Neurons In Striate Cortex Research Articles

Length and width tuning of neurons in the cat's primary visual cortex.

1. The classically defined receptive field of a visual neuron is the area of visual space over which the cell responds to visual stimuli. It is well established, however, that the discharge produced by an optimal stimulus can be modulated by the presence of additional stimuli that by themselves do not produce any response. This study examines inhibitory influences that originate from areas located outside of the classical (i.e., excitatory) receptive field. Previous work has shown that for some cells the response to a properly oriented bar of light becomes attenuated when the bar extends beyond the receptive field, a phenomenon known as end-inhibition (or length tuning). Analogously, it has been shown that increasing the number of cycles of a drifting grating stimulus may also inhibit the firing of some cells, an effect known as side-inhibition (or width tuning). Very little information is available, however, about the relationship between end- and side-inhibition. We have examined the spatial organization and tuning characteristics of these inhibitory effects by recording extracellularly from single neurons in the cat's striate cortex (Area 17). 2. For each cortical neuron, length and width tuning curves were obtained with the use of rectangular patches of drifting sinusoidal gratings that have variable length and width. Results from 82 cells show that the strengths of end- and side-inhibition tend to be correlated. Most cells that exhibit clear end-inhibition also show a similar degree of side-inhibition. For these cells, the excitatory receptive field is surrounded on all sides by inhibitory zones. Some cells exhibit only end- or side-inhibition, but not both. Data for 28 binocular cells show that length and width tuning curves for the dominant and nondominant eyes tend to be closely matched. 3. We also measured tuning characteristics of end- and side-inhibition. To obtain these data, the excitatory receptive field was stimulated with a grating patch having optimal orientation, spatial frequency, and size, whereas the end- or side-inhibitory regions were stimulated with patches of gratings that had a variable parameter (such as orientation). Results show that end- and side-inhibition tend to be strongest at the orientation and spatial frequency that yield maximal excitation. However, orientation and spatial frequency tuning curves for inhibition are considerably broader than those for excitation, suggesting that inhibition is mediated by a pool of neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

The development of somatostatin immunoreactive neurons in cat visual cortical areas

The development of somatostatin immunoreactive (SOM-ir) neurons in cat striate and extrastriate cortex was studied to determine whether temporal changes in the morphology, distribution and density of SOM-ir neurons during development would provide clues to the emergence of specific cortical areas. The visual cortical areas examined included areas 17–19 and 7, posteromedial lateral suprasylvian, posterolateral lateral suprasylvian cortex and splenial visual area. We observed that the pattern of SOM-ir neurons in the cortical plate reflects the maturation of the cortical plate. At 1 week of age, SOM-ir neurons were only found in layers V and VI of the developing cortex; by 2 weeks of age, SOM-ir neurons were found in layer IV; and by 3 weeks of age, SOM-ir neurons were located in all layers of the cortex except layer I. SOM-ir neurons in the subplate were much more numerous under lateral cortical areas than under medial areas. This difference decreased over the first 2 postnatal weeks and by the 14th day after birth (P14), the distribution and numbers of SOM-ir neurons in the subplate/white matter had reached the adult pattern. The timing of exuberant SOM expression in the subplate suggests a function in the formation of visual corticocortical connections which begin to develop during the first postnatal week in the kitten.

Neuronal organization in area 17 of cat visual cortex.

