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PubMed2004

Microarray analysis of developmental plasticity in monkey primary visual cortex.

We performed microarray gene expression analyses on the visual cortex of Old-World monkeys (Cercopithicus aethiops) in an effort to identify transcripts associated with developmental maturation and activity-driven changes during the visual critical period. Samples derived from normal animals and those subjected to monocular enucleation (ME) were hybridized to human Affymetrix HG-U95Av2 oligonucleotide microarrays (N = 12) and the results were independently validated by real-time quantitative RT-PCR. To identify genes exhibiting significant expression differences among our samples, the microarray hybridization data were processed with two software packages that use different analytical models (Affymetrix MicroArray Suite 5.0, dChip 1.2). We identified 108 transcripts within diverse functional categories that differed in their visual cortical expression at the height of the critical period when compared to adults. The expression levels of four transcripts were also globally modulated following ME during the critical period. These transcripts are particularly sensitive to ME during the critical period but are not significantly modulated in ME adults. Three of the ME-driven genes (NGFI-B, egr3, NARP) are known immediate-early genes (IEG) while the other (DUSP6) is a phosphatase that can regulate IEG expression. The putative biological significance of the ME-driven and developmentally regulated genes is discussed with respect to the critical period for activity-dependent visual cortical neuroplasticity.

Animals↗
PubMed1977

An attempt to assess the effects of monocular deprivation and strabismus on synaptic efficiency in the kitten's visual cortex.

The relative effectiveness of the two eyes in exciting cells in the visual cortex was assessed, using both natural stimulation and electrical stimulation of the optic discs. It is is argued that supramaximal electrical stimulation of the optic nerve could possibly reveal 'subliminal' synaptic inputs even after monocular deprivation or artificial strabismus has caused a loss of natural input from that eye, if such 'silent' synaptic input still survives. However, in kittens monocularly deprived for various periods of time or made artificially strabismic, there was usually excellent agreement between the relative visual excitability in the two eyes and their relative electrical excitability. In one animal, monocularly deprived continuously until 23 weeks of age, we examined the effect of reversibly turning off signals from the normal eye by pressure blinding. There was no evidence of a very rapid return of sensitivity to either electrical or natural stimulation of the deprived eye.

Animals↗
PubMed1999

Sensory regulation of immediate-early genes c-fos and zif268 in monkey visual cortex at birth and throughout the critical period.

The postnatal development of ocular dominance columns (ODCs) in monkey visual cortex provides an exquisite model for studying mechanisms of experience-guided neuronal plasticity. While the presence of columns at birth in Old World monkeys is now well established, it remains unclear whether cortical neurons at this early stage are capable of modulating gene expression in response to changing sensory conditions. Using a set of monocular deprivation and stimulation protocols, we examined activity-driven expression of the immediate-early genes (IEGs) c-fos and zif268 during the critical period of development. We observed well-delineated patterns of ODCs produced by sensory regulation of both IEGs throughout the critical period, starting as early as the first postnatal day. The expression levels are similar in layers II/II, IVC and VI throughout development, with no selective decline in the thalamorecepient layer (layer IVC) of adult monkeys. A narrow strip of non-columnar c-Fos expression was observed at the border of layers IVC and V. Our results show that neurons in monkey visual cortex are equipped at birth with the molecular machinery for coupling sensory inputs to active genomic responses and that this responsivity extends throughout the critical period. The findings are discussed within the context of a possible role for IEGs in sensory-driven cortical plasticity during development.

Animals↗
PubMed1998

Anatomical comparison of the macaque and marsupial visual cortex: common features that may reflect retention of essential cortical elements.

