Structural Changes of Brain Areas Involved in Emotion and Memory Processing across Lifespan

Abstract

People are defined by their genes, familiar background and personal experiences, that can have either a negative or positive impact. Altogether, this represents and shapes their decisions, behaviours and relationships with others, but also their brain and body. In particular, external stimuli can have a big impact on the brain anatomy, resulting in specific behavioural and emotional responses. Cognitive abilities, such as memory, attention, emotional processing, are modulated by anatomical and functional connections between brain regions that process external stimuli from the environment and produce specific behavioural responses. This thesis work aims to investigate the brain areas that are more structurally sensitive to physiological changes and environmental stimuli during two critical periods of time in life, such as adolescence and aging. In this thesis, three studies will be presented, exploring structural brain changes due to stress and brain aging with three different structural neuroimaging approaches. In Chapter 1, a general overview of the brain areas involved in emotion and memory processing is presented, along with a description of magnetic resonance imaging (MRI), which is the neuroimaging technique used in all the studies. Chapter 2 illustrates the first study forming this thesis. Brain connectivity changes are investigated between two groups of adolescents with different levels of stress due to negative life events (Low vs High stress), by using both a graph theory and whole-brain connectivity approach. The High stress group showed a decrease of betweenness centrality measure in the somato-motor cortex, as well as an increase of degree centrality in the visual network and dorsal attention network. The whole-brain connectivity showed an increase of connectivity strength between regions of the limbic and attentional networks. In Chapter 3, the effect of stress on the hippocampus subfields volume was investigated between the two groups of adolescents from the previous study. The relationship between and hippocampus and the personality trait of Neuroticism was also considered. A relationship between Neuroticism and volume changes was seen in more than one subfield in the left hemisphere of adolescents perceiving higher stress levels. The second part of the analysis explored longitudinal changes of the subfields volume across two time points representing two stages of adolescence. Negative results were found after statistical correction, showing no relationship between hippocampal volumes and stress over time. In Chapter 4, microstructural changes of the cingulum bundle were explored in normal aging, by dividing the whole tract into three branches. Tractography was run on each branch for both hemispheres, and diffusivity measures were extracted to investigate between-group differences. A bilateral reduced microstructural integrity was found in the subgenual (the most anterior) branch in older healthy people. Overall, this thesis shows how brain areas involved in emotion and memory processing are those that are more affected and sensitive to changes during two critical stages of life, namely adolescence and aging. Structural alterations in these areas may lead to the development of psychiatric disorders, as well as to the acceleration of neurodegenerative processes. More knowledge about the impact that external factors have on the brain can help developing more effective therapeutic interventions.