Multi-Scale Codes in the Nervous System: The Problem of Noise Correlations and the Ambiguity of Periodic Scales

Encoding information about continuous variables using noisy computational units is a challenge; nonetheless, asymptotic theory shows that combining multiple periodic scales for coding can be highly precise despite the corrupting influence of noise (Mathis et al., Phys. Rev. Lett. 2012). Indeed, cortex seems to use such stochastic multi-scale periodic `grid codes' to represent position accurately. We show here how these codes can be read out without taking the asymptotic limit; even on short time scales, the precision of neuronal grid codes scales exponentially in the number N of neurons. Does this finding also hold for neurons that are not statistically independent? To assess the extent to which biological grid codes are subject to statistical dependencies, we analyze the noise correlations between pairs of grid code neurons in behaving rodents. We find that if the grids of the two neurons align and have the same length scale, the noise correlations between the neurons can reach 0.8. For increasing mismatches between the grids of the two neurons, the noise correlations fall rapidly. Incorporating such correlations into a population coding model reveals that the correlations lessen the resolution, but the exponential scaling of resolution with N is unaffected.Comment: 11 pages, 9 figure

Optimal Population Codes for Space: Grid Cells Outperform Place Cells

Rodents use two distinct neuronal coordinate systems to estimate their position: place fields in the hippocampus and grid fields in the entorhinal cortex. Whereas place cells spike at only one particular spatial location, grid cells fire at multiple sites that correspond to the points of an imaginary hexagonal lattice. We study how to best construct place and grid codes, taking the probabilistic nature of neural spiking into account. Which spatial encoding properties of individual neurons confer the highest resolution when decoding the animal’s position from the neuronal population response? A priori, estimating a spatial position from a grid code could be ambiguous, as regular periodic lattices possess translational symmetry. The solution to this problem requires lattices for grid cells with different spacings; the spatial resolution crucially depends on choosing the right ratios of these spacings across the population. We compute the expected error in estimating the position in both the asymptotic limit, using Fisher information, and for low spike counts, using maximum likelihood estimation. Achieving high spatial resolution and covering a large range of space in a grid code leads to a trade-off: the best grid code for spatial resolution is built of nested modules with different spatial periods, one inside the other, whereas maximizing the spatial range requires distinct spatial periods that are pairwisely incommensurate. Optimizing the spatial resolution predicts two grid cell properties that have been experimentally observed. First, short lattice spacings should outnumber long lattice spacings. Second, the grid code should be self-similar across different lattice spacings, so that the grid field always covers a fixed fraction of the lattice period. If these conditions are satisfied and the spatial “tuning curves” for each neuron span the same range of firing rates, then the resolution of the grid code easily exceeds that of the best possible place code with the same number of neurons

Resolution of Nested Neuronal Representations Can Be Exponential in the Number of Neurons

Collective computation is typically polynomial in the number of computational elements, such as transistors or neurons, whether one considers the storage capacity of a memory device or the number of floating-point operations per second of a CPU. However, we show here that the capacity of a computational network to resolve real-valued signals of arbitrary dimensions can be exponential in N, even if the individual elements are noisy and unreliable. Nested, modular codes that achieve such high resolutions mirror the properties of grid cells in vertebrates, which underlie spatial navigation

Immunologic and Molecular Characteristics of Encephalitozoon-Like Microsporidia Isolated from Humans and Rabbits Indicate That Encephalitozoon cuniculi Is a Zoonotic Parasite

To assess the zoonotic potential of Encephalitozoon-like microsporidia, we isolated and cultivated spores from specimens of urine, respiratory secretions, and stool from six patients infected with human immunodeficiency virus and from nine rabbits. Because spores of Encephalitozoon-like species are indistinguishable by microscopy, we characterized the isolates by western blot analysis and by restriction enzyme analysis of the small subunit (SSU) rDNA after amplification by the polymerase chain reaction. We identified Septata intestinalis in one patient and Encephalitozoon hellem in two symptomatic patients. Encephalitozoon cuniculi was found in all rabbits and in three patients. One of these patients had clinical manifestations of infection with this parasite (severe interstitial pneumonitis). We observed abatement of symptoms and cessation of parasite excretion when these patients were treated with albendazole. Our findings suggest that E. cuniculi may be pathogenic in humans and that it is a zoonotic parasit

