Dynamics Of Orientation Tuning Research Articles

Relationship between the Dynamics of Orientation Tuning and Spatiotemporal Receptive Field Structures of Cat LGN Neurons

Simple cells in the cat primary visual cortex usually have elongated receptive fields (RFs), and their orientation selectivity can be largely predicted by their RFs. As to the relay cells in cats’ lateral geniculate nucleus (LGN), they also have weak but significant orientation bias (OB). It is thus of interest to investigate the fine spatiotemporal receptive field (STRF) properties in LGN, compare them with the dynamics of orientation tuning, and examine the dynamic relationship between STRF and orientation sensitivity in LGN. We mapped the STRFs of the LGN neurons in cats with white noise and characterized the dynamics of the orientation tuning by flashing gratings. We found that most of the LGN neurons showed elongated RFs and that the elongation axes were consistent with the preferred orientations. STRFs and the dynamics of orientation tuning were closely correlated temporally: the elongation of RFs and OB emerged, peaked and decayed at the same pace, with unchanged elongation axis of RF and preferred orientation but consistently changing aspect ratio of RF and OB strength across time. Importantly, the above consistency between RF and orientation tuning was not influenced by the ablation of the primary visual cortex. Furthermore, biased orientation tuning emerged 20–30 ms earlier than those in the primary visual cortex. These data demonstrated that similar to the primary visual cortex, the orientation sensitivity was closely reflected by the RF properties in LGN. However, the elongated RF and OB in LGN did not originate from the primary visual cortex feedback.

Active Vision: Dynamic Reformatting of Visual Information by the Saccade-Drift Cycle

Visual processing depends on rapid parsing of global features followed by analysis of fine detail. A new study suggests that this transformation is enabled by a cycle of saccades and fixational drifts, which reformat visual input to match the spatiotemporal sensitivity of fast and slow neuronal pathways.

Orientation enhancement in early visual processing can explain time course of brightness contrast and White’s illusion

Dynamics of orientation tuning in V1 indicates that computational model of V1 should not only comprise of bank of static spatially oriented filters but also include the contribution for dynamical response facilitation or suppression along orientation. Time evolution of orientation response in V1 can emerge due to time- dependent excitation and lateral inhibition in the orientation domain. Lateral inhibition in the orientation domain suggests that Ernst Mach's proposition can be applied for the enhancement of initial orientation distribution that is generated due to interaction of visual stimulus with spatially oriented filters and subcortical temporal filter. Oriented spatial filtering that appears much early (<70 ms) in the sequence of visual information processing can account for many of the brightness illusions observed at steady state. It is therefore expected that time evolution of orientation response might be reflecting in the brightness percept over time. Our numerical study suggests that only spatio-temporal filtering at early phase can explain experimentally observed temporal dynamics of brightness contrast illusion. But, enhancement of orientation response at early phase of visual processing is the key mechanism that can guide visual system to predict the brightness by "Max-rule" or "Winner Takes All" (WTA) estimation and thus producing White's illusions at any exposure.

Theoretical analysis of reverse-time correlation for idealized orientation tuning dynamics

A theoretical analysis is presented of a reverse-time correlation method used in experimentally investigating orientation tuning dynamics of neurons in the primary visual cortex. An exact mathematical characterization of the method is developed, and its connection with the Volterra-Wiener nonlinear systems theory is described. Various mathematical consequences and possible physiological implications of this analysis are illustrated using exactly solvable idealized models of orientation tuning.

Neuronal Selectivity and Local Map Structure in Visual Cortex

The organization of primary visual cortex (V1) into functional maps makes individual cells operate in a variety of contexts. For instance, some neurons lie in regions of fairly homogeneous orientation preference (iso-orientation domains), while others lie in regions with a variety of preferences (e.g., pinwheel centers). We asked whether this diversity in local map structure correlates with the degree of selectivity of spike responses. We used a combination of imaging and electrophysiology to reveal that neurons in regions of homogeneous orientation preference have much sharper tuning. Moreover, in both monkeys and cats, a common principle links the structure of the orientation map, on the spatial scale of dendritic integration, to the degree of selectivity of individual cells. We conclude that neural computation is not invariant across the cortical surface. This finding must factor into future theories of receptive field wiring and map development.

