Selectivity of visual cortical neurons of rabbits to magnitude of moving stimuli

Unit responses of the rabbit visual cortex were investigated in relation to size of visual stimuli moving in their receptive field. With an increase in size of the stimulus in a direction perpendicular to the direction of movement ("width" of the stimulus) an initial increase in the intensity of the unit response through spatial summation of excitory effects is followed by a decrease through lateral inhibition. This inhibition is observed between zones of the receptive field which behave as activating when tested by a stimulus of small size. Each neuron has its own "preferred" size of stimuli evoking its maximal activation. No direct correlation is found between the "preferred" stimulus size and the size of the receptive field. With a change in stimulus size in the direction of movement ("length" of the stimulus) the responses to stimuli of optimal size may be potentiated through mutual facilitation of the effects evoked by the leading and trailing edges of the stimulus and weakened in response to stimuli of large size. The selective behavior of the neurons with respect to stimulus size is intensified in the case of coordinated changes in their length and width. It is postulated that the series of neurons responding to stimuli of different "preferred" dimensions may constitute a system classifying stimuli by their size.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 636–644, November–December, 1972.     

‘Vector white noise’: a technique for mapping the motion receptive fields of direction-selective visual neurons

A technique is described and tested for mapping the sensitivities and preferred directions of motion at different locations within the receptive fields of direction-selective motion-detecting visual neurons. The procedure is to record the responses to a number of visual stimuli, each stimulus presentation consisting of a set of short, randomly-oriented, moving bars arranged in a square grid. Each bar moves perpendicularly to its long axis. The vector describing the sensitivity and preferred direction of motion at each grid location is obtained as a sum of the unit vectors defining the directions of motion of the bars in each of the stimuli at that location, weighted by the strengths of the corresponding responses. The resulting vector field specifies the optimum flow field for the neuron. The advantage of this technique over the conventional approach of probing the receptive field sequentially at each grid location is that the parallel nature of the stimulus is sensitive to nonlinear interactions (such as shunting inhibition for mutual facilitation) between different regions of the visual field. The technique is used to determine accurately the motion receptive fields of direction-selective motion detecting neurons in the optic lobes of insects. It is potentially applicable to motion-sensitive neurons with highly structured receptive fields, such as those in the optic tectum of the pigeon or in area MST of the monkey.     

Characteristics of inhibition in receptive fields of the cat visual cortex

Unit responses of neurons of zone 17 in the cat striate cortex to stripes of different widths were studied. Changes in the number of spikes during different time intervals (cuts) from the beginning of the response were analyzed in relation to stimulus area. Comparison of the results with those obtained by the study of receptive fields of the lateral geniculate body showed a significant difference in the dynamics of inhibition between cortical and geniculate receptive fields. Similar results were obtained when cortical unit responses to simultaneous and consecutive appearance of two stripes in the receptive field, one in the excitatory zone and the other at the inhibitory periphery, were studied. Evidence of the longer duration of cortical inhibition also was obtained by the same technique. When both stripes were placed in the excitatory center of the field another feature of cortical inhibition was revealed: its dependence on the order of stimulus application. If the order of stimulus application coincided with the optimal direction of movement of the stripe for the given field, the unit response to the next stimulus was strongly facilitated by the action of the stimulus applied previously. Application of stimuli in the opposite order invoked inhibition. The sensitivity of inhibition to the order of stimulus application was observed in the center of the field; it diminished toward the periphery, where application of the stimuli in any order evokes inhibition of the response.Medical Academy, Sofia, Bulgaria, I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 339–346, July–August, 1977.     

Unit responses of the squirrel visual cortex to shaped visual stimuli

Visual cortical unit responses of the squirrelSciurus vulgaris to shaped visual stimuli (stationary and moving spots and bands) were studied. Neurons responding selectively to the direction of stimulus movement and orientation of lines and those not responding selectively to these features were distinguished. Many neurons, whether responding selectively or not to movement direction, were specifically sensitive to high speeds of movement, of the order of hundreds of degrees per second. This selectivity in neurons responding selectively to movement direction persisted at these high speeds, despite the short time taken by the stimulus to move across the receptive field. Neurons responding selectively to line orientation were sensitive to lower speeds of stimulus movement — from units to tens of degrees per second. Neuronal sensitivity to high speeds of stimulus movement is achieved through rapid summation of excitation from large areas of the receptive field crossed by the fast-moving stimulus. Selectivity of the response to movement direction is produced under these conditions with the aid of directed short-latency inhibition, inhibiting unit activity for stimulus movement in "zero" direction.     

