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PubMed1996

Voltage-clamp measurement of visually-evoked conductances with whole-cell patch recordings in primary visual cortex.

Whole cell patch recordings have been realized in the primary visual cortex of the anesthetized and paralyzed cat, in order to better characterize input resistance and time constant of visual cortical cells in vivo. Measurements of conductance changes evoked by visual stimulation were derived from voltage clamp recordings achieved in continuous mode at two or more different subthreshold holding potentials. They show that the magnitude of the conductance increase can reach up to 300% of the mean conductance at rest. The observation of similar changes for the preferred and antagonist responses, when flashing ON and OFF, a test stimulus in pure ON and OFF subfields supports the hypothesis of a role for shunting inhibition in the spatial organization of simple receptive fields.

Animals↗
PubMed1992

Temporal-frequency tuning of direction selectivity in cat visual cortex.

Responses of 71 cells in areas 17 and 18 of the cat visual cortex were recorded extracellularly while stimulating with gratings drifting in each direction across the receptive field at a series of temporal frequencies. Direction selectivity was most prominent at temporal frequencies of 1-2 Hz. In about 20% of the total population, the response in the nonpreferred direction increased at temporal frequencies of around 4 Hz and direction selectivity was diminished or lost. In a few cells the preferred direction reversed. One consequence of this behavior was a tendency for the preferred direction to have lower optimal temporal frequencies than the nonpreferred direction. Across the population, the preferred direction was tuned almost an octave lower. In spite of this, temporal resolution was similar in the two directions. It appeared that responses in the nonpreferred direction were suppressed at low frequencies, then recovered at higher frequencies. This phenomenon might reflect the convergence in visual cortex of lagged and nonlagged inputs from the lateral geniculate nucleus. These afferents fire about a quarter-cycle apart (i.e. are in temporal quadrature) at low temporal frequencies, but their phase difference increases to a half-cycle by about 4 Hz. Such timing differences could underlie the prevalence of direction-selective cortical responses at 1 and 2 Hz and the loss of direction selectivity in many cells by 4 or 8 Hz.

Animals↗
PubMed1980

[Linear and nonlinear properties of cat visual cortex receptive fields].

Impulse responses of the simple fields cat visual cortex were found to be modulated by gratings passing the field. The complex fields proved to be of three types: with modulated responses, unmodulated responses, and with modulated responses against unmodulated background. Amplitude-phase characteristic (APC) measured were inverse Fourier transformed to obtain the field's weighting function. Simultaneously the APC was reconstructed from the responses to edges and bars, with the use of the Fourier transform. Cross-comparison of the reconstructed APC and the WF showed that a RF has some linear properties but, strictly considered, is a non-linear system. Simple fields display the largest degree of linearity. The more complex field is the greater departures from linearity. As linear methods are inadequate for dealing with cortical RFs, their identification was performed in model experiments on a computer. The evidence obtained suggest that the RFs form a system of operators which perform the expansion of the image in non-classical pattern. Such an expansion can be termed quasi-Fourier-description.

Animals↗
PubMedDate not supplied

[Comparative analysis of the latent periods of adjacent neurons in microareas of the visual cortex].

Latencies of responses to heteromodal stimuli were determined for neurones of the cat visual cortex recorded with different amplitudes of action potentials (AP). Latencies of responses of three neighbouring neurones recorded with one microelectrode were compared. It was shown that in the case of light stimulation, the neurone recorded with a smaller AP amplitude, as a rule entered the reaction before the neurone recorded with a greater AP amplitude; in response to acoustic stimulation, the reverse relationship was observed. In most of the microareas in which response latencies of the neighbouring cells differed slightly, crosscorrelograms revealed action of "the common input". Comparative analysis has shown that an afferent wave excites each of the microarea cells separately.

Action Potentials↗
PubMed1987

Immunohistochemical localization of calcium-binding proteins, parvalbumin and calbindin-D 28k, in the adult and developing visual cortex of cats: a light and electron microscopic study.

