Analytical Methods for Assessing Retinal Cell Coupling Using Cut-Loading

Electrical coupling between retinal neurons contributes to the functional complexity of visual circuits. “Cut-loading” methods allow simultaneous assessment of cell-coupling between multiple retinal cell-types, but existing analysis impedes direct comparison with gold standard direct dye injection techniques. Therefore cut-loading was used to assess coupling strength in a-type horizontal cells in dark-adapted Guinea pig retinae (n=29) using the standard protocol (Method 1) compared with two non-linear methods. Method 1 describes the distance of dye-diffusion (space constant), while Method 2 extracted the coupling coefficient (kj) and Method 3 measured the diffusion coefficient (De). Dye transfer was measured after one of five diffusion times (1-20 mins), or with a coupling inhibitor, meclofenamic acid (MFA) (50–500µM after 20 mins diffusion). Method 1 includes background fluorescence, producing less accurate coupling estimates than measuring the fluorescence of individual cell-soma (p<0.001). The space constant (Method 1) increased with diffusion time (p<0.01), whereas Methods 2 (p=0.54) and 3 (p=0.63) produced consistent results across all diffusion times. Method 1 was less sensitive to detecting changes induced by MFA than Methods 2 (p<0.01) and 3 (p<0.01). Comparatively, Methods 2 and 3 proved more sensitive and generalisable; allowing for detailed assessment of the coupling between different populations of gap-junction linked cell networks.

Characterization of light penetration through brain tissue, for optogenetic stimulation

The recent development of optogenetic tools, to manipulate neuronal activity using light, provides opportunities for novel brain-machine interface (BMI) control systems for treating neurological conditions. An issue of critical importance, therefore, is how well light penetrates through brain tissue. We took two different approaches to estimate light penetration through rodent brain tissue. The first employed so-called “nucleated patches” from cells expressing the light-activated membrane channel, channelrhodopsin (ChR2). By recording light-activated currents, we used these nucleated patches as extremely sensitive, microscopic, biological light-meters, to measure light penetration through 300-700µm thick slices of rodent neocortical tissue. The nucleated patch method indicates that the effective illumination drops off with increasing tissue thickness, corresponding to a space constant of 317µm (95% confidence interval between 248-441µm). We compared this with measurements taken from directly visualizing the illumination of brain tissue, orthogonal to the direction of the light. This yielded a contour map of reduced illumination with distance, which along the direction of light delivery, had a space constant, t, 453µm. This yields a lower extinction coefficient, µe (the reciprocal of t, ~3mm-1) than previous estimates, implying better light penetration from LED sources than these earlier studies suggest.

Synaptic propagation in neuronal networks with finite-support space dependent coupling

1AbstractTraveling waves of electrical activity are ubiquitous in biological neuronal networks. Traveling waves in the brain are associated with sensory processing, phase coding, and sleep. The neuron and network parameters that determine traveling waves’ evolution are synaptic space constant, synaptic conductance, membrane time constant, and synaptic decay time constant. We used an abstract neuron model to investigate the propagation characteristics of traveling wave activity. We formulated a set of evolution equations based on the network connectivity parameters. We numerically investigated the stability of the traveling wave propagation with a series of perturbations with biological relevance.

Shear measurement bias

We present a study of the dependencies of shear bias on simulation (input) and measured (output) parameters, noise, point-spread function anisotropy, pixel size, and the model bias coming from two different and independent galaxy shape estimators. We used simulated images from GALSIM based on the GREAT3 control-space-constant branch, and we measured shear bias from a model-fitting method (GFIT) and a moment-based method (Kaiser-Squires-Broadhurst). We show the bias dependencies found on input and output parameters for both methods, and we identify the main dependencies and causes. Most of the results are consistent between the two estimators, an interesting result given the differences of the methods. We also find important dependences on orientation and morphology properties such as flux, size, and ellipticity. We show that noise and pixelization play an important role in the bias dependencies on the output properties and galaxy orientation. We show some examples of model bias that produce a bias dependence on the Sérsic index n as well as a different shear bias between galaxies consisting of a single Sérsic profile and galaxies with a disc and a bulge. We also see an important coupling between several properties on the bias dependences. Because of this, we need to study several measured properties simultaneously in order to properly understand the nature of shear bias. This paper serves as a first step towards a companion paper that describes a machine learning approach to modelling shear bias as a complex function of many observed properties.

Cultural Cartography with Word Embeddings

Using the presence or frequency of keywords is a classic approach in the formal analysis of text, but has the drawback of glossing over the relationality of word meanings. Word embedding models overcome this problem by constructing a standardized meaning space where words are assigned a location based on relations of similarity to, and difference from, other words based on how they are used in natural language samples. We show how word embeddings can be put to the task of interpretation via two kinds of navigation. First, one can hold terms constant and measure how the embedding space moves around them—much like astronomers measured the changing of celestial bodies with the seasons. Second, one can also hold the embedding space constant and see how documents or authors move relative to it—just as ships use the stars on a given night to determine their location. Using the empirical case of immigration discourse in the United States, we demonstrate the merits of these two broad strategies to advance formal approaches to cultural analysis.

