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Title

Temporal and Spatial Properties of the Negative Bold Response in the DMN

Creator

Gholipour Picha, Saman

Date

2024

Description

The Negative Blood Oxygen Level Dependent (BOLD) Response (NBR) remains less explored than its positive counterpart (PBR) in functional...
Show moreThe Negative Blood Oxygen Level Dependent (BOLD) Response (NBR) remains less explored than its positive counterpart (PBR) in functional Magnetic Resonance Imaging (fMRI) studies. This dissertation aims to advance the understanding of the NBR by investigating its task-specific spatial patterns, comparing its specificity to the PBR, validating its reproducibility across different subject groups, examining its relationship with functional connectivity patterns during cognitive tasks, and assessing its linearity with respect to stimulus duration.Firstly, we analyzed the spatial patterns of NBR and PBR across a diverse set of cognitive tasks using a novel paradigm that grouped twelve tasks into four cognitive domains. Our findings revealed that both NBR and PBR exhibit distinct, task-specific spatial patterns, with the NBR predominantly occurring within the Default Mode Network (DMN). Notably, the NBR demonstrated greater task specificity compared to the PBR, suggesting a unique role in differentiating cognitive processes. To validate these observations, we replicated the analyses in a separate cohort, confirming the reproducibility and consistency of the task-specific NBR spatial patterns across different subject groups. This consistency underscores the reliability of NBR patterns and their potential generalizability. Additionally, we investigated the functional connectivity patterns of major brain networks during cognitive tasks. Our analyses showed that functional connectivity within networks such as the DMN and the dorsal attention network (DAN) remained stable across different tasks. This implies that task-specific BOLD signal changes are likely not due to alterations in functional connectivity but result from local neural dynamics. Furthermore, we assessed the linearity of the NBR with respect to stimulus duration. Contrary to our initial hypothesis, the NBR did not exhibit a clear linear relationship with stimulus duration, differing from the established linearity of the PBR. This suggests fundamental differences in neurovascular coupling mechanisms between positive and negative BOLD responses and indicates that linear models may not suffice for accurately analyzing NBR data. Methodologically, we developed a robust fMRI data analysis pipeline incorporating motion correction, distortion correction using TopUp, spatial normalization via an in-house technique utilizing outputs from FreeSurfer and ANTs, and noise reduction through ICA-AROMA. This pipeline ensured high-quality preprocessing and reliable first-level statistical analyses. In conclusion, this research enhances the understanding of the NBR by highlighting its greater task specificity and non-linearity compared to the PBR. The findings emphasize the importance of considering both activation and deactivation processes in cognitive neuroscience. They have significant implications for theoretical models of brain function, analytical approaches in fMRI research, and potential clinical applications, paving the way for future investigations into the complex dynamics of neural activation and deactivation.
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