Spatio-temporal organization of receptive fields of the cat striate cortex

The responses of cortical cells to gratings and bars were compared. The excitatory and inhibitory on-and off-zones of a simple cell are composed of on- and off-subfields of CGL. Any zone is formed by an opponent pair of subfields one of which gives an excitatory effect, the other — inhibitory. Such organization assumes the linear properties of a simple field. The deviations from linearity are due to spatial dis-placements of the subfields, heterogeneity of subfields, or the absence of one subfield in the opponent pair. Subfields may be both phasic and tonic, even in the same RF. Analysis of the most common type of a complex cell with modulated responses against unmodulated background shows that a mask eliminating stimulation of any half of the RF causes (according to the theory of filtres) increasing the bandwidth due to the increase or the appearance of responses to side low and high frequencies. The modulated components of the responses from both halves of the RF are out of phase. Analysis of this fact and the responses to thin bars suggests that a complex field is formed by linear and nonlinear subsystems converging onto output neuron. Other types of complex fields are organized by different combinations of subsystems. Limited in area by masking the RF responds to much higher spatial frequencies than the whole RF. The optimal frequency in two-dimensional spatial frequency characteristics of the RF does not change with orientation. Simple RFs and a part of complex RF calculate the amplitude and the phase of the stimulus, the other part of complex RFs (with unmodulated response) calculate only amplitude. Given all this, the RFs are grating filters of spatial frequency.     

用脑光学成像术研究不同空间拓扑位置猫初级视皮层的空间频率反应特性

采用基于内源信号的脑光学成像方法,在大范围视皮层研究了不同空间拓扑位置对应的皮层区的对光栅刺激空间频率反应特性。结果表明,周边视野对应区对高空间频率刺激反应极弱或没有反应,中心视野对应区对较宽的空间频率范围内的刺激均有反应,但对高频刺激反应更强;无论在周边对应区还是中心对应区,其视野越靠近中心,其空间频率调谐曲线和截止空间频率越靠近高频,而且这种过渡是平缓的。以上结果说明,猫初级视皮层空间频率反应     

Development of spatial coarse-to-fine processing in the visual pathway

The sequential analysis of information in a coarse-to-fine manner is a fundamental mode of processing in the visual pathway. Spatial frequency (SF) tuning, arguably the most fundamental feature of spatial vision, provides particular intuition within the coarse-to-fine framework: low spatial frequencies convey global information about an image (e.g., general orientation), while high spatial frequencies carry more detailed information (e.g., edges). In this paper, we study the development of cortical spatial frequency tuning. As feedforward input from the lateral geniculate nucleus (LGN) has been shown to have significant influence on cortical coarse-to-fine processing, we present a firing-rate based thalamocortical model which includes both feedforward and feedback components. We analyze the relationship between various model parameters (including cortical feedback strength) and responses. We confirm the importance of the antagonistic relationship between the center and surround responses in thalamic relay cell receptive fields (RFs), and further characterize how specific structural LGN RF parameters affect cortical coarse-to-fine processing. Our results also indicate that the effect of cortical feedback on spatial frequency tuning is age-dependent: in particular, cortical feedback more strongly affects coarse-to-fine processing in kittens than in adults. We use our results to propose an experimentally testable hypothesis for the function of the extensive feedback in the corticothalamic circuit.     

