[SciShow Intro plays]

[Text: QQS: Why can't you remember being a baby?]

Michael: Remember that one time when you were a baby? No, of course you don't. Because if you are a teenager or older, chances are you can't remember anything that happened before you were three. The process of forgetting these really early memories is called "Childhood Amnesia." It happens to pretty much everyone and it has to do with the way our brains develop as we grow up.

Childhood amnesia starts to set in between the ripe old ages of 8 and 9. Before then, most children can remember things that happened when they were really young like visiting a family member or winning a teddy bear from one of those impossible carnival games, but the passage of time by itself isn't enough to explain childhood amnesia. After all, when you're 30, you can remember certain things that happened 20 years ago when you were 10. But when you're 20, you can't remember being an infant at all.

Plus, we don't forget everything from when we were little. Some things like language or motor skills that we pick up stick with us. But we do tend to forget episodic memories memories of specific events and details. So scientists think that childhood amnesia must have something to do with the way our brains change between infancy and adulthood. It turns out that some parts of our brains don't finish developing until long after we're born.

One of those parts is the Hippocampus, which helps us form and store episodic memories. Even as adults our brains are always producing new cells called neurons in the Hippocampus. But when you're a young growing child, your brain produces a lot of new neurons a lot faster. So to see how brain cell growth affected memory, a research team from Toronto took adult mice and experimentally made their hippocampuses produce more new neurons and it turned out that the mice became more forgetful. They seem to lose memories just like humans do with childhood amnesia. But when researchers slow down the growth of new brain cells in young mice, those mice seem to forget less of their mousy childhoods.

So the question is: why would making new brain cells be bad for your memory? Well it's not, in the long term, which is why we can keep making new episodic memories as adults. But it seems like trying to fit all those new neurons into your hippocampus when you're young could cause a problem. The new neurons shuffle around with the old ones to form new memory connections and this could make it harder for the brain to find where earlier memories were kept. It might even erase them completely.

Still, not all of our memories are kept in the hippocampus so this doesn't explain everything about childhood amnesia. There are other parts of the brain involved in memory including the amygdala and the prefrontal cortex, so scientists are studying these to see if they also make different amounts of new neurons when we're children compared to when we're adults. We don't fully understand childhood amnesia yet but we do know it happens to everyone. So you can't remember your first birthday party, don't worry neither can anyone else.

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