This study identifies fundamental anatomical features of primary visual cortex, area V1 of macaque monkey cerebral cortex, i.e., features that are present in area V1 of phylogenetically distant mammals of quite different lifestyle and features that are common to other regions of cortex. We compared anatomical constituents of macaque V1 with V1 of members of the two principal marsupial lines, the dunnart and the quokka, that diverged from the eutherian mammalian line over 135 million years ago. Features of V1 common to both macaque and marsupials were then compared with anatomical features we have previously described for macaque prefrontal cortex. Despite large differences in overall area and thickness of V1 cortex between these animals, the absolute size of pyramidal neurons is remarkably similar, as are their specific dendritic branch patterns and patterns of distribution of intrinsic axons. Pyramidal neuron patchy connections exist in the supragranular V1 in both the marsupial quokka and macaque as well as in macaque prefrontal cortex. Several specific types of aspinous interneurons are common to area V1 in both marsupial and macaque and are also present in macaque prefrontal cortex. Spiny stellate cells are a common feature of the thalamic-recipient, mid-depth lamina 4 of V1 in all three species. Because these similarities exist despite the very different lifestyles and evolutionary histories of the animals compared, this finding argues for a highly conserved framework of cellular detail in macaque primary visual cortex rather than convergent evolution of these features.

Anatomy, Artistic↗
PubMed1984

Alterations in response properties in the lateral and dorsal terminal nuclei of the cat accessory optic system following visual cortex lesions.

The response properties of cells in the lateral (LTN) and dorsal (DTN) terminal nuclei of the accessory optic system (AOS) were examined in 14 cats which underwent unilateral visual cortex ablation. Following decortication, single units in the LTN and DTN no longer showed the high degree of binocular convergence characteristic of the intact animal, but instead LTN and DTN units became almost completely dominated by the contralateral eye. In addition, responsivity of LTN and DTN cells to high stimulus velocities was abolished by removal of cortical input. This decrement in high velocity response was observed in both the excitatory and the inhibitory components of the velocity response profile. While the incidence of direction selective neurons in both the LTN or the DTN was not affected by decortication, the distribution of preferred and nonpreferred directions was dramatically altered in the LTN, and to a lesser extent in the DTN. In the LTN, there was a severe reduction in the number of cells which displayed maximal excitation for upward stimulus motion. Instead, most LTN units in the decorticate cat preferred downward directed stimulus motion. In the DTN, most units still preferred horizontal stimulus motion as in the intact animal, but the overall distribution of preferred directions displayed a clear downward vertical vector component. In other respects, such as receptive field size and position in visual space, on/off responses, and resting discharge rate, LTN and DTN units appeared unaffected by cortical lesions. These experiments demonstrate that the cortical input to the LTN and DTN plays a highly significant role in the formation of response properties of cells located in these nuclei. The results presented in this report indicate that the visual cortex is a major source of ipsilateral eye input, high velocity responses, and upward direction selectivity for the AOS units examined in these experiments.

Animals↗
PubMed2006

Cognitive control signals in visual cortex: flashes meet spotlights.

At the intersection of two intensely belabored fields, primary visual cortex (V1) function and neural mechanisms of cognitive control, Jack et al. (in this issue of Neuron) report a neural signal that is neither related to stimulus representation nor spatial attention. Instead, this endogenous signal correlates with task structure and raises new questions.

Afferent Pathways↗
PubMed1995

Effect of sensory deafferentation on immunoreactivity of GABAergic cells and on GABA receptors in the adult cat visual cortex.

To investigate the effects of sensory deafferentation on the cortical GABAergic circuitry in adult cats, glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) immunoreactivity and GABA receptor binding were studied in the visual cortex of normal cats and compared with cats that had received restricted binocular central lesions of the retina and had survived for 2 weeks postlesion in a normal visual environment. In the visual cortex of lesioned cats, two changes were observed in the number of GAD-immunoreactive elements in the regions affected by the retinal lesions: the number of GAD-positive puncta decreased, whereas that of GAD-immunoreactive somata increased. In contrast, no detectable changes were measured in the number of GABA-immunopositive somata or puncta. At the receptor level, we observed no differences in either the laminar distribution or the affinity of cortical GABAA and GABAB receptors labeled with [3H]-muscimol and [3H]-baclofen, respectively, in the lesioned versus normal cats. We present the hypothesis that sensory deafferentation in these adult cats (1) leads to a reduction of cortical GABAergic inhibition in the deafferented region, and (2) that this decreased inhibition may permit changes in efficiency of synapses and (3) that these changes may represent a first stage of events underlying the retinotopic reorganization preceeding the structural changes.

