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Hippocampus has an extended developmental trajectory, with refinements occurring in the trisynaptic circuit until adolescence. While structural change should suggest a protracted course in behavior, some studies find evidence of precocious hippocampal development in the first postnatal year and continuity in memory processes beyond. However, a number of memory functions, including binding and relational inference, can be cortically supported. Evidence from the animal literature suggests that tasks often associated with hippocampus (visual paired comparison, binding of a visuomotor response) can be mediated by structures external to hippocampus. Thus, a complete examination of memory development will have to rule out cortex as a source of early memory competency. We propose that early memory must show properties associated with full function of the trisynaptic circuit to reflect "adult-like" memory function, mainly (1) rapid encoding of contextual details of overlapping patterns, and (2) retention of these details over sleep-dependent delays. A wealth of evidence suggests that these functions are not apparent until 18-24 months, with behavioral discontinuities reflecting shifts in the neural structures subserving memory beginning approximately at this point in development. We discuss the implications of these observations for theories of memory and for identifying and measuring memory function in populations with typical and atypical hippocampal function. (C) 2015 The Authors. Published by Elsevier Ltd.

Recent research provides evidence for new conceptualizations of memory, including the brain's drive to predict and anticipate future events based on past experiences, a narrowing gap between perceptual and mnemonic functions, and the importance of sleep-dependent memory consolidation. These new perspectives, which highlight the interactive nature of the brain bases of memory, are rarely applied to the study of memory in neurodevelopmental disorders. In the present work, I adopted some of these theoretical perspectives to rethink the study of memory in typical development and in neurodevelopmental disorders such as Down syndrome (Trisomy 21). Given that several studies have reported atypical patterns of brain connectivity in individuals with Down syndrome, this dissertation aims to assess the integrity of memory processing in this population by examining different levels of cross-regional communication measured at the neuropsychological level. I first provide evidence of impaired rapid interactions between the brain areas that mediate high-level influences on figure-ground perception and relatively unimpaired integration of neural inputs across local areas of visual cortex (Spanò, Peterson, Nadel, Rhoads, & Edgin, 2015; see Appendix A). In the second study, I demonstrate spared use of anticipatory scene representation, thought to rely on top-down information from the hippocampus and likely to support our understanding of the properties of the visual world (Spanò, Intraub, & Edgin, submitted; see Appendix B). Finally, the third study reveals impaired sleep-dependent memory consolidation of arbitrary object-label associations, symptomatic of a weak dialogue between prefrontal cortex and hippocampus (Spanò, Gómez, Demara, Alt, Cowen, & Edgin, in preparation; see Appendix C). Based on these findings, treatments for Down syndrome, and other developmental disorders affecting functional connectivity, should be aimed at establishing balanced neural communication and cross-regional connectivity early on in development.

There is an extensive debate in the adult literature on whether recognition memory can better be explained by a single- or a dual-process account. Single-process accounts assume that a single memory strength signal underlies recognition. Dual-process accounts propose two independent processes, namely recollection (slow and associated with contextual details) and familiarity (fast and automatic). The aim of this dissertation was to advance this debate using a cognitive developmental approach. By investigating age-related changes of recognition memory across childhood as a function of theoretically motivated experimental manipulations, predictions drawn from single- and dual-process models of recognition memory were tested. We adapted the Process Dissociation Paradigm (PDP; Jacoby, 1991) to disentangle processes underlying recognition memory in 5-, 7-, and 11-year-olds and adults using a Dual-Process Signal Detection cognitive modelling approach (DPSD; Yonelinas, 1996). Experiments 1 – 6 demonstrated that 5-year-olds are able to recollect items based on perceptual details. Consistent with dual-process theory, across all age groups a response time limit decreased recollection while leaving familiarity unaffected (Chapter 2). Converging evidence consistent with dissociations during childhood was found after repeated item presentation (Chapter 3). Finally, after a thorough empirical validation of our approach, the new paradigm was used to investigate the developmental perceptual to semantic shift (Chapter 4). These findings, using a double dissociation logic, have advanced the theoretical debate on the nature of recognition memory by showing that one process is insufficient to account for the developmental and experimental findings reported here. Recollection and familiarity follow different developmental trajectories and are affected by encoding and retrieval manipulations (i.e., repetition and time limits). This provides a challenge for existing theories of recognition memory.

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The experiments in this thesis explored the development of executive function in 5- to 11-year-old children. Developmentally-appropriate versions of the task-switching paradigm, go/no-go task and self-ordered pointing test were used to measure shifting, inhibition and working memory respectively. These executive skills were examined independently and within-task experimental manipulations were used to explore both the executive and non-executive processes that influenced children’s performance. These allowed the investigation of not only when, but also how executive function develops. It was found that shifting development, as measured by the task-switching paradigm was highly influenced by the specific tasks switched between and the conflict created by the overlap of the tasks, as well as by previous task experience. Working memory for pictures was also influenced by previous experience and task difficulty, however the predicted relationship between memory for nameable objects and language ability was not found. Inhibition on the go/no-go paradigm appeared to be driven by an improvement in the efficiency of response inhibition enabling older children to inhibit a response at an earlier stage during the movement. Shifting, inhibition and working memory all showed developmental improvements during mid-childhood, demonstrating the protracted development of executive function. Shifting and working memory showed a similar pattern of development whereas inhibition reached a stable level of performance at an earlier age. There were no correlations between the three executive skills studied in this thesis, supporting the fractionation of executive function.