Connections between wide-field monocular and binocular movement detectors in the brain of a hawk moth

Summary Recordings were made in the brain of Sphinx ligustri of pairs of directionally selective movement detectors, and the spike trains analysed with a computer for possible synaptic connections between two classes of movement detector. (1) Neurones with large binocular fields which arise in the medial protocerebrum and project to the medulla or lobula of one optic lobe, or to the ventral nerve cord. (2) Movement detectors which project from the lobula complex of one optic lobe to the opposite medial protocerebrum. The majority of the second group had back-to-front preferred directions over the ipsilateral eye, and of these many were weakly sensitive to stimuli to the opposite eye. The ipsilateral receptive field covered most of the eye.Optic lobe output cells with the appropriate preferred direction provide a powerful excitatory input to the binocular movement detectors centrifugal to the medulla. Each centrifugal movement detector probably receives excitatory inputs from no more than two optic lobe output cells with back-to-front preferred direction. The same set of optic lobe output neurones probably feeds several cells projecting to the medulla and lobula of both optic lobes, and, possibly, to the ventral nerve cord.Evidence was obtained that the optic lobe output cells themselves receive few excitatory inputs, and that therefore the receptive fields of their input cells are large.Two moving stimuli were presented in different areas of the receptive field. Movement through the null direction in one area inhibited the response to movement in the preferred direction in another area. This suppression was stronger in optic lobe output cells with front-to-back preferred direction than in units with back-to-front preferred direction. Thus the optic lobe output cells, or wide-field units feeding them, receive inhibitory inputs from wide-field units with the opposite preferred direction.Similar tests in which moving stimuli were presented to both eyes gave results indicating that the binocular centrifugal movement detectors may receive inhibitory inputs from movement detectors with back-to-front preferred direction. The possible functional significance of these inhibitory inputs is discussed.I am very greatful to F. A. Miles for helpful discussion and criticism. Financial support came from the U. K. Science Research Council.     

Orientation-selective neurons in the squirrel visual cortex

The organization of receptive fields of neurons sensitive to orientation of visual stimuli was investigated in the squirrel visual cortex. Neurons with mutually inhibitory on- and off-areas of the receptive field, with partially and completely overlapping excitatory and inhibitory mechanisms, were distinguished. Neurons of the second group are most typical. They exhibit orientation selectivity within the excitatory area of the receptive field because, if the stimulus widens in the zero direction, perpendicular to the preferred direction, lateral inhibition is much stronger than if it widens in the preferred direction. Additional inhibitory areas (outside the excitatory area) potentiate this inhibition and increase selectivity. It is suggested that there is no strict separation of simple (with separate excitatory and inhibitory mechanisms in the receptive field) and complex (with overlapping of these mechanisms) neurons in the squirrel visual cortex.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 540–549, November–December, 1979.     

Structural organization of receptive fields of lateral suprasylvian cortical neurons in cats

The substructural organization of receptive fields of lateral suprasylvian cortical neurons, sensitive to movement of visual stimuli, was investigated in cats. The experimental results showed that receptive fields of neurons in this cortical area, judging by responses to movement, consist mainly of cells with qualitatively different characteristics. With the unmasked method of presentation of a moving stimulus, a reduction in the amplitude of movement as a rule evoked a directional response of the cell, whereas with the masked method, and with the same amplitudes of movement, a nondirectional response appeared. The receptive fields of some neurons were particularly sensitive to movement of borders but did not respond to the body of the stimulus like receptive fields of neurons described in other visual structures. Heterogeneity of the substructural organization of receptive fields of lateral suprasylvian cortical neurons can be explained by convergence of inputs on the neuron and it is regarded as the basis of integrative mechanisms in this structure.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 293–300, May–June, 1985.     