Fairness-Aware Demand Prediction for New Mobility

Emerging transportation modes, including car-sharing, bike-sharing, and ride-hailing, are transforming urban mobility yet have been shown to reinforce socioeconomic inequity. These services rely on accurate demand prediction, but the demand data on which these models are trained reflect biases around demographics, socioeconomic conditions, and entrenched geographic patterns. To address these biases and improve fairness, we present FairST, a fairness-aware demand prediction model for spatiotemporal urban applications, with emphasis on new mobility. We use 1D (time-varying, space-constant), 2D (space-varying, time-constant) and 3D (both time- and space-varying) convolutional branches to integrate heterogeneous features, while including fairness metrics as a form of regularization to improve equity across demographic groups. We propose two spatiotemporal fairness metrics, region-based fairness gap (RFG), applicable when demographic information is provided as a constant for a region, and individual-based fairness gap (IFG), applicable when a continuous distribution of demographic information is available. Experimental results on bike share and ride share datasets show that FairST can reduce inequity in demand prediction for multiple sensitive attributes (i.e. race, age, and education level), while achieving better accuracy than even state-of-the-art fairness-oblivious methods.

Genre originality of R. Riggs’ novel „Miss Peregrine’s Home for Peculiar Children”

The article carries out a systematic study of the genre of R. Riggs’ work „Miss Peregrine’s Home for Peculiar Children”, establishes its genre originality, states the features of different types of genre in the structure of one work, which is manifested in the multi-genre nature of the work. The article thoroughly and consistently proves that the work of R. Riggs „Miss Peregrine’s Home for Peculiar Children” is a novel form, which is characterized by genre syncretism, as the genre structure combines features of fantasy, adventure, social novels and oral folklore, thoroughly decorated with philosophical motives. This „universality” is formed due to the relevant themes, issues, eidology, plot and compositional features. „Miss Peregrine’s Home for Peculiar Children” is a multi-genre novel that combines several genres. The genre of the work can be called a fantastic-social novel-fairy tale, where the philosophical and psychological themes are constant. The author managed to reveal important social and psychological themes within the fantastic chronotope, which is presented by comparing real and unreal time-space. Constant in the novel is the image of the protagonist, who is the narrator, through the perspective of which the story achieves its subjectivity. The novel is characterized by a set of motives: social (war, genocide, inclusion, etc.), existential (meaning of life, existence of personality), psychological (loneliness, soul, loss), socio-historical (war, friendship, love, help), philosophical (good and evil, death, life), etc., which, combined, form a complex and unique artistic world of the novel form.

Wide-area low-energy surface stimulation of large mammalian ventricular tissue

The epicardial and endocardial surfaces of the heart are attractive targets to administer antiarrhythmic electrotherapies. Electrically stimulating wide areas of the surfaces of small mammalian ventricles is straightforward given the relatively small scale of their myocardial dimensions compared to the tissue space constant and electrical field. However, it has yet to be proven for larger mammalian hearts with tissue properties and ventricular dimensions closer to humans. Our goal was to address the feasibility and impact of wide-area electrical stimulation on the ventricular surfaces of large mammalian hearts at different stimulus strengths. This was accomplished by placing long line electrodes on the ventricular surfaces of pig hearts that span wide areas, and activating them individually. Stimulus efficacy was assessed and compared between surfaces, and tissue viability was evaluated. Activation time was dependent on stimulation strength and location, achieving uniform linear stimulation at 9x threshold strength. Endocardial stimulation activated more tissue transmurally than epicardial stimulation, which could be considered a potential target for future cardiac electrotherapies. Overall, our results indicate that electrically stimulating wide areas of the ventricular surfaces of large mammals is achievable with line electrodes, minimal tissue damage, and energies under the human pain threshold (100 mJ).

GAUSSIAN CURVATURE AND UNICITY PROBLEM OF GAUSS MAPS OF VARIOUS CLASSES OF SURFACES

In this article, we establish a new estimate for the Gaussian curvature of open Riemann surfaces in Euclidean three-space with a specified conformal metric regarding the uniqueness of the holomorphic maps of these surfaces. As its applications, we give new proofs on the unicity problems for the Gauss maps of various classes of surfaces, in particular, minimal surfaces in Euclidean three-space, constant mean curvature one surfaces in the hyperbolic three-space, maximal surfaces in the Lorentz–Minkowski three-space, improper affine spheres in the affine three-space and flat surfaces in the hyperbolic three-space.