Showing papers on "Orientation column published in 1992"

Receptive field dynamics in adult primary visual cortex

Abstract: THE adult brain has a remarkable ability to adjust to changes in sensory input. Removal of afferent input to the somatosensory, auditory, motor or visual cortex results in a marked change of cortical topography1–10. Changes in sensory activity can, over a period of months, alter receptive field size and cortical topography11. Here we remove visual input by focal binocular retinal lesions and record from the same cortical sites before and within minutes after making the lesion and find immediate striking increases in receptive field size for cortical cells with receptive fields near the edge of the retinal scotoma. After a few months even the cortical areas that were initially silenced by the lesion recover visual activity, representing retinotopic loci surrounding the lesion. At the level of the lateral geniculate nucleus, which provides the visual input to the striate cortex, a large silent region remains. Furthermore, anatomical studies show that the spread of geniculocortical afferents is insufficient to account for the cortical recovery. The results indicate that the topographic reorganization within the cortex was largely due to synaptic changes intrinsic to the cortex, perhaps through the plexus of long-range horizontal connections.

Columns for visual features of objects in monkey inferotemporal cortex

Abstract: At early stages of the mammalian visual cortex, neurons with similar stimulus selectivities are vertically arrayed through the thickness of the cortical sheet and clustered in patches or bands across the surface. This organization, referred to as a 'column', has been found with respect to one-dimensional stimulus parameters such as orientation of stimulus contours, eye dominance of visual inputs, and direction of stimulus motion. It is unclear, however, whether information with extremely high dimensions, such as visual shape, is organized in a similar columnar fashion or in a different manner in the brain. Here we report that the anterior inferotemporal area of the monkey cortex, the final station of the visual cortical stream crucial for object recognition, consists of columns, each containing cells responsive to similar visual features of objects.

Visual response latencies in striate cortex of the macaque monkey

Abstract: 1 Many lines of evidence suggest that signals relayed by the magnocellular and parvocellular subdivisions of the primate lateral geniculate nucleus (LGN) maintain their segregation in cortical processing We have examined two response properties of units in the striate cortex of macaque monkeys, latency and transience, with the goal of assessing whether they might be used to infer specific geniculate contributions Recordings were made from 298 isolated units and 1,129 multiunit sites in the striate cortex in four monkeys Excitotoxin lesions that selectively affected one or the other LGN subdivision were made in three animals to demonstrate directly the magnocellular and parvocellular contributions An additional 435 single units and 551 multiunit sites were recorded after the ablations 2 Most units in striate cortex had visual response latencies in the range of 30-50 ms under the stimulus conditions used The earliest neuronal responses in striate cortex differed appreciably between individuals The shortest latency recorded in the four animals ranged from 20 to 31 ms Comparable values were obtained from both single unit and multiunit sites After lesions were made in the magnocellular subdivision of the LGN in two animals, the shortest response latencies were 7 and 10 ms later than before the ablations A larger lesion in the parvocellular subdivision of another animal produced no such shift Thus it appears that the first 7-10 ms of cortical activation can be attributed to activation relayed by the magnocellular layers of the LGN 3 The units with the shortest latencies were all found in layers 4C or 6 and their responses were among the most transient in striate cortex Furthermore, their responses all showed a pronounced periodicity at a frequency of 50-100 Hz This periodicity was stimulus locked, and the responses of all short-latency units oscillated in phase 4 An index of response transience was computed for the units recorded in striate cortex The distribution of this index was unimodal and gave no suggestion of distinct contributions from the geniculate subdivisions Magnocellular and the parvocellular lesions affected the overall transience of responses in striate cortex The changes, however, were very small; extremely transient responses and extremely sustained responses survived both types of lesions 5 A characteristic profile was observed in the response latencies in superficial layers Latencies appeared to increase monotonically from layer 4 toward the surface of cortex, with the most superficial neurons not becoming active until 15 ms after responses were observed in layer 4C(ABSTRACT TRUNCATED AT 400 WORDS)

Half-squaring in responses of cat striate cells.

