Scientists have discovered that blocking the activity of microglia, which are specialized immune cells in the brain, can prevent infantile amnesia and improve memory in mice. This finding provides evidence that microglia play a key role in memory formation and forgetting during early development.
Infantile amnesia refers to the rapid loss of memories from infancy observed across several species, including humans. The underlying mechanisms for this phenomenon have been unclear until now. In a study published in PLOS Biology, researchers investigated how inhibiting microglial activity in young mice affected their ability to remember a fearful event.
The team focused on two brain regions involved in memory: the dentate gyrus of the hippocampus and the amygdala. They found that suppressing microglia led to improved memory retention in young mice. Additionally, using glowing tags to track engram cells—neurons linked to specific memories—the researchers observed greater activation of these cells when microglia were inhibited, suggesting a direct link between microglial function and memory recall.
Previous research by the same group showed that offspring of mothers with activated immune systems did not experience infantile amnesia. By modulating microglial activity shortly after birth in these mice, they restored typical patterns of forgetting.
The authors propose that while other cell types may also contribute, microglia are essential for infantile amnesia and may help shape how memory networks develop in the brain.
Dr Erika Stewart, lead author and Postdoctoral Research Scientist at Columbia University Irving Medical Center, conducted this work as part of her PhD under Professor Tomás Ryan at Trinity College Dublin's School of Biochemistry and Immunology. Dr Stewart stated: "Microglia, the resident immune cells of the central nervous system, can be considered the 'memory managers' in the brain. Our paper highlights their role in infantile amnesia specifically and indicates that common mechanisms may exist between infantile amnesia and other forms of forgetting – both in everyday life and in disease."
She added: "The biology of infantile amnesia may give us insight into how forgetting happens in the brain in general. Furthermore, being able to manipulate infantile amnesia opens doors into new ways of imagining how learning, and forgetting, might work during the early years of life. It will be interesting and important to identify humans that don't experience infantile amnesia, to learn how their brains work, and understand their experience of early childhood education."
The study also discusses whether there is an adaptive reason for infantile amnesia. This phenomenon is mostly seen in altricial mammals—species born helpless and reliant on caregivers—while precocial mammals like guinea pigs do not show such patterns of forgetting. The researchers suggest it is possible that memories formed during periods of extreme vulnerability are less reliable or useful but note that more research is needed to answer these questions.