More Time to Taste. Focus on “Variability in Responses and Temporal Coding of Tastants of Similar Quality in the Nucleus of the Solitary Tract of the Rat”

The taste system is ideal for investigations of temporal coding, because neural taste responses are time extensive and often difficult to differentiate by magnitude alone. In a recent article, [Roussin et al. 2008][1] show that spike-time patterning provides a necessary and efficient source of

Dynamics of orientation tuning in cat V1 neurons depend on location within layers and orientation maps

Analysis of the timecourse of the orientation tuning of responses in primary visual cortex (V1) can provide insight into the circuitry underlying tuning. Several studies have examined the temporal evolution of orientation selectivity in V1 neurons, but there is no consensus regarding the stability of orientation tuning properties over the timecourse of the response. We have used reverse-correlation analysis of the responses to dynamic grating stimuli to re-examine this issue in cat V1 neurons. We find that the preferred orientation and tuning curve shape are stable in the majority of neurons; however, more than forty percent of cells show a significant change in either preferred orientation or tuning width between early and late portions of the response. To examine the influence of the local cortical circuit connectivity, we analyzed the timecourse of responses as a function of receptive field type, laminar position, and orientation map position. Simple cells are more selective, and reach peak selectivity earlier, than complex cells. There are pronounced laminar differences in the timing of responses: middle layer cells respond faster, deep layer cells have prolonged response decay, and superficial cells are intermediate in timing. The average timing of neurons near and far from pinwheel centers is similar, but there is more variability in the timecourse of responses near pinwheel centers. This result was reproduced in an established network model of V1 operating in a regime of balanced excitatory and inhibitory recurrent connections, confirming previous results. Thus, response dynamics of cortical neurons reflect circuitry based on both vertical and horizontal location within cortical networks.

Standing Waves and Traveling Waves Distinguish Two Circuits in Visual Cortex

The visual cortex represents stimuli through the activity of neuronal populations. We measured the evolution of this activity in space and time by imaging voltage-sensitive dyes in cat area V1. Contrast-reversing stimuli elicit responses that oscillate at twice the stimulus frequency, indicating that signals originate mostly in complex cells. These responses stand clear of the noise, whose amplitude decreases as 1/frequency, and yield high-resolution maps of orientation preference and retinotopy. We first show how these maps are combined to yield the responses to focal, oriented stimuli. We then study the evolution of the oscillating activity in space and time. In the orientation domain, it is a standing wave. In the spatial domain, it is a traveling wave propagating at 0.2-0.5 m/s. These different dynamics indicate a fundamental distinction in the circuits underlying selectivity for position and orientation, two key stimulus attributes.

Imaging the dynamics of orientation tuning in visual cortex

Imaging the dynamics of orientation tuning in visual cortex

Stimulation of non‐classical receptive field enhances orientation selectivity in the cat

We have investigated how the nonclassical receptive field (nCRF) affects dynamic orientation selectivity of cells in the primary visual cortex (V1) in anaesthetized and paralysed cats using the reverse correlation method. We found that tuning to the orientation of the test stimulus depends on the size of the stimulation area. A significant sharpening of orientation tuning was induced by nCRF stimulation, with the magnitude of the effect increasing with the size of stimulation. The effect of the nCRF on the temporal dynamics of orientation tuning was also investigated by examining the tuning over a range of delays from stimulus onset. We found small but detectable changes in both the preferred orientation and the bandwidth of tuning over time when the classical receptive field (CRF) was stimulated alone. Stimulation in nCRF significantly increased the magnitude of these temporal changes. Thus, nCRF stimulation not only enhances the overall orientation selectivity, but also enriches the temporal dynamics of cortical neurones, which may increase the computational power of the visual cortex in information processing.

Spatial Structure of Complex Cell Receptive Fields Measured with Natural Images

Neuronal receptive fields (RFs) play crucial roles in visual processing. While the linear RFs of early neurons have been well studied, RFs of cortical complex cells are nonlinear and therefore difficult to characterize, especially in the context of natural stimuli. In this study, we used a nonlinear technique to compute the RFs of complex cells from their responses to natural images. We found that each RF is well described by a small number of subunits, which are oriented, localized, and bandpass. These subunits contribute to neuronal responses in a contrast-dependent, polarity-invariant manner, and they can largely predict the orientation and spatial frequency tuning of the cell. Although the RF structures measured with natural images were similar to those measured with random stimuli, natural images were more effective for driving complex cells, thus facilitating rapid identification of the subunits. The subunit RF model provides a useful basis for understanding cortical processing of natural stimuli.

