Midget Cells Research Articles

Connectivity between the OFF bipolar type DB3a and six types of ganglion cell in the marmoset retina.

Parallel visual pathways originate at the first synapse in the retina, where cones make connections with cone bipolar cells that in turn contact ganglion cells. There are more ganglion cell types than bipolar types, suggesting that there must be divergence from bipolar to ganglion cells. Here we analyze the contacts between an OFF bipolar type (DB3a) and six ganglion cell types in the retina of the marmoset monkey (Callithrix jacchus). Ganglion cells were transfected via particle-mediated gene transfer of an expression plasmid for the postsynaptic density 95-green fluorescent protein (PSD95-GFP), and DB3a cells were labeled via immunohistochemistry. Ganglion cell types that fully or partially costratified with DB3a cells included OFF parasol, OFF midget, broad thorny, recursive bistratified, small bistratified, and large bistratified cells. On average, the number of DB3a contacts to parasol cells (18 contacts per axon terminal) is higher than that to other ganglion cell types (between four and seven contacts). We estimate that the DB3a output to OFF parasol cells accounts for at least 30% of the total DB3a output. Furthermore, we found that OFF parasol cells receive approximately 20% of their total bipolar input from DB3a cells, suggesting that other diffuse bipolar types also provide input to OFF parasol cells. We conclude that DB3a cells preferentially contact OFF parasol cells but also provide input to other ganglion cell types.

Letter identification and the neural image classifier.

Letter identification is an important visual task for both practical and theoretical reasons. To extend and test existing models, we have reviewed published data for contrast sensitivity for letter identification as a function of size and have also collected new data. Contrast sensitivity increases rapidly from the acuity limit but slows and asymptotes at a symbol size of about 1 degree. We recast these data in terms of contrast difference energy: the average of the squared distances between the letter images and the average letter image. In terms of sensitivity to contrast difference energy, and thus visual efficiency, there is a peak around ¼ degree, followed by a marked decline at larger sizes. These results are explained by a Neural Image Classifier model that includes optical filtering and retinal neural filtering, sampling, and noise, followed by an optimal classifier. As letters are enlarged, sensitivity declines because of the increasing size and spacing of the midget retinal ganglion cell receptive fields in the periphery.

Morphological and functional diversity of retinal ganglion cells in the common marmoset

Retinal ganglion cells are projecting neurons that send visual information from the retina to the brain. They generate different patterns of action potentials in response to different kinds of visual information. In the retinas of mammals such as mice or rabbits, there are functionally and morphologically diverse retinal ganglion cells. However, in the primate retina, midget and parasol cells are believed to be dominant, and show less diversity. In this study, we performed organotypic culture of retinas and acute gene transfection of GFPs by gene-gun. We found more diverse retinal ganglion cells, including directional selective ganglion cells, than we expected, even in the retinas of primates such as common marmosets. Further, we found a third pathway from the retina to the brain via the thalamus, in addition to the magnocellular and parvocellular pathways.

Synaptic connections of amacrine cells containing vesicular glutamate transporter 3 in baboon retinas.

The goals of these experiments were to describe the morphology and synaptic connections of amacrine cells in the baboon retina that contain immunoreactive vesicular glutamate transporter 3 (vGluT3). These amacrine cells had the morphology characteristic of knotty bistratified type 1 cells, and their dendrites formed two plexuses on either side of the center of the inner plexiform layer. The primary dendrites received large synapses from amacrine cells, and the higher-order dendrites were both pre- and postsynaptic to other amacrine cells. Based on light microscopic immunolabeling results, these include AII cells and starburst cells, but not the polyaxonal amacrine cells tracer-coupled to ON parasol ganglion cells. The vGluT3 cells received input from ON bipolar cells at ribbon synapses and made synapses onto OFF bipolar cells, including the diffuse DB3a type. Many synapses from vGluT3 cells onto retinal ganglion cells were observed in both plexuses. At synapses where vGluT3 cells were presynaptic, two types of postsynaptic densities were observed; there were relatively thin ones characteristic of inhibitory synapses and relatively thick ones characteristic of excitatory synapses. In the light microscopic experiments with Neurobiotin-injected ganglion cells, vGluT3 cells made contacts with midget and parasol ganglion cells, including both ON and OFF types. Puncta containing immunoreactive gephyrin, an inhibitory synapse marker, were found at appositions between vGluT3 cells and each of the four types of labeled ganglion cells. The vGluT3 cells did not have detectable levels of immunoreactive γ-aminobutyric acid (GABA) or immunoreactive glycine transporter 1. Thus, the vGluT3 cells would be expected to have ON responses to light and make synapses onto neurons in both the ON and the OFF pathways. Taken with previous results, these findings suggest that vGluT3 cells release glycine at some of their output synapses and glutamate at others.