Afferent Pathways↗
PubMed1989

Synaptic density of caudate-putamen and visual cortex following exposure to ethanol in utero.

Pregnant Long-Evans rats were fed a liquid diet containing ethanol (30% of total calories) during days 3-19 of gestation. Controls were given ad libitum access to liquid diet lacking ethanol, or pair-fed isocaloric amounts based on consumption by the animals in the ethanol group. Brain development of female offspring was evaluated by analysis of electron micrographs of caudate-putamen and visual cortex. Numbers of presynaptic terminals and synaptic junctions (synaptic density) per unit area were compared for 14- and 28-day-old offspring of dams from the three treatment groups. Synaptic density of the caudate-putamen and visual cortex was not affected by ethanol at 14 or 28 days. Although exposure to ethanol during a period comparable to the first two trimesters of human development with minimal or no undernutrition did not affect numerical density of synapses in visual cortex or caudate-putamen, synaptogenesis of caudate-putamen was altered in offspring of pair-fed animals.

Animals↗
PubMed1997

Adaptation to contingencies in macaque primary visual cortex.

We tested the hypothesis that neurons in the primary visual cortex (V1) adapt selectively to contingencies in the attributes of visual stimuli. We recorded from single neurons in macaque V1 and measured the effects of adaptation either to the sum of two gratings (compound stimulus) or to the individual gratings. According to our hypothesis, there would be a component of adaptation that is specific to the compound stimulus. In a first series of experiments, the two gratings differed in orientation. One grating had optimal orientation and the other was orthogonal to it, and therefore did not activate the neuron under study. These experiments provided evidence in favour of our hypothesis. In most cells adaptation to the compound stimulus reduced responses to the compound stimulus more than it reduced responses to the optimal grating, and the responses to the compound stimulus were reduced more by adaptation to the compound stimulus than by adaptation to the individual gratings. This suggests that a component of adaptation was specific to (and caused by) the simultaneous presence of the two orientations in the compound stimulus. To test whether V1 neurons could adapt to other contingencies in the stimulus attributes, we performed a second series of experiments, in which the component gratings were parallel but differed in spatial frequency, and were both effective in activating the neuron under study. These experiments failed to reveal convincing contingent effects of adaptation, suggesting that neurons cannot adapt equally well to all types of contingency.

Adaptation, Ocular↗
PubMed2000

Orientation tuning of input conductance, excitation, and inhibition in cat primary visual cortex.

The input conductance of cells in the cat primary visual cortex (V1) has been shown recently to grow substantially during visual stimulation. Because increasing conductance can have a divisive effect on the synaptic input, theoretical proposals have ascribed to it specific functions. According to the veto model, conductance increases would serve to sharpen orientation tuning by increasing most at off-optimal orientations. According to the normalization model, conductance increases would control the cell's gain, by being independent of stimulus orientation and by growing with stimulus contrast. We set out to test these proposals and to determine the visual properties and possible synaptic origin of the conductance increases. We recorded the membrane potential of cat V1 cells while injecting steady currents and presenting drifting grating patterns of varying contrast and orientation. Input conductance grew with stimulus contrast by 20-300%, generally more in simple cells (40-300%) than in complex cells (20-120%), and in simple cells was strongly modulated in time. Conductance was invariably maximal for stimuli of the preferred orientation. Thus conductance changes contribute to a gain control mechanism, but the strength of this gain control does not depend uniquely on contrast. By assuming that the conductance changes are entirely synaptic, we further derived the excitatory and inhibitory synaptic conductances underlying the visual responses. In simple cells, these conductances were often arranged in push-pull: excitation increased when inhibition decreased and vice versa. Excitation and inhibition had similar preferred orientations and did not appear to differ in tuning width, suggesting that the intracortical synaptic inputs to simple cells of cat V1 originate from cells with similar orientation tuning. This finding is at odds with models where orientation tuning in simple cells is achieved by inhibition at off-optimal orientations or sharpened by inhibition that is more broadly tuned than excitation.

Action Potentials↗
PubMedDate not supplied

Self-organization of local cortical circuits and cortical orientation maps: a nonlinear Hebbian model of the visual cortex with adaptive lateral couplings.

