Infantile amnesia results from differential memory retrieval in humans

S. D. Power; A. Werwach; A. Peikert; M. Fey; T. Forbes-Mitchell; J. Hild; C. Buss; U. Lindenberger; T. J. Ryan; M. Werkle-Bergner

doi:10.64898/2026.10.19.755340

AI summary · DOI: 10.64898/2026.10.19.755340 · bioRxiv: Neuroscience

Infantile amnesia results from differential memory retrieval in humans

S. D. Power, A. Werwach, A. Peikert, M. Fey, T. Forbes-Mitchell, J. Hild, C. Buss, U. Lindenberger,

and 2 more authors

T. J. Ryan, M. Werkle-Bergner

Original paper Published on 20 Oct. 2026 bioRxiv preprint License: CC BY-NC-ND 4.0 Also in: fr

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The essentials

Toddlers’ early memories show heterogeneous forgetting, with retrieval-related EEG activity and prenatal maternal immune activation implicating memory accessibility rather than simple erasure.

Based on the abstract only: check the details in the original paper.

Question

Does infantile amnesia arise because early memories fail to form, decay, or persist but become inaccessible? The study examines encoding and retrieval across time in toddlers.

Method

Toddlers aged 18–24 months were tested longitudinally using a novel naturalistic episodic memory paradigm, covering encoding, retrieval one day later, and delayed retrieval up to six months later. The study used computational modelling and retrieval-related EEG measures, and leveraged the COVID-19 pandemic as a natural experiment to examine maternal immune activation during pregnancy.

Findings

Result Computational modelling identified heterogeneous forgetting, with full retention and complete loss equally likely and nearly a quarter of toddlers retaining only part of the memory.
See the passage in the paper
Computational modelling revealed that forgetting during the infantile amnesia period was heterogeneous. Toddlers were as likely to retain the full memory as to lose it completely, while nearly a quarter retained only part of the memory.
Result Encoding accuracy predicted full memory retention one day later but not at the delayed test up to six months later.
See the passage in the paper
Encoding accuracy predicted which toddlers retained the full memory at the test one day later, but not at the delayed test up to six months on.
Result A retrieval-specific EEG signature predicted complete, but not partial, memory retrieval before toddlers responded behaviourally.
See the passage in the paper
Instead, a retrieval-specific EEG signature predicted complete, but not partial, memory retrieval, distinguishing which toddlers had retained the full memory before their behavioural response.
Result The pandemic-based natural experiment linked maternal immune activation during pregnancy to altered vulnerability to infantile forgetting.
See the passage in the paper
Finally, leveraging the COVID-19 pandemic as a natural experiment, we found that maternal immune activation during pregnancy, as in rodents, alters vulnerability to infantile forgetting in humans.
Authors’ interpretation The authors interpret the findings as evidence that early memories persist but become increasingly inaccessible, with trajectories shaped by retrieval mechanisms and the prenatal environment.
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Together, these findings show that early memories formed during the infantile amnesia period are not simply erased but persist in an increasingly inaccessible form, a transformation whose trajectory can be shaped by both the neural retrieval mechanism and the prenatal environment.

Limitations

The reported observations concern toddlers aged 18–24 months followed for up to six months, so they do not directly establish memory accessibility later in childhood or adulthood.

Why it matters

The authors argue that infantile amnesia reflects increasing inaccessibility of persisting memories rather than simple erasure. Their findings implicate both neural retrieval mechanisms and the prenatal environment in shaping early forgetting.

Written by AI from the paper. Passages are checked word for word against the text we analysed; the rest may contain errors.

AI-generated keywords: Infantile amnesia Episodic memory Memory retrieval EEG Maternal immune activation

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Comprehensive Summary
Layman's Summary
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Original abstract

This study examines why people cannot recall experiences from their earliest years, a phenomenon known as infantile amnesia. The central question is whether early memories fail to form, disappear over time, or remain stored but become difficult to retrieve. Power and colleagues investigated these possibilities by tracking toddlers’ memories from initial learning through later recall. Their findings suggest that early forgetting follows several patterns and that retrieval, rather than initial encoding alone, plays an important role in whether a memory can later be recalled. The researchers conducted a longitudinal study of toddlers aged 18–24 months using a novel, naturalistic episodic memory task designed to assess memory for specific experiences or events. Assessments covered initial encoding, retrieval one day later, and delayed retrieval up to six months afterward. Computational modelling distinguished patterns of memory retention and forgetting. The researchers also examined a retrieval-specific EEG signal and used the COVID-19 pandemic as a natural experiment to investigate whether maternal immune activation during pregnancy was associated with differences in infantile forgetting. The modelling identified several distinct memory outcomes rather than a uniform pattern of gradual decline. Toddlers were approximately equally likely to retain the full memory or lose it completely, while nearly one quarter retained only part of it. The abstract does not report exact percentages for full retention or complete loss. These findings highlight partial remembering as a substantial outcome during this developmental period and suggest that classifying memories simply as present or absent would overlook meaningful variation. Predictors of successful recall also differed over time. Accuracy during initial encoding predicted full retention one day later but not at the delayed test, conducted up to six months afterward. A retrieval-specific EEG signature predicted complete, but not partial, memory retrieval and distinguished toddlers who retained the full memory before they gave their behavioural response. This finding supports the importance of retrieval-related neural processes, although the abstract does not describe the signal’s characteristics or report its predictive accuracy. The prenatal-environment analysis suggested that maternal immune activation during pregnancy altered vulnerability to infantile forgetting, a finding the authors describe as consistent with rodent studies. However, the abstract does not specify the direction or magnitude of the association, how immune activation was measured, or which potential confounding factors were addressed. The available information therefore does not establish whether a particular prenatal exposure increased or decreased forgetting. Overall, the authors conclude that memories formed during the infantile amnesia period are not necessarily erased but may persist while becoming increasingly inaccessible. They propose that neural retrieval mechanisms and the prenatal environment shape this trajectory. These conclusions require caution. The paper is a bioRxiv preprint, and only its title, author information, and abstract are available here; the full text is unavailable under the stated licensing restriction. Sample size, task details, statistical estimates, EEG procedures, and controls therefore cannot be assessed. Although the abstract supports a role for retrieval in early forgetting, it does not establish that every forgotten memory persists or directly explain how toddlers’ memory outcomes relate to adults’ inability to recall infancy.

