Emergent epileptiform activity in neural networks with weak excitatory synapses.

Brain electrical activity recorded during an epileptic seizure is frequently associated with rhythmic discharges in cortical networks. Current opinion in clinical neurophysiology is that strongly coupled networks and cellular bursting are prerequisites for the generation of epileptiform activity. Contrary to expectations, we found that weakly coupled cortical networks can create synchronized cellular activity and seizure-like bursting. Evaluation of a range of synaptic parameters in a detailed computational model revealed that seizure-like activity occurs when the excitatory synapses are weakened. Guided by this observation, we confirmed experimentally that, in mouse neocortical slices, a pharmacological reduction of excitatory synaptic transmission elicited sudden onset of repetitive network bursting. Our finding provides powerful evidence that onset of seizures can be associated with a reduction in synaptic transmission. These results open a new avenue to explore network synchrony and may ultimately lead to a rational approach to treatment of network pathology in epilepsy.     

Sample size and error in the determination of mode shapes by principal components analysis

Principal components analysis (PCA) is a multivariate statistical technique that transforms a data set having a large number of inter-related variables to a new set of uncorrelated variables called the principal components, determined to allow the dimensionality of the data set to be reduced while retaining as much of the variation present as possible. PCA can be applied to dynamic structural response data to identify the predominant modes of vibration of the structure. Because PCA is a statistical technique, there are errors in the computed modes due to the use of a sample of finite size. The aim of this paper is to study the effect of sample size on the accuracy with which the modes of vibration can be computed. The paper focuses predominantly on elastic response data and examines the potential influence of various parameters such as the period of the structure, the input excitation, and the spatial distribution of mass over the structure. Issues relating to errors in the modes of nonlinear structures are also discussed.     

A statnet Tutorial

The statnet suite of R packages contains a wide range of functionality for the statistical analysis of social networks, including the implementation of exponential-family random graph (ERG) models. In this paper we illustrate some of the functionality of statnet through a tutorial analysis of a friendship network of 1,461 adolescents.     

Validation of language subtypes in learning disabled children.

Hypothesized that children characterized by deficits in narrative skills, relative to other language skills (e.g., syntactic and semantic), would be most at risk for general academic problems, especially in reading comprehension. Using data from a previous longitudinal study by the 1st author and J. D. McKinney (see record 1985-02522-001), different subtypes of language disability were identified in 63 6- and 7-yr-old learning disabled (LD) children. Comparison data had been obtained from 66 non-LD children matched to the LD sample on age, race, and sex. Results, obtained with hierarchical cluster analysis, indicate that 6 language subtypes were derived and that these were both internally consistent and externally valid, being differentially linked to reading and math achievement over a 3-yr period. Narrative ability was shown to be relatively important in predicting academic outcomes. The 3 subtypes showing the poorest academic outcomes had the highest relative scores in syntax and semantics. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensitivity to the locomotor stimulant effects of ethanol and allopregnanolone is influenced by common genes.

Allopregnanolone is a neuroactive steroid that, like ethanol (EtOH), has stimulant, anxiolytic, ataxic, and depressant effects. Two experiments tested the hypothesis that sensitivity to the locomotor stimulant effects of these drugs is influenced by a common set of genes. Sensitivity to the locomotor stimulant effects of allopregnanolone was determined in 24 BXD recombinant inbred (RI) strains. Strain means were positively correlated with extant means for EtOH stimulation in 20 of the same strains. Quantitative trait locus (QTL) analysis provisionally identified many loci, including several known to influence sensitivity to EtOH. Sensitivity to allopregnanolone was also measured in FAST and SLOW mice, which were selectively bred for differential locomotor response to EtOH, to determine whether selection has also altered allopregnanolone sensitivity. FAST mice were more sensitive to the stimulant effects of allopregnanolone compared with SLOW mice. These data suggest that sensitivity to the locomotor stimulant effects of these drugs is influenced by common genes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Australian influences on Elton Mayo: The construct of revery in industrial society.

Elton Mayo was born in Australia and spent most of his first 42 years living in that country. This article explores the Australian context in which he developed his views of industrial society. There are key differences between the political context of Australia compared with that of the United States during the time that Mayo developed his approach to psychology and the role of workers in industry. In addition, the social context in which Mayo established his career was shaped by significant political events in Australia. The construct of revery, which describes a specific state of consciousness, is central to Mayo's early theorizing and was developed by Mayo partly in reaction to political and industrial conflict occurring in Australia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phase-Based Frequency Estimation: A Review

Fowler, M. L., Phase-Based Frequency Estimation: A Review, Digital Signal Processing12 (2002) 590–615This paper provides a review of efficient frequency estimation methods that use only the phases of the signal samples. Such methods continue to attract attention in various applications such as radar, electronic warfare, and next-generation communication systems. We present the details of the basic phase-based method, including its theoretical basis and its performance characterization, and provide an integrated presentation of its threshold behavior. In addition, we review several improvements, implementations, and extensions of the basic method and give some new results and viewpoints. In particular, the paper shows that Kay's method is equivalent to Tretter's method together with a simple phase unwrapping algorithm (thus, Kay's method does not really avoid phase unwrapping errors). We also show that a phase-based method for estimating chirp parameters has an advantage when applied to sinusoids: improved threshold behavior. We present a method that, unlike most of the other phase-based methods, can start processing the signal before knowing the number of samples.     

Human monocyte-derived macrophages express an approximately 120-kD Ox-LDL binding protein with strong identity to CD68

A protein that specifically binds oxidized LDL (Ox-LDL) has recently been characterized in mouse peritoneal macrophages and identified as macrosialin, a protein with a molecular weight of 95 kD. First, the present work shows that human monocyte-derived macrophages express a membrane protein with a molecular weight of approximately 120 kD that selectively binds Ox-LDL. Second, we tested whether this approximately 120-kD Ox-LDL binding protein had any relation to CD68, the human homologue of macrosialin. The following evidence was obtained to support the role of CD68 as an Ox-LDL binding protein: (1) Ligand blots with Ox-LDL and Western blots with Ki-M6, an anti-human CD68 monoclonal antibody, revealed a single band with a molecular weight of approximately 120 kD under reducing and nonreducing condition. (2) The expression patterns of the approximately 120-kD Ox-LDL binding membrane protein and of CD68 paralleled each other during monocyte/macrophage differentiation. (3) Digestion with N-glycosidase F demonstrated that both CD68 and the Ox-LDL binding protein are glycoproteins; both showed a similar shift of approximately 18 kD in apparent molecular weight. (4) CD68, probed with monoclonal antibody Ki-M6, and the approximately 120-kD Ox-LDL binding protein were coprecipitated with EMB11, another anti-CD68 antibody. About 5000 molecules of CD68 are expressed on the cell surface of human macrophages. Ligation of 125I-Ki-M6 to cells leads to its internalization and degradation. This capacity would be sufficient to allow for the specific uptake and degradation of Ox-LDL. Taken together, these data support a role for CD68 as a specific Ox-LDL binding protein in human monocyte-derived macrophages.