Strategic Flexibility and Age-Related Cognitive Change

This series of projects aims to explore the potential role of strategic flexibility in cognitive aging, and whether this construct can serve as an effective mechanistic proxy for cognitive reserve. Study 1 introduces the task designed for this series, based on stimuli from a classic test of fluid reasoning and formatted as a task-switching paradigm to explore strategic characteristics in a structured way. This study suggests that such a task is subject to age-related effects. Study 2 introduces a redesigned version of this task, matching it more closely to existing paradigms of task-switching, and explores how covariates interact with measured performance. Study 3 draws upon an existing sample of extensive neuropsychological and neuroimaging data, and aims to describe the associations among this set of data and measures of strategic flexibility. Results overall indicate that age negatively affects strategic flexibility, but cognitive reserve may mitigate this impairment

Efficiency, Capacity, Compensation, Maintenance, Plasticity: Emerging Concepts in Cognitive Reserve

Cognitive reserve (CR) is a concept meant to account for the frequent discrepancy between an individual's measured level of brain pathology and her expected cognitive performance. It is particularly important within the context of aging and dementia, but has wider applicability to all forms of brain damage. As such, it has intimate links to related compensatory and neuroprotective concepts, as well as to the related notion of brain reserve. In this article, we introduce the concept of cognitive reserve and explicate its potential cognitive and neural implementation. We conclude that cognitive reserve is compatible and complementary with many related concepts, but that each much draw sharper conceptual boundaries in order to truly explain preserved cognitive function in the face of aging or brain damage

LATE LIFE DEPRESSION AND LATE ONSET DEPRESSION: ARE THE SAME CLINICAL AND PATHOPSYSIOLOGICAL PICTURE?

Phenomenological differences between older patients with late- and early-onset depression may reflect differences in aetiology and neuropathological processes involved in these two types of depression. Early- onset depression has been mainly correlated to a family history of depression while late-onset depression has been principally correlated to vascular dysfunction. The same cortical and sub-cortical areas are involved in both types of depression. However, lesions in these brain areas and cognitive impairment are most pronounced in late-onset depression. Based on these observations we propose a common neuroanatomical substrate but different pathophysiological processes implicated in these two types of depression

Study of Silicon Nitride resonators for optomechanics and security applications

In this work the design, fabrication and characterization of silicon nitride nano-mechanical resonators is presented, starting from silicon nitride thin films deposited on Si wafers according to ten different recipes. The properties of such devices will depend on design and material properties. As demonstrated in the previous work, silicon nitride material properties (such as stoichiometry, stress, roughness, refractive index, Young’s modulus) are strongly influenced by the deposition conditions (temperature, pressure, gas ratio and total gas flow). The long term goal of this project is to achieve the highest performances in NEMS resonators, and so high quality factors, finding out the best combination between deposition condition and device design. Most of the project is based on the microfabrication of membranes, cantilevers and beams. Two fabrications runs are performed: the purpose of the first fabrication run is to complete all the necessary trainings needed to use the tools in the cleanroom; the issues encountered during the first run are the starting point for the second fabrication run whose process flow is partially modified and optimized. In the last part of the thesis, some measurements about cantilevers deflection are shown. These measurements are carried out by using an optical profiler providing a 3D surface profile of devices

Neuroimaging Explanations of Age-Related Differences in Task Performance

Advancing age affects both cognitive performance and functional brain activity and interpretation of these effects has led to a variety of conceptual research models without always explicitly linking the two effects. However, to best understand the multifaceted effects of advancing age, age differences in functional brain activity need to be explicitly tied to the cognitive task performance. This work hypothesized that age-related differences in task performance are partially explained by age-related differences in functional brain activity and formally tested these causal relationships. Functional MRI data was from groups of young and old adults engaged in an executive task-switching experiment. Analyses were voxel-wise testing of moderated-mediation and simple mediation statistical path models to determine whether age group, brain activity and their interaction explained task performance in regions demonstrating an effect of age group. Results identified brain regions whose age-related differences in functional brain activity significantly explained age-related differences in task performance. In all identified locations, significant moderated-mediation relationships resulted from increasing brain activity predicting worse (slower) task performance in older but not younger adults. Findings suggest that advancing age links task performance to the level of brain activity. The overall message of this work is that in order to understand the role of functional brain activity on cognitive performance, analysis methods should respect theoretical relationships. Namely, that age affects brain activity and brain activity is related to task performance