An antibody to microtubule-associated protein 2 (MAP2) has been used to examine the arrangements of neurons in striate cortex of the cat. It is found that the apical dendrites of medium-sized and large pyramidal cells in layer V group together to form clusters that have a center-to-center spacing of about 56 microns. As these clusters ascend, the apical dendrites of pyramidal cells in layer II/III are added to them. The thinner apical dendrites of the smaller pyramidal cells in layer VIa also form groups that are referred to as bundles. These bundles ascend into layer IV independent of the clusters, and their arrangement suggests that the bundles are formed so that the apical dendrites of the layer VIa pyramids can pass between the groups of cell bodies of the layer V neurons. It is proposed that the clusters formed from the apical dendrites of the layer V and layer II/III pyramidal cells represent the axes of vertical modules of pyramidal cells, which represent the basic neuronal aggregates within area 17 of cat visual cortex. And it is suggested that these modules can be recruited in various combinations, most obviously by the excitation provided by the thalamic inputs, to form the functional columns, such as the ones that are concerned with eye preference and orientation. Based upon the distribution of the dendritic clusters, the pyramidal cell modules would have diameters of 56 microns, and since they are considered to extend through the depth of the cortex, each one would contain some 203 neurons. The striate cortex of one hemisphere contains 160,000 of these modules, which is about the same as the number of X-cells projecting to one hemisphere from the dorsal lateral geniculate nucleus and twice the number of X- or beta-ganglion cells in the retina. The form of the pyramidal cell modules in cat striate cortex is compared to those present in monkey striate cortex, in which the similar modules are about 10 times more numerous, but only 31 microns in diameter (Peters and Sethares, 1991a).

Predicting responses of nonlinear neurons in monkey striate cortex to complex patterns

The overwhelming majority of neurons in primate visual cortex are nonlinear. For those cells, the techniques of linear system analysis, used with some success to model retinal ganglion cells and striate simple cells, are of limited applicability. As a start toward understanding the properties of nonlinear visual neurons, we have recorded responses of striate complex cells to hundreds of images, including both simple stimuli (bars and sinusoids) as well as complex stimuli (random textures and 3-D shaded surfaces). The latter set tended to give the strongest response. We created a neural network model for each neuron using an iterative optimization algorithm. The recorded responses to some stimulus patterns (the training set) were used to create the model, while responses to other patterns were reserved for testing the networks. The networks predicted recorded responses to training set patterns with a median correlation of 0.95. They were able to predict responses to test stimuli not in the training set with a correlation of 0.78 overall, and a correlation of 0.65 for complex stimuli considered alone. Thus, they were able to capture much of the input/output transfer function of the neurons, even for complex patterns. Examining connection strengths within each network, different parts of the network appeared to handle information at different spatial scales. To gain further insights, the network models were inverted to construct "optimal" stimuli for each cell, and their receptive fields were mapped with high-resolution spots. The receptive field properties of complex cells could not be reduced to any simpler mathematical formulation than the network models themselves.

Morphology and laminar distribution of neuropeptide Y immunoreactive neurons in the human striate cortex.

The morphology, laminar distribution, and distribution relative to cytochrome oxidase patches of neuropeptide-Y immunoreactive (NPY-ir) neurons were studied in the human striate cortex. The density of NPY-ir cells was highest in the white matter. NPY-ir neurons were sparsely distributed within the cortical layers. NPY-ir neurons were located in both cytochrome oxidase dense patch and interpatch regions. However, the paucity of NPY-ir neurons in layer III, where cytochrome oxidase patches are most clearly demonstrated, precluded establishing a clear relationship of NPY-ir neurons to cytochrome oxidase patches. NPY-ir neurons exhibited a variety of nonpyramidal morphologies, and many of them had axons with recurrent or looped trajectories. A dense plexus of NPY-ir axons was located just beneath the pia, and these axons were concentrated at the entry points of pial blood vessels. Other NPY-ir neurons had cell bodies or processes in close proximity to cerebral capillaries. These results suggest a role of NPY in cortical metabolism, control of cerebral circulation, or activity-related changes in local blood flow.

