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Evaluation by magnetic resonance imaging of functional and structural connectivities of neurofunctional networks in mild Alzheimer's disease dementia and amnestic mild cognitive impairment subjects

Author(s):
Marina Weiler
Total Authors: 1
Document type: Doctoral Thesis
Institution: Universidade Estadual de Campinas. Faculdade de Ciências Médicas
Defense date:
Examining board members:
João Ricardo Sato; Edson Amaro Junior; Marcondes Cavalcante França Junior; Florindo Stella
Advisor: Marcio Luiz Figueredo Balthazar
Abstract

Alzheimer¿s (AD) is a neurodegenerative disease that presents with cognitive, neuropsychiatric and functional alterations. Recent studies in the neuroimaging field of AD have shown that the alterations observed in these patients are not limited to specific anatomic structures (as shown in chapter 2) but also compromise neurofunctional networks, which can lead to memory and executive function impairment, among others. Due to the structural alterations such as atrophy, burden of amyloid beta and hyperphosphorilated tau, and metabolism reduction presented in its regions, the Default Mode Network (DMN) has become the most studied network in the AD field. Thus, the main objective of this thesis was to evaluate the functional and structural connectivities of the neurofunctional networks in AD ¿ emphasizing the DMN, and the relationship with cognition. Besides that, we have also studied some other anatomical aspects in AD, such as alterations in white and grey matter. In Chapter 1, we have shown that the alterations caused by the disease also affect subcortical areas such as the thalamus and the corpus callosum, which correlates to the cognitive deficit of the patients. In another exploratory study (Chapter 6), we observed that as the disease progressed, the alterations in white matter occurred were more extensive than expected, considering the structural alterations of the grey matter. Our results suggest that damage in white matter can occur independently of grey matter damage. In this context, Chapter 8 brings molecular and imaging results that reinforce the hypothesis that neurodegenerative diseases affect specific neurofunctional networks, and the propagation of altered proteins occur through white matter tracts (along DMN tracts). Keeping this in mind, in Chapter 4 we had as a main objective to isolate only the DMN tracts, in order to evaluate its structural connectivity in AD. Indeed, we observed that structural microalterations are present in DMN tracts of AD patients, contributing to their cognitive deficits. In Chapter 5, we not only investigated the functional connectivity of DMN regions, but also the amplitude of low frequency fluctuations (ALFF) of the blood oxygenation level signal of these regions. We found that amnestic mild cognitive impairment subjects (aMCI ¿ subjects at risk for developing AD) for instance, have decreased ALFF in specific regions of the DMN, though not presenting alterations in functional connectivity. AD patients, however, present both reduced ALFF and connectivity in the DMN regions. Interestingly, ALFF values did not correlate with the cognitive impairment of the patients; but connectivity values did. In Chapter 3, we have shown that other networks such as the Language and Executive Functions are also altered in AD. The functional connectivity of the DMN, in turn, correlated with episodic memory function. In Chapter 7, our main objective was to explore some other hypothesis involving the DMN function. Here, we mentioned the alterations in the self presented in AD patients and suggest a relationship with the brain intrinsic activity and the feeling of self continuity across time. (AU)

FAPESP's process: 13/10431-9 - Anatomical and functional connectivity in Default Mode and Salience Networks in mild dementia of Alzheimer's Disease and amnestic mild cognitive impairment
Grantee:Marina Weiler
Support type: Scholarships in Brazil - Doctorate (Direct)