Specialized receptive fields of the cat's retina

Organization, Function, and Development of the Mouse Retinogeniculate Synapse

Visual information is encoded in distinct retinal ganglion cell (RGC) types in the eye tuned to specific features of the visual space. These streams of information project to the visual thalamus, the first station of the image-forming pathway. In the mouse, this connection between RGCs and thalamocortical neurons, the retinogeniculate synapse, has become a powerful experimental model for understanding how circuits in the thalamus are constructed to process these incoming lines of information. Using modern molecular and genetic tools, recent studies have suggested a more complex circuit organization than was previously understood. In this review, we summarize the current understanding of the structural and functional organization of the retinogeniculate synapse in the mouse. We discuss a framework by which a seemingly complex circuit can effectively integrate and parse information to downstream stations of the visual pathway. Finally, we review how activity and visual experience can sculpt this exquisite connectivity.

Receptive Field Properties of Koniocellular On/Off Neurons in the Lateral Geniculate Nucleus of Marmoset Monkeys

The koniocellular (K) layers of the primate dorsal lateral geniculate nucleus house a variety of visual receptive field types, not all of which have been fully characterized. Here we made single-cell recordings targeted to the K layers of diurnal New World monkeys (marmosets). A subset of recorded cells was excited by both increments and decrements of light intensity (on/off-cells). Histological reconstruction of the location of these cells confirmed that they are segregated to K layers; we therefore refer to these cells as K-on/off cells. The K-on/off cells show high contrast sensitivity, strong bandpass spatial frequency tuning, and their response magnitude is strongly reduced by stimuli larger than the excitatory receptive field (silent suppressive surrounds). Stationary counterphase gratings evoke unmodulated spike rate increases or frequency-doubled responses in K-on/off cells; such responses are largely independent of grating spatial phase. The K-on/off cells are not orientation or direction selective. Some (but not all) properties of K-on/off cells are consistent with those of local-edge-detector/impressed-by-contrast cells reported in studies of cat retina and geniculate, and broad-thorny ganglion cells recorded in macaque monkey retina. The receptive field properties of K-on/off cells and their preferential location in the ventral K layers (K1 and K2) make them good candidates for the direct projection from geniculate to extrastriate cortical area MT/V5. If so, they could contribute to visual information processing in the dorsal ("where" or "action") visual stream.SIGNIFICANCE STATEMENT We characterize cells in an evolutionary ancient part of the visual pathway in primates. The cells are located in the lateral geniculate nucleus (the main visual afferent relay nucleus), in regions called koniocellular layers that are known to project to extrastriate visual areas as well as primary visual cortex. The cells show high contrast sensitivity and rapid, transient responses to light onset and offset. Their properties suggest they could contribute to visual processing in the dorsal ("where" or "action") visual stream.

The receptive fields of cat retinal ganglion cells in physiological and pathological states: where we are after half a century of research

Studies on the receptive field properties of cat retinal ganglion cells over the past half-century are reviewed within the context of the role played by the receptive field in visual information processing. Emphasis is placed on the work conducted within the past 20 years, but a summary of key contributions from the 1950s to 1970s is provided. We have sought to review aspects of the ganglion cell receptive field that have not been featured prominently in previous review articles. Our review of the receptive field properties of X- and Y-cells focuses on quantitative studies and includes consideration of the function of the receptive field in visual signal processing. We discuss the non-classical as well as the classical receptive field. Attention is also given to the receptive field properties of the less well-studied cat ganglion cells-the W-cells-and the effect of pathology on cat ganglion cell properties. Although work from our laboratories is highlighted, we hope that we have given a reasonably balanced view of the current state of the field.

Visual motion detection in man is governed by non-retinal mechanisms

It is generally assumed that there is no sizable proportion of motion detectors in the primate retina. To test this specifically for humans, visual evoked potentials (VEPs) and electroretinograms (ERGs) were recorded simultaneously to visual motion onset (9.3 degrees /s) of an expanding or contracting 'dartboard'. The degree of motion-specific responses in cortex and retina was assessed by testing the direction specificity of motion adaptation with three conditions in a fully balanced paradigm: motion-onset potentials were measured after adaptation to: (1) a stationary pattern; (2) motion in the same direction as the test stimulus; and (3) motion in the opposite direction. Motion-onset responses in the VEP were dominated by the typical N2 at 150 ms, in the ERG by a positivity at 70 ms. Onset of contraction or expansion evoked virtually identical VEP and ERG responses (P>0.5). Motion adaptation produced strong direction-specific effects in the VEP (P<0.05), but not in the ERG (P=0.58): In the adapting and non-adapting direction the VEP (N2) was reduced by 75 and 50% (P<0.001), the ERG by 32 and 26% (P<0.01 and 0.05), respectively. The striking difference of the direction-specificity of motion adaptation between cortex and retina suggests that in humans the vast majority of motion-specific processing occurs beyond the retinal ganglion cells.

