60 research outputs found
Verbal short-term memory deficits in Down syndrome: phonological, semantic, or both?
The current study examined the phonological and semantic contributions to the verbal short-term memory (VSTM) deficit in Down syndrome (DS) by experimentally manipulating the phonological and semantic demands of VSTM tasks. The performance of 18 individuals with DS (ages 11–25) and 18 typically developing children (ages 3–10) matched pairwise on receptive vocabulary and gender was compared on four VSTM tasks, two tapping phonological VSTM (phonological similarity, nonword discrimination) and two tapping semantic VSTM (semantic category, semantic proactive interference). Group by condition interactions were found on the two phonological VSTM tasks (suggesting less sensitivity to the phonological qualities of words in DS), but not on the two semantic VSTM tasks. These findings suggest that a phonological weakness contributes to the VSTM deficit in DS. These results are discussed in relation to the DS neuropsychological and neuroanatomical phenotype
Belediye Müzesi
Taha Toros Arşivi, Dosya No: 114-Müzelerİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033
Developmental malformation of the corpus callosum: a review of typical callosal development and examples of developmental disorders with callosal involvement
This review provides an overview of the involvement of the corpus callosum (CC) in a variety of developmental disorders that are currently defined exclusively by genetics, developmental insult, and/or behavior. I begin with a general review of CC development, connectivity, and function, followed by discussion of the research methods typically utilized to study the callosum. The bulk of the review concentrates on specific developmental disorders, beginning with agenesis of the corpus callosum (AgCC)—the only condition diagnosed exclusively by callosal anatomy. This is followed by a review of several genetic disorders that commonly result in social impairments and/or psychopathology similar to AgCC (neurofibromatosis-1, Turner syndrome, 22q11.2 deletion syndrome, Williams yndrome, and fragile X) and two forms of prenatal injury (premature birth, fetal alcohol syndrome) known to impact callosal development. Finally, I examine callosal involvement in several common developmental disorders defined exclusively by behavioral patterns (developmental language delay, dyslexia, attention-deficit hyperactive disorder, autism spectrum disorders, and Tourette syndrome)
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
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