Spatial properties of goldfish ganglion cells

We systematically classified goldfish ganglion cells according to their spatial summation properties using the same techniques and criteria used in cat and monkey research. Results show that goldfish ganglion cells can be classified as X-, Y-, or W-like based on their responses to contrast-reversal gratings. Like cat X cells, goldfish X-like cells display linear spatial summation. Goldfish Y-like cells, like cat Y cells, respond with frequency doubling at all spatial positions when the contrast-reversal grating consists of high spatial frequencies. There is also a third class of neurons, which is neither X- nor Y-like; many of these cells' properties are similar to those of the "not-X" cells found in the eel retina. Spatial filtering characteristics were obtained for each cell by drifting sinusoidal gratings of various spatial frequencies and contrasts across the receptive field of the cell at a constant temporal rate. The spatial tuning curves of the cell depend on the temporal parameters of the stimulus; at high drift rates, the tuning curves lose their low spatial frequency attenuation. To explore this phenomenon, temporal contrast response functions were derived from the cells' responses to a spatially uniform field whose luminance varied sinusoidally in time. These functions were obtained for the center, the surround, and the entire receptive field. The results suggest that differences in the cells' spatial filtering across stimulus drift rate are due to changes in the interaction of the center and surround mechanisms; at low temporal frequencies, the center and surround responses are out-of-phase and mutually antagonistic, but at higher temporal rates their responses are in-phase and their interaction actually enhances the cell's responsiveness.     

Receptive field mechanisms of cat X and Y retinal ganglion cells

We investigated receptive field properties of cat retinal ganglion cells with visual stimuli which were sinusoidal spatial gratings amplitude modulated in time by a sum of sinusoids. Neural responses were analyzed into the Fourier components at the input frequencies and the components at sum and difference frequencies. The first-order frequency response of X cells had a marked spatial phase and spatial frequency dependence which could be explained in terms of linear interactions between center and surround mechanisms in the receptive field. The second-order frequency response of X cells was much smaller than the first-order frequency response at all spatial frequencies. The spatial phase and spatial frequency dependence of the first-order frequency response in Y cells in some ways resembled that of X cells. However, the Y first-order response declined to zero at a much lower spatial frequency than in X cells. Furthermore, the second-order frequency response was larger in Y cells; the second-order frequency components became the dominant part of the response for patterns of high spatial frequency. This implies that the receptive field center and surround mechanisms are physiologically quite different in Y cells from those in X cells, and that the Y cells also receive excitatory drive from an additional nonlinear receptive field mechanism.     

Responses of neurons in cat primary somatosensory cortex to repetitive stimulation of vibrissae

Extra- and intracellular responses of neurons in the primary somatosensory cortex to repetitive mechanical stimulation of the vibrissae at different frequencies were studied in unanesthetized curarized adult cats. Unlike responses to electrical stimulation of the combined afferent input (the infraorbital nerve) spike discharges of neurons in response to vibrissal stimulation can reproduce rather higher frequencies of stimulation and their initial character changes more often in the course of the repetitive series. Most cortical neurons were characterized by limitation of the area of their peripheral receptive fields with an increase in the frequency of adequate repetitive stimulation. A group of cortical neurons was distinguished by its ability to respond to high-frequency stimulation and to generate burst discharges. Comparison of the frequency characteristics of spike responses of these cells and of inhibitory synaptic action in other cortical neurons led to the conclusion that this group of cells thus distinguished may be inhibitory cortical neurons. The role of interaction between excitatory and inhibitory processes arising in cortical neurons during repetitive stimulation of different areas of their receptive fields is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 164–171, March–April, 1982.     

Patterns in the discharge of simple and complex visual cortical cells

The activity of visual cortical neurons (area 17) was recorded in anaesthetized cats in response to sinusoidal drifting gratings. The statistical structure of the discharge of simple and complex cells has been studied as a function of the various parameters of a drifting grating: spatial frequency, orientation, drifting velocity and contrast. For simple cells it has been found that the interspike interval distributions in response to drifting gratings of various spatial frequencies differ only by a time scale factor. They can be reduced to a unique distribution by a linear time transformation. Variations in the spatial frequency of the grating induce variations in the mean firing rate of the cell but leave unchanged the statistical structure of the discharge. On the contrary, the statistical structure of the simple cell activity changes when the contrast or the velocity of the stimulus is varied. For complex cells it has been found that the invariance property described above for simple cells is not valid. Complex cells present in their activity in response to visual stimuli two different firing patterns: spikes organized in clusters and spikes that do not show this organization ('isolated spikes'). The clustered component is the only component of the complex cell discharge that is tuned for spatial frequency and orientation, while the isolated spike component is correlated with the contrast of the stimulus.     