A formula for human retinal ganglion cell receptive field density as a function of visual field location.

In the human eye, all visual information must traverse the retinal ganglion cells. The most numerous subclass, the midget retinal ganglion cells, are believed to underlie spatial pattern vision. Thus the density of their receptive fields imposes a fundamental limit on the spatial resolution of human vision. This density varies across the retina, declining rapidly with distance from the fovea. Modeling spatial vision of extended or peripheral targets thus requires a quantitative description of midget cell density throughout the visual field. Through an analysis of published data on human retinal topography of cones and ganglion cells, as well as analysis of prior formulas, we have developed a new formula for midget retinal ganglion cell density as a function of position in the monocular or binocular visual field.

Latency and rate coding in a spiking model of retina

We describe a family of spiking retina computational models for large-scale simulations of the visual pathways. The models reproduce the overall spatial, temporal, and chromatic structure of the receptive fields of midget and parasol retinal ganglion cells (RGCs) of the primate retina, as well as their contrast response, while using fairly simple models of bipolar, horizontal, amacrine, and RGCs. These retina models provide input to a realistic model of visual cortex, presented in a separate submission. The retina model simulates cone and bipolar cell dynamics using a damped wave equation. Parameters are so chosen that an impulse retinal input gives rise to a damped biphasic output current, and that a coherent stimulus elicits a substantially stronger response than an incoherent stimulus of the same power (Figure ​(Figure1).1). Static or low-frequency visual inputs are smoothly rejected. In contrast to biology, this stage of the model is linear; rectification and adaptation mechanisms are all realized in the spiking ganglion cell layer. In the ganglion cell layer parasol, midget, and SBC cells are simulated. The spatio-temporal receptive fields of different RGCs are not prewired; they emerge via the lateral interactions between the horizontal, bipolar, and amacrine cells. Spike generation in the RGCs is modeled using spiking neurons with two dynamic variables and an intrinsic adaptation mechanism. Midget RGCs have an additional leaky temporal integration of the input current, to account for the relatively tonic character of their responses. Parasol RGCs have an additional partial divisive normalization of the input current, to reproduce the saturating parasol response to relative contrast of the stimulus. Simplified amacrine-cell dynamics is introduced to provide for the spatiotemporal structure of the parasol receptive field surrounds. Figure 1 A-E: model response to coherent vs. randomized stimulus. Moving edge stimulus is presented (A) and elicits strong response (B). Same stimulus with fixed random permutation of pixels (C) elicits much weaker response (D). (E) compares the total responses ... Desired latency encoding of input features is achieved by calibrating the parameters of the spiking RGC conductance dynamics. A near logarithmic latency to the first spike, for a step up in the input signal, provides for a good contrast invariance of the relative spike timing in the response. A combination of spike-latency and spike-count encoding of the input stimulus, together with the enhanced response of the simulated retina to coherent stimuli, results in an informative yet not too noisy spiking input to the LGN and V1; the information content analysis of the RGC spike-train vocabulary will be presented. This retina model was used to produce a fully-emergent orientation tuning in a spiking model [1] of V1 cortex.