Development of axonal arbors of layer 4 spiny neurons in cat striate cortex

Spiny neurons in layer 4 of cat striate cortex are the primary recipients of geniculocortical afferents and provide crucial links to other cortical layers for processing visual information. Using intracellular staining, we examined the development of the local axonal projections of these neurons to determine (1) whether the laminar specificity of their projections emerged specifically or was sculpted from transient exuberant projections and (2) whether the emergence of excitatory connections from layer 4 to layer 2/3 could contribute to the activity-dependent development of clustered horizontal connections of layer 2/3 pyramidal neurons. Differences in the extent of projections to infragranular (layers 5 and 6, which receive sparse projections) versus superficial layers (layers 2/3 and 4, which receive extensive projections) developed specifically from the outset. By postnatal day 15 (P15) projections to infragranular layers matured and were indistinguishable from those in the oldest animal studied (P33). In contrast, projections to superficial layers continued to increase in complexity after P15. Projections within layer 4, which were the most elaborate at all ages studied, reached maturity at about P20, while those to layer 2/3 continued to increase in complexity through P33. No evidence for exuberant projections to any of these cortical layers was observed. At very early postnatal ages (P5) projections to the subplate region were evident. These disappeared by P8-P11, suggesting the presence of transient connections from layer 4 spiny neurons to subplate neurons. Binocular deprivation did not prevent the emergence of projections from layer 4 spiny neurons into layer 2/3 or development of normal laminar differences in projection density. Connections from layer 4 to layer 2/3 emerged after horizontal connections in layer 2/3 were crudely clustered, but in synchrony with the later refinement of clusters. Collaterals from layer 4 cells first crossed into layer 3 at P11, but were extremely short (extending only 50-200 microns beyond the laminar boundary) and uncommon (only 4 of 19 cells). Since by P8 horizontal projections of layer 2/3 pyramidal neurons are already crudely clustered, the emergence of crude clustering is probably independent of layer 4 to layer 2/3 excitatory projections. The proportion of cells projecting to layer 2/3 and the complexity of their arbors both increased in the subsequent weeks, closely matching the timing of both the refinement of crudely clustered horizontal connections and the emergence of visual responsiveness in layer 2/3.(ABSTRACT TRUNCATED AT 400 WORDS)

Prenatal development of GABA-immunoreactive neurons in the human striate cortex

The prenatal development of neurons immunoreactive to γ-aminobutyric acid (GABA) in the striate cortex (area 17) of human foetuses aged from 14 weeks to term was studied immunocytochemically. In the 14 week foetus GABA-immunoreactive cells occurred in all layers of area 17 with the highest density in the marginal zone (MZ), subplate (SP), deep intermediate zone (IZ) and ventricular zone (VZ). The cortical plate (CP), which gives rise to most of the definitive adult cortical layers, had relatively low concentrations of GABAergic cells. By 17 weeks the density in the proliferative VZ had declined. At 20 weeks some of the adult layers were recognisable; the density of GABA-positive neurons was now highest in the definitive cortex, especially the deep layers (layers VI and V), was lower in the superficial cortical plate, and was lowest in IZ, where the white matter would form. The peak of GABA-immunoreactive neuronal density continued to move superficially during development, and was in layer IVc by 30 weeks. The laminar distribution stabilised from 30 weeks with three dense bands: in layer IVc and superficial V, layer IVa, and layers II and superficial III. The tangential distribution of GABAergic neurons was determined in two older brains (32 and 39 weeks) and no unequivocal spatial periodicity was observed in this plane. The mean cross-sectional area of GABAergic neurons in area 17 increased with foetal age, and also increased from superficial to deep layers at each age. Most GABA-immunoreactive neurons in younger brains contained immunonegative or weakly positive nuclei and had few visible processes, while in the older brains most neurons contained positive nuclei and had more visible processes. The proportion of GABA-immunoreactive bipolar cells declined during development while that of multipolar cells increased. GABAergic neurons thus differentiate early in human foetal striate cortex. They are initially most numerous in the proliferative layers deep to the developing definitive cortex; from 20 weeks of gestation, their peak moves superficially into the maturing deep layers (VI and V) and a stable laminar distribution is attained by 30 weeks, with peaks in layers II/IIIm, IVa and IVc/V. There is no obvious horizontal periodic distribution before term.

