Browsing by Author "Silva, J."

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    Gestão da informação e aprendizagem no instituto euvaldo lodi de minas gerais
    (2014) Silva, J.; Saraiva, Alex Silva; Briones Salazar, Leopoldo
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    Impact of acute psychosocial stress on attentional control in humans. A study of evoked potentials and pupillary response
    (2023) Rojas Thomas, Felipe Eduardo; Artigas, C.; Wainstein, G.; Morales, Juan-Pablo; Arriagada, M.; Soto, D.; Dagnino-Subiabre, A.; Silva, J.; López, V.Rojas Thomas, Felipe Eduardo; Artigas, C.; Wainstein, G.; Morales, Juan-Pablo; Arriagada, M.; Soto, D.; Dagnino-Subiabre, A.; Silva, J.; López, V.
    Psychosocial stress has increased considerably in our modern lifestyle, affecting global mental health. Deficits in attentional control are cardinal features of stress disorders and pathological anxiety. Studies suggest that changes in the locus coeruleus-norepinephrine system could underlie the effects of stress on top-down attentional control. However, the impact of psychosocial stress on attentional processes and its underlying neural mechanisms are poorly understood. This study aims to investigate the effect of psychosocial stress on attentional processing and brain signatures. Evoked potentials and pupillary activity related to the oddball auditory paradigm were recorded before and after applying the Montreal Imaging Stress Task (MIST). Electrocardiogram (ECG), salivary cortisol, and subjective anxiety/stress levels were measured at different experimental periods. The control group experienced the same physical and cognitive effort but without the psychosocial stress component. The results showed that stressed subjects exhibited decreased P3a and P3b amplitude, pupil phasic response, and correct responses. On the other hand, they displayed an increase in Mismatch Negativity (MMN). N1 amplitude after MIST only decreased in the control group. We found that differences in P3b amplitude between the first and second oddball were significantly correlated with pupillary dilation and salivary cortisol levels. Our results suggest that under social-evaluative threat, basal activity of the coeruleus-norepinephrine system increases, enhancing alertness and decreasing voluntary attentional resources for the cognitive task. These findings contribute to understanding the neurobiological basis of attentional changes in pathologies associated with chronic psychosocial stress.
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    Tribromophenol and pentachlorophenol uptake from sawdust to horticultural products
    (TAYLOR & FRANCIS LTD, 2009) Mardones, C.; Von Baer, D.; Silva, J.; Ruff, A.; Gutierrez, L.; Berg, A.
    This paper presents a study of the uptake of 2,4,6-tribromophenol (TBP), pentachlorophenol (PCP), and its metabolite pentachloroanisole (PCA) from contaminated sawdust from the forest industry in horticultural products such as apples, raspberries, and fodder maize for cattle feed. The samples were obtained from Bio-Bio Province in South Chile between 2002 and 2006. The analytical parameters of the methodology applied to the different matrices are presented and discussed. The chromatographic method was applied to determine the residues in 413 horticultural product samples. Eleven per cent of fodder maize samples showed detectable or quantifiable levels of PCP, TBP or PCA, 3% of samples presented quantifiable levels, although the concentrations surpassed the maximum allowed concentrations for vegetables (10 mu g kg-1) in only two samples. Traces of TBP were detected in eight samples, PCA was detected in 15, and PCP in 14 samples. Based on these results, a risk analysis was performed, indicating a low probability, 0.4% for PCA, 1.6% for TBP and 1.9% for PCP, to find concentrations higher than the allowed maximum. For apples and raspberries, no residues of these compounds were detected. These results indicate that those cultivars directly exposed to sawdust, like fodder maize, could contain detectable residues in several samples. To confirm this observation, a field assay was performed on fodder maize cultivated in the presence of sawdust artificially contaminated with 30 mg of TBP and/or PCP under controlled conditions. The results showed that under the experimental conditions used in the study, TBP can be transferred from sawdust to the plant, with an uptake rate of 0.04% from the TBP applied initially with sawdust but not to the corn ear. Also, the degradation of PCP to PCA was observed in the soil.