Response histogram shapes and tuning curves: The predicted responses of several cortical cell types to drifting gratings stimuli

The responses to visual stimuli of simple cortical cells show linear spatial summation within and between their receptive field subunits. Complex cortical cells do not show this linearity. We analyzed the simulated responses to drifting sinusoidal grating stimuli of simple and of several types of complex cells. The complex cells, whose responses are seen to be half-wave rectified before pooling, have receptive fields consisting of two or more DOG (difference-of-Gaussians) shaped subunits. In both cases of stimulation by contrast-reversal gratings or drifting gratings, the cells' response as a function of spatial frequency is affected by the subunit distances 2 and the stimulation frequency . Furthermore, an increased number of subunits (a larger receptive field) yields a narrower peak tuning curve with decreased modulation depth for many of the spatial frequencies. The average and the peak response tuning curves are compared for the different receptive field types.     

Complex Cell Response depends on Interslit Spacing

PSYCHOPHYSICAL studies have established that the human central visual system contains a large number of independent channels each of which responds maximally to a selectively oriented sine wave grating of a given spatial frequency and hardly at all to gratings of spatial frequencies differing by a factor of two^1–4. Electrophysiological studies with moving sinusoidally modulated grating patterns have demonstrated that there exists a class of neurones in the striate cortex of cats⁵ and monkeys⁶ each member of which is maximally selective to a given spatial frequency and orientation.     

Prediction of orientation selectivity from receptive field architecture in simple cells of cat visual cortex

From the intracellularly recorded responses to small, rapidly flashed spots, we have quantitatively mapped the receptive fields of simple cells in the cat visual cortex. We then applied these maps to a feedforward model of orientation selectivity. Both the preferred orientation and the width of orientation tuning of the responses to oriented stimuli were well predicted by the model. Where tested, the tuning curve was well predicted at different spatial frequencies. The model was also successful in predicting certain features of the spatial frequency selectivity of the cells. It did not successfully predict the amplitude of the responses to drifting gratings. Our results show that the spatial organization of the receptive field can account for a large fraction of the orientation selectivity of simple cells.     

Spatiotemporal frequency responses of cat retinal ganglion cells

Spatiotemporal frequency responses were measured at different levels of light adaptation for cat X and Y retinal ganglion cells. Stationary sinusoidal luminance gratings whose contrast was modulated sinusoidally in time or drifting gratings were used as stimuli. Under photopic illumination, when the spatial frequency was held constant at or above its optimum value, an X cell's responsivity was essentially constant as the temporal frequency was changed from 1.5 to 30 Hz. At lower temporal frequencies, responsivity rolled off gradually, and at higher ones it rolled off rapidly. In contrast, when the spatial frequency was held constant at a low value, an X cell's responsivity increased continuously with temporal frequency from a very low value at 0.1 Hz to substantial values at temporal frequencies higher than 30 Hz, from which responsivity rolled off again. Thus, 0 cycles X deg-1 became the optimal spatial frequency above 30 Hz. For Y cells under photopic illumination, the spatiotemporal interaction was even more complex. When the spatial frequency was held constant at or above its optimal value, the temporal frequency range over which responsivity was constant was shorter than that of X cells. At lower spatial frequencies, this range was not appreciably different. As for X cells, 0 cycles X deg-1 was the optimal spatial frequency above 30 Hz. Temporal resolution (defined as the high temporal frequency at which responsivity had fallen to 10 impulses X s-1) for a uniform field was approximately 95 Hz for X cells and approximately 120 Hz for Y cells under photopic illumination. Temporal resolution was lower at lower adaptation levels. The results were interpreted in terms of a Gaussian center-surround model. For X cells, the surround and center strengths were nearly equal at low and moderate temporal frequencies, but the surround strength exceeded the center strength above 30 Hz. Thus, the response to a spatially uniform stimulus at high temporal frequencies was dominated by the surround. In addition, at temporal frequencies above 30 Hz, the center radius increased.     