In the cat primary visual cortex, we investigated with immunohistochemical techniques the developmental changes in the cellular and subcellular localization of the Ca2+-binding proteins parvalbumin (PV) and calbindin-D 28K (CBP), in order to determine whether there is a correlation between the expression of Ca2+-dependent processes and the time course of the critical period for use-dependent plasticity. On the 54th day of gestation and at 1 week postnatally, both calcium-binding proteins were present only in a subpopulation of neurons in layers V and VI. During subsequent maturation, the number of PV(+) and CBP(+) neurons increased significantly and labeled cells were detected in more superficial layers. Moreover, the homogeneous labeling of some CBP(+) neurons in layers IV to VI decreased and changed to a punctate pattern. In adult cats PV(+) neurons were evenly distributed throughout layers II to VI, whereas CBP(+) neurons were concentrated in layers II/III. Only a few immunoreactive cells had morphological features characteristic of pyramidal cells; the large majority were nonpyramidal. Electron microscopy confirmed the presence of PV- and CBP-reaction product within the perikarya, axons, and dendrites of labeled cells. It was associated preferentially with microtubules, postsynaptic densities, and intracellular membranes. Immunoreactive neurons received immunonegative asymmetric synapses on their dendritic shafts and made symmetric synaptic contacts with labeled and unlabeled somata and with unlabeled dendritic shafts. The large number and widespread distribution of immunoreactive neurons implies that PV and CBP play an important role in the regulation of calcium-dependent processes in the visual cortex. Furthermore, the developmental redistribution of PV and CBP points to changes in the organization of Ca2+-dependent processes during maturation.

Aging↗
PubMed1981

[Role of the contralateral cortex on the receptive field properties in the visual cortex of cats].

The aim of this series of experiments was to evaluate the receptive field properties of visual cells receiving part of their input the corpus callosum. Normal (control) and chiasma sectioned cats were recorded using conventional methods. The recording sites were the 17-18 border and the lateral suprasylvian (LS) cortex. The results indicated (a) the ocular dominance distribution was shifted towards the ipsilateral eye in the split chiasma cats; (b) orientation tunning and/or directional specificity were identical for the two eyes; (c) R.F. positions of binocular cells were also similar for each eye and were clustered near the vertical meridian, which they sometimes straddled; (d) R.F. sizes were larger in L.S. than in primary visual cortex but generally of equal dimensions for each eye. The results are interpreted with respect to the various functions which have been postulated for the corpus callosum.

Animals↗
PubMed1994

Double orientation tuning in the cat visual cortex units.

Orientation tuning of 271 neurons of the cat visual cortex (area 17) was studied with a light bar flashing in the receptive field. Under different conditions, 27-57% of units were found to have double-orientation tuning: they demonstrated the main preferred orientation and an additional preferred orientation. The statistical reliability and reproducibility of additional preferred orientation were shown. The quality of orientation tuning in the second maximum did not differ statistically from the first one. The angle between preferred orientation and additional preferred orientation was either 90 degrees (29% of cases) or an acute one (60.1 +/- 3.1 degrees, 71% of cases). The ratio of discharge frequency in responses to additional preferred orientation and preferred orientation was equal to 0.74 +/- 0.05. Neurons with double-orientation tuning clearly preferred 67 degrees and 157 degrees, while monomodal units preferred 0 degrees and 90 degrees. Probability of the double-tuning increased under bar lengths of near 3 degrees and near 10 degrees and with increase of stimulus/background contrast. At the same time some neurons displayed double-orientation tuning only with relatively low stimulus/background contrast. The proportion of units with double-orientation tuning was lowered by about 1.5-times under general Nembutal narcotization as compared with local anesthesia of the animal. In about one-third of units simultaneous stimulation by two flashing lines crossing in the receptive field center under an angle specific for the cell, evoked a response from 1.5 to four times larger than to the preferred orientation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Contributions of individual layer 2-5 spiny neurons to local circuits in macaque primary visual cortex.

