical cells following deafferentation.

Animals↗
PubMed2005

Orientation selectivity without orientation maps in visual cortex of a highly visual mammal.

In mammalian neocortex, the orderly arrangement of columns of neurons is thought to be a fundamental organizing principle. In primary visual cortex (V1), neurons respond preferentially to bars of a particular orientation, and, in many mammals, these orientation-selective cells are arranged in a semiregular, smoothly varying map across the cortical surface. Curiously, orientation maps have not been found in rodents or lagomorphs. To explore whether this lack of organization in previously studied rodents could be attributable to low visual acuity, poorly differentiated visual brain areas, or small absolute V1 size, we examined V1 organization of a larger, highly visual rodent, the gray squirrel. Using intrinsic signal optical imaging and single-cell recordings, we found no evidence of an orientation map, suggesting that formation of orientation maps depends on mechanisms not found in rodents. We did find robust orientation tuning of single cells, and this tuning was invariant to stimulus contrast. Therefore, it seems unlikely that orientation maps are important for orientation tuning or its contrast invariance in V1. In vertical electrode penetrations, we found little evidence for columnar organization of orientation-selective neurons and little evidence for local anisotropy of orientation preferences. We conclude that an orderly and columnar arrangement of functional response properties is not a universal characteristic of cortical architecture.

Action Potentials↗