FORGOTTEN BEGINNINGS: STUDYING INFANTILE AMNESIA IN TODDLERS USING A NATURALISTIC LEARNING PARADIGM

Why do we forget our earliest memories from childhood? Despite children’s remarkable learning abilities, memories formed during the first 2-3 years of life are rarely retained, a phenomenon known as infantile amnesia (IA). Although IA is observed across mammalian species, its duration and developmental boundaries in humans remain unclear. Traditionally assumed to reflect uniform forgetting, rodent studies suggest that susceptibility to IA may vary across individuals and developmental conditions. Here, we applied a naturalistic paradigm, developed as a human analogue of the rodent Barnes maze, to examine memory retention in toddlers 18-24 months. Memory was assessed after a 24-hour delay and again after delays of 1, 3, or 6 months, capturing the developmental window in which IA is thought to emerge. To probe the origins of inter-individual variability in memory formation and maintenance, analyses incorporate (i) markerless pose estimation using DeepLabCut, (ii) trajectory-based profiling of variability in search strategies and (iii) mobile electroencephalography to examine neural correlates of memory encoding and retention. Findings show that toddlers successfully encode and retain complex object-place-context associations. Critically, many toddlers retain these associations after long-term delays of 6 months. Across the18-24-month age range, there were no reliable effects of age at encoding or delay duration. Instead, substantial inter-individual differences emerge, suggesting that early memory formation and maintenance are far from uniform and may be shaped by factors beyond age alone. These findings challenge the view that infantile amnesia reflects uniform forgetting and highlight the importance of individual-level approaches to understanding early memory development.