We studied excitatory local circuits in the macaque primary visual cortex (VI) to investigate their relationships to the magnocellular (M) and parvocellular (P) streams. Sixty-two intracellularly labeled spiny neurons in layers 2-5 were analyzed. We made detailed observations of the laminar and columnar specificity of axonal arbors and noted correlations with dendritic arbors. We find evidence for considerable mixing of M and P streams by the local circuitry in VI. Such mixing is provided by neurons in the primary geniculate recipient layer 4C, as well as by neurons in both the supragranular and infragranular layers. We were also interested in possible differences in the axonal projections of neurons with different dendritic morphologies. We found that layer 4B spiny stellate and pyramidal neurons have similar axonal arbors. However, we identified two types of layer 5 pyramidal neuron. The majority have a conventional pyramidal dendritic morphology, a dense axonal arbor in layers 2.4B, and do not project to the white matter. Layer 5 projection neurons have an unusual "backbranching" dendritic morphology (apical dendritic branches arc downward rather than upward) and weak or no axonal arborization in layers 2-4B, but have long horizontal axonal projections in layer 5B. We find no strong projection from layer 5 pyramidal neurons to layer 6. In macaque V1 there appears to be no single source of strong local input to layer 6; only a minority of cells in layers 2-5 have axonal branches in layer 6 and these are sparse. Our results suggest that local circuits in V1 mediate interactions between M and P input that are complex and not easily incorporated into a simple framework.

Animals↗
PubMed1991

Functional specificity of a long-range horizontal connection in cat visual cortex: a cross-correlation study.

Anatomical investigations of the visual cortex revealed a regular set of interlaminar connections and long-range horizontal connections. An important component of the intrinsic cortical circuit is the projection from layer 5 to layer 6 over long horizontal distances. Previous work has shown that when layer 5 is locally inactivated, layer 6 cells lose their response in a segment of their receptive fields corresponding to the blocked area in layer 5. It has therefore been proposed that the long receptive fields characteristic of layer 6 cells might be generated by concatenating layer 5 cells with similar orientation preferences. In the present study, we used cross-correlation analysis to examine both source and target cells of the interlaminar connection from layer 5 to layer 6. We found correlated firing between cells separated by up to 4.2 mm, the longest horizontal distance studied. The occurrence of correlated firing depended on the functional properties and on the topographic position of the cells in layer 5 and layer 6. Interactions were only observed if the cells had matching orientation tuning and similar eye preference and if the layer 5 cells lay within the summation area of the layer 6 cells. Both simple and complex cells in layer 6 fired in synchrony with layer 5 cells. In layer 5, mainly standard complex cells, but very few special complex cells, participated in correlated firing with layer 6 cells. These results suggest that cells in layer 6 receive their input from cooriented, coaxially aligned standard complex cells in layer 5. This topographic arrangement and the length summation properties of standard complex cells in layer 5 are well suited to generate long receptive fields in layer 6. Thus, our experiments provide evidence for the functional specialization of a particular component of cortical circuitry.

Animals↗
PubMed1999

Effects of blocking non-N-methyl-D-aspartate receptors on visual responses of neurons in the cat visual cortex.

To elucidate the function of non-N-methyl-D-aspartate types of glutamate receptors in the primary visual cortex of the adult cat, we studied the effects of the iontophoretically applied glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione and D-amino-5-phosphonovalerate. Antagonists were applied with ejecting currents that selectively blocked non-N-methyl-D-aspartate receptors. Among 93 cells in which stable recordings were obtained, 6-cyano-7-nitroquinoxaline-2,3-dione reduced the visual response in all cells. The average response magnitude during 6-cyano-7-nitroquinoxaline-2,3-dione administration was reduced to 11.7% of the control (average ejecting current: 41.2 nA). The effect of 6-cyano-7-nitroquinoxaline-2,3-dione was obvious throughout all cortical layers. The effect of D-amino-5-phosphonovalerate on the visual response was tested in 14 cells and it was also effective in blocking the visual response: the average response magnitude during D-amino-5-phosphonovalerate administration was 45.0% of the control (average ejecting current: 41.4 nA). The effect of 6-cyano-7-nitroquinoxaline-2,3-dione on the response was compared in individual cells at both high and low firing rates in order to determine whether a differential effect exists on the level of firing activity of cells due to secondary inactivation of voltage-dependent N-methyl-D-aspartate receptors. However, no indication of response dependency on firing rate was seen with 6-cyano-7-nitroquinoxaline-2,3-dione. We suggest that excitatory transmission at the geniculocortical and corticocortical synapses seems to be strongly dependent on non-N-methyl-D-aspartate receptors throughout the primary visual cortex of the adult cat, and that both non-N-methyl-D-aspartate and N-methyl-D-aspartate type glutamate receptors function additively.