Spatial receptive-field structure of cat retinal W cells

We have used frequency-domain methods to characterize the spatial receptive-field structure of cat retinal W cells. For most ON- and OFF-center tonic and phasic W cells, measurements of responsivity to drifting gratings at various spatial frequencies could be adequately described by a difference-of-Gaussians (DOG) function, consistent with the presence of center and surround mechanisms that are approximately Gaussian in shape and whose signals are combined additively. Estimates of the responsivity of the center mechanisms of tonic and phasic W cells were similar, but both were significantly lower than the corresponding values for X or Y cells. The width of the center mechanisms of tonic W cells, phasic W cells, and Y cells did not differ significantly from each other, but all were significantly larger than the width of X-cell centers. Surround parameters did not vary significantly among the four groups of ganglion cells. Measurements of contrast gain in both tonic and phasic W cells gave values that were significantly lower than in X or Y cells. Virtually all of the phasic W cells in our sample displayed evidence of spatial non-linearities in their receptive fields, in the form of either d.c. responses to drifting sine-wave gratings or second harmonic responses to counterphased gratings. The spatial resolution of the mechanism underlying these nonlinearities was typically higher than that of the center mechanism of these cells. Most tonic W cells exhibited linear spatial summation, although a subset gave strong second harmonic responses to counterphased gratings. Spatial-responsivity measurements for most ON-OFF and directionally selective W cells were not adequately described by DOG functions. These cells did, however, show evidence of spatial nonlinearities similar to those seen in phasic W cells. Suppressed-by-contrast cells gave both modulated and unmodulated responses to drifting gratings which both appeared to involved rectification, but which differed from each other in both spatial resolution and contrast gain. These data confirm earlier reports that the receptive fields of tonic and most ON- or OFF-center phasic W cells appear to include classical center and surround mechanisms. However, the receptive fields of some phasic cells, as well as ON-OFF and directionally selective W cells may have quite different structures. Our results also suggest that phasic, ON-OFF, directionally selective, suppressed-by-contrast, and a subset of tonic W cells may all receive nonlinear inputs with characteristics similar to those described in the receptive fields of retinal Y cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Early dendritic outgrowth of primate retinal ganglion cells

The pattern of dendritic stratification of retinal ganglion cells in the fetal monkey (Macaca mulatta) was examined using horseradish peroxidase and retinal explants. Ganglion cells in the rhesus monkey are born between embryonic day (E) 30-70 (LaVail et al., 1983). At E60, E67, and E68, approximately 50% of all ganglion cells within the central 3.0 mm of the retina had dendritic arbors that were unistratified within the inner plexiform layer (IPL), while the remaining 50% had bistratified arbors. Unistratified cells had relatively flat arbors that ramified within a restricted portion of the IPL. In contrast, bistratified cells had one portion of the arbor that branched in the inner half of the IPL and a second portion that branched in the outer half of the IPL. Relatively few bistratified cells were encountered in the central 1.0 mm of the retina but were more numerous with increasing eccentricity. At E81, E90, and E110, the dendritic arbors of ganglion cells increased in both area and complexity, but occupied a relatively small percentage of the total depth of the IPL. The bistratified cells encountered at these fetal ages were typically located in the far retinal periphery. Between E125-E140, the dendritic arbors of individual ganglion cells increased in area and depth to occupy a greater proportion of the total IPL than at earlier fetal ages. These observations suggest that ganglion cells in the macaque undergo at least three stages of dendritic stratification: (1) an initial period of dendritic growth during which the cells have either unistratified or bistratified dendritic arbors; (2) a loss of the majority of bistratified cells through cell death or remodeling of the arbor; and (3) growth or expansion of the arbor to occupy a greater percentage of the total depth of the IPL. The first two stages are similar to recent observations in the fetal cat (Maslim & Stone, 1988) with the exception that dendritic development in the primate lacks an initial diffuse ingrowth to the IPL. Additionally, primate ganglion cells undergo a third stage of dendritic growth in late fetal development during which the arbor occupies a greater proportion of the depth of the IPL.