Abstract: Simple cells in striate cortex have been depicted as rectified linear operators, and complex cells have been depicted as energy mechanisms (constructed from the squared sums of linear operator outputs). This paper discusses two essential hypotheses of the linear/energy model: (1) that a cell's selectivity is due to an underlying (spatiotemporal and binocular) linear stage; and (2) that a cell's firing rate depends on the squared output of the underlying linear stage. This paper reviews physiological measurements of cat striate cell responses, and concludes that both of these hypotheses are supported by the data.

Differential imaging of ocular dominance and orientation selectivity in monkey striate cortex.

Abstract: Differential images of ocular dominance, acquired by comparing responses to the two eyes, reveal dark and light bands where cortical cells are dominated by the right and left eyes. These include most (but not all) histochemically stained cytochrome oxidase blobs in their centers. Differential images of orientation, acquired by comparing responses to orthogonal orientations, reveal dark and light bands that are reminiscent of the "orientation columns" reported earlier, on the basis of 2-deoxyglucose (2DG) autoradiograms (Hubel et al., 1978). However, they are shorter and more fragmented because they do not include regions lacking selectivity for orientation. Even though these "bands" derive from orientation-selective areas, comparisons with differential images of other orientations reveal that regions along their centers prefer different orientations. Hence, the orientation preferences inferred from "bands" in single differential images, or single 2DG autoradiograms, are not necessarily incorrect. Interactions between ocular dominance and orientation were investigated by comparing differential images of orientation obtained with binocular and monocular stimulation, as well as by comparing differential images of ocular dominance obtained with different orientations. In both cases, the elicited interactions were minimal, indicating a remarkable and unexpected independence that subsequent experiments revealed arises, at least in part, from a lateral segregation of regions most selective for one eye and regions most selective for one orientation, in the centers and edges of ocular dominance columns. Since this can also be viewed as a lateral correlation between binocularity and orientation selectivity, it fits with the simultaneous emergence of these properties in layers receiving input from layer 4c, and suggests that each of these properties requires the other.

Synchronization of oscillatory neuronal responses in cat striate cortex: temporal properties.

Abstract: Previously, we have demonstrated that a subpopulation of visual cortical neurons exhibit oscillatory responses to their preferred stimuli at a frequency near 50 Hz (Gray & Singer, 1989). These responses can selectively synchronize over large distances of cortex in a stimulus-specific manner (Gray et al., 1989; Engel et al., 1990a). Here we report the results of a new analysis which reveals the fine temporal structure inherent in these interactions. We utilized pairs of recordings of the local field potential (LFP) activity from area 17 in the anesthetized cat which met two criteria. The LFP was correlated with the underlying unit activity at each site and the recording sites were at least 5 mm apart in cortex. A moving-window technique was applied to compute cross correlograms on 100-ms epochs of data repeated at intervals of 30 ms for a period of 3 s during each direction of stimulus movement. A statistical test was devised to determine the significance of detected correlations. In this way we were able to determine the magnitude, phase difference, frequency, and duration of correlated oscillations as a function of time. The results demonstrate that (1) the duration of synchrony is variable and lasts from 100–900 ms; (2) the phase differences between and the frequencies of synchronized responses are also variable within and between events and range from +3 to —3 ms and 40–60 Hz, respectively; and (3) multiple correlation events often occur within a single stimulus period. These results demonstrate a high degree of dynamic variability and a rapid onset and offset of synchrony among interacting populations of neurons which is consistent with the requirements of a mechanism for feature integration.

Temporal-frequency tuning of direction selectivity in cat visual cortex.