Postnatal development of thalamic recipient neurons in the monkey striate cortex: Somatic inhibitory synapse acquisition by spiny stellate neurons of layer 4C

The development of type 2 (Colonnier, '81) synapses on the cell bodies of thalamic recipient spiny stellate neurons in layers 4C alpha and 4C beta of primary visual cortex neurons was examined over the first 36 postnatal weeks and in the adult monkey. The type 2 synapses, known to be GABAergic (Ribak, '78) and therefore presumed to be inhibitory, developed faster on the alpha neurons than the beta neurons. Both neuron groups show a marked increase and then decline in the percentage of the somatic membrane covered by type 2 synaptic appositions during this 36-week time period. The time course of the type 2 synapses development is compared to that of the spine synapse development described in previous studies (Lund and Holbach, '91; Lund et al., '91), and it is clear that on both neuron groups this inhibitory synapse population is put in place and refined later than the spine synapses. These findings suggest that each cortical neural circuit has a unique time course for its early development within an overall time window (Rakic et al., '86), or sensitive period (Hubel and Wiesel, '70). Visual deprivation, although causing the alpha and beta neurons to adopt a more similar temporal and numerical developmental pattern than normal, did not prevent acquisition and loss phases of type 2 synapses or the assumption of a normal numerical loading by 36 weeks of age.

Postnatal development of thalamic recipient neurons in the monkey striate cortex: Influence of afferent driving on spine acquisition and dendritic growth of layer 4c spiny stellate neurons

This study uses Golgi-impregnated material to examine the effects of altering the nature of afferent driving on the maturation of spines and dendrites on thalamic recipient spiny stellate neurons in layers 4C alpha and beta of the monkey striate cortex. These two laminae receive input from different sets of thalamic afferents with different functional properties. The development of dendritic spine and dendritic branch populations on these neurons in experimental animals is compared to the same features on similar groups of neurons in a series of normal animals described in the preceding study (Lund and Holbach, '91). Three conditions of rearing were used to alter afferent driving from normal: complete darkness (with in some cases return to normal diurnal light-dark cycle), bilateral eye lid suture, and monocular eye lid suture. Some of the normal and dark-reared infant monkeys were examined behaviorally for visual capacity in an earlier study (Regal et al., '76). All conditions of abnormal afferent driving caused changes from the normal developmental patterns of spine and dendritic arbor growth in these first-order neurons of the cortex and each condition differed in the nature of change produced. Major findings of this study are: 1. Vigorous spine acquisition and dendritic growth occurs under all conditions of visual deprivation on alpha and beta neurons. Eventual spine and dendritic attrition occurs under at least conditions of bilateral or monocular lid suture to produce a rather constant adult morphology. We assume, therefore, that visually driven activity is a modulator or shaper of the developmental process for thalamic recipient neurons of visual cortex, rather than being an initiator, terminator, or driving force for their maturation. 2. An innate "clock," whose nature is unknown but is apparently not driven by visual input, initiates and terminates a period of growth of the thalamic recipient neurons between birth and 30-32 weeks of age. 3. Factors controlling dendritic arbor growth and retraction are different from those controlling spine synapse addition or attrition. 4. Whereas the alpha and beta neurons normally show quite different early growth patterns between birth and 30 weeks of age, when both eyes are simultaneously deprived of vision, an early temporal and numerical convergence occurs in patterns of spine population development on the two groups of neurons. This convergent pattern assumes a different form in dark-reared and lid-sutured animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Postnatal development of thalamic recipient neurons in the monkey striate cortex: Comparison of spine acquisition and dendritic growth of layer 4C alpha and beta spiny stellate neurons

