How Infants Form Memories: The Science Behind Infantile Amnesia and Early Episodic Encoding

The episode revisits the mystery of infantile amnesia, examining how infants form memories and why early experiences often fade from later recall. Yale psychologist Nick Turk-Brown explains that episodic memory begins to emerge around 12 months, with the hippocampus showing stronger encoding for memories that are later remembered. The discussion covers evidence from infant fMRI studies, animal experiments using optogenetics, and ongoing work tracking memories via parent videos over the first two years of life. The potential adaptive value of early memory, retrieval challenges, and future questions about consolidation and access illuminate how early experiences shape cognitive development and behavior.

Introduction: The Enigma of Early Memories

The Science Weekly episode revisits infantile amnesia, the observation that most people cannot recall specific events from their first years. Nick Turk-Brown, a cognitive neuroscience professor at Yale, outlines how infancy is a period of rapid learning—from language to social cues—yet episodic memories from this era are largely inaccessible later in life. The host frames memory as central to identity and decision making, prompting a deep dive into what memories babies actually form and how researchers study them without relying on verbal reports.

"Memory is who we are. It’s our personality, it’s our fears, it’s our dreams, and understanding when it comes about and how it comes about, I think is one of the most fundamental questions about what it means to be human." - Nick Turk-Brown, Professor of Psychology and Neuroscience, Yale University

What Is Episodic Memory and Why It Matters in Early Life

The discussion distinguishes episodic memory—memory for specific events in a time and place—from semantic memory, which concerns general knowledge. The hippocampus, a seahorse-shaped brain region, is identified as the key structure for encoding new experiences and supporting later recollection after consolidation to the cortex. The conversation connects infancy to a high learning period, while noting that access to early episodes remains elusive for most adults, raising questions about development and retrieval cues.

"the hippocampus in an infant's brain responds more strongly when it's having an experience that it'll later remember than one that it later forgets." - Nick Turk-Brown

Animal Models Illuminate Early Memory Encoding

Turk-Brown highlights infantile amnesia across the animal kingdom, with mouse studies offering precise insight. In experiments, baby mice form hippocampal traces when learning a maze; as adults, they often fail to recall the maze path unless researchers reactivates the tagged cells with light through optogenetics, which restores memory. This cross-species evidence suggests that memory formation occurs early, but access or retrieval mechanisms may differ with development, prompting the central question: are early memories formed and simply inaccessible, or not encoded at all?

"optogenetics where you can Activate neurons with light, you can reactivate those cells that were tagged in the baby mouse, and now the mouse remembers where to go and knows how to escape." - Nick Turk-Brown

New Insights from Infant fMRI and Encoding into Memory

The core of the episode focuses on Turk-Brown’s study where infants aged 4 to 24 months were scanned with functional MRI while being shown new photos of faces, toys, and scenes. After a short delay, their memory was inferred by measuring looking time: if infants spent more time looking at a previously seen image, it suggested recognition. The key finding is that beginning around 12 months, hippocampal activity during encoding differentiates between items that will be remembered versus forgotten, with stronger effects in babies who overall remember more across trials. This indicates the onset of episodic memory encoding around the one-year mark, rather than a late emergence.

"the hippocampus in an infant's brain responds more strongly when it's having an experience that it'll later remember than one that it later forgets." - Nick Turk-Brown

From Encoding to Retrieval: How Long Do Baby Memories Last?

Turk-Brown emphasizes that the study demonstrates encoding differences but does not settle how long such memories persist. The team is pursuing follow-up work, including longitudinal studies that combine home videos recorded by parents with repeated imaging. The premise is to determine whether the same hippocampal signals observed during encoding correlate with retrieval as children age, and whether memories fade due to storage, consolidation, or retrieval cues, beyond simple forgetting.

"memory is formed properly, but retrieval may be the bottleneck as the brain matures and the cues change." - Nick Turk-Brown

Adaptive Value and Implications for Caregiving

Beyond mechanism, the discussion considers why infant memories might be adaptive. Early memory could help children learn general world structure, language, and social dynamics, shaping future behavior and attention. Language and a sense of self are discussed as possible contributors to memory retrieval later in life, but the data suggest encoding begins independently of these factors. The potential implications for parenting and early education are highlighted, challenging the notion that memories before age three are irrelevant or wasted, and suggesting that even fleeting experiences might influence development in subtle, enduring ways.

"episodic memories for single events actually have a more profound impact on our behavior than we might realize." - Nick Turk-Brown

Looking Ahead: What This Means for Science

As the episode concludes, Turk-Brown outlines the ongoing research program: comparing encoding and retrieval across development, examining consolidation stages, and using home videos to test whether memories persist into preschool years. The work aims to map how early experiences shape later cognition, influence education, and inform our understanding of memory as a fundamental aspect of being human. The conversation closes with a reminder that memory is central to who we are and how we navigate the world, from infancy onward.