Differences in orientation and receptive field position between supra- and infragranular cells of cat striate cortex and their possible functional implications

On the postlateral gyrus of the cat striate cortex the cells' preferred orientation and the location of their receptive fields was measured as a function of cortical depth in penetrations as parallel as possible to the radiating fibres. In most penetrations the majority of infragranular cells showed orientation preferences 45 degrees-90 degrees different from the preferred orientations of supragranular cells. In addition, aggregate receptive fields from the same eye of supra- and infragranular cells were spatially shifted against each other. Using different columnar models these results are discussed in terms of spatial contrast enhancement for two parallel mechanisms in upper and lower layers, determined for pattern discrimination and movement detection.     

The responses to illusory contours of neurons in cortex areas 17 and 18 of the cats

Responses to illusory contours (ICs) were sampled from neurons in cortical areas 17 and 18 of the anesthetized cats. For ICs sensitive cells, the differences of receptive field properties were compared when ICs and real contour stimuli were applied. Two hundred orientation or direction selective cells were studied. We find that about 42 percent of these cells were the ICs sensitive cells. Although their orientation or direction tuning curves to ICs bar and real bars were similar, the response modes (especially latency and time course) were different. The cells’ responses to ICs were independent of the spatial phases of sinusoidal gratings, which composed the ICs. The cells’ optimal spatial frequency to composing gratings the ICs was much higher than the one to moving gratings. Therefore, these cells really responded to the ICs rather than the line ends of composing gratings. For some kinds of velocity-tuning cells, the optimal velocity to moving ICs bar was much lower than the optimal velocity to moving bars. The present results demonstrate that some cells in areas 17 and 18 of cats have the ability to respond to ICs and have different response properties of the receptive fields to ICs and luminance boundaries via different neural mechanisms.     

The responses to illusory contours of neurons in cortex areas 17 and 18 of the cats

Responses to illusory contours (ICs) were sampled from neurons in cortical areas 17 and 18 of the anesthetized cats. For ICs sensitive cells, the differences of receptive field properties were compared when ICs and real contour stimuli were applied. Two hundred orientation or direction selective cells were studied. We find that about 42 percent of these cells were the ICs sensitive cells. Although their orientation or direction tuning curves to ICs bar and real bars were similar, the response modes (especially latency and time course) were different. The cells' responses to ICs were independent of the spatial phases of sinusoidal gratings, which composed the ICs. The cells' optimal spatial frequency to composing gratings the ICs was much higher than the one to moving gratings. Therefore, these cells really responded to the ICs rather than the line ends of composing gratings. For some kinds of velocity-tuning cells, the optimal velocity to moving ICs bar was much lower than the optimal velocity to moving     

Target and temporal pattern selection at neocortical synapses

We attempt to summarize the properties of cortical synaptic connections and the precision with which they select their targets in the context of information processing in cortical circuits. High-frequency presynaptic bursts result in rapidly depressing responses at most inputs onto spiny cells and onto some interneurons. These 'phasic' connections detect novelty and changes in the firing rate, but report frequency of maintained activity poorly. By contrast, facilitating inputs to interneurons that target dendrites produce little or no response at low frequencies, but a facilitating-augmenting response to maintained firing. The neurons activated, the cells they in turn target and the properties of those synapses determine which parts of the circuit are recruited and in what temporal pattern. Inhibitory interneurons provide both temporal and spatial tuning. The 'forward' flow from layer-4 excitatory neurons to layer 3 and from 3 to 5 activates predominantly pyramids. 'Back' projections, from 3 to 4 and 5 to 3, do not activate excitatory cells, but target interneurons. Despite, therefore, an increasing complexity in the information integrated as it is processed through these layers, there is little 'contamination' by 'back' projections. That layer 6 acts both as a primary input layer feeding excitation 'forward' to excitatory cells in other layers and as a higher-order layer with more integrated response properties feeding inhibition to layer 4 is discussed.     

