Infants encode short-lived hippocampal memories

(Press-News.org) Challenging assumptions about infant memory, a novel functional magnetic resonance imaging (fMRI) study shows that babies as young as 12 months old can encode memories, researchers report. The findings suggest that infantile amnesia – the inability to remember our first few years of life – is more likely caused by memory retrieval failures rather than an inability to form memories in the first place. Despite infancy being a period of rapid learning, memories from this time do not persist into later childhood or adulthood. In general, humans cannot recall events from the first three years of life – a phenomenon known as infantile amnesia. Why grown humans have a years-long blind spot in their episodic memory for the period of infancy remains a puzzle. One theory suggests this occurs because the hippocampus, a brain region crucial for episodic memory, is not fully developed during infancy. However, research in rodents challenges this idea, showing that memory traces, or engrams, are formed in the infant hippocampus but become inaccessible over time. In humans, infants demonstrate memory through behaviors such as conditioned responses, imitation, and recognition of familiar stimuli. However, whether these abilities rely on the hippocampus or other brain structures remains unclear. In a study using fMRI to scan the brains of infants aged ~4 to 25 months while performing a memory task, Tristan Yates and colleagues aimed to determine whether the hippocampus in infants can encode individual memories. The memory task, adapted from a well-established method for adults, involved showing images to infants – faces, scenes, and objects – followed by a memory test based on preferential looking, all while undergoing neuroimaging. The findings show that the infant hippocampus has the capacity to encode memories of individual experiences beginning around 1 year of age, providing evidence that the capacity to form individual memories develops during infancy. According to the authors, the presence of encoding mechanisms for episodic memory during infancy – despite their ephemeral nature – suggests that infantile amnesia is more likely due to failures in memory retrieval mechanisms. These insights align with recent studies in rodents, which demonstrate that memories created during infancy can persist into adulthood but remain inaccessible for retrieval without direct stimulation of hippocampal engrams or reminder cues, the authors note. In a Perspective, Adam Ramsaran and Paul Frankland discuss the study in greater detail.

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