Retinal direction-sensitive input to the accessory optic system: an in vitro approach with behavioral relevance

Retinal application of gamma-aminobutyric acid (GABA) antagonists block direction-sensitive (DS) responses in turtle in two ways: (1) the selectivity of DS retinal ganglion cells in vitro, and (2) the eye's ability to track the direction of full field image motion. The experiments described below demonstrate that an important locus for retinal slip computation by the accessory optic system (AOS) occurs in the retina. Visual responses were measured physiologically and behaviorally from turtles which had their telencephalon removed. Physiological responses to visual field movement were recorded in the AOS using an in vitro brain preparation. DS responses of single cells were blocked by intravitreal application of bicuculline. The behavioral approach was to measure optokinetic nystagmus (OKN) in lesioned animals. OKN occurred in the absence of the telencephalon, yet was disrupted following an intravitreal injection of bicuculline. Thus, both experimental approaches showed that DS processing exists without the telencephalon, yet is disrupted by GABA antagonists applied to the retina.

Simulation of movement detection by direction-selective ganglion cells in the rabbit and squirrel retina

A veto-gate model of movement detection by direction-selective ganglion cells in the vertebrate retina, first proposed by Barlow and Levick (1965), provides the basis for a model described in this study. The model is a simple network consisting basically of (1) two subunits that have receptive fields with a center-surround organization and an adaptational gain control, (2) a lateral inhibitory pathway, (3) a site of nonlinear interaction, followed by (4) a leaky temporal integrator. The model is tested by comparing its basic properties to those reported in the physiological literature on rabbit and squirrel direction-selective retinal ganglion cells. It is shown that the physiological findings on sensitivity to flashes, moving spots or slits, and phi-movement stimuli, can be mimicked quite well by our model. Similarities between the component processes of the subunits and known retinal processes are pointed out. The simulation studies shed a new light on some of the known properties and suggest several new, more revealing, physiological experiments. Such experiments are necessary to develop a full specification of this type of model and to fix more parameter values than is possible at present. Results of some critical experiments are predicted to enable physiologists to falsify or corroborate the model. The simulation studies also help to distinguish use from abuse of this type of model in explanations of psychophysical findings. For example, neither the most complete Barlow-Levick detector nor any stripped-down versions that retain a temporally extended lateral inhibition (which is essential to mimick the physiological findings), respond well to moving random-pixel arrays.

Responses to sinusoidal gratings of two types of very nonlinear retinal ganglion cells of cat

Perhaps 35% of all of the ganglion cells of the cat do not have classical center-surround organized receptive fields. This paper describes, quantitatively, the responses of two such cell types to stimulation with sinusoidal luminance gratings, whose spatial frequency, mean luminance, contrast, and temporal frequency were varied independently. The patterns were well-focused on the retina of the anesthetized and paralyzed cat. In one type of cell, the maintained discharge was depressed or completely suppressed when a contrast pattern was imaged onto the receptive field (suppressed-by-contrast cell). In the other type of cell, the introduction of a pattern elicited a burst of spikes (impressed-by-contrast cell). When stimulated with drifting gratings, the cell's mean rate of discharge was reduced (suppressed-by-contrast cell) or elevated (impressed-by-contrast cell) over a limited band of spatial frequencies. There was no significant modulated component of response. The reduction in mean rate of suppressed-by-contrast cells caused by drifting gratings had a monotonic dependence on contrast, a relatively low-pass temporal-frequency characteristic and was greater under photopic than mesopic illuminance. If grating of spatial frequency, that when drifted evoked a response from these cells, were instead held stationary and contrast-reversed, the mean rate of a suppressed-by-contrast cell was also reduced and that of an impressed-by-contrast cell increased. But, for contrast-reversed gratings, the discharge contained substantial modulation at even harmonic frequencies, the largest being the second harmonic. The amplitude of this second harmonic did not depend on the spatial phase of the grating, and its dependence on spatial frequency, at least for suppressed-by-contrast cells, was similar to that of the reduction in mean rate of discharge. Our results suggest that the receptive fields of suppressed-by-contrast and impressed-by-contrast cells can be modeled with the general form of the nonlinear subunit components of Hochstein and Shapley's (1976) Y cell model.

