561 research outputs found
Causes and Correlates of Brain Atrophy: A population-based MRI study
__Abstract__
In 1906, Alois Alzheimer described for the first time a form of dementia that later became
known as Alzheimer’s disease. At necropsy, he had observed that the brain of a 51-year-old
woman with progressive cognitive decline was filled with –at that time still anonymous– amyloid
plaques and neurofibrillary tangles. Since then, numerous investigators saw in patients
with dementia the same pathological findings that Alzheimer had seen. Clinically, Alzheimer’s
disease is recognized by a long period of progressive cognitive decline. Braak and Braak
showed in the late eighties that the accumulation of plaques and tangles in the brain follows
a predictable pattern over time that parallels this cognitive decline. In their now widely accepted
staging system, they identify a long phase where the medial temporal lobe is the first
area to be afflicted whereas only in the later disease stages the pathology involves the isocortices.
However, recent pathological studies show that brains of elderly patients, unlike the
middle–aged patient that Alzheimer had observed, who in life receive a diagnosis of Alzheimer’s
disease have a rather mixed bag of brain pathology. Not only the traditionally recognized
amyloid plaques and neurofibrillary tangles are observed but also cerebrovascular disease is
found which could have contributed to the cognitive decline.
The search for causes of Alzheimer’s disease is hampered by its long preclinical period and
the pathological diversity that contribute to clinical symptoms of Alzheimer’s disease
A Bayesian network approach for coastal risk analysis and decision making
Emergency management and long-term planning in coastal areas depend on detailed assessments (meter scale) of flood and erosion risks. Typically, models of the risk chain are fragmented into smaller parts, because the physical processes involved are very complex and consequences can be diverse. We developed a Bayesian network (BN) approach to integrate the separate models. An important contribution is the learning algorithm for the BN. As input data, we used hindcast and synthetic extreme event scenarios, information on land use and vulnerability relationships (e.g., depth-damage curves). As part of the RISC-KIT (Resilience-Increasing Strategies for Coasts toolKIT) project, we successfully tested the approach and algorithm in a range of morphological settings. We also showed that it is possible to include hazards from different origins, such as marine and riverine sources. In this article, we describe the application to the town of Wells-next-the-Sea, Norfolk, UK, which is vulnerable to storm surges. For any storm input scenario, the BN estimated the percentage of affected receptors in different zones of the site by predicting their hazards and damages. As receptor types, we considered people, residential and commercial properties, and a saltmarsh ecosystem. Additionally, the BN displays the outcome of different disaster risk reduction (DRR) measures. Because the model integrates the entire risk chain with DRR measures and predicts in real-time, it is useful for decision support in risk management of coastal areas.European Community's 7th Framework Programme through the grant to RISC-KIT (Resilience-increasing Strategies for Coasts - Toolkit"), contract no. 603458
Silent brain infarcts and the risk of dementia and cognitive decline
BACKGROUND: Silent brain infarcts are frequently seen on magnetic
resonance imaging (MRI) in healthy elderly people and may be associated
with dementia and cognitive decline. METHODS: We studied the association
between silent brain infarcts and the risk of dementia and cognitive
decline in 1015 participants of the prospective, population-based
Rotterdam Scan Study, who were 60 to 90 years of age and free of dementia
and stroke at base line. Participants underwent neuropsychological testing
and cerebral MRI at base line in 1995 to 1996 and again in 1999 to 2000
and were monitored for dementia throughout the study period. We performed
Cox proportional-hazards and multiple linear-regression analyses, adjusted
for age, sex, and level of education and for the presence or absence of
subcortical atrophy and white-matter lesions. RESULTS: During 3697
person-years of follow-up (mean per person, 3.6 years), dementia developed
in 30 of the 1015 participants. The presence of silent brain infarcts at
base line more than doubled the risk of dementia (hazard ratio, 2.26; 95
percent confidence interval, 1.09 to 4.70). The presence of silent brain
infarcts on the base-line MRI was associated with worse performance on
neuropsychological tests and a steeper decline in global cognitive
function. Silent thalamic infarcts were associated with a decline in
memory performance, and nonthalamic infarcts with a decline in psychomotor
speed. When participants with silent brain infarcts at base line were
subdivided into those with and those without additional infarcts at
follow-up, the decline in cognitive function was restricted to those with
additional silent infarcts. CONCLUSIONS: Elderly people with silent brain
infarcts have an increased risk of dementia and a steeper decline in
cognitive function than those without such lesions
Homocysteine and brain atrophy on MRI of non-demented elderly
Patients with Alzheimer's disease have higher plasma homocysteine levels
than controls, but it is uncertain whether higher plasma homocysteine
levels are involved in the early pathogenesis of the disease. Hippocampal,
amygdalar and global brain atrophy on brain MRI have been proposed as
early markers of Alzheimer's disease. In the Rotterdam Scan Study, a
population-based study of age-related brain changes in 1077 non-demented
people aged 60-90 years, we investigated the association between plasma
homocysteine levels and severity of hippocampal, amygdalar and global
brain atrophy on MRI. We used axial T(1)-weighted MRIs to visualize global
cortical brain atrophy (measured semi-quantitatively; range 0-15) and a 3D
HASTE (half-Fourier acquisition single-shot turbo spin echo) sequence in
511 participants to measure hippocampal and amygdalar volumes. We had
non-fasting plasma homocysteine levels in 1031 of the participants and in
505 of the participants with hippocampal and amygdalar volumes.