The Influence of Cognitive Reserve on Strategy Selection in Normal Aging

Cognitive reserve (CR) has been proposed as a latent variable that can account for the frequent discrepancy between an individual's underlying level of brain pathology and their observed clinical outcome. A possible behavioral manifestation of CR is best strategy choice. Older adults have been shown to choose sub-optimal strategies for performing various tasks. The present study attempted to investigate whether greater levels of CR could predict greater strategy selection, particularly in older adults. A computational estimation task was administered to 20 healthy young adults (mean age = 24.7 +/- 3.6; 20-31 years) and 18 healthy older adults (68.2 +/- 4.5; 62-77 years) wherein participants needed to estimate the product of two two-digit numbers by using one of two strategies. The results revealed an effect of age group on strategy choice and supported the hypothesis that CR is associated with increased strategy selection abilities

Cognitive Neuroscience Neuroimaging Repository for the Adult Lifespan

With recent advances in neuroimaging technology, it is now possible to image human brain function in vivo, which revolutionized the cognitive neuroscience field. However, like any other newly developed technique, the acquisition of neuroimaging data is costly and logistically challenging. Furthermore, studying human cognition requires acquiring a large amount of neuroimaging data, which might not be feasible to do by every researcher in the field. Here, we describe our group's efforts to acquire one of the largest neuroimaging datasets that aims to investigate the neural substrates of age-related cognitive decline, which will be made available to share with other investigators. Our neuroimaging repository includes up to 14 different functional images for more than 486 subjects across the entire adult lifespan in addition to their 3 structural images. Currently, data from 234 participants have been acquired, including all 14 functional and 3 structural images, which is planned to increased to 375 participants in the next few years. A complete battery of neuropsychological tests was also administered to all participants. The neuroimaging and accompanying psychometric data will be available through an online and easy-to-use data sharing website

Breadth and Age-Dependency of Relations between Cortical Thickness and Cognition

Recent advances in neuroimaging have identified a large number of neural measures that could be involved in age-related declines in cognitive functioning. A popular method of investigating neural-cognition relations has been to determine the brain regions in which a particular neural measure is associated with the level of specific cognitive measures. Although this procedure has been informative, it ignores the strong interrelations that typically exist among the measures in each modality. An alternative approach involves investigating the number and identity of distinct dimensions within the set of neural measures and within the set of cognitive measures before examining relations between the 2 types of measures. The procedure is illustrated with data from 297 adults between 20 and 79 years of age with cortical thickness in different brain regions as the neural measures and performance on 12 cognitive tests as the cognitive measures. The results revealed that most of the relations between cortical thickness and cognition occurred at a general level corresponding to variance shared among different brain regions and among different cognitive measures. In addition, the strength of the thickness-cognition relation was substantially reduced after controlling the variation in age, which suggests that at least some of the thickness-cognition relations in age-heterogeneous samples may be attributable to the influence of age on each type of measure

The Role of Education and Verbal Abilities in Altering the Effect of Age-Related Gray Matter Differences on Cognition

Evidence suggests that individual variability in lifetime exposures influences how cognitive performance changes with advancing age. Brain maintenance and cognitive reserve are theories meant to account for preserved performance despite advancing age. These theories differ in their causal mechanisms. Brain maintenance predicts more advantageous lifetime exposures will reduce age-related neural differences. Cognitive reserve predicts that lifetime exposures will not directly reduce these differences but minimize their impact on cognitive performance. The present work used moderated-mediation modeling to investigate the contributions of these mechanisms at explaining variability in cognitive performance among a group of 39 healthy younger (mean age (standard deviation) 25.9 (2.92) and 45 healthy older adults (65.2 (2.79)). Cognitive scores were computed using composite measures from three separate domains (speed of processing, fluid reasoning, and memory), while their lifetime exposures were estimated using education and verbal IQ measures. T1-weighted MR images were used to measure cortical thickness and subcortical volumes. Results suggest a stronger role for cognitive reserve mechanisms in explaining age-related cognitive variability: even with age-related reduced gray matter, individuals with greater lifetime exposures could perform better given their quantity of brain measures