Coordinated optimization of visual cortical maps (I) Symmetry-based analysis

In the primary visual cortex of primates and carnivores, functional architecture can be characterized by maps of various stimulus features such as orientation preference (OP), ocular dominance (OD), and spatial frequency. It is a long-standing question in theoretical neuroscience whether the observed maps should be interpreted as optima of a specific energy functional that summarizes the design principles of cortical functional architecture. A rigorous evaluation of this optimization hypothesis is particularly demanded by recent evidence that the functional architecture of OP columns precisely follows species invariant quantitative laws. Because it would be desirable to infer the form of such an optimization principle from the biological data, the optimization approach to explain cortical functional architecture raises the following questions: i) What are the genuine ground states of candidate energy functionals and how can they be calculated with precision and rigor? ii) How do differences in candidate optimization principles impact on the predicted map structure and conversely what can be learned about an hypothetical underlying optimization principle from observations on map structure? iii) Is there a way to analyze the coordinated organization of cortical maps predicted by optimization principles in general? To answer these questions we developed a general dynamical systems approach to the combined optimization of visual cortical maps of OP and another scalar feature such as OD or spatial frequency preference.Comment: 90 pages, 16 figure

Coverage, Continuity and Visual Cortical Architecture

The primary visual cortex of many mammals contains a continuous representation of visual space, with a roughly repetitive aperiodic map of orientation preferences superimposed. It was recently found that orientation preference maps (OPMs) obey statistical laws which are apparently invariant among species widely separated in eutherian evolution. Here, we examine whether one of the most prominent models for the optimization of cortical maps, the elastic net (EN) model, can reproduce this common design. The EN model generates representations which optimally trade of stimulus space coverage and map continuity. While this model has been used in numerous studies, no analytical results about the precise layout of the predicted OPMs have been obtained so far. We present a mathematical approach to analytically calculate the cortical representations predicted by the EN model for the joint mapping of stimulus position and orientation. We find that in all previously studied regimes, predicted OPM layouts are perfectly periodic. An unbiased search through the EN parameter space identifies a novel regime of aperiodic OPMs with pinwheel densities lower than found in experiments. In an extreme limit, aperiodic OPMs quantitatively resembling experimental observations emerge. Stabilization of these layouts results from strong nonlocal interactions rather than from a coverage-continuity-compromise. Our results demonstrate that optimization models for stimulus representations dominated by nonlocal suppressive interactions are in principle capable of correctly predicting the common OPM design. They question that visual cortical feature representations can be explained by a coverage-continuity-compromise.Comment: 100 pages, including an Appendix, 21 + 7 figure

New genetic loci link adipose and insulin biology to body fat distribution.

Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms

New susceptibility loci associated with kidney disease in type 1 diabetes

WOS:000309817900008Diabetic kidney disease, or diabetic nephropathy (DN), is a major complication of diabetes and the leading cause of end-stage renal disease (ESRD) that requires dialysis treatment or kidney transplantation. In addition to the decrease in the quality of life, DN accounts for a large proportion of the excess mortality associated with type 1 diabetes (T1D). Whereas the degree of glycemia plays a pivotal role in DN, a subset of individuals with poorly controlled T1D do not develop DN. Furthermore, strong familial aggregation supports genetic susceptibility to DN. However, the genes and the molecular mechanisms behind the disease remain poorly understood, and current therapeutic strategies rarely result in reversal of DN. In the GEnetics of Nephropathy: an International Effort (GENIE) consortium, we have undertaken a meta-analysis of genome-wide association studies (GWAS) of T1D DN comprising ∼2.4 million single nucleotide polymorphisms (SNPs) imputed in 6,691 individuals. After additional genotyping of 41 top ranked SNPs representing 24 independent signals in 5,873 individuals, combined meta-analysis revealed association of two SNPs with ESRD: rs7583877 in the AFF3 gene (P = 1.2×10(-8)) and an intergenic SNP on chromosome 15q26 between the genes RGMA and MCTP2, rs12437854 (P = 2.0×10(-9)). Functional data suggest that AFF3 influences renal tubule fibrosis via the transforming growth factor-beta (TGF-β1) pathway. The strongest association with DN as a primary phenotype was seen for an intronic SNP in the ERBB4 gene (rs7588550, P = 2.1×10(-7)), a gene with type 2 diabetes DN differential expression and in the same intron as a variant with cis-eQTL expression of ERBB4. All these detected associations represent new signals in the pathogenesis of DN.Peer reviewe