A quantitative study has been made from Golgi impregnations of the maturation of dendrites and their spines on spiny stellate neurons in the macaque monkey primary visual cortex. The neurons studied lay within either the alpha or the beta division of lamina 4C; previous workers have shown the alpha division neurons to be contacted by thalamic axon terminals arising from the magnocellular division of the lateral geniculate nucleus (LGN) of the thalamus and the beta division neurons to be contacted by parvocellular LGN inputs. Most thalamic terminals and perhaps the majority of other type 1 (Colonnier, '81), presumed excitatory, inputs to these cells make synaptic contacts on the tips of their dendritic spines. Measurement was made of relative changes in the total number of spines on these alpha and beta spiny neurons over age by measuring both spine density along the dendrites and dendritic arbor size in single 90-microns sections from Golgi rapid preparations. Our previous work (Lund et al., '77; Boothe et al., '79) showed a marked proliferation and attrition of spines and dendritic branches to occur in the early postnatal weeks; Rakic et al. ('86) have since proposed that there is a cortexwide synchrony of synapse acquisition and loss during this same period. However, different visual capacities channelled via the magnocellular and parvicellular geniculate relays show different maturational rates (Harwerth et al., '86). This study indicates that the anatomical maturation of spines on the alpha and beta neurons is not temporally coincident from birth to 30 weeks. During this period, phases of spine acquisition and loss on alpha neurons precedes similar phases on beta neurons. The alpha neurons carry a peak spine population at 5-8 weeks postnatal, whereas the beta neurons carry their peak spine populations between 8 and 24 weeks postnatal. At all ages prior to 30 weeks, the two sets of neurons carry quite different total spine populations. Close to 30 weeks of age, the total spine coverage has fallen on both sets of neurons and becomes identical between the alpha and beta neurons. In animals aged 30 weeks to adult, spine coverage per neuron is maintained at a common figure for the alpha and beta neurons despite further growth and disparate dendritic arbor sizes and different local spine densities in the two groups; this suggests that some common sampling paradigm between pre- and postsynaptic elements is adopted by the alpha and beta neurons and also suggests the development of a close functional correlation between the two sets of neurons.

Dynamic stabilization of receptive fields of cortical neurons (VI) during fixation of gaze in the macaque

The positions of receptive field borders of striate cortical neurons were measured repeatedly in awake monkeys during attentive fixation of a small target. The border position, as marked by the onset of evoked activity in response to a moving stimulus, did not show the variability expected from previous measures of eye position variability during fixation. Measured variability was smaller than expected. Trial-by-trial comparisons suggest that receptive field borders are not shifted by the small eye movements occurring during attentive fixation. It is our hypothesis that attentive fixation engages a mechanism that gates incoming information to achieve a stabilization of the receptive field relative to the external world. Such a dynamic positional compensation may underlie preliminary evidence showing that the response of stereo-sensitive neurons in striate cortex is consistent with stimulus disparity measures and, within limits, does not reflect the retinal disparities produced by the changes in binocular alignment during fixation.

Calcium‐binding proteins as markers for subpopulations of GABAergic neurons in monkey striate cortex

Recent studies have shown that the presence of immunoreactivity for parvalbumin (PV-IR) and calbindin-D 28k (Cal-IR) can be used as markers for certain types of gamma-aminobutyric acid (GABA) immunoreactive interneurons in monkey cerebral cortex. Little quantitative information is available regarding the features that distinguish these two subpopulations, however. Therefore, in this study we localized PV-IR and Cal-IR neurons in Macaca monkey striate cortex and analyzed quantitatively their laminar distribution, cell morphology, and co-localization with GABA by double-labeling immunocytochemistry. PV-IR was found in nonpyramidal cells in all layers of the cortex, although PV-IR cells in layer 1 were rare. In contrast, Cal-IR was found mainly in nonpyramidal cells in two bands corresponding to layers 2-3 and 5-6. We found very few double-labeled PV-IR/Cal-IR cells but confirmed that almost all PV-IR and Cal-IR cells are GABAergic. Overall, 74% of GABA neurons in striate cortex displayed PV-IR compared to only 12% that displayed Cal-IR and 14% that were GABA-IR only. Quantitative analysis indicated that the relative proportion of GABA cells that displayed PV-IR or Cal-IR showed conspicuous laminar differences, which were often complementary. Cell size measurements indicated that PV-IR/GABA cells in layers 2-3 and 5-6 were significantly larger than Cal-IR/GABA cells. Analysis of the size, shape, and orientation of stained cell bodies and proximal dendrites further demonstrated that each subpopulation contained several different types of smooth stellate cells, suggesting that Cal-IR and PV-IR are found in functionally and morphologically heterogeneous subpopulations of GABA neurons. There was a thick bundle of PV-IR axons in the white matter underlying the striate but not prestriate cortex. PV-IR punctate labeling matched the cytochrome oxidase staining pattern in layers 4A and 4C, suggesting that PV-IR is present in geniculocortical afferents as well as intrinsic neurons. Cal-IR neuropil staining was high in layers 1, 2, 4B, and 5, where cytochrome oxidase staining is relatively low. We did not find a preferential localization of either PV-IR or Cal-IR cell bodies in any cytochrome oxidase compartments in layers 2-3 of the cortex. These findings indicate that PV and Cal are distributed into different neuronal circuits.

