That's Joe, from It's Okay To Be Smart.

Now all those neurons live in particular regions of your brain. Take these here, those are

the ones that help you see, whereas, well, way over here, those are the ones that help

you move.

And it's pretty amazing to think that these neurons connect with other neurons in all

of these areas to form this crazy network that controls all of your thoughts, feelings

and actions.

It makes me wonder -- where do all these neurons come from? It is determined when your brain

starts growing which neurons will be responsible for you getting excited about history or math

or labradoodles? Is it weird that I wonder these things?

It's okay to be smart.

Well your brain starts growing when your whole body is smaller than a dime. The speed of

growth is incredible. During early pregnancy, neurons develop at the rate of 250,000 every

minute.

Of the 40 weeks it takes a baby to grow, your neurons are mainly developed between 10 and

20 weeks and then these newly formed neurons start to migrate. This part is really cool.

They head off to regions of the brain where they're gonna live the rest of your life.

Now each neuron carries a special code that tells it exactly where it's going to end up.

And as they migrate, they start off as just cell bodies, the control centres and factories

of the neuron.

And It's not always fun travelling by yourself. With your neurons migrating, glial cells glue

neurons together to give your brain structure.

Once the cells reach their final destinations, then connections among them begin to develop.

Synapses form, the tiny space between neurons that let them communicate with each other.

And a fetus lets you know when this is happening. They start to have periods of activity and

rest -- they can nap! And even yawn.

During the last 8 weeks of a pregnancy, a fetus can hear, smell, respond to touch and

light. And they can learn. In one study women read The Cat in the Hat

out loud for the last 6 weeks of their pregnancy. And when their babies were born, they were

able to suck on special pacifiers that allowed them to hear their Mother reading that story

to them. And they quickly adapted to do it in just the right way to hear their Mother's

voice.

Babies brains are incredibly adaptable. They form 700 new connections between neurons every

second in the first years of life and by the time they're 3, their brains have formed 1000

trillion connections.

By age six, your brain is 90% of your adult brain size. While it doesn't grow a lot more

in size, your brain development extends through late adolescence, and arguably throughout

the rest of your life.

While you'll develop new connections for the rest of your life, most of your brain has

been there before you were even born.

So why are our brains in our heads to begin with? Head over to It's Okay To Be Smart,

where Joe tackles evolution head on. And if you haven't already, subscribe to BrainCraft!

I have a new episode out every other week.