Spontaneous emergence of simple and complex receptive fields in a spiking model of V1

Brain Corporation is engaged in a multi-year project to build a spiking model of vision, paying special attention to the anatomy and physiology of the mammalian visual system. While it is relatively easy to hand-tune V1 to get simple and complex cells, it is not clear how to arrange connectivity in other cortical areas to get appropriate receptive fields, or what the appropriate receptive fields even should be. Instead of pre-wiring cortical connectivity according to a computational theory of how vision should work, we start with a generic tabula rasa spiking network having multiple cortical layers and neuronal types (single-compartment RS, FS, LTS cells). The goal is to find the anatomical and physiological parameters so that the appropriate connectivity emerges through STDP and visual experience. Since we know exactly what kind of receptive fields and visual responses are in V1, we build a smaller model of retina-LGN-V1 pathway and tune the STDP parameters so that the expected responses emerge. Admittedly, there are many free parameters that could be tuned to get V1-like responses; our choice is motivated by in-vitro recordings and other published data, whenever possible. Once we trust what we see in V1, we are ready to copy and paste the cortical model to implement V2, V3, V4, and IT areas with the hope that useful connectivity, receptive fields, and visual responses emerge. Our large-scale simulations of the spiking model of the visual system show spontaneous emergence of simple and complex cells, orientation domains, end-stopping receptive fields, extra-classical receptive fields with tuned surround suppression, color opponency that depends on the eccentricity of the receptive field, contrast invariance, and many other features that are routinely recorded in V1. Since the visual model exhibits micro- and full saccades, we observe perceptual behavior, such as the emergence of bottom-up (pop-out) attention. The model underscores the importance of spike-timing dynamics, inhibition, saccadic mechanism, and it imposes important restrictions on the possible types of STDP to model early visual processing. This presentation is meant to be a flagship introduction to the whole effort by Brain Corporation to build spiking model of vision. There are multiple other submissions elaborating details of our modeling effort. The figure summarizes the gross anatomy of the spiking model of the visual system, including area MT, Superior Colliculus (SC), Frontal Pursuit Area (FPA), Flocculus (Floc), and Brainstem (B.Stem). The retina covers 10 by 10 degrees of visual field with the density of L, M, and S cones and receptive field sizes of Midget, Parasol, and SBC retino-ganglion cells corresponding to 4 degrees of eccentricity of a primate retina (collaboration with EJ Chichilnisky lab at Salk Institute). The model consists of more than 1M single-compartment neurons of RS, FS, and LTS types (Izhikevich, 2007 Dynamical Systems in Neuroscience) and 0.25B synapses having AMPA, NMDA, GABA_A and GABA_B conductances, axonal conduction delays, and STDP. In this presentation, we summarize these and other anatomical and physiological assumptions, describe major results and point to other submissions by Brain Corporation scientists for more details. Figure 1

Regulation of Spatial Selectivity by Crossover Inhibition

Signals throughout the nervous system diverge into parallel excitatory and inhibitory pathways that later converge on downstream neurons to control their spike output. Converging excitatory and inhibitory synaptic inputs can exhibit a variety of temporal relationships. A common motif is feedforward inhibition, in which an increase (decrease) in excitatory input precedes a corresponding increase (decrease) in inhibitory input. The delay of inhibitory input relative to excitatory input originates from an extra synapse in the circuit shaping inhibitory input. Another common motif is push-pull or "crossover" inhibition, in which increases (decreases) in excitatory input occur together with decreases (increases) in inhibitory input. Primate On midget ganglion cells receive primarily feedforward inhibition and On parasol cells receive primarily crossover inhibition; this difference provides an opportunity to study how each motif shapes the light responses of cell types that play a key role in visual perception. For full-field stimuli, feedforward inhibition abbreviated and attenuated responses of On midget cells, while crossover inhibition, though plentiful, had surprisingly little impact on the responses of On parasol cells. Spatially structured stimuli, however, could cause excitatory and inhibitory inputs to On parasol cells to increase together, adopting a temporal relation very much like that for feedforward inhibition. In this case, inhibitory inputs substantially abbreviated a cell's spike output. Thus inhibitory input shapes the temporal stimulus selectivity of both midget and parasol ganglion cells, but its impact on responses of parasol cells depends strongly on the spatial structure of the light inputs.