Analysis of the elastic net model applied to the formation of ocular dominance and orientation columns

The development and structure of orientation (OR) and ocular dominance (OD) maps in the primary visual cortex of cats and monkeys can be modelled using the elastic net algorithm, which attempts to iind an 'optimal' cortical representation of the input features. Here we analyse this behaviour in terms of parameters of the feature space. We derive expressions for the OR periodicity, and the first bifurcation point as a function of the annealing parameter using the methods of Durbin et al (Durbin R, Szeliski R and Yuille A 1989 Neural Computation 1 348-58). We also investigate the effect of the relative order of OR and OD development on overall map structure. This analysis suggests that developmental order can be predicted from the final OR and OD periodicities. In conjunction with experimentally measured values for these periodicities, the model predicts that (i) in normal macaques OD develops first, (ii) in normal cats OR develops first and (iii) in strabismic cats OD develops first

DELAYED FEEDBACK SUPPRESSION OF COLLECTIVE RHYTHMIC ACTIVITY IN

We analyze the delayed feedback approach to suppression of collective synchrony in a population of globally or randomly coupled neurons. In particular, we consider the main factors of imperfection of the control scheme and their influence on the suppression efficiency. Next, with the help of a realistic model of synaptically coupled population of inhibitory and excitatory neurons we demonstrate the potential of the suppression scheme for neurophysiological applications

Hemochromatosis associated with endothelial dysfunction: Evidence for the role of iron stores in early atherogenesis

Impaired endothelium-dependent, flow-mediated dilatation of the brachial artery was observed in a 50-year-old premenopausal female non-smoker with idiopathic hemochromatosis. Endothelial dysfunction observed in this patient supports a relationship between body iron stores and early atherosclerotic process

Molecular analysis of the estrogen receptor alpha gene in men with coronary artery disease: association with disease status

Background: The vasoprotective effects of estrogens are known to be mediated by their respective estrogen receptors (ER) alpha (ERalpha) and beta (ERbeta), which are present on the vascular wall. The amino-terminal part of the ERalpha appears to be important; genetic alterations in this region have been associated with arterial hypertension. This region has not been studied in atherosclerotic disease. In the present study, we examined the association between coronary artery disease (CAD) and alterations of the NH2-terminal part of ERalpha coding region. Methods: Genomic DNA was isolated from 50 healthy men and 40 men with CAD confirmed by coronary angiography. The coding sequences of exons 1 and 2 were amplified by polymerase chain reaction (PCR) and analyzed by either denaturing gradient gel electrophoresis (DGGE) or single stranded conformational polymorphism (SSCP), or both, sequencing and restriction fragment length polymorphism (RFLP), as appropriate. In the same subjects, biochemical and vascular parameters were also determined by using the appropriate methodology. Results: In exon 1, the codon 10 polymorphism was detected in both patients and healthy men either in heterozygous or homozygous form. The codon 87 polymorphism was detected mainly in homozygous form and only five individuals were heterozygotes. No mutations were found in exon 2. Statistical analysis of the allele distribution for either codon 10 or 87 between patients and healthy men showed no significant difference. In patients, the biochemical parameters were not statistically significantly different between ERalpha codon 10 genotypes or alleles. However, there was a clear effect of the TCT/TCT genotype and TCT allele on the vascular parameters whereas the right internal carotid artery (RICA) intima-media thickness was significantly associated with TCT/TCT genotype and TCT allele. Conclusions: We conclude that ERalpha genotypes play no role in the incidence of CAD disease, however, ERalpha codon 10 may be a genetic factor controlling some vessels’ angiographic complications. (C) 2003 Elsevier Science B.V. All rights reserved