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Activity Variation (activity + variation)

Distribution by Scientific Domains
Life Sciences50%

Selected Abstracts

Differential patterns of cortical activation as a function of fluid reasoning complexity

HUMAN BRAIN MAPPING, Issue 2 2009
Bernardo Perfetti
Abstract Fluid intelligence (gf) refers to abstract reasoning and problem solving abilities. It is considered a human higher cognitive factor central to general intelligence (g). The regions of the cortex supporting gf have been revealed by recent bioimaging studies and valuable hypothesis on the neural correlates of individual differences have been proposed. However, little is known about the interaction between individual variability in gf and variation in cortical activity following task complexity increase. To further investigate this, two samples of participants (high-IQ, N = 8; low-IQ, N = 10) with significant differences in gf underwent two reasoning (moderate and complex) tasks and a control task adapted from the Raven progressive matrices. Functional magnetic resonance was used and the recorded signal analyzed between and within the groups. The present study revealed two opposite patterns of neural activity variation which were probably a reflection of the overall differences in cognitive resource modulation: when complexity increased, high-IQ subjects showed a signal enhancement in some frontal and parietal regions, whereas low-IQ subjects revealed a decreased activity in the same areas. Moreover, a direct comparison between the groups' activation patterns revealed a greater neural activity in the low-IQ sample when conducting moderate task, with a strong involvement of medial and lateral frontal regions thus suggesting that the recruitment of executive functioning might be different between the groups. This study provides evidence for neural differences in facing reasoning complexity among subjects with different gf level that are mediated by specific patterns of activation of the underlying fronto-parietal network. Hum Brain Mapp, 2009. © 2007 Wiley-Liss, Inc. [source]

Climatic signals in tree-rings of Araucaria angustifolia in the southern Brazilian highlands

AUSTRAL ECOLOGY, Issue 2 2010
JULIANO MORALES OLIVEIRA
Abstract Araucaria angustifolia (Bertol.) O. Kuntze (Araucariaceae) is a Neotropical tree, widely distributed in subtropical mountain rain forests and nearby natural grasslands of Southern Brazil. This species produces annual growth rings, but its dendroclimatic potential is barely known. In the present paper, the long-term growth patterns of A. angustifolia were investigated using annual growth ring time series and association to climate over the last century. Wood cores of A. angustifolia trees growing in forest and grassland habitats were obtained with an increment borer. The cores were surfaced, measured and cross-dated. The dated ring-width time series were standardized and submitted to correlation and principal component analysis to verify growth trends among sites and trees. Growth-climate relationships were investigated using correlation and regression analyses, comparing the ordination axes scores to regional time series of precipitation and temperature. Due to anatomical irregularities, mainly partial rings, only 35 out of 60 trees were cross-dated. The correlation and ordination analyses showed common tree-growth trends within and between sites, indicative of a regional environmental force determining inter-annual cambial activity variation. Despite growing in distinct habitats and disturbance regimes, A. angustifolia trees share a common long-term growth pattern, which is significantly related to thermal conditions during the current and previous growing seasons. Moreover, site-specific characteristics may have influenced opposite growth responses and association to climate conditions between forest and grassland trees. [source]

The 1999 Leonid meteor storm: verification of rapid activity variations by observations at three sites

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2000
W. Singer
We report observations of an unpredicted fine structure in the activity profile of the Leonid meteor storm of 1999 November 18. Our observations were obtained at three widely separated sites (on the Iberian peninsula, in Germany, and in northern Sweden) and with two totally different techniques (video cameras and meteor radars). The observations clearly show quasi-periodic variations of the meteor rate with temporal separations of individual maxima in the 6- to 9-min range. These temporal variations translate into spatial variations within the dust trail with scales between 10 000 and 30 000 km, depending in which reference frame or direction one chooses to compare. The times for the central three maxima as observed at the three sites agree within 2 min of each other after application of the appropriate topocentric time corrections. We consider a number of potential causes for the observed density variations within the meteor stream. [source]

Metabolic activity variations in the sea urchins (Paracentrotus lividus) treated with magnesium and subjected to handling stress and aerial exposure

AQUACULTURE RESEARCH, Issue 9 2010
Soumaya Arafa
Abstract This study assessed the impact of the use of magnesium chloride as a relaxant for the echinoid Paracentrotus lividus on the metabolic activity of individuals subjected to handling stress and aerial exposure. The variation in the gonad moisture content and biochemical composition was compared in sea urchins (P. lividus) treated with magnesium and untreated controls before transport and during 15 days of laboratory acclimation. Sea urchins treated with magnesium maintained higher levels of protein and carbohydrate throughout the trial in comparison with controls. However, the lipid level and fatty acid percentage remained stable during the experiment and no differences were found between treated or non-treated sea urchins . [source]