Dynamics of Orientation Tuning in Macaque V1: The Role of Global and Tuned Suppression

The temporal development of neural selectivity to physical attributes of a visual stimulus, such as its orientation and spatial frequency, can provide important clues about mechanisms of cortical tuning. We measured the dynamics of orientation tuning in macaque primary visual cortex (V1) and found several dynamical features in the data: changes in global enhancement and suppression, narrowing of orientation bandwidth, small but significant shifts in preferred orientation, and "Mexican-hat" tuning curves. The dynamics data were analyzed with a model that sums two fixed, tuned components (enhancement and suppression) and one global (untuned) component. The analysis suggests that there is early global enhancement followed by global and tuned suppression. Tuned suppression accounts for the dynamical reduction of orientation bandwidth and for the generation of Mexican-hat tuning profiles. Our findings imply that global and tuned suppression are important factors that determine the selectivity and dynamics of V1 responses to orientation.

Nonlinear analysis of spatio-temporal receptive fields: III. RF-reconstruction from mean-field approximations

Nonlinear neural field models describe spatio-temporal cortical activation patterns by one or several layers of locally interconnected neurons. Impulse response functions in such models relate to dynamic receptive fields in the considered sensory domain. I recently presented a new method to calculate approximate amplitudes and tuning widths of such functions and demonstrated that the amplitude reponses can often already be obtained from a low-dimensional set of “mean-field-type” ordinary differential equations. In the present work, I show how approximations of the full spatio-temporal response functions can be reconstructed from this mean-field approximation. The reconstruction method is applied to the dynamics of orientation tuning in V1 neurons (Nature 387 (1997) 281) and it is argued that these data are consistent with feedback as well as feedforward models.

Spatial frequency and orientation tuning dynamics in area V1.

Spatial frequency (SF) and orientation tuning are intrinsic properties of neurons in primary visual cortex (area V1). To investigate the neural mechanisms mediating selectivity in the awake animal, we measured the temporal dynamics of SF and orientation tuning. We adapted a high-speed reverse-correlation method previously used to characterize orientation tuning dynamics in anesthetized animals to estimate efficiently the complete spatiotemporal receptive fields in area V1 of behaving macaques. We found that SF and orientation tuning are largely separable over time in single neurons. However, spatiotemporal receptive fields also contain a small nonseparable component that reflects a significant difference in response latency for low and high SF stimuli. The observed relationship between stimulus SF and latency represents a dynamic shift in SF tuning, and suggests that single V1 neurons might receive convergent input from the magno- and parvocellular processing streams. Although previous studies with anesthetized animals suggested that orientation tuning could change dramatically over time, we find no substantial evidence of dynamic changes in orientation tuning.

A population approach to cortical dynamics with an application to orientation tuning

A typical functional region in cortex contains thousands of neurons, therefore direct neuronal simulation of the dynamics of such a region necessarily involves massive computation. A recent efficient alternative formulation is in terms of kinetic equations that describe the collective activity of the whole population of similar neurons. A previous paper has shown that these equations produce results that agree well with detailed direct simulations. Here we illustrate the power of this new technique by applying it to the investigation of the effect of recurrent connections upon the dynamics of orientation tuning in the visual cortex. Our equations express the kinetic counterpart of the hypercolumn model from which Somers et al (Somers D, Nelson S and Sur M 1995 J. Neurosci. 15 5448–65) computed steady-state cortical responses to static stimuli by direct simulation. We confirm their static results. Our method presents the opportunity to simulate the data-intensive dynamical experiments of Ringach et al (Ringach D, Hawken M and Shapley R 1997 Nature 387 281–4), in which 60 randomly oriented stimuli were presented each second for 15 min, to gather adequate statistics of responses to multiple presentations. Without readjustment of the previously defined parameters, our simulations yield substantial agreement with the experimental results. Our calculations suggest that differences in the experimental dynamical responses of cells in different cortical layers originate from differences in their recurrent connections with other cells. Thus our method of efficient simulation furnishes a variety of information that is not available from experiment alone.

