Semiparametric Bayesian Analysis of Nutritional Epidemiology Data in the Presence of Measurement Error

Summary : We propose a semiparametric Bayesian method for handling measurement error in nutritional epidemiological data. Our goal is to estimate nonparametrically the form of association between a disease and exposure variable while the true values of the exposure are never observed. Motivated by nutritional epidemiological data, we consider the setting where a surrogate covariate is recorded in the primary data, and a calibration data set contains information on the surrogate variable and repeated measurements of an unbiased instrumental variable of the true exposure. We develop a flexible Bayesian method where not only is the relationship between the disease and exposure variable treated semiparametrically, but also the relationship between the surrogate and the true exposure is modeled semiparametrically. The two nonparametric functions are modeled simultaneously via B‐splines. In addition, we model the distribution of the exposure variable as a Dirichlet process mixture of normal distributions, thus making its modeling essentially nonparametric and placing this work into the context of functional measurement error modeling. We apply our method to the NIH‐AARP Diet and Health Study and examine its performance in a simulation study.     

Early Holocene human skeletal remains from Santana do Riacho,Brazil: implications for the settlement of the New World

In this study we compare the cranial morphology of several late Paleoindian skeletons uncovered at Santana do Riacho, Central Brazil, with worldwide human cranial variation. Mahalanobis Distance and Principal Component Analysis are used to explore the extra-continental morphological affinities of the Brazilian Paleoindian sample. Santana do Riacho is a late Paleoindian burial site where approximately 40 individuals were recovered in varying states of preservation. The site is located at Lagoa Santa/Serra do Cipó, State of Minas Gerais. The first human activities in this rockshelter date back to the terminal Pleistocene, but the burials are bracketed between circa 8200 and 9500BP. The collection contains only six skulls well-enough preserved to be measured. The Santana do Riacho late Paleoindians present a cranial morphology characterized by long and narrow neurocrania, low and narrow faces, with low nasal apertures and orbits. The multivariate analyses show that they exhibit strong morphological affinities with present day Australians and Africans, showing no resemblance to recent Northern Asians and Native Americans. These findings confirm our long held opinion that the settlement of the Americas was more complicated in terms of biological input than has been widely assumed. The working hypothesis is that two very distinct populations entered the New World by the end of the Pleistocene, and that the transition between the cranial morphology of the Paleoindians and the morphology of later Native Americans, which occurred around 8-9ka, was abrupt. This, in our opinion, is a more parsimonious explanation for the diversity detected than a long, local microevolutionary process mediated by selection and drift. The similarities of the first South Americans with sub-Saharan Africans may result from the fact that the non-Mongoloid Southeast Asian ancestral population came, ultimately, from Africa, with no major modification in the original cranial bau plan of the first modern humans.     

Oscillatory neural network model of attention focus formation and control

A new mechanism to control attention focus formation and switching in the model of selective attention is suggested and studied. The model is based on an oscillatory neural network (ONN) with the star-like architecture and phase shifts in connections between oscillators. Attention is modelled as a dynamical mode of partial synchronisation between a particular subgroup of oscillators and the central oscillator (CO). A new theoretical method to study full and partial synchronisation in the system is presented. Equations for the frequency of synchronisation are derived which allow the programming of the dynamical behaviour of the system depending on the parameters. In particular, we show that phase shifts in connections between oscillators provide an efficient mechanism of attention control.     

NK cells respond to pulmonary infection with Mycobacterium tuberculosis, but play a minimal role in protection

Both innate and adaptive immune systems contribute to host defense against infection with Mycobacterium tuberculosis. NK cells have been associated with early resistance against intracellular pathogens and are known to be potent producers of the cytokine IFN-gamma. In C57BL/6 mice infected by aerosol exposure with M. tuberculosis, NK cells increased in the lungs over the first 21 days of infection. Expansion of the NK cell subset was associated with increased expression of activation and maturation markers. In addition, NK cells isolated from the infected lungs were capable of producing IFN-gamma and became positive for perforin. In vivo depletion of NK cells using a lytic Ab had no influence on bacterial load within the lungs. These findings indicate that NK cells can become activated during the early response to pulmonary tuberculosis in the mouse model and are a source of IFN-gamma, but their removal does not substantially alter the expression of host resistance.     

Visual perception of ambiguous figures: synchronization based neural models

We develop and study two neural network models of perceptual alternations. Both models have a star-like architecture of connections with a central element connected to a set of peripheral elements. A particular perception is simulated in terms of partial synchronization between the central element and some sub-group of peripheral elements. The first model is constructed from phase oscillators and the mechanism of perceptual alternations is based on chaotic intermittency under fixed parameter values. Similar to experimental evidence, the distribution of times between perceptual alternations is represented by the gamma distribution. The second model is built of spiking neurons of the Hodgkin–Huxley type. The mechanism of perceptual alternations is based on plasticity of inhibitory synapses which increases the inhibition from the central unit to the neural assembly representing the current percept. As a result another perception is formed. Simulations show that the second model is in good agreement with behavioural data on switching times between percepts of ambiguous figures and with experimental results on binocular rivalry of two and four percepts. This article is part of a special issue on Neuronal Dynamics of Sensory Coding. This special issue is in honour of Professor Pepe Segundo who is one of the pioneers in the study of neural coding. Pepe has been an active participant in many Neural Coding Workshops sharing his great knowledge and experience of research in this field. I (R. Borisyuk) was very happy to meet Pepe for the first time in Prague when attending the first Neural Coding Workshop in 1995. From that time we regularly met at Neural Coding Workshops and these meetings have always been very stimulating and fruitful for my research. Remarkably, the first paper I studied at the beginning of my scientific career was a seminal paper by Moore et al. (1970). For me, this paper provided a great opportunity to learn the basic statistical techniques for the analysis of multiple spike trains and neural coding. According to the Institute of Scientific Information, this paper has been cited 380 times! This exciting paper has inspired my research into the synaptic and functional connectivity of neural circuits derived from spike-train recordings (Borisyuk et al. 1985; Stuart et al. 2005) and guided my search for new ideas on neural coding.     

Effects of anionic polyacrylamide on maize growth: a short term 14C labeling study

Plant and Soil - Various anionic polyacrylamide polymers (PAMs) are frequently used to improve soil properties and reduce erosion. However, the effects of their application on plant growth remain...