Abstract: Responses of 71 cells in areas 17 and 18 of the cat visual cortex were recorded extracellularly while stimulating with gratings drifting in each direction across the receptive field at a series of temporal frequencies. Direction selectivity was most prominent at temporal frequencies of 1-2 Hz. In about 20% of the total population, the response in the nonpreferred direction increased at temporal frequencies of around 4 Hz and direction selectivity was diminished or lost. In a few cells the preferred direction reversed. One consequence of this behavior was a tendency for the preferred direction to have lower optimal temporal frequencies than the nonpreferred direction. Across the population, the preferred direction was tuned almost an octave lower. In spite of this, temporal resolution was similar in the two directions. It appeared that responses in the nonpreferred direction were suppressed at low frequencies, then recovered at higher frequencies. This phenomenon might reflect the convergence in visual cortex of lagged and nonlagged inputs from the lateral geniculate nucleus. These afferents fire about a quarter-cycle apart (i.e. are in temporal quadrature) at low temporal frequencies, but their phase difference increases to a half-cycle by about 4 Hz. Such timing differences could underlie the prevalence of direction-selective cortical responses at 1 and 2 Hz and the loss of direction selectivity in many cells by 4 or 8 Hz.

Development of orientation columns via competition between ON- and OFF-center inputs.

Abstract: Development of orientation-selective receptive fields in primary visual cortex of higher mammals can occur through activity-dependent competition between ON-center and OFF-center inputs. This competition yields orientation and spatial-frequency-selective `simple cells' if the dark activity of ON (or OFF)-center inputs is best correlated with that of other ON (or OFF)-center inputs at small retinotopic separations and with that of OFF (ON)-center inputs at larger separations. Features of cat and monkey cortical organization emerge, including continuous and periodic arrangement of preferred orientation across the cortex. A new feature, systematic variation of receptive field spatial phase, is predicted. Experimental tests of this hypothesis are proposed.

Broadband temporal stimuli decrease the integration time of neurons in cat striate cortex.

Abstract: We have studied the responses of striate cortical neurons to stimuli whose contrast is modulated in time by either a single sinusoid or by the sum of eight sinusoids. The sum-of-sinusoids stimulus resembles white noise and has been used to study the linear and nonlinear dynamics of retinal ganglion cells (Victor et al., 1977). In cortical neurons, we have found different linear and second-order responses to single-sinusoid and sum-of-sinusoids inputs. Specifically, while the responsivity near the optimal temporal frequency is lower for the sum-of-sinusoids stimulus, the responsivity at higher temporal frequencies is relatively greater. Along with this change in the response amplitudes, there is a systematic change in the time course of responses. For complex cells, the integration time, the effective delay due to a combination of actual delays and low-pass filter stages, changes from a median of 85 ms with single sinusoids to 57 ms with a sum of sinusoids. For simple cells, the integration times for single sinusoids range from 44-100 ms, but cluster tightly around 40 ms for the sum-of-sinusoids stimulus. The change in time constant would argue that the increased sensitivity to high frequencies cannot be explained by a static threshold, but must be caused by a fundamental alteration in the response dynamics. These effects are not seen in the retina (Shapley & Victor, 1981) and are most likely cortical in origin.

A model for the coordinated development of columnar systems in primate striate cortex

Abstract: The existence of patchy regions in primate striate cortex in which orientation selectivity is reduced, and which lie in the centers of ocular dominance stripes is well established (Hubel and Livingstone 1981) Analysis of functional maps obtained with voltage sensitive dyes (Blasdel and Salama 1986) has suggested that regions where the spatial rate of change of orientation preference is high, tend to be aligned either along the centers of ocular dominance stripes, or to intersect stripe borders at right angles In this paper I present results from a developmental model which show that a tendency for orientation selectivity to develop more slowly in the centers of ocular dominance stripes would lead to the observed relationships between the layout of ocular dominance and the map of orientation gradient This occurs despite the fact that there is no direct connection between the measures of preferred orientation (from which the gradient map is derived) and orientation selectivity (which is independent of preferred orientation) I also show that in both the monkey and the model, orientation singularities have an irregular distribution, but tend to be concentrated in the centers of the ocular dominance stripes The average density of singularities is about 3/?? 2, where ?? is the period of the orientation columns The results are based on an elaboration of previous models (Swindale 1980, 1982) which show how, given initially disordered starting conditions, lateral interactions that are short-range excitatory and long-range inhibitory can lead to the development of patterns of orientation or ocular dominance that resemble those found in monkey striate cortex To explain the coordinated development of the two kinds of column, it is proposed that there is an additional tendency in development for the rate of increase in orientation selectivity to be reduced in the centers of emerging ocular dominance stripes This might come about if a single factor modulates plasticity in each cell, or column of cells Thus plasticity may be turned off first in regions in the centers of ocular dominance stripes where relatively extreme and therefore stable ocular dominance values are achieved early in development Consequently it will be hard for cells in these columns to modify other properties such as orientation preference or selectivity

