Now, when I’m browsing through Instagram getting my weekly dose of baby photos, there
are two things I notice:
First, babies have such big heads.
That’s because when you’re born, you already have almost all the neurons you’re ever
going to have.
Second, babies are kinda helpless – their neurons aren’t actually capable of doing
that much.
They’re overly connected, so instead of clean, useful circuits, babies have a big
glob of a super-connected brain.
So how do we get from our baby glob-brains to fully functioning adult brains?
The way this happens can have a big impact on how your brain functions for the rest of
your life.
To become a fully functioning adult brain, there are two big things that need to happen.
First our neurons develop myelin sheaths to help them work faster and more efficiently.
Second, your brain gets rid of a bunch of connections between your neurons, called synapses,
and these fewer connections lead to that cleaner circuit, which allows your brain to do more.
This is called Synaptic Pruning – it mostly happens in childhood, but can continue until
you’re twenty-five.
And researchers have recently discovered how it happens.
Synaptic pruning is the idea that not the whole cell is being removed, but bits of the
cell.
Extra synapses that you start out with get remodeled or pruned away.
But how does your brain know which connections to keep, and which to lose?
So it’s long been known that we start off with these extra connections, but the cool
thing is that some of them get remodeled or removed permanently through experience.
That’s the idea of use it or lose it.
So connections that are meaningful get strengthened and connections that are less meaningful get
removed.
And it’s long been thought that neurons themselves controlled the removal, but now
more and more evidence is pointing to glial cells.
While neurons often steal the limelight, you have another type of brain cell called glial
cells.
They’re like the construction and maintenance workers of your brain.
They outnumber neurons, in some parts of the brain, by a factor of 10 to 1.
And they’re vital in making sure your brain traffic stays on track.
If there’s damage to the roadways, like a traumatic brain injury, your glial cells
help clean up the damage.
They support your brain’s super highway system and to some extent, they can even help
your neurons heal.
They help reinforce the connections that exist, but more importantly, they help destroy the
connections you don’t need – glial cells are responsible for synaptic pruning.
When a synapse needs to be pruned, one type of glial cells, called microglia, surround
and destroy it.
And the neurons actually communicate to the microglia that they want them to nibble away
some of their connections.
It’s called an “eat me signal”
And microglia have these little receptors on their processes that are recognizing signals
that are on neurons and so if that process had compliment on it, an eat me signal, it
would then come and actually literally engulf, right, or eat that bit, just that bit.
You can find bits of this material inside the processes of these microglia cells, and
even inside their bellies.
We were one of the key labs that discovered it.
But in some people, their cells are either pruned either too much or too little.
Our brains maintain a pretty delicate balance, so this can have some pretty big impacts on
your life.
So in development, defects in pruning either too little or too much could underlie disorders
like autism or schizophrenia or other neurodevelopmental or neuropsychiatric disorders.
Now that’s a hypothesis at this point, it’s been pretty difficult to test because you
can’t go into a human’s brain and ask that question very directly, but there’s
some indirect evidence.
But I think where it’s been even more carefully and more definitively shown, in terms of synaptic
loss, is in diseases of the aged brain, like Alzheimer’s disease.
So that’s one of the things we’ve been studying more recently is to ask the question
are some of the more fundamental mechanisms that normally regulate pruning in development,
which is a good thing, could that go awry in various diseases like Alzheimer’s disease.
We’re still figuring out why pruning goes awry in our development.
But luckily, for those of us with adult brains, they’re still plastic and malleable to some
extent for our entire life.
So how can you help your glial cells maintain a happy brain?
We’d all like to know if there was some magic pill we could take to preserve our synapses
and—
You haven’t discovered that?
No, we haven’t discovered that.
But I think in the meantime, I think there are things that we know we should all be doing;
things like sleep, very important for cognition, probably really important for your synapses.
You know, eating healthy, having a good lifestyle, and certainly exercise.
But I also think going back to that saying that I started with, this idea of use it or
lose it.
Just pushing yourself, challenging your brain as much as possible, learning new things,
reading new things, doing crossword puzzles, all those things are essentially helping to
strengthen those connections in your brain, I think that’s one of the things we can
always do, I think continue that all the way through life.
I’m sure you’ve heard “use it or lose it” before, but it’s true.
Exploring and learning new things does lead to a better brain.
So feed your curiosity and your brain will thank you for it.