At What Age Does Memory Formation Come “Online?”
Post by Anastasia Sares
The takeaway
This study shows that the hippocampus, a crucial brain structure involved in forming memories, is active as young as 1 year of age. This may indicate that memory formation is present early on, but the ability to maintain or retrieve memories is slower to develop.
What's the science?
Humans don’t remember what happened in the first three years of their lives. This is referred to as infantile amnesia. Why does infantile amnesia exist? It’s still a mystery. One idea that has been suggested is that the hippocampus, a brain region involved in forming memories, might still be developing during these early years, and it might not be fully functional. On the other hand, studies of infant behavior show that infants can react to familiar objects and situations as early as 3 months of age.
This week in Science, Yates and colleagues used functional MRI to examine infant brain activity during a memory task to understand how infant memory works.
How did they do it?
The authors examined infants’ brain activity using functional MRI while they completed a memory task. The infants ranged from 4 to 25 months in age. Infants, of course, can’t respond in the usual way during an fMRI task, since they are unable to press buttons in response to instructions. Instead, the researchers use a preferential looking task, where an infant is shown two objects while their gaze is tracked to determine which object they are looking at. It is assumed that infants will gaze longer at an image they have recently seen compared to a completely new image (however, if the old image becomes too familiar, they may instead switch to looking at the new image, something the authors avoided in this study).
In this study, infants were familiarized with single images appearing in the center of the screen while inside the MRI. Periodically throughout the experiment, there would be a test trial with two images – an image that the infant had seen before, and an image they hadn’t seen before. The amount of time they spent looking at each image was tracked. If the infant looked at the familiar image more than the new image, this counted as “remembering” the old image. Then, the researchers went back and looked at the brain activity in the hippocampus when the infant had first seen each image, comparing remembered images to non-remembered images. They expected more brain activity in the hippocampus for remembered images.
What did they find?
Activity in the hippocampus (specifically, the posterior portion) was significantly greater for remembered images compared to non-remembered images only for older infants, from around 1 year of age onwards. This shows that even though infantile amnesia occurs for approximately the first three years of life, our ability to encode memories is present within the first year. What, then, accounts for the gap in memory for years two and three? It is important to recognize that remembering something involves more than just the initial commitment to memory. We have to maintain that memory and then retrieve it when needed. The authors suggest that infantile amnesia past age 1 may be related to these maintenance and retrieval components, but more research is needed to understand this fully.
What's the impact?
This study improves our understanding of the timeline of human memory development, helping us identify the first 12 months as crucial for encoding in the hippocampus. Longitudinal studies focused on this developmental period, and studies investigating other brain areas will help us to further crack the code of infantile amnesia.