2-Amino-5-phosphonovalerate↗
PubMed1995

Developmental expression of the immediate early gene EGR-1 mirrors the critical period in cat visual cortex.

Immediate early gene (IEG) expression in the central nervous system is thought to play a role in coupling extracellular stimulation with the transcriptional events responsible for long-term functional changes in neurons. The goal of the present study was to determine the postnatal developmental profile of EGR-1 protein (also termed zif268, Krox-24, NGFI-A) expression across the layers of cal visual cortex and relate it to the state of visual cortical development and plasticity. Using a polyclonal antibody, EGR-1 immunoreactivity was studied in animals of various postnatal ages (from 0.5 week to adult). In very young animals (0.5 weeks), EGR-1 positive cells were restricted to deep cortical layers (layer VI/Subplate). With the increasing age, EGR-1 immunoreactivity spread across layers of the visual cortex in an inside-outside manner, and by 5 weeks of age, EGR-1 protein was highly expressed in all layers. EGR-1 expression remained high until approximately 10 weeks of age and then gradually began to decline in layer IV with little change in supra- and infragranular layers. In adult animals, EGR-1 was located predominantly in the layers above and below layer IV. This pattern of EGR-1 expression in developing cat visual cortex has both temporal and laminar similarities with the development of visual cortical connectivity, with the development of orientation selective receptive field properties, and with the level of visual cortical plasticity, suggesting an involvement of EGR-1 expression in these processes.

Animals↗
PubMed1986

The binocular organization of complex cells in the cat's visual cortex.

We have studied the manner by which inputs from the two eyes are combined in complex cells of the cat's visual cortex. The stimuli are drifting sinusoidal gratings presented dichoptically at optimal spatial frequency and orientation. The relative phase between the gratings for left and right eyes is varied over 360 degrees. Approximately 40% of complex cells show phase-specific binocular interaction where response amplitudes vary depending on the relative phase of the gratings shown to the two eyes. This interaction is similar to that observed for most simple cells. We devised a test to examine whether the phase-specific interaction in complex cells results from linear convergence of neural signals at subunits of the receptive fields. The data from this test are consistent with a linear combination model. The phase-specific binocular interaction data from complex cells imply that the optimal relative phase of the receptive field subunits is closely matched. Another type of complex cell, approximately 40% of the total, could be driven through either eye, but exhibited non-phase-specific responses to dichoptically presented gratings. This type of interaction is found only in complex cells. Binocularly non-phase-specific complex cells may have subunits whose optimal relative phases are random or monocular. The division of complex cells into these two major groups (binocularly phase specific and non-phase specific) is independent of whether they are standard or special complex-cell types. A small proportion (8%) of complex cells that appear monocular by alternate tests of each eye show a purely inhibitory influence from the silent eye. This inhibition is not generally dependent on the relative phase of the gratings. Unlike simple cells, complex cells are not a homogeneous group. However, nearly half of complex cells show phase-specific binocular interaction that is probably the result of linear convergence. Combined with the results from simple cells, the majority of binocular interaction in the striate cortex may be accounted for by linear summation of neural signals from each eye. This provides a simplified view of the nature of binocular interaction in the visual cortex.

Animals↗
PubMed1999

Spatial attention affects brain activity in human primary visual cortex.

Functional MRI was used to test whether instructing subjects to attend to one or another location in a visual scene would affect neural activity in human primary visual cortex. Stimuli were moving gratings restricted to a pair of peripheral, circular apertures, positioned to the right and to the left of a central fixation point. Subjects were trained to perform a motion discrimination task, attending (without moving their eyes) at any moment to one of the two stimulus apertures. Functional MRI responses were recorded while subjects were cued to alternate their attention between the two apertures. Primary visual cortex responses in each hemisphere modulated with the alternation of the cue; responses were greater when the subject attended to the stimuli in the contralateral hemifield. The attentional modulation of the brain activity was about 25% of that evoked by alternating the stimulus with a uniform field.

Attention↗
PubMed1991

EEG alpha-wave in the visual cortex: check of the hypothesis of the scanning process.

