37 research outputs found
Cortisol, cognition and the ageing prefrontal cortex
The structural and functional decline of the ageing human brain varies by brain
region, cognitive function and individual. The underlying biological mechanisms are
poorly understood. One potentially important mechanism is exposure to
glucocorticoids (GCs; cortisol in humans); GC production is increasingly varied with
age in humans, and chronic exposure to high levels is hypothesised to result in
cognitive decline via cerebral remodelling. However, studies of GC exposure in
humans are scarce and methodological differences confound cross-study comparison.
Furthermore, there has been little focus on the effects of GCs on the frontal lobes and
key white matter tracts in the ageing brain. This thesis therefore examines
relationships among cortisol levels, structural brain measures and cognitive
performance in 90 healthy, elderly community-dwelling males from the Lothian
Birth Cohort 1936. Salivary cortisol samples characterised diurnal (morning and
evening) and reactive profiles (before and after a cognitive test battery). Structural
variables comprised Diffusion Tensor Imaging measures of major brain tracts and a
novel manual parcellation method for the frontal lobes. The latter was based on a
systematic review of current manual methods in the context of putative function and
cytoarchitecture. Manual frontal lobe brain parcellation conferred greater spatial and
volumetric accuracy when compared to both single- and multi-atlas parcellation at
the lobar level. Cognitive ability was assessed via tests of general cognitive ability,
and neuropsychological tests thought to show differential sensitivity to the integrity
of frontal lobe sub-regions. The majority of, but not all frontal lobe test scores shared
considerable overlap with general cognitive ability, and cognitive scores correlated
most consistently with the volumes of the anterior cingulate. This is discussed in
light of the diverse connective profile of the cingulate and a need to integrate
information over more diffuse cognitive networks according to proposed de-differentiation
or compensation in ageing. Individuals with higher morning, evening
or pre-test cortisol levels showed consistently negative relationships with specific
regional volumes and tract integrity. Participants whose cortisol levels increased
between the start and end of cognitive testing showed selectively larger regional
volumes and lower tract diffusivity (correlation magnitudes <.44). The significant
relationships between cortisol levels and cognition indicated that flatter diurnal
slopes or higher pre-test levels related to poorer test performance. In contrast, higher
levels in the morning generally correlated with better scores (correlation magnitudes
<.25). Interpretation of all findings was moderated by sensitivity to type I error,
given the large number of comparisons conducted. Though there were limited
candidates for mediation analysis, cortisol-function relationships were partially
mediated by tract integrity (but not sub-regional frontal volumes) for memory and
post-error slowing. This thesis offers a novel perspective on the complex interplay
among glucocorticoids, cognition and the structure of the ageing brain. The findings
suggest some role for cortisol exposure in determining age-related decline in
complex cognition, mediated via brain structure
Planning Skills in Autism Spectrum Disorder Across the Lifespan: A Meta-analysis and Meta-regression
Exceptionally Narrow-Band Quantum Dot Infrared Photodetector
Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de NÃvel Superior (CAPES)InGaAlAs/InGaAs/InGaAlAs/InAs/InP quantum-dot structures have been investigated for the development of infrared photodetectors capable of generating photocurrent peaks exceptionally narrow for sharp wavelength discrimination. Our specially designed structure displays a photocurrent peak at 12 mu m with a full width at half maximum, limited by inhomogeneous broadening, of only 4.5 meV. In agreement with two independent energy level calculations, we attribute this peak to photon absorption between InAs quantum dot bound states, followed by a three step carrier extraction mechanism in which the coupling to the adjacent InGaAs quantum well is a key feature. The possible role played by intraband Auger scattering, multiphoton sequential absorption and tunneling in generating the observed current peak is also addressed.481013601366WPIFWF SFB IR-ONEC NoE SANDIEConselho Nacional de Desenvolvimento CientÃfico e Tecnológico (CNPq)FINEPCoordenação de Aperfeiçoamento de Pessoal de NÃvel Superior (CAPES)Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ)Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de NÃvel Superior (CAPES
Torre de Londres e Torre de Hanói: contribuições distintas para avaliação do funcionamento executivo Tower of London and Tower of Hanoi: distinct contributions to the assessment of executive functioning
OBJETIVO: Realizar um estudo teórico sobre comparações de aspectos cognitivos e metodológicos envolvidos no desempenho das Torres de Hanói e de Londres em indivÃduos normais. MÉTODO: Revisão narrativa da literatura. RESULTADOS: O desempenho nesses instrumentos não compartilha a variância esperada em virtude das similaridades aparentes em sua estrutura e demanda de solução. Verificaram-se correlações significativas, porém moderadas, entre o desempenho das duas torres, refletindo em média 75% da variância não compartilhada. CONCLUSÕES: Ambas as torres recrutam diferentes processos executivos para solução da tarefa e não podem ser utilizadas como instrumentos permutáveis.<br>OBJECTIVE: To produce theoretical study about comparisons of cognitive and methodological aspects involved in the performance of Towers of Hanoi and London in normal individuals. METHOD: Narrative review of the literature. RESULTS: The performances in these instruments do not share the expected variance due to the apparent similarities in your structure and solution demand. Correlations significant, however moderate, among the two towers performance, were found reflecting the average of 75% of the nonshared variance. CONCLUSIONS: Both towers recruit different executive processes for task solution and cannot be used as exchangeable instruments