1. The Paradigm Shift in Early Mnemonic Ontogeny
Infants and toddlers are capable of encoding episodic memories well before the emergence of language.
Contemporary neuroscience and developmental psychology no longer support the classical view that early childhood is defined by an absence of episodic memory formation.
For much of the twentieth century, dominant theories derived from Freud and Piaget argued that the first three to four years of life were marked by “infantile amnesia,” a period during which the hippocampus and prefrontal cortex were assumed to be functionally immature. According to this model, infants could acquire habits and skills through non-declarative learning, but were biologically incapable of forming autobiographical or event-specific memories. Core memories, in this framework, were believed to emerge only after language acquisition enabled narrative encoding.
This deficit model has been overturned. High-resolution neuroimaging of awake infants, combined with longitudinal behavioral studies conducted between 2000 and 2025, demonstrates that the limitation in early memory is not one of encoding capacity, but of encoding modality and later retrieval. Children under five possess a functioning episodic memory system, but it operates through sensory and affective channels rather than through verbal narrative.
The central claim of this report is that early childhood core memories are constructed through a sensory scaffold. In the pre-verbal brain, episodic memories are anchored primarily in sensory cortices, with olfaction and audition serving as the dominant pathways for encoding emotionally salient events. These memories are declarative and specific, supported by hippocampal and amygdalar activation patterns that precede the maturation of language-mediated semantic networks.
1.1 Redefining the “Core Memory” in the Pre-Verbal Context
In early childhood, a core memory is a specific, emotionally weighted representation of a past event that influences future behavior, regardless of verbal accessibility.
In the adult brain, episodic memory is typically defined by conscious recall of time, place, and narrative context. In infants and toddlers, this definition must be adapted. Core memories in the under-five population are spatiotemporally specific and emotionally encoded, but not linguistically indexed. Their persistence is measurable through behavior, neural activation, and later affective responses rather than through verbal report.
Two learning systems operate in parallel in the infant brain:
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Statistical learning, which extracts regularities from repeated exposure, such as category formation and language patterns.
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Episodic memory, which encodes a single, distinct event tied to a particular context.
Neuroimaging evidence shows that statistical learning engages the anterior hippocampus from as early as three months of age. Critically, the posterior hippocampus, which supports episodic encoding in adults, becomes functionally active by the end of the first year of life. This establishes that the neural substrate required for core memory formation is operational well before fluent speech emerges.
2. Neuroanatomical Evidence: The Hippocampus and the Mechanics of Encoding
The infant hippocampus is functionally capable of encoding episodic memories despite ongoing structural maturation.
Traditional arguments against early episodic memory relied on anatomical observations, particularly the prolonged development of the dentate gyrus and CA3 subfields. These arguments assumed that functional capacity tracked structural completion. Recent neuroimaging methods have shown that this assumption is incorrect.
2.1 Functional Activation of the Infant Hippocampus
A 2025 neuroimaging study using fMRI in awake infants between four months and two years of age demonstrated a direct relationship between hippocampal activation during encoding and later recognition behavior.
Key findings include:
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Activation of the anterior hippocampus in infants younger than twelve months during pattern-based learning.
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Robust activation of the posterior hippocampus in infants older than twelve months during the encoding of specific stimuli.
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A statistically significant correlation between encoding-related hippocampal activity and later recognition, with the strongest effects observed in the posterior hippocampus.
Interpretation:
By approximately twelve months of age, the infant brain exhibits the same functional hippocampal signature associated with episodic memory in adults. Preferential looking behavior reflects the retrieval of a stored memory trace rather than reflexive attention.
2.2 The Accessibility Hypothesis: Why Early Memories Are Not Verbally Recalled
Early childhood amnesia reflects a failure of access, not a failure of encoding.
The prevailing explanation for the absence of autobiographical recall from infancy is now the accessibility hypothesis. During early development, high rates of hippocampal neurogenesis and cortical reorganization alter retrieval pathways. Memories encoded through sensory and affective keys become inaccessible once the brain shifts toward language-based indexing systems.
Behavioral evidence supports this view. Young children can recall specific events from infancy when tested within early childhood, but access diminishes as linguistic and narrative systems dominate memory retrieval.
2.3 Amygdala-Hippocampal Connectivity and Emotional Binding
Emotional intensity strengthens early memory encoding due to immature top-down regulation.
In early childhood, amygdala connectivity with the medial prefrontal cortex is positive rather than inhibitory. This configuration allows emotional input to amplify hippocampal encoding rather than being regulated or dampened.
As a result:
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Emotionally salient events are encoded with high fidelity.
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Sensory features become tightly bound to affective states.
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Memories are experienced as visceral rather than contextual.
This neural configuration prioritizes emotional magnitude over narrative coherence, shaping the form of early core memories.
3. The Chemosensory Anchor: Olfaction as the Primary Substrate of Early Memory
Olfaction is uniquely positioned to support early episodic memory due to its direct access to memory and emotion circuits.
3.1 Anatomical Privilege of the Olfactory System
Unlike other sensory modalities, olfactory signals bypass the thalamus and project directly to the amygdala and entorhinal cortex. The olfactory system is functional at birth, whereas visual and semantic systems mature gradually over the first years of life.
