Synchronization and Redundancy: Implications for Robustness of Neural Learning and Decision Making

Learning and decision making in the brain are key processes critical to survival, and yet are processes implemented by non-ideal biological building blocks which can impose significant error. We explore quantitatively how the brain might cope with this inherent source of error by taking advantage of two ubiquitous mechanisms, redundancy and synchronization. In particular we consider a neural process whose goal is to learn a decision function by implementing a nonlinear gradient dynamics. The dynamics, however, are assumed to be corrupted by perturbations modeling the error which might be incurred due to limitations of the biology, intrinsic neuronal noise, and imperfect measurements. We show that error, and the associated uncertainty surrounding a learned solution, can be controlled in large part by trading off synchronization strength among multiple redundant neural systems against the noise amplitude. The impact of the coupling between such redundant systems is quantified by the spectrum of the network Laplacian, and we discuss the role of network topology in synchronization and in reducing the effect of noise. A range of situations in which the mechanisms we model arise in brain science are discussed, and we draw attention to experimental evidence suggesting that cortical circuits capable of implementing the computations of interest here can be found on several scales. Finally, simulations comparing theoretical bounds to the relevant empirical quantities show that the theoretical estimates we derive can be tight.Comment: Preprint, accepted for publication in Neural Computatio

Prevalence of Acanthosis Nigricans in an urban population in Sri Lanka and its utility to detect metabolic syndrome

<p>Abstract</p> <p>Background</p> <p>Insulin resistance (IR) plays a major role in the pathogenesis of metabolic syndrome. Acanthosis nigricans (AN) is an easily detectable skin condition that is strongly associated with IR. The aims of this study were, firstly, to investigate the prevalence of AN among adults in an urban Sri Lankan community and secondly, to describe its utility to detect metabolic syndrome.</p> <p>Findings</p> <p>In a community based investigation, 35-64 year adults who were selected using stratified random sampling, underwent interview, clinical examination, liver ultrasound scanning, and biochemical and serological tests. Metabolic syndrome was diagnosed on revised ATP III criteria for Asian populations. AN was identified by the presence of dark, thick, velvety skin in the neck.</p> <p>2957 subjects were included in this analysis. The prevalence of AN, metabolic syndrome and type 2 diabetes mellitus were 17.4%, 34.8% and 19.6%, respectively. There was a strong association between AN and metabolic syndrome. The sensitivity, specificity, positive predictive value and negative predictive value of AN to detect metabolic syndrome were 28.2%, 89.0%, 45.9% and 79.0% for males, and 29.2%, 88.4%, 65.6% and 62.3% for females, respectively.</p> <p>Conclusions</p> <p>AN was common in our study population, and although it did not have a high enough sensitivity to be utilized as a screening test for metabolic syndrome, the presence of AN strongly predicts metabolic syndrome.</p

Acanthosis nigricans: relation with type 2 diabetes mellitus, anthropometric variables, and body mass in Indians

Objective: To determine the prevalence of acanthosis nigricans (AN) in type 2 diabetes mellitus (T2DM) and its correlation with various anthropometric measurements in Indians. Methods: One hundred and fifty consecutive subjects with T2DM attending the diabetes clinic at a tertiary referral centre in North India were considered as cases and 150 age and sex matched healthy attendants of non-diabetic subjects as controls. All the cases and controls were screened for the presence of AN and its severity. Anthropometric measurements of all of them were measured in standard method. Regression analysis was done to determine the association of AN with T2DM and various anthropometric measurements. Results: The prevalence of AN in subjects with diabetes and healthy controls was 62.6% and 40% respectively, and this difference was significant (p<0.05). Body mass index (BMI) between cases and controls was comparable by chance. There was a statistically significant correlation of increasing severity of AN with increasing BMI, waist circumference, hip circumference, waist-hip ratio, skinfold thickness, and body fat percentage in diabetic patients. However, in regression analysis after considering all the confounding factors there was a significant correlation of AN, only with diabetes mellitus and BMI. Conclusions: Indians have high prevalence of AN and it is an independent cutaneous marker of both T2DM and BMI

Primary Biliary Cholangitis: A Brief Overview.

http://aasldpubs.onlinelibrary.wiley.com/hub/journal/10.1002/(ISSN)2046-2484/video/15-3-reading-louie a video presentation of this article