Individuals with higher plasma homocysteine levels had, on average, more
cortical atrophy [0.23 units (95% CI 0.07-0.38 units) per standard
deviation increase in plasma homocysteine levels] and more hippocampal
atrophy [difference in left hippocampal volume -0.05 ml (95% CI -0.09 to
-0.01) and in right hippocampal volume -0.03 ml (95% CI -0.07 to 0.01) per
standard deviation increase in plasma homocysteine levels]. No association
was observed between plasma homocysteine levels and amygdalar atrophy.
These results support the hypothesis that higher plasma homocysteine
levels are associated with more atrophy of the hippocampus and cortical
regions in elderly at risk of Alzheimer's disease
Higher estrogen levels are not associated with larger hippocampi and better memory performance
BACKGROUND: Estrogens may prevent cognitive decline and Alzheimer disease.
Animal study findings have shown beneficial effects of estrogen on the
brain, particularly on the hippocampus, a structure related to memory
performance and early Alzheimer disease. OBJECTIVE: To investigate whether
higher levels of endogenous estradiol in older women and men are
associated with larger hippocampal volumes on magnetic resonance imaging
and better memory performance. DESIGN AND SETTING: Cross-sectional
analysis within the Rotterdam Scan Study, a population-based study in the
Netherlands of elderly subjects who do not have dementia. PARTICIPANTS:
Two hundred ten women and 202 men, aged 60 to 90 years, with plasma levels
of total estradiol and, in part, 162 women and 149 men also with levels of
bioavailable and free estradiol. MAIN OUTCOME MEASURE: Hippocampal volumes
on magnetic resonance imaging and memory performance (delayed recall).
RESULTS: Women with higher total estradiol levels had smaller hippocampal
volumes and poorer memory performance -0.29 mL (95% confidence interval,
-0.57 to -0.00) and -0.4 (95% confidence interval, -1.3 to 0.5) fewe
Synergistic effects of drought and deforestation on the resilience of the south-eastern Amazon rainforest
The south-eastern Amazon rainforest is subject to ongoing deforestation and is expected to become drier due to climate change. Recent analyses of the distribution of tree cover in the tropics show three modes that have been interpreted as representing alternative stable states: forest, savanna and treeless states. This situation implies that a change in environmental conditions, such as in the climate, could cause critical transitions from a forest towards a savanna ecosystem. Shifts to savanna might also occur if perturbations such as deforestation exceed a critical threshold. Recovering the forest would be difficult as the savanna will be stabilized by a feedback between tree cover and fire. Here we explore how environmental changes and perturbations affect the forest by using a simple model with alternative tree-cover states. We focus on the synergistic effects of precipitation reduction and deforestation on the probability of regime shifts in the south-eastern Amazon rainforest. The analysis indicated that in a large part of the south-eastern Amazon basin rainforest and savanna could be two alternative states, although massive forest dieback caused by mean-precipitation reduction alone is unlikely. However, combinations of deforestation and climate change triggered up to 6.6 times as many local regime shifts than the two did separately, causing large permanent forest losses in the studied region. The results emphasize the importance of reducing deforestation rates in order to prevent a climate-induced dieback of the south-eastern Amazon rainforest
Alcohol intake in relation to brain magnetic resonance imaging findings in older persons without dementia
BACKGROUND: Consumers of light-to-moderate amounts of alcohol have a lower risk of dementia and, possibly, Alzheimer disease than do abstainers. Because vascular disease may contribute to symptoms of Alzheimer disease, reduction of cerebrovascular disease in consumers of light amounts of alcohol could account for that observation. However, a low concentration of alcohol may also have direct effects on the hippocampus, a brain structure highly affected by Alzheimer disease. OBJECTIVE: We investigated alcohol intake in relation to brain magnetic resonance imaging (MRI) findings of presumed vascular
Feature selection and novelty in computational aesthetics
[Abstract] An approach for exploring novelty in expression-based evolutionary art systems is presented. The framework is composed of a feature extractor, a classifier, an evolutionary engine and a supervisor. The evolutionary engine exploits shortcomings of the classifier, generating misclassified instances. These instances update the training set and the classifier is re-trained. This iterative process forces the evolutionary algorithm to explore new paths leading to the creation of novel imagery. The experiments presented and analyzed herein explore different feature selection methods and indicate the validity of the approach.Portugal. Fundação para a Ciência e a Tecnologia; PTDC/EIA–EIA/115667/2009Galicia.ConsellerÃa de Innovación, Industria e Comercio ; PGIDIT10TIC105008P
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