Non-stationarity of ocular dominance in cat striate cortex

Effects of selective pressure block of Y-type optic nerve fibers on the receptive-field properties of neurons in the striate cortex of the cat

In an aseptic operation under surgical anesthesia, one optic nerve of a cat was exposed and subjected to pressure by means of a special cuff. The conduction of impulses through the pressurized region was monitored by means of electrodes which remained in the animal after the operation. The pressure was adjusted to selectively eliminate conduction in the largest fibers (Y-type) but not in the medium-size fibers (X-type). The conduction block is probably due to a demyelination and remains complete for about 3 weeks. Within 2 weeks after the pressure-block operation, recordings were made from single neurons in the striate cortex (area 17, area V1) of the cat anesthetized with N2O/O2 mixture supplemented by continuous intravenous infusion of barbiturate. Neurons were activated visually via the normal eye and via the eye with the pressure-blocked optic nerve ("Y-blocked eye"). Several properties of the receptive fields of single neurons in area 17 such as S (simple) or C (complex) type of receptive-field organization, size of discharge fields, orientation tuning, direction-selectivity indices, and end-zone inhibition appear to be unaffected by removal of the Y-type input. On the other hand, the peak discharge rates to stimuli presented via the Y-blocked eye were significantly lower than those to stimuli presented via the normal eye. As a result, the eye-dominance histogram was shifted markedly towards the normal eye implying that there is a significant excitatory Y-type input to area 17. In a substantial proportion of area 17 neurons, this input converges onto the cells which receive also non-Y-type inputs. In one respect, velocity sensitivity, removal of the Y input had a weak but significant effect. In particular, C (but not S) cells when activated via the normal eye responded optimally at slightly higher stimulus velocities than when activated via the Y-blocked eye. These results suggest that the Y input makes a distinct contribution to velocity sensitivity in area 17 but only in C-type neurons. Overall, our results lead us to the conclusion that the Y-type input to the striate cortex of the cat makes a significant contribution to the strength of the excitatory response of many neurons in this area. However, the contributions of Y-type input to the mechanism(s) underlying many of the receptive-field properties of neurons in this area are not distinguishable from those of the non-Y-type visual inputs.

Areal influences on complex cells in cat striate cortex: stimulus-specificity of width and length summation

In single neurones recorded from the striate cortex of cats anaesthetized with N2O/O2/halothane, receptive field dimensions, length specificity and areal extent of drive were assessed for different classes of visual stimuli. Receptive fields were mapped as rectangular minimum response fields (MRFs). Spatial summation along the axis of preferred orientation was assessed: for moving bars whose length was varied (length summation); and for height variation of a square-wave grating patch against a uniform grey background, or a patch of moving texture against a stationary background of similar texture. In complementary tests a moving square-wave grating background was progressively occluded by a uniform grey foreground mask of variable height; or a mask of stationary texture of variable height progressively occluded a background of moving texture. In parallel measurements, the width of grating or textured patches or masks was varied whilst maintaining height constant. Broadly speaking, the areal influence of each class of stimulus was comparable, and distinct from extra-receptive field phenomena in evoking responses from within the receptive field, but not from surrounding areas. The masking paradigm provided the most sensitive measure of receptive field height and width. However, in some neurones length summation, the degree of end-stopping, and the directional bias depended critically on the stimulus configuration used. Length summation tended to be more dramatic for short bars than for gratings. Length summation for texture was significantly more pronounced than for an oriented bar in special and in intermediate complex neurones. By contrast, endstopping was typically less intense for gratings than for bars, and least pronounced for texture. Because of stimulus specificity, complex neurones assigned to particular functional subgroups on the basis of their response to oriented bars may exhibit quite different patterns of behaviour for other classes of stimuli.

Ocular dominance and disparity coding in cat visual cortex

The orientation selectivity, ocular dominance, and binocular disparity tuning of 272 cells in areas 17 and 18 of barbiturate-anesthetized, paralyzed cats were studied with automated, quantitative techniques. Disparity was varied along the axis orthogonal to each cell's best orientation. Binocular correspondence was established by means of a reference electrode positioned at the boundary of lamina A and A1 in the area centralis representation of the lateral geniculate nucleus. Measures were derived that expressed each cell's disparity sensitivity and best disparity and the shape and slope of its tuning curve. Cells were found that corresponded to categories described by previous authors ("disparity-insensitive," "tuned excitatory," "near," and "far" cells), but many others had intermediate response patterns, or patterns that were difficult to categorize. Quantitative analysis suggested that the various types belong to a continuum. No relationship could be established between a cell's best orientation and its ocular dominance or any aspect of its disparity tuning. There was no relationship between a cell's ocular dominance and its sensitivity to disparity. Ocular dominance and best disparity were related. As reported by others, cells with best disparities close to zero (the fixation plane) tended to have balanced ocularity, while cells with best disparities in the near or far range had a broad distribution of ocular dominance. Among cells with receptive fields near the vertical meridian, those preferring far disparities tended to be dominated by the contralateral eye, and those preferring near disparities by the ipsilateral eye. It is suggested that this relationship follows from the geometry of near and far images and the pattern of decussation in the visual pathway. There was a significant grouping of cells with similar best disparities along tangential electrode tracks. We believe that this grouping is due to the columnar organization for ocular dominance and the relationship between ocular dominance and best disparity. No evidence was found for a columnar segregation of disparity-sensitive and disparity-insensitive cells.

