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.     

The role of visual experience in the development of cat striate cortex

By the third postnatal week, intrinsic developmental programs have established a framework within the cat visual system; this will be used to guide the course of subsequent experience-dependent development. Key elements in this framework are precociously mature cells in visual cortex area 17. These orientation-selective cells are predominantly first-order neurons, they are concentrated in layers IV and VI of area 17, most of them are activated monocularly, many may receive their direct excitatory input from lateral geniculate nucleus X cells, and the distribution of their preferred orientations is biased toward horizontal and vertical. Between the third and the sixth postnatal week, most of the remaining cells in area 17 develop orientation selectivity; this extension of orientation selectivity is blocked or delayed if kittens are deprived of normal patterned visual stimulation. Furthermore, exposure to a limited range of stimulus orientations can lead to an increase in the proportion of orientation-selective cells, and the range of orientation preferences that the cells acquire is restricted by the range of orientations to which the animal is exposed. This occurs with no apparent change in the physiology or morphology of intrinsically selective area 17 cells. Thus selective exposure may have its effect by influencing the connections between the intrinsically selective cells and higher-order neurons in area 17. Experience-dependent changes in the visual system may function to "fine-tune" sensory processing and thus optimize the system's response to the dominant features of the environment. This experience-dependent process could help the young animal to focus its "attention" on those features of its environment that are critical to its survival.     

Self-organization of orientation sensitive cells in the striate cortex

A nerve net model for the visual cortex of higher vertebrates is presented. A simple learning procedure is shown to be sufficient for the organization of some essential functional properties of single units. The rather special assumptions usually made in the literature regarding preorganization of the visual cortex are thereby avoided. The model consists of 338 neurones forming a sheet analogous to the cortex. The neurones are connected randomly to a retina of 19 cells. Nine different stimuli in the form of light bars were applied. The afferent connections were modified according to a mechanism of synaptic training. After twenty presentations of all the stimuli individual cortical neurones became sensitive to only one orientation. Neurones with the same or similar orientation sensitivity tended to appear in clusters, which are analogous to cortical columns. The system was shown to be insensitive to a background of disturbing input excitations during learning. After learning it was able to repair small defects introduced into the wiring and was relatively insensitive to stimuli not used during training.     

Computer evaluation of cat brain activation by means of striate cortex ecog

We analyzed striate cortex electrocorticograms of 12 cats in the following states: at rest with eyes closed and with eyes open; after light electrical stimulation of the ears; drowsiness; opening of the eyes after drowsiness; narcotic sleep. Spectral and periodometric analyses of the ECOG revealed state-dependent differences in power spectra from cats in two frequency bands (2.8–5.0 and 13.8–20.8 Hz). It is suggested that the ratio of ECOG power spectra in these frequency bands can be used to evaluate brain activation in cats.Vilnius University, Lithuania. Translated from Neirofiziologiya, Vol. 24, No. 6, pp. 672–678, November–December, 1992.     

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.Neirofiziologiya/Neurophysiology, Vol. 27, No. 2, pp. 100–109, March–April, 1995.     

Morphological bases of suppressive and facilitative spatial summation in the striate cortex of the cat

In V1 of cats and monkeys, activity of neurons evoked by stimuli within the receptive field can be modulated by stimuli in the extra-receptive field (ERF). This modulating effect can be suppressive (S-ERF) or facilitatory (F-ERF) and plays different roles in visual information processing. Little is known about the cellular bases underlying the different types of ERF modulating effects. Here, we focus on the morphological differences between the S-ERF and F-ERF neurons. Single unit activities were recorded from V1 of the cat. The ERF properties of each neuron were assessed by area-response functions using sinusoidal grating stimuli. On completion of the functional tests, the cells were injected intracellularly with biocytin. The labeled cells were reconstructed and morphologically characterized in terms of the ERF modulation effects. We show that the vast majority of S-ERF neurons and F-ERF neurons are pyramidal cells and that the two types of cells clearly differ in the size of the soma, in complexity of dendrite branching, in spine size and density, and in the range of innervations of the axon collaterals. We propose that different pyramidal cell phenotypes reflect a high degree of specificity of neuronal connections associated with different types of spatial modulation.     

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 organization of double bouquet cells in monkey striate cortex

In previous publications we proposed a model of cortical organization in which the pyramidal cells of the cerebral cortex are organized into modules. The modules are centred around the clusters of apical dendrites that originate from the layer 5 pyramidal cells. In monkey striate cortex such modules have an average diameter of 23 μm and the outputs originating from the modules are contained in the vertical bundles of myelinated axons that traverse the deeper layers of the cortex. The present study is concerned with how the double bouquet cells in layer 2/3 of striate cortex relate to these pyramidal cell modules. The double bouquet cells are visualized with an antibody to calbindin, and it has been shown that their vertically oriented axons, or horse tails, are arranged in a regular array, such that there is one horse tail per pyramidal cell module. Within layer 2/3 the double bouquet cell axons run alongside the apical dendritic clusters, while in layer 4C they are closely associated with the myelinated axon bundles. However, the apical dendrites are not the principal targets of the double bouquet cell axons. Most of the neuronal elements post-synaptic to them are the shafts of small dendrites (60%) and dendritic spines, with which they form symmetric synapses. This regular arrangement of the axons of the double-bouquet cells and their relationship to the components of the pyramidal cells modules supports the concept that there are basic, repeating neuronal circuits in the cortex.     