Interaction between impulses evoked by stimuli of different modalities in neurons of the parietal associative cortex

In acute experiments on cats anesthetized with chloralose and nembutal interaction between visual, auditory, and electrodermal stimuli in neurons of the parietal association cortex was studied. Two types of interaction were found; the first characterized by inhibition or by inhibition followed by facilitation of the response to the test stimulus, the second by facilitation or by facilitation followed by inhibition of spontaneous impulses. Interaction between stimuli of different modalities was shown to depend on the properties of the neuron. In polysensory neurons ability to interact was much higher than in bimodal or monomodal neurons.M. Gorkii Donetsk Medical Institute. Kemerovo Medical Institute. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 223–229, May–June, 1976.     

Inhibitory components in the neuronal response of the lateral suprasylvian cortical area in the cat

Inhibitory components in the response evoked by presentation of mobile visual stimuli in neurons belonging to the lateral suprasylvian area of the cerebral cortex were investigated in cats. It was demonstrated by comparing poststimulus histograms of neuronal response to movement in two opposite directions that the location of discharge centers within the receptive fields changed in relation to movement direction. No spatial area giving rise to the inhibitory component of response could be found in any of the neurons with monotone stationary structure of their receptive fields. Findings from experiments involving techniques of stimulating a test area of the receptive field separately indicated that inhibitory components of response in neurons of the lateral suprasylvian area with monotone organization of the receptive field could represent inhibitory after-response following the neuronal excitation produced by the visual stimulus traveling across this field.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 299–308, May–June, 1987.     

Organization of receptive fields of motion-senstitive neurons in the cat pulvinar

The distribution of 70 visually sensitive neurons in the cat pulvinar sensitive to motion in the receptive fields was studied. The experimental results showed that components with directional characteristics are present in the structure of these fields of both direction-selective and unselective neurons. In the receptive fields of direction-selective neurons the directional elements of the substructure have identical preferred directions, which coincide with the preferred directions of response to stimulus movement over the entire receptive field. The organization of receptive fields of direction-selective neurons of the visual association structure thus does not differ significantly from that of analogous fields of visual projection neurons. Directional elements of the receptive fields of direction-unselective neurons were found to have different preferred directions, thereby providing a basis for organization of the nondirectional response of the neuron to a stimulus moving across the entire receptive field.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 339–346, July–August, 1982.     

Spontaneously emerging direction selectivity maps in visual cortex through STDP

It is still an open question as to whether, and how, direction-selective neuronal responses in primary visual cortex are generated by feedforward thalamocortical or recurrent intracortical connections, or a combination of both. Here we present an investigation that concentrates on and, only for the sake of simplicity, restricts itself to intracortical circuits, in particular, with respect to the developmental aspects of direction selectivity through spike-timing-dependent synaptic plasticity. We show that directional responses can emerge in a recurrent network model of visual cortex with spiking neurons that integrate inputs mainly from a particular direction, thus giving rise to an asymmetrically shaped receptive field. A moving stimulus that enters the receptive field from this (preferred) direction will activate a neuron most strongly because of the increased number and/or strength of inputs from this direction and since delayed isotropic inhibition will neither overlap with, nor cancel excitation, as would be the case for other stimulus directions. It is demonstrated how direction-selective responses result from spatial asymmetries in the distribution of synaptic contacts or weights of inputs delivered to a neuron by slowly conducting intracortical axonal delay lines. By means of spike-timing-dependent synaptic plasticity with an asymmetric learning window this kind of coupling asymmetry develops naturally in a recurrent network of stochastically spiking neurons in a scenario where the neurons are activated by unidirectionally moving bar stimuli and even when only intrinsic spontaneous activity drives the learning process. We also present simulation results to show the ability of this model to produce direction preference maps similar to experimental findings     

On the mechanisms underlying appearance of responses to movement,directional sensitivity and velocity tuning of the cat's striate cortical neurons