Time course of stratification of the dendritic fields of ganglion cells in the retina of the cat

The inner plexiform layer (IPL) of the retina has been shown by previous workers to comprise a number of sublayers (sublaminae or strata), each containing a distinct component of its circuitry. Using horseradish peroxidase applied to cultured whole retinas, we have observed the segregation of the dendrites of ganglion cells of the cat retina into two sublayers of the IPL. These sublayers appear to correspond to the a and b sublaminae described in studies of the adult IPL. As the dendritic fields of ganglion cells form, in mid-gestation, they are diffuse, spreading through the ganglion cell and inner plexiform layers. A few weeks before birth the dendrites become restricted to the IPL, but it is not until after birth, between P(postnatal day)2 and P5, that they segregate into inner and outer sublayers of the IPL. The process of segregation may involve the loss or 'pruning' of excess dendrites formed in 'wrong' sublayers. The segregation of dendrites into sublayers occurs concurrently with the formation of synapses by bipolar cells and may be induced by contacts made by bipolar cells onto the dendrites of ganglion cells.

Neural interactions mediating the detection of motion in the retina of the tiger salamander

The neural circuitry underlying movement detection was inferred from studies of amacrine cells under whole-cell patch clamp in retinal slices. Cells were identified by Lucifer yellow staining. Synaptic inputs were driven by "puffing" transmitter substances at the dendrites of presynaptic cells. Spatial sensitivity profiles for amacrine cells were measured by puffing transmitter substances along the lateral spread of their processes. Synaptic pathways were separated and identified with appropriate pre- and postsynaptic pharmacological blocking agents. Two distinct amacrine cell types were found: one with narrow spread of processes that received sustained excitatory synaptic current, the other with very wide spread of processes that received transient excitatory synaptic currents. The transient currents found only in the wide-field amacrine cell were formed presynaptically at GABAB receptors. They could be blocked with baclofen, a GABAB agonist, and their time course was extended by AVA, a GABAB antagonist. Baclofen and AVA had no direct affect upon the wide-field amacrine cell, but picrotoxin blocked a separate, direct GABA input to this cell. The narrow-field amacrine cell was shown to be GABAergic by counterstaining with anti-GABA antiserum after it was filled with Lucifer yellow. Its narrow, spatial profile and sustained synaptic input are properties that closely match those of the GABAergic antagonistic signal that forms transient activity (described above), suggesting that the narrow-field amacrine cell itself is the source of the GABAergic interaction mediating transient activity in the inner plexiform layer (IPL). Other work has shown a GABAB sensitivity at some bipolar terminals, suggesting a population of bipolars as the probable site of interaction mediating transient action. The results suggest that two local populations of amacrine cell types (sustained and transient) interact with the two populations of bipolar cell types (transient forming and nontransient forming). These interactions underlie the formation of the change-detecting subunits. We suggest that local populations of these subunits converge to form the receptive fields of movement-detecting ganglion cells.

Functional properties of models for direction selectivity in the retina

Poggio and Reichardt (Kybernetik, 13:223-227, 1973) showed that if the average response of a visual system to a moving stimulus is directionally selective, then this sensitivity must be mediated by a nonlinear operation. In particular, it has been proposed that at the behavioral level, motion-sensitive biological systems are implemented by quadratic nonlinearities (Hassenstein and Reichardt: Z. Naturforsch., 11b:513-524, 1956; van Santen and Sperling: J. Opt. Soc. Am. [A] 1:451-473, 1984; Adelson and Bergen: J. Opt. Soc. Am. [A], 2:284-299, 1985). This paper analyzes theoretically two nonlinear neural mechanisms that possibly underlie retinal direction selectivity and explores the conditions under which they behave as a quadratic nonlinearity. The first mechanism is shunting inhibition (Torre and Poggio: Proc. R. Soc. Lond. [Biol.], 202:409-416, 1978), and the second consists of the linear combination of the outputs of a depolarizing and a hyperpolarizing synapse, followed by a threshold operation. It was found that although sometimes possible, it is in practice hard to approximate the Shunting Inhibition and the Threshold models for direction selectivity by quadratic systems. For instance, the level of the threshold on the Threshold model must be close to the steady-state level of the cell's combined synaptic input. Furthermore, for both the Shunting and the Threshold models, the approximation by a quadratic system is only possible for a small range of low contrast stimuli and for situations where the rectifications due to the ON-OFF mechanisms, and to the ganglion cells' action potentials, can be linearized. The main question that this paper leaves open is, how do we account for the apparent quadratic properties of motion perception given that the same properties seem so fragile at the single cell level? Finally, as a result of this study, some system analysis experiments were proposed that can distinguish between different instances of the models.