A nonlinear, recurrent neural network model of the visual cortex is presented. Orientation maps emerge from adaptable afferent as well as plastic local intracortical circuits driven by random input stimuli. Lateral coupling structures self-organize into DOG profiles under the influence of pronounced emerging cortical activity blobs. The model's simplified architecture and features are modeled to largely mimik neurobiological findings.

Animals↗
PubMed1991

[A double-labeling study of serotonin neurons that project to the visual cortex of developing rat brain].

Immunohistochemical studies of developing rat brains revealed aggregation of serotonin terminal fibers in the visual cortex at from 7 to 14 postnatal days. This aggregation is transient, disappearing 2 weeks after birth. The cells of origin of these serotonin terminals were investigated using double-labeling with retrogradely transported WGA-apoHRP-Au and serotonin immunohistochemistry. WGA-apoHRP-Au was injected into the rat visual cortex on the 9th day after birth. The rats were allowed to survive for 2 days and sacrificed with perfusion. Cryostat sections of the brain were processed with silver-enhancement to develop the retrogradely transported WGA-apoHRP-Au, and then serotonin immunohistochemistry was performed. Double-labeled cells that were labeled with WGA-apoHRP-Au and serotonin-immunoreactive were found mostly in the raphe medianus and raphe dorsalis in rostral and caudal sections of the mesencephalon, respectively.

Animals↗
PubMed1975

Receptive fields in cat superior colliculus after visual cortex lesions.

1. The superior colliculus has been studied in intact cats and in cats with visual cortex lexions by recording the responses of single tectal units to visual stimuli. 2. Three classes of units have been identified in the superficial layers of the colliculus in these visually decorticate cats. 3. One class, comprising 5% of the units studied, has receptive fields organized concentrically in a manner similar to retinal ganglion cells. 4. The second class, comprising 12% of the units studied, responds to stimulus velocities over 300/sec, responds well to both small and large stimuli, and can be driven by strobe flashes at frequencies up to 35--40/sec. These units are termed 'flicker' cells. 5. The third class comprising 83% of the units studied, responds best to stimuli which are not larger than the activating region of the receptive field, moving at relatively low velocities. These units show strong suppressive surrounds which are sensitive to higher velocities of stimulus movement than the central activating region. Responses from the activating region in these units are dramatically inhibited by flickering dhanges in the level of background illumination. 6. In intact cats few units are found which are strongly inhibited by background flicker. 7. It is suggested that a high-velocity sensitive element such as the 'flicker' cell or phasic retinal ganglion cell is responsible for the flicker-induced inhibition of collicular units in the visually decorticate cat.

Action Potentials↗
PubMed2005

Functional organization of visual cortex in the prosimian bush baby revealed by optical imaging of intrinsic signals.

Cells in primary visual cortex (V1) of primates and carnivores respond most strongly to a visual stimulus presented to one eye, in a particular visual field location, and at a particular orientation. Each of these stimulus attributes is mapped across the cortical surface, and, in macaque monkeys and cats, strong geometrical relationships exist between these feature maps. In macaque V1 and V2, correlations between feature maps and cytochrome oxidase (CO)-rich modules have also been observed. To see if such relationships reflect a conserved principle of V1 functional architecture among primate species, we examined these maps in the prosimian bush baby, a species that has been proposed to represent the ancestral primate organization. We found that the layout of individual feature maps in bush baby V1 is similar to that of other primates, but we found an entirely different organization of orientation preference in bush baby V2 compared with that reported in simian primates. Another striking distinction between bush baby and simian species is that we observed no strong relationships among maps of orientation, ocular dominance, and CO blobs in V1. Thus our findings suggest that precise relationships between feature maps are not a common element of the functional organization in all primates and that such relationships are not necessary for achieving basic coverage of stimulus feature combinations. In addition, our results suggest that specific relationships between feature maps in V1, and the subdivision of V2 into functional compartments, may have arisen comparatively late in the evolution of primates.

Animals↗
PubMed1983

Cholinergic modulation of the functional organization of the cat visual cortex.