The responses to moving and stationary stimuli of 27 cat's striate cortical units were studied. Two stationary light bars located in different parts of the receptive field were used. The order of presentation and the time-interval between the stimuli varied; so, the presentation of a pair of stationary stimuli was an analogue of a moving stimulus.It was shown that responses occurred in neurons previously unresponsive to stationary stimuli when two stationary stimuli were presented successively in certain order. In the direction-sensitive units an asymmetry of the temporal course of the inhibitory processes was observed. The inhibitory zone located on the side of the preferred direction of movement was characterized by an early inhibitory phase followed by a phase of disinhibition and by a second inhibitory phase. For the inhibitory zone located on the side of the null direction no disinhibitory phase was demonstrated.The significance of the spatial and temporal characteristics of the receptive field for the appearance of responses to movement, the directional sensitivity and the velocity tuning in striate neurons is discussed.     

Functional characteristics of visual cortical neurons in squirrels

Depending on the organization of their receptive fields and character of their responses to shaped visual stimuli the following main groups of visual cortical neurons were distinguished in the squirrelSciurus vulgaris: nonselective for direction of movement and orientation of stimuli (14%); selective for direction of movement (30%) and selective for line orientation (49%); 7% of neurons were not classified. Cells selective for direction of movement and some nonselective cells exhibited specific sensitivity to high speeds of stimulus movement (optimal velocities of the order of hundreds of degrees per second). Neurons selective for line orientation differed in the degree of overlapping of their on- and off-zones; they could include analogs of simple and complex neurons.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 125–231, March–April, 1981.     

Changes in receptive field of tectal neurons evoked by vestibular and acoustic stimulation in pigeons

Responses to visual, acoustic, and vestibular stimuli were studied in neurons of the middle and deep layers of the tectum in the pigeon. Changes in the receptive field (RF) were assessed from comparison of unit responses to isolated movement of a shaped visual stimulus with responses to movement of a stimulus during simultaneous action of a vestibular or acoustic stimulus. Changes in RF of the neuron could be observed during the action of both a vestibular and an acoustic stimulus. These changes affected the identification of the predominant direction of movement of the stimulus, the position of the maximum in the response histogram, and the duration and number of spikes in the response. The direction of change in RF of the neuron was found not necessarily to coincide with the sign of the response to the same neuron to isolated presentation of a vestibular or acoustic stimulus. It is postulated on the basis of the results and data in the literature that the tectum transforms the flow of impulses arriving from the retina depending on the nature of the information received by it from other sensory systems.     

Peculiarities of summation processes in visual-sensitive neurons in the pretectal area of cat

Summation processes occurring in single neurons of the pretectal area in response to either moving or stationary light stimuli were studied in acute experiments on cats. In most neurons studied (85%), gradual increase of the angular size of stimulus resulted in clearly defined summation. In neurons lacking directional sensitivity (nondirectional neurons) the stimulus movement in two opposite directions caused, as a rule, similar and symmetrical changes in the number of spikes, whereas under the same conditions direction-sensitive neurons, in addition to symmetrical development of summation processes, could exhibit substantial differences in the summation curves. The responses to a preferred movement direction could be significantly inhibited or facilitated, while the responses to a non-preferred direction remained stable or changed reciprocally. Neuronal responses to different directions of the movement of stimulus might change independently of each other. This was also the case whenon andoff responses of theon—off neurons to stationary stimuli were compared. It is concluded that neurons of the pretectal area have a complex infrastructure of receptive fields that significantly influences the integration of incoming information.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 376–382, September–October, 1993.     

Functional architecture of long-range perceptual interactions

The pattern of lateral interactions in the primary visual cortex, which has emerged from recent studies, conforms to the grouping rules of similarity, proximity, smoothness and closure. The goal of this paper is to understand the perceptual salience of oriented elements that are specifically organized to form a smooth contour. An overview of recent studies, in combination with new experimental results, is presented here to emphasis the idea that visual responses depend on input from both the center and the surround of the classical receptive field (CRF). It is assumed that normal lateral interactions produce a neuronal network that is formed by two antagonistic mechanisms: (i) excitation, that is spatially organized along the optimal orientation (collinear), and is predominant near the contrast threshold of the neuron, and (ii) inhibition, that is less selective and is distributed diffusely around the cell's response field. Thus, the inputs from the CRF and the anisotropic surround are summated non-linearly. The specificity of the facilitation and suppression along the collinear direction suggests the existence of second-order elongated collinear filters, which may increase the response similarity between neurons responding to elongated stimulus, thus may enhance the perceptual salience of anisotropic configurations such as contours. This causal connection is particularly evident in amblyopes, where abnormal development of the network results in the abnormal perception of contours.     