Transmitters mediating inhibition of ganglion cells in the cat retina: iontophoretic studies in vivo

The effects of iontophoretically applied gamma-aminobutyrate (GABA) and glycine and their antagonists, bicuculline and strychnine on inhibition of retinal ganglion cells were studied in the optically intact eye of anaesthetised cats. Two kinds of inhibition were studied. One is the inhibition which occurs when a spot (a white spot for on-centre and a black spot for off-centre cells) which produces a maximal response from a cell, is removed from the receptive field centre, i.e. the central post-excitatory inhibition. The other is the inhibition which occurs when an annulus (a white annulus for on-centre and a black annulus for off-centre cells) which occupies the surround region of the receptive field, is presented, i.e. the surround inhibition. GABA enhanced and bicuculline blocked the post-excitatory inhibition at the receptive field centre and surround inhibition of on-centre but not off-centre cells regardless of whether the cell was 'sustained' or 'transient' type. On the other hand, glycine enhanced and strychnine blocked the post-excitatory inhibition at the receptive field centre and surround inhibition of off-centre but not on-centre cells, regardless of whether the cell was 'sustained' or 'transient' type. Inhibition of on-centre cells, thus, appears to be mediated by GABA, whereas that of off-centre cells, by glycine regardless of whether the cells are 'sustained' or 'transient'. Possible existence of GABAergic and glycinergic amacrine cells making postsynaptic contact with on-centre and off-centre ganglion cells, respectively, is proposed. Other possible explanations are discussed.

Single unit receptive fields in rabbit primary binocular cortex

The receptive fields of 125 single units recorded from the binocular region of rabbit primary visual cortex have been analysed. The population of 43% radially symmetric, 23% directional, and 23% orientation selective units is similar to that of rabbit monocular visual cortex. The relative scarcity of orientation selective units and the absence of orientation columns differentiates rabbit from cat primary visual cortex. However, the majority of binocular units had similar receptive fields in each eye and very unconventional receptive fields were not encountered. Tested binocular units demonstrated summation upon simultaneous stimulation of both receptive fields. In conjunction with findings reported elsewhere, these results suggest that rabbit and cat possess a similar provision for binocular vision in spite of some differences in their cortical organisation.

A quantitative analysis of the direction-specific response of Neurons in the cat's nucleus of the optic tract

All cells in the nucleus of the optic tract (NOT) of the cat, that could be activated antidromically from the inferior olive, were shown to be direction-specific, as influenced by horizontal movements of an extensive visual stimulus. Cells in the left NOT were activated by leftward and inhibited by rightward movement, while those in the right NOT were activated by rightward and inhibited by leftward movement. Vertical movements did not modulate the spontaneous activity of the cells. The mean spontaneous discharge rate in 50 NOT cells was 30 spikes/s. This direction-specific response was maintained over a broad velocity range (Less Than 0.1 degrees - Greater Than 100 degrees/s). Velocities over 200 degrees/s could inhibit NOT cells regardless of stimulus direction. All cells in the NOT were driven by the contralateral eye, about half of them by the ipsilateral eye also. In addition, activation through the contralateral eye was stronger in most binocular units. Binocular cells preferred the same direction in the visual space through both eyes. An area approximately corresponding to the visual streak in the cat's retina projected most densely onto NOT cells. This included an extensive ipsilateral projection. No clear retinotopic order was seen. The most sensitive zone in the very large receptive fields (most diameters being Greater Than 20 degrees) was along the horizontal zero meridian of the visual field. The retinal input to NOT cells was mediated by W-fibers. The striking similarities between the input characteristics of NOT-cells and optokinetic nystagmus are discussed. The direction selectivity and ocular dominance of the NOT system as a whole can provide a possible explanation for the directional asymmetry in the cat's optokinetic nystagmus when only one eye is stimulated.