A mathematical model for the self-organization of orientation columns in visual cortex.

Abstract: The visual cortex contains regular arrangements of neurons responding to specific types of visual stimulation, such as ocular dominance columns and orientation columns. These columnar structures can be considered as the functional architecture for early visual information processing. The model of ac

Effects of selective pressure block of Y-type optic nerve fibers on the receptive-field properties of neurons in the striate cortex of the cat

Abstract: In an aseptic operation under surgical anesthesia, one optic nerve of a cat was exposed and subjected to pressure by means of a special cuff. The conduction of impulses through the pressurized region was monitored by means of electrodes which remained in the animal after the operation. The pressure was adjusted to selectively eliminate conduction in the largest fibers (Y-type) but not in the medium-size fibers (X-type). The conduction block is probably due to a demyelination and remains complete for about 3 weeks. Within 2 weeks after the pressure-block operation, recordings were made from single neurons in the striate cortex (area 17, area V1) of the cat anesthetized with N2O/O2 mixture supplemented by continuous intravenous infusion of barbiturate. Neurons were activated visually via the normal eye and via the eye with the pressure-blocked optic nerve ("Y-blocked eye"). Several properties of the receptive fields of single neurons in area 17 such as S (simple) or C (complex) type of receptive-field organization, size of discharge fields, orientation tuning, direction-selectivity indices, and end-zone inhibition appear to be unaffected by removal of the Y-type input. On the other hand, the peak discharge rates to stimuli presented via the Y-blocked eye were significantly lower than those to stimuli presented via the normal eye. As a result, the eye-dominance histogram was shifted markedly towards the normal eye implying that there is a significant excitatory Y-type input to area 17. In a substantial proportion of area 17 neurons, this input converges onto the cells which receive also non-Y-type inputs. In one respect, velocity sensitivity, removal of the Y input had a weak but significant effect. In particular, C (but not S) cells when activated via the normal eye responded optimally at slightly higher stimulus velocities than when activated via the Y-blocked eye. These results suggest that the Y input makes a distinct contribution to velocity sensitivity in area 17 but only in C-type neurons. Overall, our results lead us to the conclusion that the Y-type input to the striate cortex of the cat makes a significant contribution to the strength of the excitatory response of many neurons in this area. However, the contributions of Y-type input to the mechanism(s) underlying many of the receptive-field properties of neurons in this area are not distinguishable from those of the non-Y-type visual inputs.

Fluoro-Gold tracing of zinc-containing afferent connections in the mouse visual cortices.

Abstract: To identify zinc-containing projections to the visual areas, we injected Fluoro-Gold into the occipital cortex of the mouse. Five days later, the mice underwent an intravital selenium-labeling procedure to demonstrate the somata of neurons that give rise to zinc-containing boutons. Numerous double-labeled cells were seen in the ipsi- and contralateral primary (layers II/III and VI), and secondary visual cortices (layers II/III and VI). A few double-labeled cells were apparent in other cortical areas concerned with visual processing: the orbital cortex (layers II and III), the posterior portion of the medial agranular frontal cortex (layer V/VI border), and the temporal cortex (layer VI). The cingulate, retrosplenial, perirhinal, and lateral entorhinal cortices had lamina projecting to the visual cortex and separate lamina harboring zinc-containing cells. A spatial segregation of fluorescent and zinc-containing neurons was also seen in the claustrum. This integration or segregation of projecting and zinc-containing neurons may reflect the function of the cortical areas. N-methyl-d-aspartate receptor function is antagonized by physiological concentrations of zinc in vitro. It is proposed that zinc-positive projections from areas that perform basic visual functions are less likely to be modified by N-methyl-d-aspartate receptor-mediated processes than the zinc-negative connections from associational areas.