In computer-controlled experiments the recognition by seven human observers of tachistoscopically presented geometrical figures of different size (from 0.5 to 9 angular degrees) or of different eccentricity (from 3 up to 16 degrees) in the visual field was studied. The onset of figures presentation coincided with different phases of the EEG alpha-wave in the occipital region. According to the criterion of an increase of recognition probability, an inverse dependence was revealed between the distance of the figures contour from the gaze (up to 9 degrees) and the succession of phases of alpha-wave. Small or more centrally localized figures were significantly better recognized when presented at relatively earlier phases of EEG alpha-wave, while bigger or relatively more peripherally localized figures - at earlier phases. At 16 degrees form the gaze no reliable dependence of recognition on the alpha-wave phases was revealed. The data obtained are discussed in connection with Pitts and McCulloch (1947) hypothesis about a periodical (with alpha-wave frequency) scanning wave spreading over the visual cortex. Possibility of a synchronous excitability fluctuation in the whole visual cortex with alpha-rhythm frequency that imitated the spreading process is also discussed. Data obtained and simulation of the mentioned possibilities confirmed the first explanation and thus confirmed Pitt's and McCulloch's ideas on the EEG alpha-wave as a reflection of the scanning process in the visual cortex.

Adult↗
PubMed1979

[Squirrel visual cortex neurons selective for contour orientation].

The receptive field organization of orientation-selective neurons was studied in the squirrel visual cortex. Neurons with mutual inhibiting on- and off-areas of the receptive field, partially and completely overlapping excitatory and inhibitory mechanisms were observed. Neurons of the second group are the most typical. They reveal orientation selectivity if the stimuli are in the excitatory area of the receptive field, the inhibitory areas outside the excitatory area sharpen the selectivity. It is supposed that no obvious differentiation between simple and complex neurons exist in the squirrel visual cortex.

Animals↗
PubMed2006

Always returning: feedback and sensory processing in visual cortex and thalamus.

Feedback projections are an integral part of the mammalian visual system. Although it is tempting to relegate them to a subsidiary role in visual processing, because their supposed latency and lag might appear to be unfavourable for an involvement in fast processing, this is a dangerous simplification. Certainly for the world in motion, feedback from higher motion areas can influence the transfer of ascending input when, or even before, the input arrives. Here, we consider the circuit formed by layer 6 feedback cells in the visual cortex and how this straddles the retinothalamic and thalamocortical transfer of visual input. We discuss its links to feedback from the cortical motion area MT (V5), and suggest that motion perception involves a dynamic interplay between MT, V1 and the thalamus. This review is part of the TINS special issue on The Neural Substrates of Cognition.

Animals↗
PubMed2000

Seeing beyond the receptive field in primary visual cortex.

Recent studies on the response properties of neurons in primary visual cortex emphasize the dynamics and the complexities of facilitatory and suppressive interactions between the receptive field center and surrounding areas of visual space. These observations raise new questions about the circuitry responsible for receptive field surround effects and their contribution to visual perception.

Animals↗
PubMed1985

Organization of the rostral thalamus in the rat: evidence for connections to layer I of visual cortex.

The present study demonstrates the organization of a thalamocortical projecting system which terminates within layer I of the visual cortex in the hooded rat. Horseradish peroxidase (HRP) injections restricted to layer I resulted in retrograde labeling of large and medium-sized multipolar and fusiform neurons that are located within the ventromedial (VM) nucleus and a dorsomedial subunit of the ventral anterolateral nucleus (VAL). Retrograde cellular labeling also occurs within the anteromedial nucleus (AM) following these injections. After restriction of HRP injections to layer I, peroxidase labeling was not found within neurons of the classically defined intralaminar system, i.e., central medial, paracentral, and central lateral nuclei, or within the rostral continuations of the intralaminar system. Since the VM, dorsomedial VAL, and AM nuclei are directly adjacent to portions of the internal medullary lamina, we refer to this amalgam of rostral thalamic nuclei that project to layer I as the "paralaminar" system. We also provide cytoarchitectonic criteria that can be used to distinguish three separate subdivisions within the VAL complex, including that portion of the VAL which is part of the "paralaminar" system. In contrast, when control injections of WGA-HRP are placed within either the cellular supragranular or infragranular layers of the visual cortex, no appreciable number of neurons are labeled within the VM, VAL, or AM.

Animals↗