Conduction velocity distribution of the retinal input to the hamster's superior colliculus and a correlation with receptive field characteristics

Cells driven reliably by shocks delivered to the optic nerve or optic chiasm were encountered throughout the depth of the colliculus. The incidence of such cells, however, decreased markedly in the laminae ventral to the stratum opticum. The distribution of conduction velocities for the retinal afferents to the tectum was quite broad (range: 1.7-25.5 m/sec) and clearly biomodal with peaks at about 6 and 12 m/sec. A small number of cells were innervated by rapidly (greater than 15 m/sec) conducting axons. No evidence of an indirect-fast pathway from the retina to the colliculus via the lateral geniculate nucleus and visual cortex was obtained. Afferent conduction velocity was not correlated with retinal eccentricity, collicular depth or speed selectivity. It was, however, clearly related to directional selectivity. Ninety percent of the tectal neurons receiving inputs from axons having conduction velocities of less than 5 m/sec were directionally selective while only 41% of those neurons innervated by more rapidly conducting fibers (greater than 5 m/sec) exhibited selectivity. One hundred and sixteen cells in the anterior portion of the colliculus were tested with shocks delivered to the ipsilateral optic nerve and photic stimulation of the ipsilateral eye. Of these, 11% exhibited some degree of binocularity and only 6% were responsive to optic nerve shocks. These electrophysiological findings were correalted with the limited nature of the retinal input to the ipsilateral superior colliculus.

Distribution of retinal ganglion cells in five mammalian species (pig, sheep, ox, horse, dog)

In order to ascertain shape and location of the central area, the distribution of ganglion cells was measured in whole mounts of the retina from pig, sheep, ox, horse, and dog. Although exact comparison of corresponding points of measurement in different animals was not possible, the measurements allowed the mapping of retinal ganglion cell density, typical for the particular species. In all ungulates a streak of high cell density extends along a straight horizontal line, dorsal to the optic disc. As a rule a maximum of ganglion cell density is found close to the temporal end of the visual streak. In the dog a well demarcated oval portion of the streak continues into a short temporal (variable) and a long nasal linear arm. The functional significance of these findings is discussed.

Properties of ganglion cells in the visual streak of the cat's retina

The properties of ganglion cells in the visual streak of the cat's retina have been investigated. Evidence is presented that the streak is formed principally, but not entirely, by a concentration of small-bodied ganglion cells with the receptive field properties and slow-conducting axons typical of W-cells.

Form and function of cat retinal ganglion cells

Recent explorations of the morphology of retinal neurones, combined with neurophysiological recordings have made it possible to link specific anatomical types with particular physiological classes. At the same time, the relatively complete anatomical mapping of the retina has revealed some bias in the sampling of neurones by electrophysiological techniques.

Cat retinal ganglion cells: size and shape of receptive field centres

1. Receptive field centres of 144 sustained and transient retinal ganglion cells were mapped in cats under light pentobarbitone anaesthesia.2. Sustained on-centre, sustained off-centre, transient on-centre and transient off-centre cells had different mean sizes of receptive field centre, with some overlap between their distributions.3. For each class of cell, central fields had the smallest field-centres; progressively larger field-centres were encountered more peripherally.4. All classes of ganglion cells tended to have slightly elliptical receptive field centres. Major axes of over half of all receptive fields were oriented within 20 degrees of horizontal. These trends were independent of pupil dimensions, or of receptive field eccentricity or position in the visual field. The results almost certainly reflect asymmetry in retinal wiring.5. Two cells of thirty-nine tested were sensitive to axis of motion; in both cases the preferred and major axis were horizontal. A further cell was orientation specific.

The morphological types of ganglion cells of the domestic cat's retina

1. Three distinct morphological types of cat retinal ganglion cells have been identified and categorized as alpha, beta and gamma. Alpha ganglion cells have dendritic field diameters from 180 to 1000 mum; beta, about 25 to 300 mum; gamma, 180 to 800 mum, possibly more.2. The dimensions of the alpha and beta ganglion cell dendritic fields increase monotonically from the central area outwards to the periphery; those of the gamma cells do not. Seemingly a spectrum of sizes of the gamma cells is found at most locations in the retina.3. All three morphological types of ganglion cells are found in the central area.4. Possible further anatomical types of ganglion cells are discussed. Correlations are suggested between the morphological category alpha cells and the physiological class Y cells; between beta cells and the X cells and between the gamma cells and the W cells.