Lateral inhibitory interactions in areas 17 and 18 of the cat visual cortex.

Abstract: Publisher Summary This chapter discusses the topographical aspects of horizontal connections and the possible functions of gamma-aminobutyric acid–releasing (GABAergic) lateral inhibitory processes in areas 17 and 18 of the feline visual cortex. Orientation selectivity and direction selectivity, as well as length tuning, have been originally described as typical properties of visual cortical cells in response to moving bar-shaped stimuli. The presence of laterally directed axons as morphological substratum for lateral signal processing in the visual cortex was initially shown by degeneration methods in monkeys and cats. Following the demonstration of the clusters of terminals emitted at regular intervals by intracellularly labelled pyramidal cell axons spanning several mm of horizontal distance and the observation of periodic patchy labeling in the visual cortex of monkeys and cats, increasing interest was directed toward horizontal interactions within areas 17 and 18. This interest was focused on the long-range axonal systems of pyramidal cells and predominantly on excitatory functions as shown with cross-correlation analysis of recordings from the pairs of cells with similar orientation specificity. Lateral inhibitory interactions could play a significant role in generating or sharpening specific response properties of visual cortical neurons.

The synaptic inputs to simple cells of the cat visual cortex.

Abstract: Publisher Summary This chapter focuses on a subset of cortical neurons—the simple cells of layer 4 in the visual cortex of the cat. Simple cells are the primary recipient of the major visual input from the thalamus—the relay cells of the lateral geniculate nucleus (LGN). Simple cells are highly sensitive to the orientation, direction and speed of motion, retinal disparity (depth), and spatial frequency (size) of a visual stimulus, while geniculate relay cells are largely insensitive to these stimulus features. The synapse between geniculocortical axons and the simple cells of layer 4 is, therefore, the point at which many of the interesting features of cortical neurons are generated for the first time. As a result, simple cells have been the focus of many models of cortical organization and function, some of which can be tested with intracellular methods. Intracellular recording has been employed in two types of experiments: with electrical stimulation of the visual pathways or with visual stimulation.

Direction selectivity of cells in the cat's striate cortex: differences between bar and grating stimuli.

Abstract: We have investigated the notion that directional responses of cells in the visual cortex depend on the type of stimulus used to drive the cell. Specifically, we have asked if sinusoidal gratings provide a different estimate of direction selectivity than bars that are brighter or darker than the background. Using standard techniques, we recorded from 176 cells in the visual cortex of nine cats. For each cell, bright bars, dark bars, and sinusoidal gratings were presented in a randomly interleaved fashion. Complex cells exhibited around twice as many direction-selective as nondirection-selective responses. Estimates of direction selectivity were nearly identical for bright and dark bars and for gratings. For simple cells, a similar ratio of direction-selective to nondirection-selective responses was observed for gratings. However, a larger proportion of simple cells were classified as direction selective when bars were used for stimulation. A simple cell that exhibited direction selectivity to a grating behaved in a similar manner when stimulated with bright or dark bars. However, in contrast to complex cells, some simple cells classed as directionally nonselective on the basis of their responses to gratings, displayed directionally selective behavior to bars. In addition, the preferred directions for dark and bright bars sometimes differed. These results demonstrate that the classification of a simple cell as directionally selective or nonselective can depend critically on the visual stimulus used.

Retinotopic organization of striate and extrastriate visual cortex in the golden hamster (Mesocricetus auratus).

