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Brain development may explain why infants can't remember events.


Playing around with infantile amnesia
Remember your first birthday party? The cake, the confetti, the cameras flashing in your face?

young toddler in high chair with slice of cakeYou don't? Course not.

This seriously stupid question is seriously stupid precisely because infants don't remember early experiences for long. But exactly why can't we remember wearing ice-cream-cake makeup at birthday party numero uno?

It turns out that the pace of brain development explains this "infantile amnesia" for events in the first year or so of life. (Infancy, obviously, is a time of intense learning: most of us learned to walk, talk, and maybe chew gum --but we did not retain long-term memories of those events).

In recent years, neuroscientists have begun to attribute infantile amnesia to the pace of growth in the frontal cortex, a site crucial for event-memory storage, which develops rapidly at about 12 months.

That notion gets support from a recent experiment by Conor Liston, then a senior, and Jerome Kagan, a professor of psychology at Harvard University. The pair tried to teach babies aged 9, 17 or 24 months to make toys, and found that, four months later, only the older two groups of children remembered how to make the toys.

To begin, the memory researchers showed the kids how, for example, to slip a ring into a bottle to make a rattle. Then, four months later, the kids were given a ring and a bottle, and asked to make a rattle. If you do this with a 2-year-old, the resulting racket may turn your ears inside out. But the 13-month-olds looked baffled, boggled and bewildered -- indicating that they did not remember the training session four months before.

Boyz and their toyz
Why test the memory of girlz and boyz by asking them to build toyz? "The key is to use sequences that children are able to imitate," says Liston. "The objects have to be the appropriate size, the sequences have to be challenging enough that they are not likely to devise them by themselves, and simple enough that...they can imitate them."

clear plastic bottle, red cap, purple ringIf you show a 17-month-old baby how to make a rattle from these objects, he or she will remember it four months later. Why can't a 9-month-old do the same thing?

The results helped reinforce the notion that infant amnesia is due to the pace of brain development, Liston said. The frontal cortex, storehouse of long-term event memory, undergoes rapid development at around 12 months, making it available to the older, but not younger, children in the study (see "Brain Development..." in the bibliography).

But coincidence is no proof, as Liston, now an M.D.-Ph.D. student at Cornell University, acknowledges. Further research, using some type of brain measurement, would be needed to prove the link between cortex development and long-term memory for events.

In practical terms, the study may apply to the controversy about recovered memories -- often obtained under hypnosis -- among adults who say they were abused as children, says Liston. While lawyers, judges and juries debate whether these memories reflect actual events, hypnotic suggestion, or both, Liston says better understanding of infantile amnesia should help resolve the argument. "If someone claims to have memories of a traumatic event under one year, and we know the brain can't form memories under one year, we could be very skeptical," he says.

Still skeptical? Read our memorable bibliography.

The Why Files

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