Infantile amnesia results from differential memory retrieval in humans

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

bioRxiv preprint
DOI: 10.64898/2026.10.19.755340 - DOI (bioRxiv: Neuroscience)
Published on 20 Oct. 2026
License: CC BY-NC-ND 4.0
Abstract

Infantile amnesia, the inability to recall memories from our earliest years, is the most common form of forgetting in mammals. Whether early memories never form, decay, or persist but become inaccessible remains unknown. Here, we investigated the nature of forgetting during the infantile amnesia period by longitudinally testing toddlers aged 18-24 months across the complete memory cycle from encoding, initial retrieval one day later, and delayed retrieval up to six months later, in a novel naturalistic episodic memory paradigm. 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. 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. 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. 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. 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.

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    Infantile amnesia: forgotten but not gone
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    Abstract

    Unlike adult memories that can be remembered for many years, memories that are formed early in life are more fragile and susceptible to being forgotten (a phenomenon known as “infantile” or “childhood” amnesia). Nonetheless, decades of research in both humans and nonhuman animals demonstrate the importance of early life experiences on later physical, mental, and emotional functioning. This raises the question of how early memories can be so influential if they cannot be recalled. This review presents one potential solution to this paradox by considering what happens to an early memory after it has been forgotten. Specifically, we describe evidence showing that these forgotten early-acquired …

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    Charles Jennings, Rogier Landman, Yang Zhou et al. · 2016 · Nature Neuroscience · cited 145 times · Not summarized yet
    Abstract

    Episodic memories formed during the first postnatal period are rapidly forgotten, a phenomenon known as 'infantile amnesia'. In spite of this memory loss, early experiences influence adult behavior, raising the question of which mechanisms underlie infantile memories and amnesia. Here we show that in rats an experience learned during the infantile amnesia period is stored as a latent memory trace for a long time; indeed, a later reminder reinstates a robust, context-specific and long-lasting memory. The formation and storage of this latent memory requires the hippocampus, follows a sharp temporal boundary and occurs through mechanisms typical of developmental critical periods, including the …

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    C. Alberini · 2026 · Annual Review of Developmental Psychology · Not summarized yet
    Abstract

    Infantile amnesia, the adult loss of autobiographical and episodic-like memories from early childhood, has long been a fascinating mystery. How, as many studies suggest they do, can forgotten early-life memories influence an individual's life? Numerous investigations have concluded that this memory loss results from the immaturity of the infant hippocampus- or medial temporal lobe–dependent system, which lacks the ability to consolidate, store, or retrieve memories. Based on our studies, we proposed a novel view of infantile learning and memory: The infant hippocampus-dependent memory system actively consolidates long-lasting, latent childhood memories and mental schemas that facilitate rele…

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    H. B. Madsen, J. Kim · 2016 · Behavioural Brain Research · cited 84 times · Not summarized yet
    Abstract

    Given the profound influence that early life experiences can have upon psychosocial functioning later in life, it is intriguing that most adults fail to recall autobiographical events from their early childhood years. Infantile amnesia is the term used to describe this phenomenon of accelerated forgetting during infancy, and it is not unique to humans. Over the years, information garnered from animal studies has provided clues as to the neurobiological basis of infantile amnesia. The purpose of this review is to provide a neurobiological update on what we now know about infantile amnesia since the publication of Campbell and Spear's seminal review on the topic more than 40 years ago. We pres…

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    Immune activation state modulates infant engram expression across development
    Sarah D. Power, E. Stewart, Louisa G Zielke et al. · 2023 · Science Advances · cited 25 times · Not summarized yet
    Abstract

    Infantile amnesia is possibly the most ubiquitous form of memory loss in mammals. We investigated how memories are stored in the brain throughout development by integrating engram labeling technology with mouse models of infantile amnesia. Here, we found a phenomenon in which male offspring in maternal immune activation models of autism spectrum disorder do not experience infantile amnesia. Maternal immune activation altered engram ensemble size and dendritic spine plasticity. We rescued the same apparently forgotten infantile memories in neurotypical mice by optogenetically reactivating dentate gyrus engram cells labeled during complex experiences in infancy. Furthermore, we permanently rei…

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    A. Golbabaei, A. I. Ramsaran, A. Rashid et al. · 2026 · bioRxiv · preprint, not peer reviewed · Not summarized yet
    Abstract