Abstract: The visual topography within striate and lateral extrastriate visual cortices was studied in adult hamsters. The cortical areas 17 and 18a in the left hemisphere were electrophysiologically mapped upon stimulation of the right eye, correlating receptive field positions in the visual field with cortical recording sites. Reference lesions were placed at selected cortical sites. Like in rats and other mammals, the lateral extrastriate cortex contained multiple representations of the visual field. Rostral area 18a contained the rostrolateral maps, with medial and lateral divisions. More caudally and sharing a common border with V1, maps in lateromedial, posterolateral and posterior areas were found. More laterally and forming a "third tier" of visual maps, anterolateral, laterolateral-anterior, laterolateral and laterolateral-posterior areas were found. There was also an indication of a possible pararhinal map. The plan so defined is virtually identical to that of rats. The results may be useful to understand a basic mammalian plan in the organization of the visual cortex.

Generation of direction selectivity by isotropic intracortical connections

Abstract: To what extent do the mechanisms generating different receptive field properties of neurons depend on each other? We investigated this question theoretically within the context of orientation and direction tuning of simple cells in the mammalian visual cortex. In our model a cortical cell of the "simple" type receives its orientation tuning by afferent convergence of aligned receptive fields of the lateral geniculate nucleus (Hubel and Wiesel 1962). We sharpen this orientation bias by postulating a special type of radially symmetric long-range lateral inhibition called circular inhibition. Surprisingly, this isotropic mechanism leads to the emergence of a strong bias for the direction of motion of a bar. We show that this directional anisotropy is neither caused by the probabilistic nature of the connections nor is it a consequence of the specific columnar structure chosen but that it is an inherent feature of the architecture of visual cortex.

Visual Cortex: Window on the Biological Basis of Learning and Memory

Abstract: Publisher Summary This chapter discusses the visual cortex. Visual cortex, just as the rest of cortex of all primates, is a highly complex structure composed of many layers and columns, many different types of cells interconnected with one another with an almost bewildering variety of synaptic contacts and receptors and numerous different transmitters. Cortical neurons receive afferents from many sources. In visual cortex, the principle afferents are those from the lateral geniculate nucleus and from other cortical neurons. The behavior of visual cortical cells in various rearing conditions suggests that some cells respond more rapidly to environmental changes than others. In monocular deprivation, for example, some cells remain responsive to the closed eye despite the very large shift of most cells to the open eye. The single cell theory for the development of selectivity and ocular dominance in visual cortex has been generalized to incorporate more realistic neural networks that approximate the actual anatomy of small regions of cortex. The chapter discusses a network consisting of excitatory and inhibitory cells, both of which may receive information from lateral geniculate nucleus. These two cortical cell types then interact through intracortical connections that are either excitatory or inhibitory.

Cortical Information Processing as Viewed from the Mass-Action Domain of Evoked Potentials

Abstract: The two most fundamental fields concerned with the cortical processing of visual information, anatomy and single-cell physiology, have yielded rather divergent results. Anatomical investigations, on the one hand, have revealed a rather chaotic, dense net of local and widespread interconnections between the cortical neurons. This net of interconnections lacks any apparent spatial order with respect to lengths or densities in the vertical and horizontal directions (Schuz, Braitenberg, this volume). The physiological studies of single cells’ response properties, on the other hand, have demonstrated that external information is represented in the visual cortex in a highly specific manner and arranged in a very precise spatial order. The individual cells’ receptive fields (RFs) are small; the retinotopic relation is preserved for these RFs between hypercolumns. Moreover, each hypercolumn is further spatially subdifferentiated into ocular dominance- and orientation columns and in the monkey, additionally into color-, motion-, and form-processing subregions (Barlow, this volume). Thus, in contradiction to the results of the intracortical network, RF studies indicate that afferent information is processed in the cortex in a parallel fashion, and in a rather independent manner within each subregion or microcolumn, without strong lateral interactions.