Stimulus-Dependent Neuronal Oscillations in Cat Visual Cortex: Inter-Columnar Interaction as Determined by Cross-Correlation Analysis.

We have demonstrated previously that neurons in cat striate cortex, in response to their preferred stimuli, exhibit oscillatory responses in a frequency range of 40 - 60 Hz. Recently, we obtained evidence that such oscillatory responses can synchronize across columns. We have now performed an extensive analysis of this phenomenon for both unit and field potential responses. In addition, we studied the stimulus conditions leading to intercolumnar synchronization. We recorded both multi-unit activity and local field potentials from area 17 of adult cats with arrays of several electrodes. Interelectrode distances ranged from 0.4 to 12 mm. For all pairs of unit (n=200) and field potential (n=174) recordings, we computed auto- and cross-correlation functions. The modulation of the correlograms was quantified by fitting a damped sine wave (Gabor) function to the data. Cross-correlation analysis of the unit data revealed that in 90 out of 200 cases the recorded cells established a constant phase-relationship of their oscillatory responses. This occurred, on average, with no phase difference. If the receptive fields were nonoverlapping, we observed a synchronization primarily between cells with similar orientation preferences. Cells with overlapping receptive fields also showed a high incidence of synchronization if their orientation preferences were different. In this latter group, synchronization occurred even in cases where the stimulus was optimal for only one of the recording sites. Under conditions of monocular instead of binocular stimulation the oscillatory modulation of the responses was attenuated, but the cross-correlogram still indicated a significant interaction. Similar effects were seen with the application of stationary instead of moving stimuli. A synchronization of oscillatory field potential responses was observed in 136 out of 174 paired recordings. At all distances investigated, the probability of synchronization of field potential responses was independent of the orientation preferences of the cells. However, the strength of interaction decreased with increasing spatial separation. Control experiments showed that the synchronization of field potential responses was not due to volume conduction. The results demonstrate that oscillatory responses at separate cortical sites can transiently synchronize. The probability and strength of synchronization are dependent on the spatial separation of the recorded cells and their orientation preferences. In addition, the cross-columnar synchronization is influenced by features of the visual stimulus. It is suggested that this synchronization provides a mechanism for the formation of neuronal assemblies in the visual cortex.

Selectivity for orientation and direction of motion of single neurons in cat striate and extrastriate visual cortex

