br Conflict of interest br Acknowledgments This study

Conflict of interest
Acknowledgments This study was funded by the UK Medical Research Council (MRC) (G0802226) and the Behavioural and Clinical Neuroscience Institute (BCNI) at the University of Cambridge (jointly funded by the MRC and Wellcome Trust). Additional support was given by the National Institute for Health Research (NIHR) Cambridge Biomedical Research Centre. We thank the participants and their zip inhibitor for taking part in the study. We would also like to thank the Cambridge and Peterborough NHS Foundation trust, Child and Adolescent Mental Health services and members of the IMPACT team. We are grateful to Rebecca Eliot for her advice on the analysis design.
Introduction Episodic memory, or the ability to remember specific past events in the context in which they occurred, improves considerably during middle and late childhood (Brainerd et al., 2004; Ghetti and Angelini, 2008; Shing and Lindenberger, 2011). The hippocampus has been implicated in the encoding and integrating the contextual features of our experiences into bound representations and the retrieval of these representations (Diana et al., 2007; Eichenbaum et al., 2007). Thus, understanding developmental changes in hippocampal function in critical for understanding the development of episodic memory. Although several studies have compared hippocampal function in children and adults in an attempt to explain age-related differences in episodic memory, these studies have yielded varying results. The majority of studies have found age-related differences in hippocampal activation profiles between children and adults (DeMaster and Ghetti, 2013; DeMaster et al., 2013; Ghetti et al., 2010; Paz-Alonso et al., 2008); however, the apparent nature of these developmental differences has not been consistent. For example, children have been found to show decreased memory-related hippocampal selectivity for episodic retrieval compared to adults across the entire hippocampus (DeMaster et al., 2013). However, in other studies developmental differences were restricted to the hippocampal head or tail (e.g., DeMaster and Ghetti, 2013; Paz-Alonso et al., 2008). Finally, other studies have failed to find age-related differences in hippocampal function altogether (Güler and Thomas, 2013; Ofen et al., 2012). Part of this inconsistency may be due to the relatively small child sample sizes in previous studies. It is critical to examine age-related differences with large enough sample sizes to differentiate among children of different ages, not just between children and adults, when investigating a developmental period in which behavioral change is robust. Middle childhood is one such period of rapid change in memory performance. For example, several studies have shown consistent age-related improvements among children in this age range in assessments of episodic recollection (Ghetti and Angelini, 2008), source memory (Riggins, 2014) and recall (Schwenk et al., 2007). Developmental differences in hippocampal structure have similarly been reported during this period (DeMaster et al., 2014; Gogtay et al., 2006). Given these robust changes, studies that examine age differences among children are more likely to successfully characterize developmental processes than those which consider children as a single group. Results from one of the few studies of memory development in which children of multiple ages were examined separately (Ghetti et al., 2010) illustrate this possibility. In that study, there was evidence of non-linear change from middle childhood into adolescence, such that subsequent item-memory effects were observed in 8-year-olds, no subsequent memory effects were observed in 10- to 11 year-olds and subsequence source-memory effects were evident in 14-year-old and adults. This non-linear pattern underscores the importance of differentiating among children, and the risk of attenuating or misrepresenting age differences when children of different ages are examined together.