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Developmental biology - Hippocampus|
Our Early Development of Memory
One of the most fascinating questions in psychology and neuroscience pertains to how young children gain the capacity to remember their past. Early hippocampal processes have been implicated in this ability, but a lack of viable methods has hindered assessments of their contribution in early human development. We employed a functional magnetic resonance imaging paradigm that captures memory-related hippocampal function during natural nocturnal sleep in toddlers. Our results provide direct evidence of a connection between hippocampal function and early memory ability. This experimental approach overcomes previous challenges and promises to pave the way to investigations linking changes in brain function to early development of learning mechanisms, including applications to typical and atypical development.
Nonhuman research has implicated developmental processes within the hippocampus in the emergence and early development of episodic memory, but methodological challenges have hindered assessments of this possibility in humans. Here, we delivered a previously learned song and a novel song to 2-year-old toddlers during natural nocturnal sleep and, using functional magnetic resonance imaging, found that hippocampal activation was stronger for the learned song compared with the novel song. This was true regardless of whether the song was presented intact or backwards. Toddlers who remembered where and in the presence of which toy character they heard the song exhibited stronger hippocampal activation for the song. The results establish that hippocampal activation in toddlers reflects past experiences, persists despite some alteration of the stimulus, and is associated with behavior. This research sheds light on early hippocampal and memory functioning and offers an approach to interrogate the neural substrates of early memory.
Authors: Janani Prabhakar, Elliott G. Johnson, Christine Wu Nordahl, and Simona Ghetti. Additional authors are graduate student Elliott Johnson and Christine Nordahl, associate professor at the UC Davis MIND Institute and Department of Psychiatry and Behavioral Sciences.
The authors declare no conflict of interest.
Funding: The work was funded by the National Institutes of Health.
This article is a PNAS Direct Submission.
Data deposition: The data reported in this paper have been deposited in Open Science Framework and can be accessed using the following website: https://osf.io/6nu9s/. Data is provided in wide form and has identifying and demographic information (subject ID number, age in months, sex), as well as outcome level data for each subject (mean parameter estimates for target > novel and reversed > novel contrasts in the left and right hippocampus, source memory accuracy, and composite memory score).
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MRI study of 22 toddlers found that hippocampal activity was higher when sleeping children heard a song, previously learned, than when hearing a new song. This was regardless of whether the learned song was played as recorded or played in reverse. The highest response was observed in toddlers who remembered where they learned the song and a toy associated with the song. Image credit: pixabay.com