Diversity of Retinal Ganglion Cells Identified by Transient GFP Transfection in Organotypic Tissue Culture of Adult Marmoset Monkey Retina

The mammalian retina has more diversity of neurons than scientists had once believed in order to establish complicated vision processing. In the monkey retina, morphological diversity of retinal ganglion cells (RGCs) besides dominant midget and parasol cells has been suggested. However, characteristic subtypes of RGCs in other species such as bistratified direction-selective ganglion cells (DSGC) have not yet been identified. Increasing interest has been shown in the common marmoset (Callithrix jacchus) monkey as a “super-model” of neuroscientific research. Here, we established organotypic tissue culture of the adult marmoset monkey retina with particle-mediated gene transfer of GFP to survey the morphological diversity of RGCs. We successfully incubated adult marmoset monkey retinas for 2 to 4 days ex vivo for transient expression of GFP. We morphologically examined 121 RGCs out of more than 3240 GFP-transfected cells in 5 retinas. Among them, we identified monostratified or broadly stratified ganglion cells (midget, parasol, sparse, recursive, thorny, and broad thorny ganglion cells), and bistratified ganglion cells (recursive, large, and small bistratified ganglion cells [blue-ON/yellow-OFF-like]). By this survey, we also found a candidate for bistratified DSGC whose dendrites were well cofasciculated with ChAT-positive starburst dendrites, costratified with ON and OFF ChAT bands, and had honeycomb-shaped dendritic arbors morphologically similar to those in rabbits. Our genetic engineering method provides a new approach to future investigation for morphological and functional diversity of RGCs in the monkey retina.

Amacrine and bipolar inputs to midget and parasol ganglion cells in marmoset retina

Retinal ganglion cells receive excitatory synapses from bipolar cells and inhibitory synapses from amacrine cells. Previous studies in primate suggest that the strength of inhibitory amacrine input is greater to cells in peripheral retina than to foveal (central) cells. A comprehensive study of a large number of ganglion cells at different eccentricities, however, is still lacking. Here, we compared the amacrine and bipolar input to midget and parasol ganglion cells in central and peripheral retina of marmosets (Callithrix jacchus). Ganglion cells were labeled by retrograde filling from the lateral geniculate nucleus or by intracellular injection. Presumed amacrine input was identified with antibodies against gephyrin; presumed bipolar input was identified with antibodies against the GluR4 subunit of the AMPA receptor. In vertical sections, about 40% of gephyrin immunoreactive (IR) puncta were colocalized with GABAA receptor subunits, whereas immunoreactivity for gephyrin and GluR4 was found at distinct sets of puncta. The density of gephyrin IR puncta associated with ganglion cell dendrites was comparable for midget and parasol cells at all eccentricities studied (up to 2 mm or about 16 degrees of visual angle for midget cells and up to 10 mm or >80 degrees of visual angle for parasol cells). In central retina, the densities of gephyrin IR and GluR4 IR puncta associated with the dendrites of midget and parasol cells are comparable, but the average density of GluR4 IR puncta decreased slightly in peripheral parasol cells. These anatomical results indicate that the ratio of amacrine to bipolar input does not account for the distinct functional properties of parasol and midget cells or for functional differences between cells of the same type in central and peripheral retina.

Spatial distributions of cone inputs to cells of the parvocellular pathway investigated with cone-isolating gratings.

Receptive fields of midget ganglion cells and parvocellular lateral geniculate nucleus (LGN) neurons show color-opponent responses because they receive antagonistic input from the middle- and long-wavelength sensitive cones. It has been controversial as to whether this opponency can derive from random connectivity; if receptive field centers of cells near the fovea are cone-specific due to midget morphology, this would confer some degree of color opponency even with random cone input to the surround. A simple test of this mixed surround hypothesis is to compare spatial frequency tuning curves for luminance gratings and gratings isolating cone input to the receptive field center. If tuning curves for luminance gratings were bandpass, then with the mixed surround hypothesis tuning curves for gratings isolating the receptive field center cone class should also be bandpass, but to a lesser extent than for luminance. Tuning curves for luminance, chromatic, and cone-isolating gratings were measured in macaque retinal ganglion cells and LGN cells. We defined and measured a bandpass index to compare luminance and center cone-isolating tuning curves. Midget retinal ganglion cells and parvocellular LGN cells had bandpass indices between 0.1 and 1 with luminance gratings, but the index was usually near 1 (meaning low-pass tuning) when the receptive field center cone class alone was modulated. This is strong evidence for a considerable degree of cone-specific input to the surround. A fraction of midget and parvocellular cells showed evidence of incomplete specificity. Fitting the data with receptive field models revealed considerable intercell variability, with indications in some cells of a more complex receptive structure than a simple difference of Gaussians model.