Spatial frequency response functions obtained from cat visual evoked potentials

Visual evoked potentials (VEPs) were obtained from the surface of teh cat visual cortex in response to contrast reversing sinusoidal gratings. Gratings of different spatial frequency were presented either separately, using signal averaging to increase the signal-to-noise ratio, or as a spatial frequency sweep, in which spatial frequency was sequentially increased every 5 sec during a 40 sec trial (3.99 Hz) or every 3 sec during a 24 sec trial (6.65 Hz). The second harmonic amplitude- and phase-spatial frequency functions derived from averaging or from sweep trials were similar, indicating that the swept stimulus method can be used to provide a rapid and reliable measure of the VEP-spatial frequency function. Intravenous administration of physostigmine, an acetylcholinesterase inhibitor, evoked a spatial frequency-dependent change in VEP amplitude. At 3.99 Hz, responses to low spatial frequencies were enhanced to a greater extent than were responses to high spatial frequency stimuli. At 6.65 Hz, responses to mid-range spatial frequencies were enhanced to a greater extent than were responses to low and high spatial frequency stimuli. VEP phase at both 3.99 and 6.65 Hz was advanced to a greater degree at the higher spatial frequencies. These results indicate that the swept spatial frequency method may be useful in studying spatial frequency-dependent pharmacological effects on the VEP and support the possibility that pharmacological disruption of the cholinergic visual system can produce such changes.     

Contrast transfer function of the visual system]

Visually evoked potentials were used to determine the spatial contrast response function of the visual system and the visual acuity of the pigeon. The spatial contrast response describes the relationship between the contrast in a pattern of vertical stripes, whose luminance is a function of position, and the amplitude of the visually evoked response at various spatial frequencies for a given temporal frequency (pattern reversal frequency); it indicates how particular spatial frequencies are attenuated in the visual system. The visually evoked responses were recorded using monopolar stainless steel electrodes inserted into the stratum griseum superficiale of the optic tectum; the depth of penetration was determined on the basis of a stereotactic atlas. The stimulus patterns were generated on a video monitor placed 75 cm in front of the animal's eye perpendicular to the optic axis. The spatial contrast response function measured at 10% contrast and 0.5 Hz reversal frequency shows a peak at a spatial frequency of 0.5 c/deg, corresponding to 1 degree of visual angle, and decreases progressively at higher spatial frequencies. The high-frequency limit (cut-off frequency) for resolution of sinusoidal gratings, estimated from the contrast response function, is 15.5 c/deg, corresponding to a visual acuity of 1.9 min of arc.     

Receptive field properties of near neighbor orientation selective neurons in the visual cortex: a modeling study

The primary visual cortex is organized into clusters of cells having similar receptive fields (RFs). A purely feedforward model has been shown to produce realistic simple cell receptive fields. The modeled cells capture a wide range of receptive field properties of orientation selective cortical cells. We have analyzed the responses of 78 nearby cell pairs to study which RF properties are clustered. Orientation preference shows strongest clustering. Orientation tuning width (hwhh) and tuning height (spikes/sec) at the preferred orientation are not as tightly clustered. Spatial frequency is also not as tightly clustered and RF phase has the least clustering. Clustering property of orientation preference, orientation tuning height and width depend on the location of cells in the orientation map. No such location dependence is observed for spatial frequency and RF phase. Our results agree well with experimental data.     

Profound contrast adaptation early in the visual pathway

Prior exposure to a moving grating of high contrast led to a substantial and persistent reduction in the contrast sensitivity of neurons in the lateral geniculate nucleus (LGN) of macaque. This slow contrast adaptation was potent in all magnocellular (M) cells but essentially absent in parvocellular (P) cells and neurons that received input from S cones. Simultaneous recordings of M cells and the potentials of ganglion cells driving them showed that adaptation originated in ganglion cells. As expected from the spatiotemporal tuning of M cells, adaptation was broadly tuned for spatial frequency and lacked orientation selectivity. Adaptation could be induced by high temporal frequencies to which cortical neurons do not respond, but not by low temporal frequencies that can strongly adapt cortical neurons. Our observations confirm that contrast adaptation occurs at multiple levels in the visual system, and they provide a new way to reveal the function and perceptual significance of the M pathway.