Local transmission of the eye worm Thelazia callipaeda in southern Germany

This report describes the first assumed locally transmitted case of the eye worm Thelazia callipaeda in a dog living in southern Germany. A 4-year-old male golden retriever from the town of Bühl in north eastern Baden-Württemberg, about 10km from the German-French border, showed one sided lacrimation for over 2weeks. Despite the application of antibiotics, there was no improvement, and the dog additionally showed blepharospasmus, epiphora and red conjunctivas. A deepened eye inspection revealed five whitish filiform parasites that were morphologically identified as T. callipaeda. The partial sequence of the mitochondrial cytochrome c oxidase subunit 1 gene (cox1, 605bp) from one specimen revealed a novel haplotype, which differs by 1.3% from the only one (haplotype 1) identified in Europe so far. Since the infected dog had never been abroad with the exception of two daytrips to the close Alsace region in France, the transmission of T. callipaeda most probably was domestic. With the presence of end hosts and Phortica flies nourishing on lachrymal secretions acting as intermediate hosts and an increasing number of dogs travelling to and coming from endemic regions in the South, the establishment of T. callipaeda in large parts of Europe cannot be exclude

Vector competence of Aedes japonicus for chikungunya and dengue viruses

The Asian bush mosquito Aedes japonicus japonicus (Theobald, 1901) [=Ochlerotatus japonicus (sensu Reinert et al., 2004) =Hulecoeteomyia japonica (sensu Reinert et al., 2006)], has invaded large parts of North America and has recently started to spread in Central-Western Europe. The species is suspected to act as a bridge vector of West Nile virus but nothing or very little is known about its vector competence for Chikungunya and Dengue viruses. Here, we report on experiments of laboratory infections of Ae. japonicus with CHIKV and DENV, demonstrating that the species has a vector potential for both viruses. Considering the high abundance of the species in urban environments and its ability to feed on human, these results plead to include this species when processing risk assessments for mosquito-borne diseases

Polymerase chain reaction for detection of patent infections of Echinococcus granulosus ("sheep strain”) in naturally infected dogs

Polymerase chain reaction (PCR) for the identification of eggs of the tapeworm Echinococcus granulosus ("sheep strain”) was evaluated with primers derived from mitochondrial sequences. Specificity of these primers was confirmed by investigating DNA of other strains of E. granulosus and of 14 helminth species which inhabit the intestines of dogs. This PCR assay was used to investigate 131 purged dogs from Kazakhstan. Eighteen dogs harboured Echinococcus worms, ten of them in mixed infections with Taenia spp. Coproantigen detection was positive in 15 and taeniid eggs could be recovered from 13 of these specimens. Eight of the egg-containing samples were positive in the PCR for E. granulosus and four in a Echinococcus multilocularis -specific PCR revealing one mixed infection. Egg-containing faeces from two dogs harbouring both Taenia spp. and Echinococcus spp. were negative in both PCRs. The combination of egg isolation and PCR will also be of value in epidemiological studies when investigating environmental sample

Polycomplexes of Hyaluronic Acid and Borates in a Solid State and Solution: Synthesis Characterization and Perspectives of Application in Boron Neutron Capture Therapy

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Identification of field-caught Culicoides biting midges using matrix-assisted laser desorption/ionization time of flight mass spectrometry

Culicoides biting midges are of great importance as vectors of pathogens and elicitors of allergy. As an alternative for the identification of these tiny insects, matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) was evaluated. Protein mass fingerprints were determined for 4-5 field-caught reference (genetically confirmed) individuals of 12 Culicoides species from Switzerland, C. imicola from France, laboratory-reared C. nubeculosus and a non-biting midge. Reproducibility and accuracy of the database was tested in a validation study by analysing 108 mostly field-caught target Culicoides midges and 3 specimens from a non-target species. A reference database of biomarker mass sets containing between 24 and 38 masses for the different species could be established. Automated database-based identification was achieved for 101 of the 108 specimens. The remaining 7 midges required manual full comparison with the reference spectra yielding correct identification for 6 specimens and an ambiguous result for the seventh individual. Specimens of the non-target species did not yield identification. Protein profiling by MALDI-TOF, which is compatible with morphological and genetic identification of specimens, can be used as an alternative, quick and inexpensive tool to accurately identify Culicoides biting midges collected in the fiel