Binocularity in the visual cortex of the adult cat does not depend on the integrity of the corpus callosum

The importance of the corpus callosum for binocular interaction in areas 17 and 18 of the adult cat is still a matter of controversy, since its specific role in integrating information from the two eyes has been suggested by some and questioned by others. We have reanalyzed the problem by assessing binocular interaction for single neurons in areas 17 and 18 of adult cats submitted to section of the posterior two-thirds of the corpus callosum. In 5 cats this interhemispheric disconnection was performed from 10 days to 7 weeks before the electrophysiological recordings; in another cat callosal afferents to the recording sites were at first partially eliminated by an acute lesion of corresponding cortical zones in the other hemisphere, and thereafter completely interrupted by a posterior callosal section performed in the same recording session. Recordings were mainly aimed at the callosal zone of areas 17 and 18, which coincides with the border between these two areas and corresponds to visual field regions bordering the vertical meridian. Electrophysiological recordings were carried out in awake, unanesthetized animals in which all nociceptive pathways were previously interrupted by a midpontine pretrigeminal transection. The results indicate that the interhemispheric disconnection, whether acute or chronic, does not disrupt binocularity in areas 17 and 18; moreover, the analysis of the ocular dominance for binocular neurons did not reveal any imbalance between the inputs from the two eyes, since at all levels of eccentricity the majority of binocular neurons was equally activated by both eyes. Since in previous experiments on anesthetized cats, section of the corpus callosum apparently reduced binocular interaction in areas 17 and 18, we suggest that such an effect, which was lacking in our unanesthetized cats, was probably due to an interaction or summation between callosotomy and anesthesia.

Sensitivity of complex cells in cat striate cortex to relative motion

Sensitivity of 95 complex cells to relative motion between oriented bars and textured backgrounds was investigated monocularly in the striate cortex of lightly anesthetized, paralyzed cats. Cells were classified conventionally. Those in deep layers were either direction-selective, or strongly preferred one direction of motion, and responded well to background texture motion alone: backgrounds potentiated the response to the bar in the cell's preferred direction when moved in phase, or in the opposite direction when moved in antiphase; other combinations depressed the level of response compared with that for the bar alone. The majority of direction-selective or strongly direction-biased cells in superficial layers behaved similarly. The most interesting superficial-layer cells were bidirectional or weakly direction-biased, and recorded closer to the cortical surface than the direction-selective neurons. A majority showed preference for relative motion, some for antiphase, others for in-phase motion, regardless of the absolute direction of motion across the receptive field, which could not be accounted for on the basis of separate responses to bars and backgrounds alone. Three of the superficial-layer direction-selective cells also showed preference for antiphase relative motion. In a few complex cells from superficial laminae, backgrounds were either without influence on responses to oriented stimuli, or purely suppressive. Visual backgrounds against which objects are perceived are usually neither featureless nor motionless: the results suggest that most complex cells in striate cortex are sensitive to the context in which objects are seen and susceptible to relationships between objects and their backgrounds in relative motion.

Directional tuning interactions between moving oriented and textured stimuli in complex cells of feline striate cortex

In sixty-five complex cells recorded from striate cortex of lightly anaesthetized, paralysed cats we investigated directional selectivity for motion of oriented and textured stimuli, both alone and when moving simultaneously in the same direction and at the same velocity. Monocular comparisons were made over a range of velocities for the dominant eye in all cells, and for the other eye in fourteen instances. For oriented stimuli, response magnitude varied with velocity, but preferred directions(s) and sharpness of tuning remained constant. For background texture motion, directional selectivity was typically unimodal at low velocities, but became increasingly bimodal at high velocities: a trough of depressed response (in directions optimal for oriented stimuli) separated two progressively more widely disparate preferred directions. Preferred velocity and velocity bandpass were typically higher for texture than for bar motion. Directional tuning interactions revealed no important class- or layer-specific differences and were similar for each monocular input. Results for bar and texture combinations moving in unison could not be predicted from selectivity for each stimulus alone. At all velocities they closely resembled those for bar motion alone. Tuning curves for the combination stimulus were only marginally broader than those for oriented stimuli: much sharper and totally different in profile from those for texture. It is concluded that an oriented stimulus in motion induces potent blockade of complex-cell sensitivity to moving textured backgrounds. Complex cells insensitive to relative motion between objects and backgrounds (Hammond & Smith, 1982a, 1983b) may thus be excellent candidates for resolving motion of objects regardless of the context in which they are seen.

On the function of cell systems in area 18. Part II

In addition to the asymmetry of the spatial coupling and of the specific temporal combination of excitation and inhibition, the non-linearity is very pronounced in area 18. Taking the sequence of a linear operation and a stationary nonlinear characteristic as a model, the experimental findings can be systematized and cell classification specified which departs from the customary ones. The hypercomplex cell system probably originates in recurrent inhibition and leads to differentiation of the patterns along their contour line. Problems of cell classification and of the type of parallelism in the visual cortex are discussed.