1. We consider the consequences of the orientation selectivity shown by most cortical neurons for the nature of the signals they can convey about the direction of stimulus movement. On theoretical grounds we distinguish component direction selectivity, in which cells are selective for the direction of movement of oriented components of a complex stimulus, from pattern direction selectivity, or selectivity for the overall direction of movement of a pattern irrespective of the directions of its components. We employed a novel test using grating and plaid targets to distinguish these forms of direction selectivity. 2. We studied the responses of 280 cells from the striate cortex and 107 cells from the lateral suprasylvian cortex (LS) to single sinusoidal gratings to determine their orientation preference and directional selectivity. We tested 73 of these with sinusoidal plaids, composed of two sinusoidal gratings at different orientations, to study the organization of the directional mechanisms within the receptive field. 3. When tested with single gratings, the directional tuning of 277 oriented cells in area 17 had a mean half width of 20.6 degrees, a mode near 13 degrees, and a range of 3.8-58 degrees. Simple cells were slightly more narrowly tuned than complex cells. The selectivity of LS neurons for the direction of moving gratings is not markedly different from that of neurons in area 17. The mean direction half width was 20.7 degrees. 4. We evaluated the directional selectivity of these neurons by comparing responses to stimuli moved in the optimal direction with those elicited by a stimulus moving in the opposite direction. In area 17 about two-thirds of the neurons responded less than half as well to the non-preferred direction as to the preferred direction; two-fifths of the units responded less than one-fifth as well. Complex cells showed a somewhat greater tendency to directional bias than simple cells. LS neurons tended to have stronger directional asymmetries in their response to moving gratings: 83% of LS neurons showed a significant directional asymmetry. 5. Neurons in both areas responded independently to each component of the plaid. Thus cells giving single-lobed directional-tuning curves to gratings showed bilobed plaid tuning curves, with each lobe corresponding to movement in an effective direction by one of the two component gratings within the plaid. The two best directions for the plaids were those at which one or other single grating would have produced an optimal response when presented alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Behavioral determination of the spatial selectivity of contrast adaptation in cats: Some evidence for a common plan in the mammmlian visual system

An aftereffects paradigm was used to behaviorally measure contrast sensitivity of cats to gratings of three different test spatial frequencies after adaptation to gratings of various spatial frequencies, contrasts, and durations. Post-adaptation reductions in sensitivity occurred even after short periods of adaptation (less than 7 s) and could be as large as 1.0 log unit under some conditions. The magnitude of the adaptation effect varied monotonically with (1) adaptation grating contrast, (2) duration, and (3) the contrast sensitivity for the test grating. Average half-width (at half-height) of the spatial-frequency tuning curves constructed from the data was 1.4 octaves, and was not dependent upon the level of adaptation or the spatial frequency of the test grating. Post-adaptation psychometric functions of the cats showed reduced slopes and maxima suggesting that, unlike humans, in cats apparent contrast grows more slowly with increases in physical contrast after contrast adaptation. All of the characteristics observed are in excellent agreement with electrophysiologically measured properties of neurons in striate cortex of cats. In addition, there was a remarkable similarity of the cat tuning functions, both in shape and bandpass, to those measured in man with a similar paradigm suggesting that (1) the two visual systems are sufficiently similar to make the cat a useful spatial vision model and (2) there is a common functional plan to all mammalian visual systems despite significant anatomical differences between species.

Horizontal Interactions in Cat Striate Cortex: III. Ectopic Receptive Fields and Transient Exuberance of Tangential Interactions.

In this study the developmental changes of intracortical connectivity are related to changes of cortical receptor fields (RFs). The RFs of striate cortex neurons of 4- to 8.5-week-old kittens, reared under normal conditions (NR) or in a selective visual environment (SE), were analysed quantitatively and compared with adult cats. To unmask weak inputs from outside the conventional RF (CRF), cell excitability was raised by iontophoretic application of glutamate (GLU) and/or bicuculline methiodide (BIC) or by light stimulation of the CRF. Both the dominant discharge region (DDR) and the total RF (TRF) area were significantly larger in NR and SE kittens than in adult cats. Moreover, in kittens 18% of the cells had additional ectopic fields that were excitatory, had similar orientation preferences as the CRF, and ranged 4 degrees to 23 degrees from the centre of the CRF. In 74% of the cases the ectopic fields were direction-selective and 70% of them preferred stimuli moving toward the CRF. Ectopic fields occurred mainly in supragranular cells, were similarly frequent in simple and complex cells and slightly more frequent in SE (20.7%) than in NR (13.3%) kittens. In adult cats only one of 83 cells tested had an ectopic field. It is concluded that the age-dependent decrease in the RF size, the laminar distribution of cells having an ectopic RF, and the numerical reduction of these cells with age correlate well with the organization and postnatal pruning of tangential projections, suggesting that these contribute to the elaboration of specific response properties. Moreover, the authors infer from the early presence and from the selectivity of ectopic fields that the system of horizontal intrinsic connections mediates far-reaching, excitatory interactions between cortical neurons with similar functional properties and serves as a substrate for the processing of global aspects of visual patterns.