The cortex receives a cholinergic input which is considered to be involved in mediating the effects of arousal. The experiments reported here have examined the nature of the cholinergic influence on the neuronal organization of the cat visual cortex. Out of 83 cells studied, 92% exhibited a modification in their visual response properties during the iontophoretic application of ACh. These comprised 61% in which responses were facilitated and 31% in which responses were depressed. The facilitatory effects were associated with a striking increase in stimulus specific responses without any concomitant loss in the selectivity. This comment applied equally to orientation and direction selectivity. It is argued that the facilitatory action of ACh on stimulus specific responses is consistent with a modulation of potassium conductance and most probably the conductance associated with a voltage dependent channel. We found no evidence to support the view that the facilitatory action involved disinhibition; the action of bicuculline, which blocks inhibitory influences in the visual cortex, was quite distinct to that of ACh. The facilitatory and depressive effects of ACh did not show any correlation with the simple-complex classification of cells or any other obvious parameter of receptive field organization, but there was a correlation with cortical lamination. Cells facilitated by ACh were found in all cortical laminae, but those depressed by ACh were found in laminae III and IV.

Acetylcholine↗
PubMed1977

[Characteristics of inhibition in the receptive fields of the cat visual cortex].

The responses of visual cells in the 17th cortical area to stimulation with bright strips of various width were studied in immobilized cats. The impulse activity was counted in successive time intervals from the beginning of the stimulation and plotted as a function of the stimulus area. Significant differences in time course of the inhibitory process were found between the cortical and geniculate levels. The lag of inhibition behind excitation was much smaller in the cortex than in the geniculate body. Similar data were obtained from cortical response elicited by simultaneous or successive application of two bright strips, one in the excitatory centre and the second in the inhibitory zone of the receptive field. If both strips were placed in the excitatory zone of the field, inhibition depended on the order of illumination of the strips. When this order coincided with the direction in which a moving stimulus had a maximal effect, a large facilitation of the response to the second stimulus was obtained. When the order of presentation was reversed, a strong inhibition appeared. This selectivity of the inhibitory mechanism was attenuated at the periphery of the field where any succession of the stimuli elicited an inhibitory effect.

Animals↗
PubMed1987

Continuity or incontinuity of orientation columns in visual cortex: a critical evaluation of published and unpublished data.

Orientation columns in the visual cortex of cat and monkey were originally defined as small areas where all cells from layer 2 to 6 had the same preferred stimulus orientation. Large variation in preferred orientation, occasionally observed, were interpreted as biological scatter or artefacts. In contrast to this view, recent experiments revealed frequent abrupt shifts in preferred orientations at the transition from middle to lower layers. This controversial issue is of considerable relevance for models of cortical wiring. Therefore, in this report new and previously published data are quantitatively evaluated. The comparison shows that the large orientation shifts cannot be reconciled as mainly due to deviation of penetrations from the radial cell columns. The present data suggest that, in middle and lower layers of the cat's cortex, two groups of cells with approximately orthogonal orientations coexist. Comparison of results from different authors supports our evidence for the occurrence of orientation shifts. The controversy is reduced to the difference in the proportions of penetrations with and without shifts in different laboratories. A possible explanation for this remaining difference is the lower relative frequency of shifts in heavily sedated animals. Our own data were collected from awake, behaving or lightly anesthetized animals in chronic preparations.

Animals↗
PubMed1990

Functional organization of primate visual cortex revealed by high resolution optical imaging.

A high spatial resolution optical imaging system was developed to visualize cerebral cortical activity in vivo. This method is based on activity-dependent intrinsic signals and does not use voltage-sensitive dyes. Images of the living monkey striate (VI) and extrastriate (V2) visual cortex, taken during visual stimulation, were analyzed to yield maps of the distribution of cells with various functional properties. The cytochrome oxidase--rich blobs of V1 and the stripes of V2 were imaged in the living brain. In V2, no ocular dominance organization was seen, while regions of poor orientation tuning colocalized to every other cytochrome oxidase stripe. The orientation tuning of other regions of V2 appeared organized as modules that are larger and more uniform than those in V1.

Action Potentials↗