Annie Sneed highlights the work of neuroscientists Paul Frankland and Sheena Josselyn that might explain why we can’t remember being babies – “the rapid birth of many new neurons in a young brain blocks access to old memories”:
In a new experiment, the scientists manipulated the rate at which hippocampal neurons grew in young and adult mice. The hippocampus is the region in the brain that records autobiographical events. The young mice with slowed neuron growth had better long-term memory. Conversely, the older mice with increased rates of neuron formation had memory loss.
Based on these results, published in May in the journal Science, Frankland and Josselyn think that rapid neuron growth during early childhood disrupts the brain circuitry that stores old memories, making them inaccessible. Young children also have an underdeveloped prefrontal cortex, another region of the brain that encodes memories, so infantile amnesia may be a combination of these two factors.
Covering similar ground, Kristin Ohlsen explains why, to form long-term memories, “an array of biological and psychological stars must align, and most children lack the machinery for this alignment”:
The raw material of memory – the sights, sounds, smells, tastes and tactile sensations of our life experiences – arrive and register across the cerebral cortex, the seat of cognition. For these to become memory, they must undergo bundling in the hippocampus, a brain structure named for its supposed resemblance to a sea horse, located under the cerebral cortex. The hippocampus not only bundles multiple input from our senses together into a single new memory, it also links these sights, sounds, smells, tastes, and tactile sensations to similar ones already stored in the brain. But some parts of the hippocampus aren’t fully developed until we’re adolescents, making it hard for a child’s brain to complete this process.
‘So much has to happen biologically to store a memory,’ the psychologist Patricia Bauer of Emory University told me. There’s ‘a race to get it stabilised and consolidated before you forget it. It’s like making Jell-O: you mix the stuff up, you put it in a mould, and you put it in the refrigerator to set, but your mould has a tiny hole in it. You just hope your Jell-O – your memory – gets set before it leaks out through that tiny hole.’