Scientists, and parents, have long wondered why we don't remember things before the age of three.

No matter how important something happens to a three-year-old, it is quickly forgotten without a trace.

Now a study says that "infantile forgetting" may be due to the rapid growth of nerve cells in the hippocampus, which is responsible for storing new experiences as long-term memories. The research was reported by an expert at the annual meeting of the Canadian Neuroscience Society on Friday.

Paul Frankland, author of the study, said, "They can't form stable memories of things that have happened in the first few years."

"A lot of the details she doesn't remember. By now at age 4, she doesn't remember anything at all from when she was little."

"The scientific community has long suspected that this problem is related to the hippocampus," said Dr. Eric Kandel, a researcher at Columbia University. However, no one knows what changes take place in a baby's brain.

Paul Frankland suspects that these memories are actually stored as long-term memories, but that the hippocampus simply loses touch with the area where the memories are stacked during the child's period of rapid growth and development. As the hippocampus matures, many, many neurons begin to make connections. Most likely, during this whole process of developmental reconstruction, the brain has "forgotten" where it stored the memories. As the brain's expansion slows down, the brain can keep better track of where all the memories are filed, and then as the baby grows, the brain's long-term memory becomes stronger.

To test this theory, Frankland collected a group of young rats and slowed down the rate of new neuron production in the hippocampus of the young rats. Normally, young rats have the same problems with long-term memory as babies. If you teach them how to walk through a maze, they will forget the way after a few days. As the production of neurons slowed, the pups gradually developed long-term memory and were able to remember the way through the maze.

Dr. Liana Apostolova of the University of California has found the answer to the question, 'Why can't 6-year-olds remember important things?'

She says: 'It's like an overload. The hippocampus has two jobs: to make a tape recording of everything, and to dump the tape recording into long-term memory, labeling it so that people can retrieve it."

Interestingly, Frankland says he may soon be able to test his theory. He has found that many children with brain tumors who are treated with medication have slower reproduction of neurons in their brains.

"We can do tests to see if the drug treatment preserves memories from before the treatment, just like the experiments we did with young rats."