Horizontal Cell Feedback without Cone Type-Selective Inhibition Mediates “Red–Green” Color Opponency in Midget Ganglion Cells of the Primate Retina

The distinctive red-green dimension of human and nonhuman primate color perception arose relatively recently in the primate lineage with the appearance of separate long (L) and middle (M) wavelength-sensitive cone photoreceptor types. "Midget" ganglion cells of the retina use center-surround receptive field structure to combine L and M cone signals antagonistically and thereby establish a "red-green, color-opponent" visual pathway. However, the synaptic origin of red-green opponency is unknown, and conflicting evidence for either random or L versus M cone-selective inhibitory circuits has divergent implications for the developmental and evolutionary origins of trichromatic color vision. Here we directly measure the synaptic conductances evoked by selective L or M cone stimulation in the midget ganglion cell dendritic tree and show that L versus M cone opponency arises presynaptic to the midget cell and is transmitted entirely by modulation of an excitatory conductance. L and M cone synaptic inhibition is feedforward and thus occurs in phase with excitation for both cone types. Block of GABAergic and glycinergic receptors does not attenuate or modify L versus M cone antagonism, discounting both presynaptic and postsynaptic inhibition as sources of cone opponency. In sharp contrast, enrichment of retinal pH-buffering capacity, to attenuate negative feedback from horizontal cells that sum L and M cone inputs linearly and without selectivity, completely abolished both the midget cell surround and all chromatic opponency. Thus, red-green opponency appears to arise via outer retinal horizontal cell feedback that is not cone type selective without recourse to any inner retinal L versus M cone inhibitory pathways.

A model of retinal ganglion cell processing under natural viewing conditions.

Event Abstract Back to Event A model of retinal ganglion cell processing under natural viewing conditions. Garrett Greene1, 2*, Thomas Wachtler1, 2 and Tim Gollisch1, 3 1 BCCN München, Germany 2 LMU München, Germany 3 Georg-August-Universität Göttingen, Germany The retina is an important first stage of visual processing and is intensively studied. Little is known, however, about the retinal responses under atural viewing conditions. In particular, it is interesting to consider whether standard receptive field (RF) models can capture important features of the retinal response to complex non-stationary stimuli. We present a conceptually simple model of the peripheral visual system and investigate its behaviour under simulated eye movements. Specifically, we identify possible retinal mechanisms for rapid post-saccadic signalling as observed in several experimental studies. We model the retina as a simple photoreceptor grid which feeds forward to a retinal ganglion cell (RGC) layer consisting of numerous distinct RGC populations. We model four such populations: linear midget cells, both On-type and Off-type, and non-linear parasol cells, On-type and Off-type. Spatial receptive fields are given by a difference-of-Gaussians model. Temporal integration profiles for each population are described by the difference of two bi-phasic temporal filters which are combined with the spatial receptive field to form a rank-2 spatio-temporal filter. For midget RGCs, this filter is linearly convolved with the stimulus and rectified to generate a membrane potential. Neuronal spiking is simulated by a threshold function with non-linear feedback. Parasol cells implement a non-linear spatial integration, in which the receptive field is divided into sub-fields. Contributions from each sub-field are temporally integrated and rectified, before being summed to provide an estimate of the parasol cell membrane potential. The standard centre-surround RF can be recovered by combining sub-field RFs. The model reproduces several salient features in the reported behaviour of mammalian retina, including spatial and temporal modulation transfer functions. In addition, numerous studies have reported rapid post-saccadic bursting in retinal sub-populations. This behaviour is reproduced in our model, which displays strong transient responses to simulated saccades on a 10-ms timescale. These responses are observed primarily within our Off-type parasol population, and are less pronounced in On-type parasol cells. Midget RGCs do not display post-saccadic bursts. These differences in populations arise as a result of differing spatial and temporal integration profiles and the parasol integration non-linearity. Such dynamics are also implicated in the generation of latency codes for rapid post-saccadic processing. Our model thus captures prominent features relevant for understanding retinal processing during natural vision. Keywords: Eye Movements, retinal ganglion cell, sensory processing, Vision Conference: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011, Freiburg, Germany, 4 Oct - 6 Oct, 2011. Presentation Type: Poster Topic: sensory processing (please use "sensory processing" as keyword) Citation: Greene G, Wachtler T and Gollisch T (2011). A model of retinal ganglion cell processing under natural viewing conditions.. Front. Comput. Neurosci. Conference Abstract: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011. doi: 10.3389/conf.fncom.2011.53.00224 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 11 Aug 2011; Published Online: 04 Oct 2011. * Correspondence: Dr. Garrett Greene, BCCN München, München, Germany, greene@bio.lmu.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Garrett Greene Thomas Wachtler Tim Gollisch Google Garrett Greene Thomas Wachtler Tim Gollisch Google Scholar Garrett Greene Thomas Wachtler Tim Gollisch PubMed Garrett Greene Thomas Wachtler Tim Gollisch Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Cell‐type‐specific localization of protocadherin β16 at AMPA and AMPA/kainate receptor‐containing synapses in the primate retina