The contribution of intracortical inhibition to dynamics of orientation tuning in cat striate cortex neurons

Orientation tuning of some neurons in cat visual cortex (area 17) revealed successive shifts of the preferred orientation and widening of tuning in time during the first 150 ms after onset of a flashing light bar. The mechanisms of these dynamics and the possible role of intracortical inhibition are still under discussion. In this study we analysed the dynamics using the time slice method before and during blockade of GABAergic inhibition by microiontophoretic application of bicuculline and observed two main types of neuronal behaviour. The first group of neurons (39 of 68 units or 57.4%) with relatively sharp tuning and absence or relatively small shifts of preferred orientation under control conditions increased or developed this shift during bicuculline application. Changes in tuning were observed between 30 and 150 ms after stimulus onset when inhibition was blocked. Neurons of the second group (29 units or 42.6% of cases) displayed pronounced shifts of preferred orientation under control conditions which was typically diminished or lost during blockade of inhibition. The results indicate different contributions of intracortical inhibition to different neurons distinguishing by stability or time dependence of their orientation preference during normal response generation. In one group of striate cells orientation tuning was kept narrow and constant in time by intracortical inhibition, while in another group orientation tuning dynamics are induced by inhibitory mechanisms.

Role of intracortical inhibition in orientation tuning dynamics in the cat striate cortex neurons

A suggestion about the leading role of GABA-induced intracortical inhibition in the dynamics of orientation tuning (OT) of the cat striate cortical neurons was tested in acute experiments before and during the local blockade of their inhibition by iontophoretic application of bicucculine. In the course of the investigation of these dynamics, with the use of a temporal scanning method, two types of neurons differing in the inhibition blockade-induced OT changes were found. In the neurons of the first type (57%), bicuculline induced the OT dynamics or enhanced it, if it pre-existed before the bicuculline application. In the neurons of the second type (43%), bicuculline strongly reduced or eliminated the dynamic shift of a preferred orientation. These results mean that under normal conditions the inhibition stabilizes and sharpens OT in some cells, while in other cells, in contrast, it causes the OT dynamics. The following mechanisms may underlie the observed effects: an elimination of the inhibition originating from lateral non-isoorientational excitatory inputs of a receptive field; an inhibition of these inputs via the adjacent interneurons activated by a powerful discharge of the examined neuron; a long-term afterhyperpolarization of the neuron, and the dynamics of the excitatory and inhibitory zones of the receptive field.

Effect of Nembutal narcosis on dynamics of orientation tuning of cat visual cortex neurons

The dynamics of orientation tuning (OT) were investigated in acute experiments on immobilized locally anesthetized cats during response development in 40 neurons of the primary visual cortex before and after Nembutal injection. The range of OT scanning decreased in 53.8% of neurons after Nembutal administration (on the average, by 53.4±5.1°; P<0.001); the phenomenon disappeared completely in some neurons. After Nembutal anesthesia, scanning in 20.5% of units either increased or started up in cases of its absence. The scanning range remained constant in 25.6% of neurons. The mentioned changes in the scanning range were consistently more accentuated in cells for which the preferred orientation, as estimated by standard criteria, was shifted under narcosis than in cells invariant to general anesthesia. In the latter group, units with an unchanged scanning range occurred four times more often at all stages of the experiment as against the group of “unstable” neurons.

Dynamics of orientation tuning in the cat striate cortex neurons

Dynamics of orientation tuning was studied by a flashing light bar in 233 single units of cat primary visual cortex. Orientation tuning was plotted by the criterion of spike number in successive fragments of responses with a step of 10 or 20 ms. Preferred orientation and the width of orientation tuning were measured for each of such curves. It was found that successive dynamic change of preferred orientation during response was typical for 63% of units under study, while such change of orientation tuning width was typical for 93%. Neurons with or without shift in preferred orientation differed in their response characteristics: latency and duration of discharge, its frequency and response rise time, as well as quality of orientation tuning. Possible functional significance of two groups of cortical units, “scanners” (with systematic preferred orientation shift) and “timers” (without it), is discussed in accordance with the idea of spatiotemporal orientation coding in the primary visual cortex.

Dynamics of responses of V1 neurons evoked by stimulation of different zones of receptive field

The dynamics of receptive fields of 73 neurons in area 17 of cat visual cortex were studied using the temporal slice method. Three-dimensional maps of the receptive fields were plotted using the criterion of spike number in successive fragments (step 10 or 20 ms) of responses to 100 local flashes presented at different parts of the receptive field in random order. The size and configuration of such dynamically recorded receptive fields were then estimated. This allowed us to reveal the dynamic reorganization of all receptive fields 20–400 ms after stimulation. A small zone of responses appeared in the receptive field after initial latency, then it widened, received definitive configuration, and after that decreased and disappeared. The effect was reproducible under repeated estimations. The relationships between receptive field and the previously described orientation tuning dynamics, as well as between dynamics of receptive fields and their summation zones, mechanisms and possible functional meaning of the revealed effects for signal processing in the primary visual cortex are discussed.