Differential effects of Alzheimer\u27s disease and Huntington\u27s disease on the performance of mental rotation

he ability to spatially rotate a mental image was compared in patients with Alzheimer\u27s disease (AD; n = 18) and patients with Huntington\u27s disease (HD; n = 18). Compared to their respective age-matched normal control (NC) group, the speed, but not the accuracy, of mental rotation abnormally decreased with increasing angle of orientation for patients with HD. In contrast, the accuracy, but not the speed, of rotation abnormally decreased with increasing angle of orientation for patients with AD. Additional analyses showed that these unique patterns of performance were not attributable to different speed/accuracy trade-off sensitivities. This double dissociation suggests that the distinct brain regions affected in the two diseases differentially contribute to speed and accuracy of mental rotation. Specifically, the slowing exhibited by HD patients may be mediated by damage to the basal ganglia, whereas the spatial manipulation deficit of AD patients may reflect pathology in parietal and temporal lobe association cortices important for visuospatial processing. (JINS, 2005, 11, 30–39.

Do neuropsychological tests detect preclinical Alzheimer's disease: Individual-test versus cognitive-discrepancy score analyses.

Attempts to identify cognitive markers of a preclinical phase of Alzheimer’s disease (AD) have yielded inconsistent findings. The problem may stem in part from methodologies that are insensitive to potential subgroups within the at-risk, preclinical AD population (PCAD). The present study investigated the utility of asymmetric cognitive profiles in identifying individ-uals at risk for AD. Twenty elderly adults who were later diagnosed with AD (PCAD) and 20 matched control participants were compared on measures of cognitive asymmetry derived from difference scores on tests of verbal and visuospatial ability. Although both groups performed similarly on the individual tests, comparisons using difference scores revealed significantly larger discrepancies between naming and visuoconstruction skills in the PCAD group. The PCAD group also had a higher frequency of asymmetric cognitive profiles relative to a normative group. Subtle cognitive changes can precede the onset of Alz-heimer’s disease (AD) by as many as 7 to 10 years (Elias et al., 2000; Linn, Wolf, Bachman, & Knoefel, 1995). Find-ings of a long prodromal period have fostered new researc

Potential implications of practice effects in Alzheimer's disease prevention trials.

IntroductionPractice effects (PEs) present a potential confound in clinical trials with cognitive outcomes. A single-blind placebo run-in design, with repeated cognitive outcome assessments before randomization to treatment, can minimize effects of practice on trial outcome.MethodsWe investigated the potential implications of PEs in Alzheimer's disease prevention trials using placebo arm data from the Alzheimer's Disease Cooperative Study donepezil/vitamin E trial in mild cognitive impairment. Frequent ADAS-Cog measurements early in the trial allowed us to compare two competing trial designs: a 19-month trial with randomization after initial assessment, versus a 15-month trial with a 4-month single-blind placebo run-in and randomization after the second administration of the ADAS-Cog. Standard power calculations assuming a mixed-model repeated-measure analysis plan were used to calculate sample size requirements for a hypothetical future trial designed to detect a 50% slowing of cognitive decline.ResultsOn average, ADAS-Cog 13 scores improved at first follow-up, consistent with a PE and progressively worsened thereafter. The observed change for a 19-month trial (1.18 points) was substantively smaller than that for a 15-month trial with 4-month run-in (1.79 points). To detect a 50% slowing in progression under the standard design (i.e., a 0.59 point slowing), a future trial would require 3.4 times more subjects than would be required to detect the comparable percent slowing (i.e., 0.90 points) with the run-in design.DiscussionAssuming the improvement at first follow-up observed in this trial represents PEs, the rate of change from the second assessment forward is a more accurate representation of symptom progression in this population and is the appropriate reference point for describing treatment effects characterized as percent slowing of symptom progression; failure to accommodate this leads to an oversized clinical trial. We conclude that PEs are an important potential consideration when planning future trials

Correlations Between Central Massive Objects And Their Host Galaxies: From Bulgeless Spirals to Ellipticals

