EEG functional connectivity as a Riemannian mediator: An application to malnutrition and cognition.

Mediation analysis assesses whether an exposure directly produces changes in cognitive behavior or is influenced by intermediate "mediators". Electroencephalographic (EEG) spectral measurements have been previously used as effective mediators representing diverse aspects of brain function. However, it has been necessary to collapse EEG measures onto a single scalar using standard mediation methods. In this article, we overcome this limitation and examine EEG frequency-resolved functional connectivity measures as a mediator using the full EEG cross-spectral tensor (CST). Since CST samples do not exist in Euclidean space but in the Riemannian manifold of positive-definite tensors, we transform the problem, allowing for the use of classic multivariate statistics. Toward this end, we map the data from the original manifold space to the Euclidean tangent space, eliminating redundant information to conform to a "compressed CST." The resulting object is a matrix with rows corresponding to frequencies and columns to cross spectra between channels. We have developed a novel matrix mediation approach that leverages a nuclear norm regularization to determine the matrix-valued regression parameters. Furthermore, we introduced a global test for the overall CST mediation and a test to determine specific channels and frequencies driving the mediation. We validated the method through simulations and applied it to our well-studied 50+-year Barbados Nutrition Study dataset by comparing EEGs collected in school-age children (5-11 years) who were malnourished in the first year of life with those of healthy classmate controls. We hypothesized that the CST mediates the effect of malnutrition on cognitive performance. We can now explicitly pinpoint the frequencies (delta, theta, alpha, and beta bands) and regions (frontal, central, and occipital) in which functional connectivity was altered in previously malnourished children, an improvement to prior studies. Understanding the specific networks impacted by a history of postnatal malnutrition could pave the way for developing more targeted and personalized therapeutic interventions. Our methods offer a versatile framework applicable to mediation studies encompassing matrix and Hermitian 3D tensor mediators alongside scalar exposures and outcomes, facilitating comprehensive analyses across diverse research domains.

Temporal and segmental distribution of constitutive and inducible nitric oxide synthases after traumatic spinal cord injury: effect of aminoguanidine treatment.

Nitric oxide (NO) has been shown to play an important role in the pathophysiology of traumatic brain injury (TBI) and cerebral ischemia. However, its contribution to the pathogenesis of traumatic spinal cord injury (SCI) remains to be clarified. This study determined the time course of constitutive and inducible nitric oxide synthases (cNOS and iNOS, respectively) after SCI. Rats underwent moderate SCI at T10 using the NYU impactor device and were allowed to survive for 3, 6, or 24 h and 3 days after SCI (n = 5 in each group). For the determination of enzymatic activities, spinal cords were dissected into five segments, including levels rostral and caudal (remote) to the injury site. Other rats were perfusion fixed for the immunohistochemical localization of iNOS protein levels. cNOS activity was significantly decreased at 3 and 6 h within the traumatized T10 segment and at 3, 6, and 24 h at the rostral (T9) level (p < 0.05). Rostral (T8) and caudal (T11, T12) to the injury site cNOS activity was also decreased at 3 h after injury (p < 0.05). However, cNOS activity returned to control levels within 6 h at T8, T11 and T12 and at one day at T10 and T9 segments. iNOS enzymatic activity was elevated at all time points tested (p < 0.05), with the most robust increase observed at 24 h. Immunostaining for iNOS at 24 h revealed that a significant cellular source of iNOS protein appeared to be invading polymorphonuclear leukocytes (PMNLs). To assess the functional consequences of iNOS inhibition, aminoguanidine treatment was initiated 5 min after SCI and rats tested using the BBB open field locomotor score. Treated rats demonstrated significantly improved hindlimb function up to 7 weeks after SCI. Histopathological analysis of contusion volume showed that aminoguanidine treatment decreased lesion volume by 37% (p < 0.05). In conclusion, these results indicate that (1) cNOS and iNOS activities are regionally and temporally affected after moderate SCI, (2) the early accumulation of PMNLs are a potentially significant source of NO-induced cytotoxic products, and (3) acute aminoguanidine treatment significantly improves functional and histopathological outcome after SCI.

Lines of principal curvature on canal surfaces in R3.

In this paper are determined the principal curvatures and principal curvature lines on canal surfaces which are the envelopes of families of spheres with variable radius and centers moving along a closed regular curve in R3. By means of a connection of the differential equations for these curvature lines and real Riccati equations, it is established that canal surfaces have at most two isolated periodic principal lines. Examples of canal surfaces with two simple and one double periodic principal lines are given.

Tori embedded in S³ with dense asymptotic lines

In this paper are given examples of tori T² embedded in S³ with all their asymptotic lines dense.

Neste artigo são dados exemplos de toros T² mergulhados em S³ com todas as suas linhas assintóticas densas.

Texto para discussão N. 971: Iniqüidade social no Brasil: uma aproximação e uma tentativa de dimensionamento / Text for discussion N. 971: Social inequity in Brazil: an approach and an attempt at sizing

"O Plano Plurianual (PPA) 2000-2003 declara como um de seus mais importantes objetivos a redução da extrema desigualdade social existente no Brasil. A fim de avaliar o desempenho global do plano e o alcance de seus macroobjetivos, elabora um indicador sintético que capte os aspectos mais relevantes da desigualdade social."

Subsídios para organizar avaliaçöes da açäo governamental / Subsidies to organize valutions of governmental actions

Relata que a reorganização do processo de planejamento, orçamento e gestão do governo federal está em curso e que o Congresso Nacional aprovou o primeiro Plano Plurianual elaborado em novas bases conceituais e metodológicas, determinando que se proceda, anualmente, à avaliação global do plano e de cada um dos programas que o integram. Afirma que inexiste, na administração pública brasileira, uma prática consagrada ou uma cultura institucional de avaliação e que conceitos, metodologias, sistemas de informações terão que ser criados e desenvolvidos com a finalidade específica de suportar a implantação do processo regular e recorrente de avaliações da ação governamental. Traz subsídios para essa construção.

Programação convergente e controle social das ações de governo / Convergent programming and social control of government actions

Apresenta sugestões para programar e acompanhar ações dos governos. Sugere que, estrategicamente, é importante combater a miséria nas áreas onde é maior o potencial para implementação de transformações estruturais. Supõe que, havendo vontade política, é possível eliminar a fome e a miséria em não mais do que dez anos