Can retinal ganglion cell dipoles seed iso-orientation domains in the visual cortex?

It has been argued that the emergence of roughly periodic orientation preference maps (OPMs) in the primary visual cortex (V1) of carnivores and primates can be explained by a so-called statistical connectivity model. This model assumes that input to V1 neurons is dominated by feed-forward projections originating from a small set of retinal ganglion cells (RGCs). The typical spacing between adjacent cortical orientation columns preferring the same orientation then arises via Moir\'{e}-Interference between hexagonal ON/OFF RGC mosaics. While this Moir\'{e}-Interference critically depends on long-range hexagonal order within the RGC mosaics, a recent statistical analysis of RGC receptive field positions found no evidence for such long-range positional order. Hexagonal order may be only one of several ways to obtain spatially repetitive OPMs in the statistical connectivity model. Here, we investigate a more general requirement on the spatial structure of RGC mosaics that can seed the emergence of spatially repetitive cortical OPMs, namely that angular correlations between so-called RGC dipoles exhibit a spatial structure similar to that of OPM autocorrelation functions. Both in cat beta cell mosaics as well as primate parasol receptive field mosaics we find that RGC dipole angles are spatially uncorrelated. To help assess the level of these correlations, we introduce a novel point process that generates mosaics with realistic nearest neighbor statistics and a tunable degree of spatial correlations of dipole angles. Using this process, we show that given the size of available data sets, the presence of even weak angular correlations in the data is very unlikely. We conclude that the layout of ON/OFF ganglion cell mosaics lacks the spatial structure necessary to seed iso-orientation domains in the primary visual cortex.Comment: 9 figures + 1 Supplementary figure and 1 Supplementary tabl

Gender bias in scholarly peer review

Abstract Peer review is the cornerstone of scholarly publishing and it is essential that peer reviewers are appointed on the basis of their expertise alone. However, it is difficult to check for any bias in the peer-review process because the identity of peer reviewers generally remains confidential. Here, using public information about the identities of 9000 editors and 43000 reviewers from the Frontiers series of journals, we show that women are underrepresented in the peer-review process, that editors of both genders operate with substantial same-gender preference (homophily), and that the mechanisms of this homophily are gender-dependent. We also show that homophily will persist even if numerical parity between genders is reached, highlighting the need for increased efforts to combat subtler forms of gender bias in scholarly publishing

Orientation preference maps in Microcebus murinus reveal size-invariant design principles in primate visual cortex

Orientation preference maps (OPMs) are a prominent feature of primary visual cortex (V1) organization in many primates and carnivores. In rodents, neurons are not organized in OPMs but are instead interspersed in a ‘‘salt and pepper’’ fashion, although clusters of orientation-selective neurons have been reported. Does this fundamental difference reflect the existence of a lower size limit for orientation columns (OCs) below which they cannot be scaled down with decreasing V1 size? To address this question, we examined V1 of one of the smallest living primates, the 60-g prosimian mouse lemur (Microcebus murinus). Using chronic intrinsic signal imaging, we found that mouse lemur V1 contains robust OCs, which are arranged in a pinwheel-like fashion. OC size in mouse lemurs was found to be only marginally smaller compared to the macaque, suggesting that these circuit elements are nearly incompressible. The spatial arrangement of pinwheels is well described by a common mathematical design of primate V1 circuit organization. In order to accommodate OPMs, we found that the mouse lemur V1 covers one-fifth of the cortical surface, which is one of the largest V1-to-cortex ratios found in primates. These results indicate that the primate-type visual cortical circuit organization is constrained by a size limitation and raises the possibility that its emergence might have evolved by disruptive innovation rather than gradual change

A nanochannel with an embedded transverse graphene tunneling electrode for molecular probing and as a future tool for DNA sequencing

Single layer graphene, as a one-atom-thick highly conductive layer, is an exciting candidate for highly localized tunneling measurements because it is sufficiently thin to resolve a single molecule. We have fabricated graphene tunneling junctions confined within a nanochannel to explore the feasibility of developing a single-molecule sequencing tool for deoxyribonucleic acid (DNA). The unprecedented thinness of graphene electrodes allows to overcome the problems encountered using metallic electrodes, which are too bulky for single-molecule resolution. By confining of the molecule in a nanochannel, a long and narrow structure through which it can be dragged electrophoretically, it is possible to slow down the DNA sufficiently to achieve single base translocation. We show an experimental realization of the first steps towards a new graphene sequencing device. First, we present a new experimental technique for the production of nanogaps in a sheet of graphene. Applying a high current density in a graphene strip removes material from the strip resulting in the formation of nanogaps and tips. Starting from graphene grown by Chemical Vapor Deposition (CVD), we fabricate those structures. We show transport measurements of graphene devices in helium, air and vacuum demonstrating the realization of tunneling gaps. Second, we embed graphene tunneling junctions in a nanochannel and measure tunneling currents through various liquids. Using Simmons' model we calculate the work function between graphene and those liquids. Third we present evidence for inelastic tunneling through different molecules especially Rhodamine B and Adenosine monophosphate. We compare the results with data from optical spectroscopy.M.S.Includes bibliographical referencesIncludes vitaby Manuel Schottdor

Spatial correlations of dipole orientations are absent in a primate parasol receptive field mosaic.

