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Why you can't remember anything as a toddler

Teresa Tanoos's picture
New research shows why toddlers can't remember anything

Ever wonder why you don’t remember anything that happened before you were 3 years old? So have researchers, who have tried to learn why the memories of toddlers are quickly erased – even after what their parent’s remember as a momentous occasion in the young child’s life.

A new study presented Friday at the annual meeting of the Canadian Association for Neuroscience, however, shows that “infantile amnesia” may be due to the rapid growth of nerve cells in a region of the brain called the hippocampus, which is responsible for taking new experiences and storing them into long-term memory.

According to study co-author Paul Frankland, a senior scientist at the Hospital for Sick Children in Toronto, even though young children seem to remember important events for a short time after they occur, they lose such memories with the passage of time.

“They can’t form stable memories of what happens in the first few years,” Frankland said. “I have a daughter who is 4 years old and because we were working on this study, I would always ask her questions about her memories of places we visited 2, 3 months ago. It’s clear that she can form memories with quite some detail. But four years from now she won’t remember anything.”

Meanwhile, it’s long been suspected that the hippocampus had something to do with a toddler’s inability to remember events, says Dr. Eric Kandel, Kavli professor and director of the Kavli Institute for Brain Science at Columbia University and senior investigator at the Howard Hughes Medical Institute.

“The hippocampus matures slowly and probably doesn’t reach any reasonable maturity until we’re 3 or 4,” Kandel explained. “While 2- and 3-year-olds can remember things for a short time, the hippocampus is required for long-term storage of those memories.”

What actually happens in a toddler’s brain has long been a mystery. However, Frankland suspected it had something to do with their memories actually getting filed away into long-term storage, but the hippocampus forgot “where” they’d been stored during the accelerated growth phase that takes place during the first few years of a child’s life.

During that accelerated growth phase, according to Frankland, the hippocampus matures and large quantities of new neurons are created that need to be loaded into existing circuits. During this maturation process, he says, it’s likely that all that growth activity overloads the brain, causing it to “forget” the memories.

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As the maturation process recedes, the theory is that the brain stabilizes and is therefore better able to remember where memories are stored; thus, the older we get, the better our long-term memory gets, as the brain learns to keep track of where it files memories away.

To test his theory, Frankland collected some baby mice and then reduced the rate at which they created new neurons in the hippocampus.

Like human toddlers, baby mice also have long-term memory problems, rendering them unable to retain information. For example, if you teach baby mice to navigate a maze, they’ll forget how to do so after a few days. However, when you slow down the creation of new neurons in the baby mice, they’re able to better retain what they learned about navigating through the maze – therefore, enabling them to form long-term memories so they can remember how to get through the maze.

Kandel says that Frankland’s approach appears to be sensible and correct.

As for Dr. Liana Apostolova of the UCLA Brain Research Institute, she said she was delighted to have an answer to why her 6-year-old doesn’t seem to remember things that she recollects as very important.

"This is a very interesting finding,” she says. “And it ties in greatly with what's in the literature."

Apostolova says a young child’s memory problems appear to be a case of overload, with the hippocampus essentially performing two jobs: 1) tape recording each event; and 2) then filing away what it tape recorded into long-term storage, along with flags to later allow the person to retrieve it. She says that with all that energy being spent to make new neurons during the maturation process, the filing never gets done.

As for testing his theory on humans, Frankland says he may actually get a chance to do just that soon, as he sees many children with brain cancer who are on medications that slow down the generation of new neurons as a side effect.

“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 says.

SOURCE: Canadian Association for Neuroscience. "Cause of infantile amnesia revealed: New neuron formation could increase capacity for new learning, at expense of old memories." Retrieved May 25, 2013, from http://www.sciencedaily.com¬/releases/2013/05/130524104634.htm