Protocadherins (Pcdhs) are thought to be key features of cell-type-specific synapse formation. Here we analyzed the expression pattern of Pcdh subunit β16 (β16) in the primate retina by applying antibodies against β16, different subunits of ionotropic glutamate receptors (GluRs), and cell-type-specific markers as well as by coimmunoprecipitation and Western blots. Immunocytochemical localization was analyzed by confocal microscopy and preembedding electron microscopy. In the outer plexiform layer (OPL) H1, but not H2, horizontal cells expressed β16 as revealed by the strong reduction of β16 at short-wavelength-sensitive cones. β16 colocalized with the GluR subunits GluR2-4 at horizontal cell dendritic tips and with GluR2-4 and GluR6/7 at the desmosome-like junctions. At the latter, these AMPA and kainate receptor subunits were found to be clustered within single synaptic hot spots. Additionally, β16-labeled dendritic tips of OFF cone bipolar cells appeared in triad-associated positions at the cone pedicle base, pointing to β16 expression by OFF midget or DB3 bipolar cells. In the inner plexiform layer, β16 was localized also postsynaptically at most of the glutamatergic synapses. Overall, we provide evidence for a cell-type-specific localization of β16 together with GluRs at defined postsynaptic sites and a coexistence of AMPA and kainate receptors within single synaptic hot spots. This study supports the hypothesis that β16 plays an important role in the formation and/or stabilization of specific glutamatergic synapses, whereas our in vivo protein biochemical results argue against the existence of protein complexes formed by β16 and GluRs.

Correlated firing among major ganglion cell types in primate retina

Retinal ganglion cells exhibit substantial correlated firing: a tendency to fire nearly synchronously at rates different from those expected by chance. These correlations suggest that network interactions significantly shape the visual signal transmitted from the eye to the brain. This study describes the degree and structure of correlated firing among the major ganglion cell types in primate retina. Correlated firing among ON and OFF parasol, ON and OFF midget, and small bistratified cells, which together constitute roughly 75% of the input to higher visual areas, was studied using large-scale multi-electrode recordings. Correlated firing in the presence of constant, spatially uniform illumination exhibited characteristic strength, time course and polarity within and across cell types. Pairs of nearby cells with the same light response polarity were positively correlated; cells with the opposite polarity were negatively correlated. The strength of correlated firing declined systematically with distance for each cell type, in proportion to the degree of receptive field overlap. The pattern of correlated firing across cell types was similar at photopic and scotopic light levels, although additional slow correlations were present at scotopic light levels. Similar results were also observed in two other retinal ganglion cell types. Most of these observations are consistent with the hypothesis that shared noise from photoreceptors is the dominant cause of correlated firing. Surprisingly, small bistratified cells, which receive ON input from S cones, fired synchronously with ON parasol and midget cells, which receive ON input primarily from L and M cones. Collectively, these results provide an overview of correlated firing across cell types in the primate retina, and constraints on the underlying mechanisms.