Properties of rarely encountered types of ganglion cells in the cat's retina and an overall classification

1. In a reference sample of 960 cat retinal ganglion cells, seventy-three had receptive fields departing from the concentric centre-surround pattern.2. Five classes were distinguished among the subset: local edge detectors, direction-selective cells, colour-coded cells, uniformity detectors, edge inhibitory off-centre cells.3. Local edge detectors (forty-five) possessed a radially symmetrical pattern of responses to both centrifugal and centripetal movements of both black and white small targets, an on-off receptive field with a silent inhibitory surround and a low or zero maintained discharge. Their operation could be interpreted as the detection of a contrasting border confined to a small region of the visual field.4. With direction-selective units (eleven) it was possible to find an axis through the receptive field along which sharply different responses could be obtained for opposite directions of movement of small black or white targets.5. Colour units (six) were mostly of the single opponent type having excitatory input from blue-sensitive cones and inhibitory input from long wave-length cones. Both inputs coexisted at the centre of the field and either could be spatially more extensive than the other. One example changed over to rod input under scotopic conditions, another did not.6. Uniformity detectors (five) had a brisk maintained discharge which was reduced or abolished temporarily by all forms of visual stimulation.7. Edge inhibitory off-centre units (three) behaved like uniformity detectors for small targets and fine gratings but like off-centre on-surround units for large targets. Their receptive fields consisted of three concentric regions: a small sized, central edge inhibitory region; a larger zone of off-responsiveness; and an outlying annulus of on-responsiveness.8. It is argued that the above physiological types belong to the morphologically heterogeneous class of cells called gamma cells. The argument is based on similarity in the sizes of receptive fields and dendritic trees and on evidence that the axons are thinner than those of the brisk-sustained and brisk-transient ganglion cells.9. The physiological classification of cat retinal ganglion cells developed in this paper and the preceding one is summarized in a Table.10. It now appears that cat and rabbit possess a qualitatively similar complement of receptive field types among their ganglion cells; the differences reside in the quantitative expression of the various classes.

Receptive field analysis: responses to moving visual contours by single lateral geniculate neurones in the cat

1. Responses of single geniculate cells to moving light and dark bars and light/dark edges were studied in cats anaesthetized with nitrous oxide/oxygen (70%/30%).2. Over 95% (230 out of 241) of geniculate cells had antagonistic centre-surround receptive fields. Their responses could be characterized as centre-activated or centre-suppressed depending on the receptive field type (ON- or OFF-centre) and the contrast between stimulus and the background (brighter or darker than the background). Moving light and dark edges evoked responses which were very similar to the responses evoked by these stimuli in simple cells of striate cortex.3. A number of cells (45) with antagonistic centre-surround receptive fields were classified according to their X/Y (sustained/transient) properties. Units with sustained properties (X-cells) did not increase their firing rate with an increase of stimulus velocity and some of them showed a clear-cut preference for slow movement (around 1-2 degrees /sec). On the other hand, units with transient properties (Y-cells) showed a clear-cut preference for fast-moving stimuli (50-100 degrees /sec.)4. Elongation of the stimulus beyond the antagonistic surround in both X- and Y-cells produced a clear-cut reduction of amplitude of both centre and surround components of the response. Thus the existence of a suppressive field component beyond the antagonistic surround is confirmed.5. About 5% of cells had receptive fields which did not have an antagonistic centre-surround organization but gave a mixed ON-OFF discharge from the central region of the field. Around the central region there was a silent suppressive zone. These units were not directionally selective, responded preferentially to fast-moving stimuli (25-100 degrees /sec) and had a substantial (spontaneous) maintained activity.

Properties of sustained and transient ganglion cells in the cat retina

1. The functional basis for a sustained/transient classification of cat retinal ganglion cells has been strengthened by quantitative measurements of the sizes of the centre and surround components of receptive fields. Transient cells had larger surrounds than sustained; the distributions were non-overlapping. Although the distributions of centre sizes overlapped, the transient cells had very significantly larger centres on average.2. There were characteristic differences in area-threshold and annulus-threshold curves and shapes of responses to brief and long flashes of light, and relative differences in the nature of surround adaptation and maintained discharge rates.3. The distinction of sustained from transient units survived over a wide range of backgrounds including the two principle reorganizations of function: relative weakening of surround components at low background; Purkinje shift at high.4. Sustained and transient units were differentially distributed in the retina: there was an overwhelming preponderance of sustained units in the area centralis.5. It is proposed that the transient units are the so-called multidendritedeep cells and the sustained units are the variously styled small ganglion cells.