Traditional and Novel Hippocampally Mediated Cognitive Tasks in Typically and Atypically Developing Youth

Abstract

The hippocampus is known to help in the recall of associations and episodes from the past. This is a form of mental representation, and other forms of mental representation may be associated with the hippocampus as well. Five candidate complex cognitive functions involving suspected hippocampal involvement are discussed in the theoretical part of this dissertation, and a case is made for integration of the hippocampus into developmental theory. As the hippocampus is a gradually developing structure, we must consider how its slow course affects the development of cognitive functions that seem to involve it, at various stages. Following on this call to update developmental theory with integration of the hippocampus to account for a broad range of representational cognitive processes in Chapter 2, I introduce preliminary models in Chapter 3 in which I seek to test this for the case of creativity. Forty-three youth participated in cognitive data collection (21 with Down syndrome), and 38 of these participants (18 with Down syndrome) also underwent MR imaging. In modeling creativity as a function of memory and executive control, I seek to discover the extent to which memory contributes to creativity. Significant results were found for the group with Down syndrome, with associative memory and executive function emerging as predictors of creative performance. Surprisingly, these associations were absent in the typically developing group, for which the model and the variables were not significant. I also predicted that creativity and adaptive behavior would be positively correlated as representational functions that seem to have mnemonic contributions. Results included a positive correlation for creativity and adaptive behavior in the group with Down syndrome, while these functions were negatively correlated in the typically developing sample. In Chapter 4 I turn to examining the hippocampus itself. Previous studies have examined the hippocampus at the level of its subfields in adults with Down syndrome but not in youth, and while automated segmentation studies have been done with typically developing youth, there is little information on whether automated and manual methods agree for this age group. In the current study, subfield segmentations were made for youth with Down syndrome and typically developing youth using both methods in order to determine what group differences characterize the development of subfields, how well the methods concur with typical and atypical samples, and whether specific subfields relate to specific cognitive functions. The two methods showed small to moderate correlations across the subfields tested. The anterior hippocampus was correlated with associative memory in both groups and the CA1 subfield with adaptive behavior in both groups. Creativity did not show a correlation with hippocampal subfield volumes. Altogether group differences were more profound than expected in the studies described in chapters 3 and 4. Creativity, putatively linked to the hippocampus in Chapter 3, was well described by memory and executive control in the DS sample only. Possible explanations for this difference and the directionality difference between groups in the creativity to adaptive behavior study are offered. In Chapter 4, volumetric results largely supported hypotheses, but the methods produced less similar segmentations than anticipated, suggesting that continued caution is warranted in using automated methods with youth and special populations. Memory was similarly correlated with anterior hippocampus in both groups, but CA1 was only significantly related to CA1 in the DS group after correction, and creativity as a whole bore no significant relationships to subfields, although the creativity domain of flexibility was significantly related to CA and DG subfields in typically developing youth. In total, this dissertation explored hippocampal development and the concurrent development of “hippocampal” representational skills. More work is needed in order to understand how the developing hippocampal subfields interact with other brain regions and networks, how this changes across developmental time and how it may differ in various models of hippocampal impairment.