Ontogenesis of memory consolidation

Humans have the capacity to remember experienced episodes for years and even decades. This impressive ability has its ontogenetic roots in early childhood, when childhood amnesia − the inability of adults to retrieve childhood memories − offset begins around the age of 3 to 8 years. At the system level, the consolidation of memory involves post-encoding reorganization of event engrams over distributed brain circuits (Dudai and Morris, 2000). This is a temporally evolving process that involves interactions between the hippocampus (HC) and neocortex, including ventromedial prefrontal regions (vmPFC, e.g. Dudai, 2004; Takashima et al., 2006). These interactions are modulated by preexisting schema or prior knowledge, with the transfer process from HC to neocortex expedited when new memory fits into preexisting schema. Studying these processes in normally developing children and children with expected alterations in HC circuitry (like in the context of preterm birth) is an opportunity to gain insight into the dynamics of system-level memory consolidation by examining the varying structural and functional integrity of the HC−vmPFC memory network across groups and time. In typically developing children, HC maturation slows down by mid-childhood (Shing et al., 2010), but the structural and functional connectivity between HC and vmPFC develops well into adulthood (Lebel et al., 2012). Currently, understanding of how consolidation is enabled and constrained in the developing brains is limited. Using an experimental approach in combination with multimodal neuroimaging techniques (fMRI, high-resolution MRI, DTI), we will characterize the neural mechanisms underlying memory consolidation in typically developing term-born and preterm-born children aged 5−6 years before school entry (in comparison to a young adult group), with a longitudinal follow-up two years later. We will examine how consolidation across two weeks affects the neural correlates of memory retrieval with events (consisting of object and context) that can be bound with knowledge. Longitudinally, we will track how increase in knowledge over time affects the development of neural mechanisms underlying memory consolidation. Using the same object− context paradigm, we will extend to the clinical model of preterm birth associated with enduring, early onset changes in HC anatomy and function (Nosarti and Froudist−Walsh, 2016) and expected alterations in memory consolidation. Our approach capitalizes on the fact that while HC integrity is compromised among individuals born preterm, there is significant interindividual variability in the degree of their memory impairment, with some having memory performance in the normal unimpaired range. Therefore, our study aims at characterizing (1) neural processes that underlie memory consolidation in typically developing individuals, (2) neural alterations and compensational processes that underlie memory consolidation in preterm born individuals, and (3) perinatal characteristics and early neurodevelopmental trajectories that predict unimpaired memory performance despite premature birth. With this longitudinal project, new insights will be gained regarding the dynamics of within-person neural development and plasticity underlying system-level memory consolidation.

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