Functional connectivity in the retina at the resolution of photoreceptors

To understand a neural circuit requires knowing its connectivity. This paper reports measurements of functional connectivity between the input and ouput layers of the retina at single cell resolution and its implications for color vision. Multi-electrode technology was employed to record simultaneously from complete populations of the retinal ganglion cell types (midget, parasol, small bistratified) that transmit high-resolution visual signals to the brain. Fine-grained visual stimulation was used to identify the location, type and strength of the functional input of each cone photoreceptor to each ganglion cell. The populations of ON and OFF midget and parasol cells each sampled the complete population of long and middle wavelength sensitive cones. However, only OFF midget cells frequently received strong input from short wavelength sensitive cones. ON and OFF midget cells exhibited a small non-random tendency to selectively sample from either long or middle wavelength sensitive cones, to a degree not explained by clumping in the cone mosaic. These measurements reveal computations in a neural circuit at the elementary resolution of individual neurons.

The relationship between visual resolution and cone spacing in the human fovea

Visual resolution decreases rapidly outside the foveal center. The anatomical and physiological basis for this reduction is unclear. We used simultaneous adaptive optics imaging and psychophysical testing to measure cone spacing and resolution across the fovea, and show resolution is limited by cone spacing only at the foveal center. Immediately outside the center, resolution is worse than cone spacing predicts and better matches the sampling limit of midget retinal ganglion cells.

Contribution of excitatory and inhibitory conductances to receptive field structure in midget and parasol ganglion cells of macaque monkey retina

Contribution of excitatory and inhibitory conductances to receptive field structure in midget and parasol ganglion cells of macaque monkey retina

Uniform Signal Redundancy of Parasol and Midget Ganglion Cells in Primate Retina

The collective representation of visual space in high resolution visual pathways was explored by simultaneously measuring the receptive fields of hundreds of ON and OFF midget and parasol ganglion cells in isolated primate retina. As expected, the receptive fields of all four cell types formed regular mosaics uniformly tiling the visual scene. Surprisingly, comparison of all four mosaics revealed that the overlap of neighboring receptive fields was nearly identical, for both the excitatory center and inhibitory surround components of the receptive field. These observations contrast sharply with the large differences in the dendritic overlap between the parasol and midget cell populations, revealing a surprising lack of correspondence between the anatomical and functional architecture in the dominant circuits of the primate retina.

Retinal ganglion cell inputs to the koniocellular pathway

To understand the transmission of sensory signals in visual pathways we studied the morphology and central projection of ganglion cell populations in marmoset monkeys. Retinal ganglion cells were labeled by photofilling following injections of retrograde tracer in the lateral geniculate nucleus (LGN), or by intracellular injection with neurobiotin. Ganglion cell morphology was analyzed using hierarchical cluster analysis. In addition to midget and parasol ganglion cells, this method distinguished three main clusters of wide-field cells that correspond to small bistratified, sparse, and broad thorny cells identified previously. The small bistratified and sparse cells occupy neighboring positions on the hierarchical (linkage distance) tree. These cell types are presumed to carry signals originating in short-wavelength sensitive (S or "blue") cones in the retina. The linkage distance from these putative S-cone pathway ganglion cells to other wide-field cells is similar to the linkage distance from midget cells to parasol cells, suggesting that S-cone cells form a distinct functional subgroup of ganglion cells. Small bistratified cells and large sparse cells were the most commonly labeled wide-field cells following LGN injections in koniocellular layer K3. This is consistent with physiological evidence that the role of this layer includes transmission of S-cone signals to the visual cortex. Other wide-field cell types were also labeled following injections including K3, and other koniocellular LGN layers; these cell types may correspond to "non-blue koniocellular" receptive fields recorded in physiological studies.