Responses of visual cortical neurons in cats to local stimulation of the receptive field center of varied intensity

On-responses of primary visual cortical neurons to local photic stimulation of the receptive field center by stimuli of scotopic and mesopic ranges of intensity were investigated in dark-adapted curarized cats. Only phasic excitation (type I) was observed in 16% of cells studied, phasic and prolonged excitation with phasic inhibition between them (type II) was observed in 68%, and prolonged inhibition (type III) alone in 16% of cells. The thresholds of phasic excitation in the neuronal responses lay between 0.7 and 2200 trolands (td) and coincided with thresholds of activation of the cone system, whereas thresholds of prolonged excitation lay within the range 0.02–9 td and coincided with thresholds of rod inputs. Inhibitory effects were manifested as phasic inhibition observed on peristimulus histograms, disturbances of the monotony of the responses versus stimulus intensity curve, and also as prolonged inhibition in on-responses. All inhibitory effects were observed in the mesopic range of intensities (0.7–2200 td) and were connected with functioning of the cones.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 359–366, July–August, 1982.     

Activation of orientation selectivity mechanisms in neurons of the cat visual cortex by a moving visual "noise" field

A relationship was established between the response of neurons of the cat visual cortex and the direction of movement in the visual "noise" field and of a slit of light. It was shown that a shift in the preferred direction of movement in the "noise" field in relation to that of the slit was found in orientationally selective neurons only. It was concluded that the "noise" field, which is a stimulus lacking an orientation component, does activate mechanisms of neuronal orientation selectively.V. Kapsukas State University, Vilnius. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 596–601, September–October, 1985.     

Direction selectivity of excitation and inhibition in simple cells of the cat primary visual cortex

Direction selectivity in simple cells of primary visual cortex, defined from their spike responses, cannot be predicted using linear models. It has been suggested that the shunting inhibition evoked by visual stimulation is responsible for the nonlinear component of direction selectivity. Cortical inhibition would suppress a neuron's firing when stimuli move in the nonpreferred direction, but would allow responses to stimuli in the preferred direction. Models of direction selectivity based solely on input from the lateral geniculate nucleus, however, propose that the nonlinear response is caused by spike threshold. By extracting excitatory and inhibitory components of synaptic inputs from intracellular records obtained in vivo, we demonstrate that excitation and inhibition are tuned for the same direction, but differ in relative timing. Further, membrane potential responses combine in a linear fashion. Spike threshold, however, quantitatively accounts for the nonlinear component of direction selectivity, amplifying the direction selectivity of spike output relative to that of synaptic inputs.     

Development of spatiotemporal receptive fields of simple cells: II. Simulation and analysis

In part I of this article a correlation based model for the developmental process of spatiotemporal receptive fields has been introduced. In this model the development is described as an activity-dependent competition between four types of input from the lateral geniculate nucleus onto a cortical cell, viz. non-lagged ON and OFF and lagged ON and OFF inputs. In the present paper simulation results and a first analysis are presented for this model. We study the developmental process both before and after eye-opening and compare the results with experimental data from reverse correlation measurements. The outcome of the developmental process is determined mainly by the spatial and the temporal correlations between the different inputs. In particular, if the mean correlation between non-lagged and lagged inputs is weak, receptive fields with a widely varying degree of direction selectivity emerge. However, spatiotemporal receptive fields may show rotation of their preferred orientation as a function of response delay. Even if the mean correlation between two types of temporal input is not weak, direction-selective receptive fields may emerge because of an intracortical interaction between different cortical maps. In an environment of moving lines or gratings, direction-selective receptive fields develop only if the distribution of the directions of motion presented during development shows some anisotropy. In this case, a continuous map of preferred direction is also shown to develop. Received: 18 June 1997 / Accepted: 16 September 1997