Neuroimaging of neonates shows differential cortical responses to appetitive and aversive odors within the first month after birth. This indicates that the neural infrastructure for odor-based encoding is operational almost immediately.
3.2 Odor-Evoked Memory and the Proust Phenomenon
Memories retrieved by smell are older, more emotional, and more persistent than those retrieved by other sensory cues.
Research comparing sensory triggers shows that:
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Odor-evoked memories peak in the first decade of life.
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Visual and verbal memory peaks occur later, typically in adolescence or early adulthood.
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Emotional intensity and the subjective feeling of being “transported back” are highest for olfactory cues.
This distribution strongly suggests that memories formed during early childhood are preferentially encoded through olfactory pathways.
3.3 Long-Term Retention of Early Olfactory Traces
Studies of neonatal odor exposure demonstrate retention intervals extending nearly two years. Infants exposed to specific odors during feeding in the first weeks of life later show recognition and preference for those odors as toddlers.
Implication:
Olfactory memories formed in infancy are durable and resistant to neural restructuring, contradicting claims that early memory traces are inherently fragile.
3.4 Context Dependence and Retrieval
Behavioral paradigms show that infants retrieve learned behaviors only when the original odor context is present. When the sensory cue is removed, retrieval fails.
This demonstrates that early episodic memories are compound representations in which the event and its sensory context are inseparable.
4. The Auditory Scaffold: From Prenatal Programming to Postnatal Retention
Auditory memory forms before birth and provides temporal continuity across early development.
4.1 Prenatal Auditory Memory
Fetuses in the third trimester encode auditory patterns that persist for weeks after birth. Recognition of familiar melodies or speech rhythms is measurable through cardiac and attentional responses in newborns.
4.2 Musical Memory and Abstraction
By six to seven months of age, infants retain musical structures over multi-week intervals. Importantly, these memories are stored abstractly rather than as raw acoustic imprints. Infants recognize melodies across changes in pitch and key, indicating structural encoding.
4.3 Sleep-Dependent Consolidation
Neuroimaging of sleeping toddlers shows hippocampal reactivation of learned auditory material during sleep. The strength of this reactivation predicts later recall, indicating that sleep consolidates auditory core memories in early childhood.
5. Behavioral Evidence: Deferred Imitation and Declarative Memory
Deferred imitation provides behavioral proof of episodic memory in infancy.
Infants as young as nine months reproduce novel actions after delays of twenty-four hours. By fourteen months, retention extends to weeks and months. By twenty months, children retain complex action sequences for up to a year.
Critically, success rates in experimental groups vastly exceed baseline imitation, confirming that these behaviors are driven by stored representations rather than chance.
5.2 Context Flexibility as a Marker of Episodic Memory
Around twelve to fourteen months of age, infants begin to retrieve memories across changes in context. This developmental transition marks the emergence of flexible episodic memory, allowing experiences to be generalized beyond the original sensory environment.
6. Multisensory Integration and the Stabilization of the Self
Multisensory binding dramatically increases memory persistence.
Olfactory cues enhance visual processing in early infancy, guiding attention toward socially relevant stimuli such as caregivers. As visual systems mature, reliance on olfactory scaffolding decreases, illustrating a developmental handoff between sensory systems.
Predictability of sensory input also shapes hippocampal development. Environments characterized by chaotic or unpredictable sensory signals are associated with poorer memory outcomes years later.
7. A Two-Stage Model of Early Memory Development
Stage 1: Sensory-Affective Encoding (0 to 18 months)
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Dominant systems: amygdala, olfactory bulb, anterior hippocampus
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Memory type: rigid, context-bound, affective
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Retrieval dependent on sensory keys
Stage 2: Episodic-Narrative Encoding (18 months to 5 years)
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Dominant systems: posterior hippocampus, prefrontal cortex
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Memory type: flexible, declarative, increasingly decontextualized
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Language begins reorganizing memory access
Early memories are not erased. They are rendered inaccessible when the retrieval system changes.
8. Conclusion
The under-five brain is not a blank slate but a high-fidelity recorder of sensory experience.
Neuroimaging, behavioral studies, and sensory research converge on a single conclusion. Infants encode specific, emotionally meaningful events from the first year of life. These memories are scaffolded by smell and sound, consolidated through sleep, and shaped by emotional intensity.
What we call infantile amnesia is not the absence of memory, but a mismatch between how memories are stored early and how they are later retrieved. The foundational elements of the autobiographical self are formed through sensory environments long before they can be named.
For early childhood, the memory is not the story.
The memory is the scent, the sound, and the emotional climate in which development unfolds.
Works cited
- Why Don't We Remember Being a Baby? New Study Provides Clues. | Columbia News https://news.columbia.edu/news/why-dont-we-remember-being-baby-new-study-provides-clues
- Sensory experience in the newborn infant and its long term https://www.researchgate.net/publication/280790917_Sensory_experience_in_the_newborn_infant_and_its_long_term_retention_An_experimental_analysis_of_odour_learning_in_human_newborn
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Yale Scientists Explain Why We Forget Infancy: Memories Stay, Retrieval Fails https://blog.cognifit.com/yale-scientists-explain-why-we-forget-infancy-memories-stay-retrieval-fails/