You probably don’t remember the day you were born.

In fact, you probably don’t remember much from those first few years. And as you get older, your whole childhood starts getting a little fuzzy.

But you keep making new memories. Which is a good thing, because not doing that is a feature of dementia. The catch is, making room for those new memories may come at a cost.

Research suggests that your new memories are replacing your old ones. [♪ INTRO] Your brain isn’t the same as it used to be. It keeps cycling new cells into the mix and making new connections all the time. Especially in the area responsible for storing your memories.

It’s called the dentate gyrus of the hippocampus. And it continues to create new brain cells into adulthood. Like a lot more.

You make these new cells in the dentate gyrus every day. And when stimulated, the brain can more than double the proportion of new memory cells in a month. But as you get older, these new guys have a much more crowded brain space to shimmy into.

And it’s not for the reason you might be thinking. See, this process of making new brain cells doesn’t mean you’re adding to the total as much as replacing the old cells that were there before. It’s more of a refresher or Spring cleaning for your memory cells.

So it’s not more crowded up there because of the new cells. I mean, we don’t see older people walking around with heads the size of a baby elephant to make room for bigger and bigger brains with more and more cells. Instead, the thing that crowds up your brain space is all of the connections that these cells make with each other.

Like, you know when you make a mental connection that every time you eat cheese your stomach feels a little off? Well, that information is being stored in your brain as a physical connection between your brain cells. Those in the biz have a saying: “cells that fire together wire together.” Here’s how it works: The long, narrow part of a brain cell, called an axon, reaches out to other cells.

And the more you do things that associate two concepts in your mind, the more physically reinforced that connection between brain cells becomes. This way, your experiences turn into memories that become stronger and stronger every time cheese makes your stomach turn. The cells that hold those memories and feelings are literally strengthening their connections each time, making them more efficient at sending chemical signals.

Now, it’s not a perfect system. Just by thinking back on a memory, you modify it because you’re incorporating the new information you have today into that older scenario. And that’s why replacing your older memory cells with new ones is kind of the opposite of holding onto an old memory.

These new cells come in and change the way the dentate gyrus is organized just by their presence. And just by logging into Brilliant.org/SciShow, you can make new memories about thousands of concepts in science, computer science, and math. Brilliant is an online interactive learning platform, and the sponsor of this video.

With so many courses, it’s no surprise that they even have one on memory. It’s a Computer Memory course created in collaboration with two of the Brilliant software engineers. And there’s more in common between your memory and a computer’s memory than you might think.

This course covers memory layout and relocation, which you might remember from this video. But you don’t have to rely on your memory to find Brilliant. You can just click the link in the description down below or go to Brilliant.org/SciShow.

That link gives you 20% off an annual premium Brilliant subscription, along with their 30 day free trial. Thanks to Brilliant for supporting this video. Now, where were we?

Okay, so new cells in the dentate gyrus come in and start forming their own connections. This process changes the network of connections that was already in place before they showed up. It may break down connections that were there before and degrade older memories, or it might just make them harder to access because there’s new stuff in the way.

Researchers think that by bringing new memory cells in, you’re decreasing the influence of the older cells on one another. For example, smelling cheese might not make you think of being queasy as immediately because the specific pattern of those brain cells activating each other becomes rerouted or closed off. Eventually, you might forget why you even started avoiding cheese in the first place and reassociate it with your newly refined palate.

The new memory cells are making connections related to new memories. And there’s less in the way of gaining new memories once the old ones are cleared out. So adding new memory cells and getting rid of the older cells can help you make new memories.

Or, I should say, keep new memories. As it turns out, you make memories of everything. But you only keep a small portion of them.

After all, you don’t remember every single thing that you’ve ever seen or experienced. And which memories you keep or chuck has to do with when you make new memory cells. But how many memories you get rid of is also related to the amount of new memory cells.

Experiments on non-human mammals found that increasing the number of new cells in the hippocampus was associated with forgetting more stuff. This was true for young mice who were naturally making tons of new cells in the hippocampus and for adults whose new cells were promoted through physical activity like running. And young mice whose new cell-making genes were deactivated stopped forgetting as much.

So it really looks like new memory cells make you forget. Now, other animals that don’t make as many new memory cells after birth don’t show these effects, so you can only extrapolate so much from mice to humans. But the mice findings do seem to match up with computer simulations scientists have created of the human brain and how it stores memories.

And you might be thinking, “that’s all well and good, but I like my older memories and I’d like to hold onto them, thank you!” Well, some people do that. But it’s at the cost of making new memories. People diagnosed with dementia tend to have fewer new brain cells, and it might be part of the reason they can sometimes remember their loved ones who are long gone better than the ones standing in front of them.

So you can consider yourself lucky if you can’t remember things as well from your childhood as you get older. It’s a sign that you’re making new memories of today and living in the present. Life is full of trade-offs, and sometimes you have to forget in order to remember. [♪ OUTRO]