Research on infantile amnesia in humans relies on more anecdotal evidence. Some people can recall a few memories formed when they were as young as 2 or 3 years of age, but most of us can recall much more from when we were 5 or 6 years old. Studies suggest that we're not simply forgetting what happened during our earliest years; far fewer autobiographical memories exist from early childhood than simple forgetting predicts. So the fate of early memories remains puzzling; solving the mystery of infantile amnesia may go a long way towards a more general theory about how we remember and why we forget.
What Happens To Early Memories?
Theories about infantile amnesia can be divided into two broad categories: those which hold that the memory loss is due to a storage difficulty (i.e., early experiences are not properly transformed into long-term memories) and those that claim the memory loss is a retrieval problem (i.e., the memories exist, but we can't recollect them).
The idea that infantile amnesia may be caused by inadequate memory formation stems from studies which show that the neural circuitry of the brain is not fully functional in infants. For example, we know that much of the visual system is still developing after birth, and that myelination in many cortical areas isn't completed for quite a while. In many animal species, the hippocampus, a brain structure that is critical for many types of memory formation, is not entirely developed at birth. Numerous studies have illustrated that rats improve markedly on memory tasks 18 to 23 days after birth, during the time that the hippocampus becomes mature. In humans, however, the hippocampus seems nearly mature at birth, so hippocampal development is probably not at the heart of infantile amnesia. Instead, research has shown that maturation of the infereotemporal cortex and the prefrontal cortex corresponds with the improvement on a number of memory tasks. The activity of these regions may be the key to the whereabouts of our earliest memories.
The Language Link
Perhaps the largest developmental change in humans is the acquisition of language, which generally coincides with when we start to remember things (age 3-4 years). This close association has led some researchers to suggest that language development allows internal and external rehearsal of experiences, and hence better storage in long-term memory. Though there is little doubt that memory for autobiographical experiences and language ability must be linked to some degree, the fact that pre-verbal babies can demonstrate functional memories suggests that language not is necessary for long term memory storage or retrieval.
