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Browsing by Author "Thomas, Michael L., advisor"

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    Large scale brain network mental workload engagement in schizophrenia
    (Colorado State University. Libraries, 2022) Duffy, John R., author; Thomas, Michael L., advisor; Rojas, Don, committee member; Blanchard, Nathanial, committee member; Tompkins, Sara Anne, committee member
    Objective: Cognitive deficits in patients diagnosed with schizophrenia are a core feature of the disorder. There are currently no treatments for these cognitive deficits. Our aim is to examine and compare patterns of increased versus decreased activity in the central executive network (CEN), salience network (SN), and default mode network (DMN) between healthy controls (HC) and patients diagnosed with schizophrenia (SZ) as well as to explore the influence of task load on these networks between HC and SZ. Method: Analyses focused on a secondary dataset comprising Blood Oxygen-Level Dependent (BOLD) data collected from 25 HC and 27 SZ who completed a working memory (WM) task (N-back) with 5 load conditions while undergoing functional magnetic resonance imaging (fMRI). Region of interest (ROI) data were analyzed using linear mixed-effects models. Dynamic causal modeling (DCM) was used in an exploratory analysis to examine working memory load input to these networks. Results: Group activation differences were found in the posterior salience network (pSN), default mode network (DMN), dorsal default mode network (dDMN), and ventral default mode network (vDMN) showing greater activity for SZ. Specifically, pSN, SMN, dDMN, and vDMN all showed increased activity in SZ compared to HC. The curve of brain activity was consistent between HC and SZ with the exception of the vDMN, where HC show greater activation at modest mental workload (quadratic curve) and SZ showed greater brain activation at lower mental workload (linear). In the CEN, there were no group differences, and the response curve was the same for both groups. In DCM analysis, working memory load acted as an input on different networks between HC and SZ. Conclusions: These group differences demonstrate network difference between HC and SZ and could show value in treatments targeting cognitive deficits in SZ from a large-scale brain network connectivity perspective. Future studies are needed to confirm these results with higher sample size in order to examine potential subtleties of interactions between these networks.
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    Multi-dimensional aspects of mindfulness: psychometric evaluation, neurobiological underpinnings, and experiential insights
    (Colorado State University. Libraries, 2024) Duffy, John R., author; Thomas, Michael L., advisor; Davalos, Deana, committee member; Graham, Dan, committee member; Stephans, Jaclyn, committee member
    Objective: This dissertation aimed to deepen our understanding of mindfulness by exploring a psychometric evaluation of self-report scales, neurobiological underpinnings, and experiential insights in a multidimensional approach. The objective encompassed three specific aims: firstly, to evaluate the psychometric effectiveness of two self-report scales; the Mindful Attention Awareness Scale (MAAS) and the Five Facet Mindfulness Questionnaire (FFMQ) within populations diagnosed with post-traumatic stress disorder (PTSD), ensuring these tools' validity and reliability while addressing the complexity of mindfulness. Secondly, the research intended to synthesize existing literature on brain networks related to mindfulness through an umbrella review (a review of reviews / metanalyses), aimed to clarify the neural mechanisms of mindfulness. Thirdly, the study used functional magnetic resonance imaging (fMRI) to compare brain activity between a control group performing a visualization task (control) and a group engaged in a guided compassion meditation (experimental). This comprehensive framework sought to advance the field of mindfulness research by integrating psychometric analysis, brain network review synthesis, and experimental neuroimaging to enhance theoretical understanding of mindfulness. Method: We employed a three-pronged methodological approach. Firstly, a psychometric evaluation of the Mindful Attention Awareness Scale (MAAS) and the Five Facet Mindfulness Questionnaire (FFMQ) to assess their reliability and validity in a PTSD-affected veteran population. Secondly, we conducted an umbrella review to synthesize existing research on brain networks and connectivity related to mindfulness to map out neural correlates and their implications. Thirdly, an experimental study using functional magnetic resonance imaging (fMRI) compared neural activation patterns between participants engaged in a visualization task and those practicing guided compassion meditation, aimed to identify distinct neural activities associated with this mindfulness practices. Results: The psychometric evaluation of the MAAS and FFMQ confirmed their validity and reliability in assessing mindfulness in PTSD populations, highlighting mindfulness as a complex, multifaceted construct. An umbrella review of existing literature demonstrated the significant impact of mindfulness on brain connectivity, particularly in the DMN, CEN, and SN networks. The experimental fMRI study revealed distinct neural activation patterns between compassion mindfulness and a visualization task, with compassion mindfulness showing decreased activity in regions involved in emotional regulation and cognitive functions, such as the medial superior prefrontal cortex and anterior cingulate cortex. Conclusions: These findings affirm the utility of MAAS and FFMQ reliability and validity, but demand more nuanced research based on a more multifaceted concept of mindfulness. The impact of mindfulness on large-scale brain networks underscores its potential to enhance cognitive and emotional regulation through neuroplasticity. However, significant methodological variability across studies calls for standardized research protocols to ensure consistency and reliability. Future research should address these limitations, explore the long-term effects of mindfulness, and include diverse populations to improve the generalizability of mindfulness-based interventions. Finally, significant differences in neural activation patterns between visualization tasks and compassion mindfulness meditation, indicate that such mindfulness practices may uniquely influence brain regions associated with emotional regulation and cognitive processes. These findings highlight the potential of compassion mindfulness to modulate brain activity in these areas, offering insights into its mechanisms and benefits.