Synaptic organization of the individual layers of field 4 of the cat cerebral cortex]

By means of electron microscopic method, synaptic organization of some layers in the field 4 of the cat brain cortex has been studied. It has been demonstrated that: a) synaptic organization of the cortex becoms more complex from superficual layers towards deeper ones; b) axospinous and axosomatic synapses have identical structure in all the cortical layers, while the structure of axodendritic synapses depends on their localization. A possible physiological estimation of the morphological data obtained has been carried out.     

Functional organization of afferent inputs of neurons of the cat somatic cortex

Responses of cortical neurons in the posterior sigmoid gyrus to stimulation of two points of the ventro-posterolateral nucleus were investigated in cats immobilized with D-tubocurarine. Some neurons responding to stimulation of one point of this nucleus with a latent period of 2.5–4 msec, were activated by stimulation of the other point after 10 msec or longer. Conditioning stimulation of one point facilitated or inhibited the response to test stimulation of the other point. The facilitatory effect was usually exhibited if the response latency exceeded 5 msec. It is concluded that a cortical input neuron for some afferent fibers is activated by other similar afferent fibers only after intracortical relay. The system of "input" cortical neurons is thus not only a structural, but also to some extent a functional, concept; under certain conditions an incoming afferent volley activates them only polysynaptically.     

The basal dendrites of Meynert cells in the striate cortex of the monkey

A study has been made of the basal dendrites of Meynert cells in the striate cortex of the macaque monkey in sections parallel to the pial surface impregnated by the Golgi technique. The longest basal dendrite observed extended up to 0.6 mm and the average length of the longest dendrite on each cell was about 0.28 mm. In general, the dendritic field was in the form of an ellipse with mean major and minor axes of 0.22 mm and 0.11 mm respectively, and encompassing an area of about 0.13 mm2. The directions of the major axes were perpendicular to the lunate sulcus in the sections adjacent to the lunate sulcus, and parallel to the horizontal meridian in sections taken from the region of the representation of the meridian, suggesting that the basal dendritic fields are orientated in parallel with the directions of the ocular dominance bands.     

The distribution of orientation of optimal stimuli for cells of striate cortex

The mechanism mediating the adaptation of cortical Area 17 oriented line detector cells is modeled. A novel form of environment and convergence property (which places a requirement on distribution of optimal stimuli) is utilized to show that classical concepts of synaptic efficiency loss due only to disuse are inadequate under the convergence property. A reasonable alternative is presented: a form of synaptic control which reduces synaptic efficiency at non-active synapses as a function of cell firing rate. We show that adequate solutions to our convergence property exist for members of this class. Simulations of this adequate mechanism indicate that under the very disjoint environment defined, small perturbations of the environment's distribution of stimuli may lead to large perturbations of the distribution of stimuli to which Area 17 cells are optimally responsive. A simulation indicates that this effect may be accentuated by a lateral interaction which causeslike cell optimal stimuli to form near each other in cortex; and the effect may be reduced by a lateral interaction which causes like cell optimal stimuli to not form near each other. A form of neurophysiological experiment is suggested for verification.     

Antisera to gamma-aminobutyric acid. III. Demonstration of GABA in Golgi-impregnated neurons and in conventional electron microscopic sections of cat striate cortex

Two methods are described for the immunocytochemical demonstration of immunoreactive gamma-aminobutyric acid (GABA) in the visual cortex of the cat, an area that contains several types of GABAergic neurons and requires combined methods for their characterization. The first method is illustrated by a representative example of a Golgi-impregnated and gold-toned interneuron of the "bitufted" type situated in layer VI and having an ascending axon. After recording the three-dimensional features of the cell, semithin (0.5 micron) sections of the perikaryon were cut and GABA was demonstrated in the cell body by the unlabeled antibody enzyme method. While immunocytochemistry was used to determine the probable transmitter of the neuron, Golgi-impregnation of the same cell was used to identify its neuronal type. Since aldehyde-osmium fixation was used, further electron microscopic (EM) analysis of the neuron's synaptic connections was possible. The second procedure demonstrated GABA in EM sections of aldehyde-osmium-fixed cortex using protein A-gold as an immunocytochemical marker. Immunoreactivity was found in certain neurons, dendrites, axons, and boutons forming type II synaptic contacts that from previous studies have been thought to be GABAergic. Thus ultrastructural analysis using optimal conditions can now be supplemented with the identification of the transmitter in the same section.     

Excitatory actions of GABA in the cortex

Little is known about how GABAergic inputs interact with excitatory inputs under conditions that maintain physiological concentrations of intracellular anions. Using extracellular and gramicidin perforated-patch recording, we show that somatic and dendritic GABA responses in mature cortical pyramidal neurons are depolarizing from rest and can facilitate action potential generation when combined with proximal excitatory input. Dendritic GABA responses were excitatory regardless of timing, whereas somatic GABA responses were inhibitory when coincident with excitatory input but excitatory at earlier times. These excitatory actions of GABA occur even though the GABA reversal potential is below action potential threshold and largely uniform across the somato-dendritic axis, and arise when GABAergic inputs are temporally or spatially isolated from concurrent excitation. Our findings demonstrate that under certain circumstances GABA will have an excitatory role in synaptic integration in the cortex.     

Two types of neuronal synchrony in monkey striate cortex

Peaks in more than 5000 spike train correlograms, obtained from monkey striate cortex, were measured. Earlier work had shown qualitatively that there are frequent prominent peaks having widths in a range around 50 ms, and narrower peaks less than about 7 ms wide. Here we demonstrate that the distribution of peak widths shows a dichotomy.