Chromatic mechanisms in striate cortex of macaque

We measured the responses of 305 neurons in striate cortex to moving sinusoidal gratings modulated in chromaticity and luminance about a fixed white point. Stimuli were represented in a 3-dimensional color space defined by 2 chromatic axes and a third along which luminance varied. With rare exceptions the chromatic properties of cortical neurons were well described by a linear model in which the response of a cell is proportional to the sum (for complex cells, the rectified sum) of the signals from the 3 classes of cones. For each cell there is a vector passing through the white point along which modulation gives rise to a maximal response. The elevation (theta m) and azimuth (phi m) of this vector fully describe the chromatic properties of the cell. The linear model also describes neurons in l.g.n. (Derrington et al., 1984), so most neurons in striate cortex have the same chromatic selectivity as do neurons in l.g.n. However, the distributions of preferred vectors differed in cortex and l.g.n.: Most cortical neurons preferred modulation along vectors lying close to the achromatic axis and those showing overt chromatic opponency did not fall into the clearly defined chromatic groups seen in l.g.n. The neurons most responsive to chromatic modulation (found mainly in layers IVA, IVC beta, and VI) had poor orientation selectivity, and responded to chromatic modulation of a spatially uniform field at least as well as they did to any grating. We encountered neurons with band-pass spatial selectivity for chromatically modulated stimuli in layers II/III and VI. Most had complex receptive fields. Neurons in layer II/III did not fall into distinct groups according to their chromatic sensitivities, and the chromatic properties of neurons known to lie within regions rich in cytochrome oxidase appeared no different from those of neurons in the interstices. Six neurons, all of which resembled simple cells, showed unusually sharp chromatic selectivity.

Spatial- and temporal-frequency selectivity as a basis for velocity preference in cat striate cortex neurons

Measurements were made of the optimal velocity for drifting bar-shaped stimuli to excite striate cortex neurons of the cat. These data were compared to the optimal spatial and temporal frequencies of the same neurons, as determined with drifting sine-wave grating stimuli. A systematic relationship was revealed, whereby those neurons preferring higher velocities of bar motion also preferred lower spatial and higher temporal frequencies of gratings. The optimal bar velocity for a given neuron could be quantitatively predicted from the ratio of that neuron's optimal temporal frequency to its optimal spatial frequency.

The physiology of attention: participation of cat striate cortex in behavioral choice.

In the awake, behaving cat, we have compared response of striate cortex neurons to informative and to noninformative stimuli. A cat pressed a pedal in response to a flashed pattern repeated every 10 s, receiving a reward if the press was within a 0.5-1.5-s post-stimulus window. There were three trial types: 50% of the trials had only the initial informative flash, 25% had an additional physically identical, but unrewarded, flash 500 ms after the first, and 25% had an unrewarded flash 3-5 s after the informative flash. Cats learned to respond only to the rewarded flashes. Neurons were divided into two categories: 27 neurons defined as "primary" showed an early burst of firing 30-70 ms after stimulus onset, and 17 did not. The distinction was arbitrary, since all cells were exposed to the same stimulus. For stimuli preceding a pedal press, stimulus-synchronized histograms of primary neurons had a smaller early burst and more firing before and after it. Response-synchronized histograms showed an abrupt decrease in firing shortly before the pedal press. The effects were stronger for primary cells in the stimulus-synchronized data and stronger for non-primary cells in the response-synchronized data.