Evidence of hippocampal learning in human infants

The hippocampus is essential for human memory. The protracted maturation of memory capacities from infancy through early childhood is thus often attributed to hippocampal immaturity. The hippocampus of human infants has been characterized in terms of anatomy, but its function has never been tested directly because of technical challenges. Here we use recently developed methods for task-based fMRI in awake human infants to test whether the infant hippocampus supports statistical learning. Hippocampal activity increased with exposure to visual sequences of objects when the temporal order contained regularities to be learned, compared to when the order was random. Despite the hippocampus doubling in volume across infancy, learning-related functional activity bore no relationship to age. This suggests recruitment of the hippocampus for statistical learning at the youngest ages in our sample, around three months. Within the hippocampus, evidence of statistical learning was clearer in anterior than posterior divisions. This is consistent with the theory that statistical learning occurs in the monosynaptic pathway, which is more strongly represented in the anterior hippocampus. The monosynaptic pathway develops earlier than the trisynaptic pathway, linked to episodic memory, suggesting that the infant hippocampus participates in statistical learning before it can form durable memories. Beyond the hippocampus, the medial prefrontal cortex showed evidence of statistical learning, consistent with the adult role of this region in memory integration and generalization. These results suggest that the hippocampus supports the vital ability of infants to extract the structure of their environment through experience. Methods Please refer to the manuscript for details. Citation: Ellis, C. T., Skalaban, L. J., Yates, T. S., Bejjanki, V. R., Córdova, N. I., & Turk-Browne, N. B. (2021) Evidence of hippocampal learning in human infants. Current Biology