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    New evidence for age differences, within-person declines and plasticity in the aging white matter: new MRI techniques and analytical approaches
    (Colorado State University. Libraries, 2023) Mendez Colmenares, Andrea, author; Thomas, Michael L., advisor; Burzynska, Agnieszka Z., advisor; Davalos, Deana, committee member; Fisher, Gwen, committee member; Hamilton, Karyn, committee member
    White matter deterioration leads to cognitive impairments in healthy aging, Alzheimer's disease, and related dementias. Therefore, it is critical to identify interventions that can slow the white matter deterioration. Animal studies have suggested that the white matter plays an active role in brain plasticity and learning. However, evidence for experience-induced plasticity in adult human white matter remains scarce and inconsistent, especially in older age. To accurately predict the effects of interventions on the white matter, we first need to understand the direction and magnitude of naturally occurring within-person changes across adulthood. To date, white matter in aging, Alzheimer's disease, and related dementias have been studied almost solely using diffusion MRI, which provides limited information about the white matter microstructure. Because there is little evidence of white matter plasticity in adult humans, white matter has rarely been considered as a target for interventions against dementia. This dissertation comprises three scientific articles investigating the mechanisms of white matter decline and plasticity. The first article presents a study using a novel technique (T1w/T2w imaging) to examine the effects of aerobic exercise on aging white matter in a randomized controlled trial. The second article is a meta-analysis and systematic review of within-person changes in white matter. The third article shows the first application of a multimodal fusion analysis to study healthy aging white matter. Through these innovative approaches, this dissertation provides new insights into the mechanisms of white matter decline and plasticity, paving the way for the development of effective interventions to promote healthy brain aging.
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    Studying age-related changes in white matter microstructure in healthy aging using noninvasive MRI techniques
    (Colorado State University. Libraries, 2020) Mendez Colmenares, Andrea, author; Thomas, Michael L., advisor; Burzynska, Agnieszka Z., advisor; Rojas, Donald C., committee member
    Age-related deterioration of the white matter (WM), such as demyelination, is an important mechanism of cognitive decline in healthy aging. Lifestyle factors can influence the course of WM aging. Most evidence have used diffusion tensor imaging (DTI) metrics, but these are not specific to myelin or axons. Therefore, in this study we compared DTI metrics to a proposed proxy of myelin content, the T1-weighted image (T1-WI) to T2-weighted image (T2-WI) ratio with respect to their ability to: detect time-by-intervention interactions, predict processing speed ability, and their correlations with each other and age. We used longitudinal data from 169 cognitively healthy older adults (60-79yrs). MRI imaging (3T Siemens Trio) included 0.9mm3 MPRAGE, 1.7×1.7x3mm3 T2w and DTI (30 diff. dir., bval= 0 and 1000s/mm2, 1.7×1.7x3mm3). T1w/T2w was calculated using internal intensity calibration. We used FSL-FDT to extract DTI metrics, focused on major WM tracts using tract-based spatial statistics in FSL. From the WM skeleton, we calculated mean values for 12 regions-of-interest. Processing speed was assessed using the Virginia Cognitive Aging Battery. Results showed that the T1w/T2w produced greater time-by-intervention interactions than DTI-FA, especially in the posterior (β=0.27, p=0.01) and anterior (β=0.33, p=0.01) limb of the internal capsule. The T1w/T2w (in the whole WM) correlated with processing speed (β=-0.13, p=0.02). T1w/T2w correlated with DTI in regions with high fiber coherence/high myelin content; and with age in regions with high myelin content. Results suggest that the T1w/T2w offers greater ability than DTI to detect short-term longitudinal changes in WM, but they seem to reflect different microstructural properties in the WM. Further research is needed to gain a better understanding of its biological underpinnings and significance.
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    Validating a points-based effort expenditure for rewards task
    (Colorado State University. Libraries, 2024) Sturm, Emily T., author; Thomas, Michael L., advisor; Seger, Carol, committee member; Stephens, Jaclyn, committee member; Tompkins, Sara Anne, committee member
    Invalid performance on neurocognitive tests due to lack of effort expenditure is a concern for researchers and clinicians. Performance validity tests determine when adequate effort has been expended, but they fail to differentiate between subcomponents of effort that may be responsible for poor performance. The Effort Expenditure for Reward Task (EEfRT) is a task that provides separate measurements of reward processing and valuation constructs which could be informative as performance validity indicators. However, previous versions of the EEfRT use monetary performance-based rewards to investigate the expected value of effort, which can be problematic due to the influence of socio-economic factors and potential to systematically disadvantage participants with neurocognitive disorders. This study first aimed to examine the construct validity, specifically, the construct representation of a points-based version of the EEfRT online and in-person. The second aim of this study, which is exploratory, is to characterize patterns in embedded performance validity test performance obtained for separate neurocognitive measures as well as the EEfRT, thereby informing nomothetic span, or patterns of significant relations across measures of effort. This aim assessed whether the scores from the EEfRT indicate performance validity in other domains. Online participants (n = 342) from Prolific.com for the online sample and in-person participants (n = 27) were recruited via advertisements. Participants completed a battery including the EEfRT along with three working memory tasks, two executive functioning tasks, and one reward learning task. Results of regression analyses showed that, as hypothesized, both online and in-person participants chose hard tasks significantly more often at higher reward levels and at higher probability levels. However, contrary to expectations, a significant interaction between reward and group showed that points were more motivating in the online setting compared to in-person. Exploratory latent profile analysis revealed no clear pattern in embedded performance validity tests within the EEfRT or across other tasks. The results of this study suggest that a points-based version of the EEfRT is potentially valid for measuring effort-based decision making, but more research is needed before it can be called an objective measure of effort in the context of validating performance on cognitive tests.