Age is not the sole
Age is not the sole source of potential variation in hippocampal activation. Individual differences in task performance may also yield differences in activation. For example, there is evidence from previous research that differences in activation profiles may be more strongly associated with individual differences in performance than with age (Paz-Alonso et al., 2013). In this buy zip study examining the neural substrates of memory suppression, some participants were able to suppress memory retrieval and some participants were not within each age group, despite overall better performance in 10–12 year old children compared to 8–9 year old children. Individual differences in performance were more strongly predictive of differences in neural activation than were age differences. Notably, these performance-related activation differences were examined in regions associated with cognitive control, and not within the hippocampus. Thus, the extent to which age and performance differences affect hippocampal activation remains a key question for investigation. A large sample allows for the examination of potential relations between hippocampal activations during retrieval and task performance, which together may paint a more coherent picture how hippocampally-mediated binding processes contribute to the development of episodic memory.
In addition to examining age- and performance-related differences in hippocampal activation, we aimed to further investigate whether this activation would differ as a function of position along the hippocampal axis. The discussion about whether there are differences in function along the longitudinal axis of the hippocampus has gained momentum in recent years (Poppenk and Moscovitch, 2011; Poppenk et al., 2013) and, although there is no consensus about the exact meaning of these differences, initial evidence from developmental dissociations has bolstered the claim in favor of functional distinctions. This initial evidence has come both from structural and functional developmental studies. Functional differences have been reported with children failing to recruit the hippocampal head to the same extent as adults (DeMaster and Ghetti, 2013; Paz-Alonso et al., 2008), and with children, but not adults, engaging the hippocampal tail (DeMaster and Ghetti, 2013). In these studies, children ages 8–11 years were examined as one group, reducing the possibility of fully appreciating development during this period. Furthermore, in other studies, age differences in hippocampal activation extended throughout the entire structure (DeMaster et al., 2013), possibly suggesting that functional distinctions along the longitudinal axis are subtle and may depend on specific aspects of the task. The present study offers the opportunity to examine these regional differences while accounting for both age- and task-related performance.
Consistent with this functional evidence, a study of hippocampal structure has shown that in children, source retrieval was positively associated with volume in the hippocampal tail, whereas in adults Cordycepin was associated with volumes of more anterior regions (i.e., negatively with the hippocampal head and positively with the hippocampal body; DeMaster et al., 2014). Interestingly, the direction of the volume–behavior associations in adults reflected the direction of development differences: indeed, adults compared to children had a smaller hippocampal head, and adults with smaller hippocampal heads exhibited better source retrieval. Thus, there is strong evidence from anatomical as well as functional investigations for developmental differences along the longitudinal axis of the hippocampus, and consideration of these differences may be critical for understanding hippocampal contributions to improvements in episodic retrieval during childhood.
The present study The present study was aimed at examining age- and performance-related differences in hippocampal function during episodic retrieval. In addition, we were interested in investigating whether these differences varied as a function of location along the longitudinal axis of the hippocampus. To achieve these goals, we assessed a sample of 8- to 11-year-olds and young adults with a source memory task that required participants to remember which of three scenes was initially paired with individual objects. The task was designed to: (1) reflect the basic structure of source memory tasks used in prior studies (Ghetti et al., 2010); (2) be appropriate for a wide age range; and (3) incorporate meaningful item-context pairings. In particular, contextual information in this task (i.e., the scenes) is visually and semantically richer than contextual information used in previous studies such as position (DeMaster et al., 2013), colored borders (DeMaster and Ghetti, 2013), or another paired item (Güler and Thomas, 2013).