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Mysterious Infantile Amnesia Caused By Brain Overload

Update Date: May 24, 2013 11:58 AM EDT

A new study may reveal why adults cannot recall memories from early childhood.    Scientists have found evidence that infantile amnesia is caused by the formation of new brain cells in the hippocampus, an important brain region responsible for filing short-term memories into long-term memory.

Researchers said neurogenesis or new neuron production in early childhood comes at the expense of old memories because the formation of new neurons triggers a reorganization of existing brain circuits, which could lead to old memories being discarded.

However, scientists presenting at the 2013 Canadian Neuroscience Meeting believe that process that clears old memories could actually reduce interference and increase capacity for new leaning.

Infantile amnesia refers to the inability to recall long-term memory of events occurring within the first two to three years of life, and little long-term memories for events occurring until about seven years of age.  Previous studies revealed that though young children can remember evens in the short term, these memories do not persist. 

The latest study by Dr. Paul Frankland and Dr. Sheena Josselyn linked infantile amnesia to high levels of new neuron production and the hippocampus and more permanent memory formation to a reduction in neurogenesis.

For the study, Frankland and Josselyn looked at the retention of memories in young mice in which they suppressed the usual high levels of neurogenesis in the hippocampus. Researchers also stimulated increased neurogenesis in older mice.  In essence researchers replicated the circuit stability normally observed in adult mice in young mice and replicated the conditions normally seen in younger mice in adult mice.

The study found a causal relationship between a reduction in neurogenesis and increased remembering and a link between decreased remembering when neurogenesis increased.

"Why infantile amnesia exists has long been a mystery. We think our new studies begin to explain why we have no memories from our earliest years," Frankland said in a news release.

Experts explain that the rapid formation of new neurons in early childhood may put too much strain on the hippocampus. Dr. Liana Apostolova of the UCLA Brain Research Institute told NBC News that the hippocampus is responsible for recording and filing new experiences into the long-term memory box. But because much of its energy is spent making new brain cells during early childhood, the memory filing never gets done.

Researchers say they may soon be able to test out the findings in humans. Frankland, who works of the Hospital for Sick Children in Toronto, told NBC News that he often treats many children with brain cancer who receive drugs that slow down the generation of new neurons.

"We can check to see if the treatment preserves memories of things that happened just before the chemotherapy, just as it did in the mice," he explained. 

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