Recent observations by Ferrarese et al. (2006) and Wehner et al. (2006) reveal that a majority of galaxies contain a central massive object (CMO), either a supermassive black hole (SMBH) or a compact stellar nucleus, regardless of the galaxy mass or morphological type, and that there is a tight relation between the masses of CMOs and those of the host galaxies. Several recent studies show that feedback from black holes can successfully explain the \msigma correlation in massive elliptical galaxies that contain SMBHs. However, puzzles remain in spirals or dwarf spheroids that do not appear to have black holes but instead harbor a compact central stellar cluster. Here we use three-dimensional, smoothed particle hydrodynamics simulations of isolated galaxies to study the formation and evolution of CMOs in bulgeless disk galaxies, and simulations of merging galaxies to study the transition of the CMO--host mass relation from late-type bulgeless spirals to early-type ellipticals. Our results suggest that the observed correlations may be established primarily by the depletion of gas in the central region by accretion and star-formation, and may hold for all galaxy types. A systematic search for CMOs in the nuclei of bulgeless disk galaxies would offer a test of this conclusion. (Abridged)Comment: 11 pages, 8 figures, accepted to Ap

Surveying Areas in Developing Regions Through Context Aware Drone Mobility.

Developing regions are often characterized by large areas that are poorly reachable or explored. The mapping of these regions and the census of roaming populations in these areas are often difficult and sporadic. In this paper we put forward an approach to aid area surveying which relies on autonomous drone mobility. In particular we illustrate the two main components of the approach. An efficient on-device object detection component, built on Convolutional Neural Networks, capable of detecting human settlements and animals on the ground with acceptable performance (latency and accuracy) and a path planning component, informed by the object identification module, which exploits Artificial Potential Fields to dynamically adapt the flight in order to gather useful information of the environment, while keeping optimal flight paths. We report some initial performance results of the on board visual perception module and describe our experimental platform based on a fixed-wing aircraft.The project was partially funded through an Institutional GCRF EPSRC grant

Quasar Proper Motions and Low-Frequency Gravitational Waves

We report observational upper limits on the mass-energy of the cosmological gravitational-wave background, from limits on proper motions of quasars. Gravitational waves with periods longer than the time span of observations produce a simple pattern of apparent proper motions over the sky, composed primarily of second-order transverse vector spherical harmonics. A fit of such harmonics to measured motions yields a 95%-confidence limit on the mass-energy of gravitational waves with frequencies <2e-9 Hz, of <0.11/h*h times the closure density of the universe.Comment: 15 pages, 1 figure. Also available at http://charm.physics.ucsb.edu:80/people/cgwinn/cgwinn_group/index.htm

Interactive effects of vascular risk burden and advanced age on cerebral blood flow.

Vascular risk factors and cerebral blood flow (CBF) reduction have been linked to increased risk of cognitive impairment and Alzheimer's disease (AD); however the possible moderating effects of age and vascular risk burden on CBF in late life remain understudied. We examined the relationships among elevated vascular risk burden, age, CBF, and cognition. Seventy-one non-demented older adults completed an arterial spin labeling MR scan, neuropsychological assessment, and medical history interview. Relationships among vascular risk burden, age, and CBF were examined in a priori regions of interest (ROIs) previously implicated in aging and AD. Interaction effects indicated that, among older adults with elevated vascular risk burden (i.e., multiple vascular risk factors), advancing age was significantly associated with reduced cortical CBF whereas there was no such relationship for those with low vascular risk burden (i.e., no or one vascular risk factor). This pattern was observed in cortical ROIs including medial temporal (hippocampus, parahippocampal gyrus, uncus), inferior parietal (supramarginal gyrus, inferior parietal lobule, angular gyrus), and frontal (anterior cingulate, middle frontal gyrus, medial frontal gyrus) cortices. Furthermore, among those with elevated vascular risk, reduced CBF was associated with poorer cognitive performance. Such findings suggest that older adults with elevated vascular risk burden may be particularly vulnerable to cognitive change as a function of CBF reductions. Findings support the use of CBF as a potential biomarker in preclinical AD and suggest that vascular risk burden and regionally-specific CBF changes may contribute to differential age-related cognitive declines

Can Cosmic Parallax Distinguish Between Anisotropic Cosmologies?

In an anisotropic universe, observers not positioned at a point of special symmetry should observe cosmic parallax - the relative angular motion of test galaxies over cosmic time. It was recently argued that the non-observance of this effect in upcoming precision astrometry missions such as Gaia may be used to place strong bounds on the position of off-center observers in a void-model universe described by the Lemaitre-Tolman-Bondi metric. We consider the analogous effect in anisotropic cosmological models described by an axisymmetric homogeneous Bianchi type I metric and discuss whether any observation of cosmic parallax would distinguish between different anisotropic evolutions.Comment: 24 pages, 6 figure