<p><b>A</b> ON/OFF cells (empty/filled circles) for primate parasol cell receptive field mosaic G09 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086139#pone.0086139-Gauthier1" target="_blank">[36]</a>. Preferred orientation of dipoles extracted for are shown as colored bars. Colorcode as in Fig. 1C. <b>B</b> as A but for . <b>C</b> as A but for . <b>D</b> Correlation of dipole orientations for mosaic G09, calculated from dipoles extracted for . Error bars indicate 95% confidence intervals of bootstrap distributions. <b>E</b> as D but for . <b>F</b> as D but for .</p

Estimating the statistical power of the test for the presence of spatial correlations in RGC dipole angles.

<p><b>A</b> False negative rate (probability of failing to detect the positive local correlation) for mPIPP mosaics simulated with different modulation parameters as a function of the number of mosaics N and their area size (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086139#s4" target="_blank">Materials & Methods</a> for details). Green box indicates size of cat RGC mosaic data sets analyzed in the present study (N = 1, area size ). Note that even for , the false negative rate with this data set size is very small. <b>B</b> False negative rate for detecting negative correlation of dipole angles mPIPP mosaics around a distance of (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086139#pone-0086139-g005" target="_blank">Fig. 5</a>, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086139#s4" target="_blank">Materials & Methods</a> for details). In all panels, a cortical magnification of was assumed and PIPP parameters were taken from the fit to the m623 mosaic <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086139#pone.0086139-Eglen1" target="_blank">[34]</a>.</p

RGC dipoles and the statistical wiring model according to [20].

<p><b>A</b> Most left: A dipole of an ON center (empty circle) and OFF center (filled circle) retinal ganglion cell (RGC). The black line connecting the two cells indicates that the two cells form a dipole. A V1 cell with input dominated by this dipole has a receptive field with side-by-side subregions of opposite sign (middle left) and is consequently tuned to a specific orientation (middle right). We represent the preferred orientation of the V1 cell by the <i>color</i> of the bar connecting the two RGCs (most right). Note that the preferred orientation of the V1 is orthogonal to the bar connecting the two RGCs. <b>B</b> The statistical connectivity model for orientation preference maps. The receptive field midpoints of ON/OFF center RGCs are arranged in semiregular mosaics. The input to a cortical cell is dominated by a single pair of ON/OFF dipole and the cortical units have oriented receptive fields. If RGC dipole orientations are locally correlated, orientation preference within layer 4 of V1 is predicted to vary smoothly resulting in a smooth and continuous map of orientation preferences. <b>C</b> Parametrized definition of RGC dipoles. ON/OFF pairs with distance smaller than a parameter <i>d</i> are considered dipoles (black lines). For the centered OFF cell, preferred orientations of dipoles are indicated. With increasing <i>d</i>, the number of dipoles increases and one RGC can form multiple dipoles.</p

Constraining the modulation parameter with experimental data.

<p><b>A</b> Correlation functions of dipole preferred orientations for 100 mPIPP realizations (pale pink dots, , cortical magnification , ). Black drawn line indicates average correlation function, dashed lines show deviation from the mean. Red dots indicate correlation function of dipole orientations for the mosaic m623 (redrawn from Fig. 2H). Insets show the T-distribution for Monte-Carlo data (blue) to estimate the p-value for the observed value (red) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086139#s4" target="_blank">Materials and Methods</a>). Note the correlation-anti-correlation-correlation structure of the correlation function. <b>B</b> As A but for . <b>C</b> Monte-Carlo p-values (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086139#s4" target="_blank">Materials and Methods</a>) for different values of and the cortical magnification factor for m623. Red line indicates significance value. <b>D</b> as C but for mosaic w81s1.</p

Measured local correlation values depend on choice of dipole distance parameter .

<p><b>A</b> Local correlations in cat beta cell mosaics (red: m623, blue: w81s1) as a function of the dipole extraction parameter (see Fig. 1C). <b>B</b> As A but for primate parasol cell receptive field mosaic G09. <b>C</b> Weak local positive or negative correlations emerge in the same RGC configuration, depending on dipole extraction parameter . <b>D</b> As A but for simulated PIPP mosaics with parameters fitted to cat beta cell mosaics m623 (red) and w81s1 (blue). <b>E</b> As B but for simulated PIPP mosaics with parameters fitted to primate parasol receptive field mosaics G09. All error bars indicate 95% confidence intervals of bootstrap distributions.</p