Humans typically do not remember events from the first 3 years of life. Sigmund Freud named this phenomenon "infantile amnesia." One hundred years have passed since Freud raised questions about this, but scientists still have not found a precise reason why events from the first 3 years cannot be recalled.
American scientists proposed a new hypothesis regarding infantile amnesia. Nicholas Turk-Browne, a professor at Yale University, published research on the 21st in the international journal Science, stating that "infants around 12 months can form memories." He suggested that the cause of infantile amnesia is not the inability to form memories but rather the inability to recall those formed memories.
Scientists have largely divided into two camps regarding the causes of infantile amnesia. There is a hypothesis that the hippocampus, a brain region that plays a crucial role in memory formation, is not fully developed during infancy. It posits that the lack of memories from the first 3 years is due to the hippocampus not developing properly during infancy, preventing memory formation.
On the other hand, some believe that memories are indeed formed in the hippocampus during infancy. However, over time, for some reason, they are unable to access those infant memories, making it appear as though they do not exist.
To determine which view is correct, the research team conducted experiments involving infants aged 4 to 25 months. Thirteen infants below 12 months and thirteen infants aged 12 to 25 months participated in the experiment, totaling 26 infants.
The research team presented various memory tasks to determine if infants' hippocampi can form individual memories. They showed infants images of faces, scenes, and objects, and then checked their eye movements to see if they remembered the images shown. All processes were observed using functional magnetic resonance imaging (fMRI) equipment to monitor responses occurring in the infants' brains. If the infant remembers, blood flows to the hippocampus, and it appears illuminated in the fMRI images.
Results from the experiment showed a distinct difference in the responses of the infants' hippocampus when viewing previously seen images compared to new images. This difference was more pronounced around the 12-month mark. The response in the hippocampus area was clear in infants over 12 months compared to those under 12 months. The research team explained, "Around 12 months, this indicates that individual experiences can be formed into memories," adding, "It shows that the hippocampus in infants can encode visual experiences into individual memories in a short period of time."
Based on this, the research team hypothesized that the cause of infantile amnesia is not the encoding process that makes individual experiences into memories, but rather issues occurring in the subsequent retrieval process. They speculated that from around 1 year of age, the ability to encode individual experiences starts to manifest, suggesting that the cause of infantile amnesia lies in the later stages.
Similar findings emerged from prior animal experiments. The hippocampus of animals formed during infancy did not elicit memory responses in natural situations. However, when forced stimuli were presented, memory responses were retrieved even from the hippocampus formed during infancy. The research team noted, "In humans, while the hippocampus formed during infancy may support the encoding of memories, it may not allow for the natural retrieval of those memories over time."
Other scientists who reviewed the research results shared similar views. Paul W. Frankland, a professor at the University of Toronto in Canada, stated in a commentary paper published alongside the study in Science that "this discovery aligns with animal research findings that suggest infantile amnesia does not result from poor memory formation, but rather that the post-process of maintaining and retrieving formed memories is not mature, leading to their disappearance." He added that, "With appropriate memory cues or direct stimulation to the hippocampus, it may be possible to retrieve memories formed during infancy, as indicated by findings in rodent studies."
References
Science(2025), DOI: https://doi.org/10.1126/science.adt7570