br Conflict of interest br

Conflict of interest
Acknowledgements
Introduction Research examining the development of children\'s memory has often demonstrated that infants and young children show early competencies in memory function, remembering some items and associations across long term delays. For instance, 2-month-old infants can remember a specific mobile for as long as 2 weeks if encoding occurs across three 6-min sessions (Rovee-Collier, 1999), and 5–6 month olds remember a face they encode for 2min up to 2 weeks later (Fagan, 1973). Such findings have been attributed to an early-maturing hippocampus (Rovee-Collier, 1997) or the functions this structure may first subserve in its developmental course (e.g., Richmond and Nelson, 2009). However, early competency is in buy NVP-BKM120 to children\'s delayed explicit verbal memory for everyday events, which slowly develops, emerging in an immature form after 24 months and undergoing continued refinement until 7 years (Peterson et al., 2011; Rubin, 2000) and beyond (Ghetti and Bunge, 2012; Ghetti et al., 2010). For instance, although some young children can remember a small number of salient events they experience before 24 months, children retain more memories with greater detail after this age (Peterson et al., 2011), consistent with a demarcation between early- and late-developing memories. Prior to 18–24 months most children fail to form lasting, everyday memories they can consciously recollect (but see Bauer, 2015). This is often referred to as the a period of “childhood amnesia”. Consistent with such findings some have suggested that early and late developing memories may reflect development of separate memory systems, including an implicit and explicit system (Schacter and Moscovitch, 1984). Nadel and Zola-Morgan (1984) first attributed the lack of episodic detail in young children\'s memories to the late trajectory of hippocampal development, suggesting that it would not be until this structure was fully developed that children would be able to show robust episodic recall. Given rapidly emerging knowledge of the development of the hippocampus and the surrounding cortex, researchers have begun to theorize how disparate memory processes may map onto changes in these neural structures (Bachevalier, 2014; Lavenex and Banta Lavenex, 2013; Olson and Newcombe, 2014). Here we expand on recent findings in behavioral memory development and how these results may reflect the development of the medial temporal lobe (MTL) versus hippocampus. In adults, an established body of research supports the existence of distinct learning and memory systems in the brain, e.g., the basal ganglia reward system supporting procedural memory (Knowlton et al., 1996), and the MTL supporting episodic and semantic memory (Eichenbaum and Cohen, 2001; Nadel and Hardt, 2011; Tulving, 1972). There are also distinct roles for substructures within these systems. Within the MTL, for instance, perirhinal cortex [PRC] supports object recognition, parahippocampal cortex [PHC] supports scene recognition, and the hippocampus supports relational memory in its capacity to bind information from PRC and PHC (Eichenbaum and Cohen, 2001; Diana et al., 2007). The subfields of hippocampus (CA fields 1–4 and dentate gyrus) are also thought to serve specific functions. Work from animal and human neuroscience has shown that the neurons of CA3 are specialized to perform pattern completion, the dentate gyrus (DG) supports pattern separation, and CA1 has been linked to representation of space and temporal sequence over repeated exposures (Bakker et al., 2008; Gilbert et al., 2001; Nakashiba et al., 2008). The subfields of the hippocampus have different retention functions as does cortex. Memories supported by CA3 and DG neurons form rapidly in as little as one exposure in contrast to CA1, which requires repeated exposures for memory formation (Nakashiba et al., 2008). Memories are also thought to emerge gradually in networks of cortical neurons (McClelland et al., 1995) supported by architectures with shallow retention profiles that require extended or repeated exposure for long-term memory retention.