Researchers have long puzzled over why we can form memories when we’re babies, but then go on to have no recollection of those years - a phenomenon known as infantile amnesia.
Now recent research in rodents may have found the answer. It turns out all the new cells that are constantly being formed in young brains may actually be messing with our memories.
Mammals generate new brain cells all the time, but when we’re babies the rate of this process, known as neurogenesis, is at its highest. Because of all the new things we experience as infants, there’s a lot of early-life action in the hippocampus in particular - the region of the brain that is associated with memories and learning.
Usually this type of hippocampus activity is associated with improved memory, as Susannah Locke writes for Vox. But a study led by scientists from the University of Toronto in Canada has found that in babies, the extremely high rates of neurogenesis is actually having the opposite effect and increasing forgetfulness.
Their research, published in Science, suggests that all the new neurons being formed could be pushing out established memory circuits.
The team investigated the process by first creating memories in various rodents. To do this they made the animals associate a place with a mild electric shock.
They then boosted the rate of neurogenesis in some of the mice by either giving them drugs or a running wheel (both known to stimulate neuron production in the rodents), and slowed down neurogenesis in others.
They found that the young mice who’d had their neuron production slowed down were able to remember things better than those that had the process sped up.
The researchers also looked at guinea pigs and a Chilean rodent called a degu, two species which are born with a more mature brain and have naturally lower rates of neurogensis when they’re infants. Neither of these species normally experience infantile amnesia, but when the scientists increased their rates of neurogenesis above normal levels, neither could store memories from when they were babies.
Given the similarities between rodent and human brains, the researchers believe the same process could cause humans to forget their early childhood.
Previous theories have suggested that infantile amnesia comes from babies’ lack of language skills or emotional development, as Locke explains in Vox. This new research doesn’t necessarily rule out the ideas, but shows for the first time the mechanism through which our memories are suppressed.
Mazen Kheirbek, a neuroscientist from Columbia University in the US told Vox that further research is needed to work out whether it’s the new neurons that are leading to forgetting, or the learning itself. "Perhaps the forgetting seen here is actually due to the increased ability to learn new things," he said. "So there is a tradeoff there, preserving the older memories may come at the cost of making new ones."
And just in case anyone was wondering, this is what a degu looks like (adorable):