Jan 21, 2026
3 min read
Babies of all species, from mice to humans, quickly forget what happens to them—an effect called infantile amnesia.
Babies of every species from mice to humans quickly forget things that happen to them - an effect called infantile amnesia.A type of brain immune cells called microglia can control this type of forgetting in young mice, according to a study published January 20 in the open-access journal PLOS Biology by Erica Stewart of Trinity College Dublin in Ireland and colleagues.
Babies and young children grow rapidly and absorb enormous amounts of information as they grow.However, at this early stage of development, there is a deficit in episodic memory - recalling past events, such as the first birthday or the first day at kindergarten.To better understand how this childhood amnesia works, the authors of this study examined how well the activity of microglia - the brain's main immune cells - in very young mice could remember a frightening experience.examined microglial markers in the hippocampal dentate gyrus and amygdala.
The researchers found that when the activity of microglia was suppressed, not doing much in the hippocampus and amygdala, the young mice remembered the traumatic events better.The researchers also used fluorescent markers to identify engram-neurons whose activity is specifically linked to memory formation.When microglia were inhibited in the young mice, the engram cells were significantly activated, indicating memory loss.
In previous work, scientists have found that mice born to mothers with an overactive immune system are no exception to newborns.Once scientists stopped the activity of microglia in infants who did not have dementia in infants, they were able to restore it - perhaps to restore normal memory access.While other cell types may be involved, the authors suggest that microglia are required for fetal amnesia.Mice can help build a memory network in the brain.
Microglia, the immune cells that reside in the central nervous system, can be considered the 'memory managers' of the brain.Our paper highlights their role in childhood amnesia in particular and suggests that there may be common mechanisms between childhood amnesia and other forms of forgetting - both in everyday life and in diseases.
Erica Stewart, Trinity College Dublin
Co-author Tomás Ryan notes, "Infant amnesia is probably the most common form of memory loss in humans. Despite experiencing many new experiences as we grow up, most of us have no memory of our early years. It is a neglected topic in memory research precisely because we all accept it as a fact of life."
Ryan adds: "But what if those memories are still present in the brain? In the field of memory, forgetting is increasingly being viewed as a 'feature' of the brain rather than a 'defect.'It appears that the brain records the memory-storing neural units, engrams, for later use.Microglia appear to function in the brain throughout the lifespan, helping to organize life and biology.Infantile amnesia can give us insight into how forgetting occurs in the brain in general and can be manipulated. Infantal amnesia opens up new possibilities for imagining how learning and forgetting might work in the first years of life.
Ryan notes, "It will be interesting and important to identify people who do not suffer from childhood amnesia. To learn how their brains work and to understand their experience in early childhood education."
Stewart, E., et al.(2026) Microbes during postnatal development are required for neonatal amniotic fluid in the mouse.