Why Do Our Earliest Memories Become So Hard to Reach?

Most of us remember little, if anything, from our first years of life. Yet toddlers clearly learn from experience: they recognize familiar people, anticipate routines, and remember things that happened to them. What happens between those early experiences and the blank spaces we encounter when looking back as adults?

A study titled “Infile amnesia results from differential memory retrieval in humans” by S. D. Power and colleagues explores this puzzle by following toddlers’ memories over time. Its findings suggest that early forgetting is not a single process. Some memories remain fully accessible, others are remembered only partly, and some cannot be recalled at all. Crucially, the ability to retrieve a memory may matter alongside how well it was originally learned.

Three Possible Explanations for Early Forgetting

Infantile amnesia raises a deceptively difficult question: why can we not consciously recall most experiences from infancy? There are several possible explanations, each pointing to a different stage of memory processing.

Early experiences might not be encoded strongly enough to become lasting memories.
Memories might form but then deteriorate or disappear over time.
Memories might remain stored while becoming increasingly difficult to retrieve.

These possibilities are challenging to separate. When someone cannot recall an event, that failure alone does not reveal whether the memory is absent or merely inaccessible. Studying memory close to the time it forms offers a way to investigate the distinction.

Following Toddlers’ Memories Over Time

The researchers conducted a longitudinal study with toddlers aged 18–24 months. They used a novel, naturalistic episodic memory task designed to assess memory for specific events or experiences, rather than general knowledge or familiarity.

The study examined initial encoding, retrieval one day later, and delayed retrieval up to six months afterward. Tracking these stages allowed the researchers to ask whether successful learning at the beginning predicted remembering later.

They also used computational modelling to distinguish patterns of retention and forgetting. Alongside behavioural assessments, they examined a retrieval-specific EEG signal. A separate analysis used the COVID-19 pandemic as a natural experiment to explore associations between maternal immune activation during pregnancy and later infantile forgetting.

Remembering Was Not Simply All or Nothing

The modelling identified several distinct outcomes rather than one uniform pattern of gradual decline. Toddlers were approximately equally likely to retain a full memory or lose it completely, while nearly one quarter retained only part of it. The abstract does not provide exact percentages for full retention or complete loss.

Partial remembering is particularly important here. Classifying each memory as simply “remembered” or “forgotten” would miss a substantial share of the observed outcomes. A child may retain some components of an experience without being able to retrieve the whole event.

This finding suggests that early memory development involves more than whether an experience survives. It also involves how much of that experience remains accessible.

Learning Well Did Not Guarantee Long-Term Recall

Accuracy during initial encoding predicted full retention one day later. At that short interval, how well toddlers initially learned the experience helped explain whether they remembered it completely.

However, initial encoding accuracy did not predict full retention at the delayed assessment, conducted up to six months later. This difference suggests that factors beyond initial learning become important over time. It does not mean encoding is irrelevant, but it challenges an explanation based on weak initial encoding alone.

A Neural Clue to Successful Retrieval

The retrieval-specific EEG signature predicted complete retrieval, but not partial retrieval. It also distinguished toddlers who retained the full memory before they gave their behavioural response.

This supports a role for retrieval-related neural processes in successful remembering. However, the available abstract does not describe the signal’s characteristics or report its predictive accuracy. The finding therefore should not be treated as a definitive test of whether an individual child’s memory remains stored.

A Prenatal Connection That Needs Clarification

The prenatal analysis suggested that maternal immune activation during pregnancy altered vulnerability to infantile forgetting, a result the researchers describe as consistent with rodent studies.

Important details remain unavailable, however. The abstract does not specify whether the association involved increased or decreased forgetting, how immune activation was measured, or which potential confounding factors were addressed. It therefore cannot establish that a particular prenatal exposure causes memory loss, nor does it support practical recommendations for pregnant people.

What This Study Can—and Cannot—Tell Us

The paper is a bioRxiv preprint, and this discussion relies on its abstract because the full text is unavailable under the stated licensing restriction. Sample size, task details, statistical estimates, EEG procedures, and study controls cannot be assessed from the available information.

Within those limits, the study offers a useful shift in perspective: early memories may sometimes become inaccessible rather than simply vanish. It does not demonstrate that every forgotten memory persists, or directly explain adults’ inability to recall infancy. Instead, it shows why understanding early forgetting requires looking beyond whether children learned an experience—and toward how they later retrieve it.

Created on 27 Oct. 2026

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Infantile amnesia results from differential memory retrieval in humans

The essentials

Question

Method

Findings

Limitations

Why it matters

Read further

Definitions

Why Do Our Earliest Memories Become So Hard to Reach?

Three Possible Explanations for Early Forgetting

Following Toddlers’ Memories Over Time

Remembering Was Not Simply All or Nothing

Learning Well Did Not Guarantee Long-Term Recall

A Neural Clue to Successful Retrieval

A Prenatal Connection That Needs Clarification

What This Study Can—and Cannot—Tell Us

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