    Human and non-human infants can form memories for events, but these memories are not successfully consolidated into remote memory. While the neurobiological basis of this phenomenon—known as infantile amnesia—remains unclear, it is hypothesized that the neural circuits required for successful consolidation are insufficiently mature. Here we find that heightened activity in the prelimbic cortex of developing mice triggers a sequalae of maturational steps that culminates in adult-like memory persistence: Activity-dependent increases in brain-derived neurotrophic factor (BDNF) promote myelination of prelimbic circuits via activation of tyrosine kinase receptor B (TrkB) receptors on oligodendroc…

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    Microglial activity during postnatal development is required for infantile amnesia in mice
    E. Stewart, Louisa G Zielke, Antje R. de Boer et al. · 2026 · PLoS Biology · cited 2 times · Not summarized yet
    Abstract

    Infantile amnesia, the inability to recall episodic memories formed during early childhood, is a hallmark of postnatal brain development. Yet the underlying mechanisms remain poorly understood. This work aimed to gain a better mechanistic understanding of infantile amnesia. Microglia, specialized macrophages of the central nervous system, are known to play an important role in synaptic refinement during postnatal development and have recently been implicated in memory-related functions. Using mouse models, we identified microglia as key regulators of memory accessibility in infancy. We profiled dynamic changes in microglial morphology across the postnatal window that paralleled the onset of …

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    Hippocampal encoding of memories in human infants.
    T. Yates, Jared Fel, Dawoon Choi et al. · 2025 · Science · cited 47 times · Not summarized yet
    Abstract

    Humans lack memories for specific events from the first few years of life. We investigated the mechanistic basis of this infantile amnesia by scanning the brains of awake infants with functional magnetic resonance imaging while they performed a subsequent memory task. Greater activity in the hippocampus during the viewing of previously unseen photographs was related to later memory-based looking behavior beginning around 1 year of age, suggesting that the capacity to encode individual memories comes online during infancy. The availability of encoding mechanisms for episodic memory during a period of human life that is later lost from our autobiographical record implies that postencoding mech…

Prior work it builds on

  1. Close*
    Forgetting as a form of adaptive engram cell plasticity
    T. Ryan, P. Frankland · 2022 · Nature Reviews Neuroscience · cited 172 times · Not summarized yet
  2. Related
    A Frequency Band Analysis of Two-Year-Olds’ Memory Processes
    K. Cuevas, Vinayak Raj, M. A. Bell · 2011 · International Journal of Psychophysiology · cited 28 times · Not summarized yet
    Abstract

    Research on the functional meaning of EEG frequency bands during memory processing has only examined two developmental periods: infancy and from late childhood to adulthood. The purpose of this study was to examine changes in EEG power for three toddler EEG frequency bands (3–5 Hz, 6–9 Hz, 10–12 Hz) during a verbal recall task. To this end, we asked three questions: (a) Which frequency band(s) discriminate baseline from memory processing?; (b) Which frequency band(s) differentiate between memory encoding and retrieval processes?; (c) Which frequency band(s) distinguish toddlers with high and low verbal recall performance? Analysis of 2-year-olds’ (n = 79) power values revealed that all three…

  3. Related*
    Constructing a past in infancy: a neuro-developmental account.
    P. Bauer · 2006 · Trends in Cognitive Sciences · cited 135 times · Not summarized yet
  4. Related
    The Cost of Learning: Interference Effects in Memory Development
    Kevin P. Darby, V. Sloutsky · 2015 · Journal of experimental psychology. General · cited 48 times · Not summarized yet
    Abstract

    Learning often affects future learning and memory for previously learned information by exerting either facilitation or interference effects. Several theoretical accounts of interference effects have been proposed, each making different developmental predictions. This research examines interference effects across development, with the goal of better understanding mechanisms of interference and of memory development. Preschool-aged children and adults participated in a three-phased associative learning paradigm containing stimuli that were either unique or repeated across phases. Both age groups demonstrated interference effects, but only for repeated items. Whereas proactive interference eff…

  5. Related
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    R. O'Reilly, James L. McClelland · 1994 · Hippocampus · cited 979 times · Not summarized yet
    Abstract

    The hippocampus and related structures are thought to be capable of (1) representing cortical activity in a way that minimizes overlap of the representations assigned to different cortical patterns (pattern separation); and (2) modifying synaptic connections so that these representations can later be reinstated from partial or noisy versions of the cortical activity pattern that was present at the time of storage (pattern completion). We point out that there is a trade‐off between pattern separation and completion and propose that the unique anatomical and physiological properties of the hippocampus might serve to minimize this trade‐off. We use analytical methods to determine quantitative e…

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Updated on 31 October 2026.