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  • Jody B. Miller

When and How the Brain Develops: Part Two

Updated: Nov 15, 2023

The following post is Part Two of an excerpt of an explanation about development of the brain by Dr. Susan Book Heimer from UCLA.

Brain connections form distinct functional networks. There are many different kinds of networks in the brain, functional networks. In the brain, I'm just listing a few of them here for illustration.

When and How the Brain Develops: Part Two

For example, the visual network collection of brain regions, which together, allow us to see the world and to make sense of what we see figure out where things are when we see them.

When and How the Brain Develops: Part Two

The auditory network does the same thing, but with what we hear our sensory network knows where our bodies are and how we feel in our bodies.

So these are brain regions that are connected together, left hemisphere with right hemisphere and several areas across the brain that work together to perform the complex tasks of vision, hearing, sensation, moving, etc. Tut we also have some more complicated networks with more elaborate functions.

When and How the Brain Develops: Part Two

The language network, for example. There are many regions of the brain that are involved in language. They're spread all throughout our brain, although mostly for me in the left hemisphere of my brain and they all have to work together in a network.

When and How the Brain Develops: Part Two

There are attention networks; several different intention networks and there's a southern network called the salience network. This is a network of brain regions that find out what's important in the environment and distinguish what is important from things that are less important so that it can focus on that which is most meaningful and significant.

The default mode network is a completely different thing. We often call this the task negative Network. This is what you do when you're not thinking. This is what we do when we're at rest. Essentially, we turn off our brain.

When and How the Brain Develops: Part Two

We let it just wander, and it's very important for us to do this. It gives our brain a rest. It allows our memories to be consolidated without being bothered by the things that we are seeing and hearing and it's probably very active while we're sleeping, and we need all of these networks as well as many more.

We can measure these functional brain networks with techniques including functional MRI, so functional MRI is a MRI technique. It requires no radiation, it requires no injections. It's perfectly safe and it measures blood flow in the brain. We can measure it during task performance. So if I were in a brain scanner right now - and I were doing a language task, more blood would flow to my language areas of my brain and we'd be able to see that in the MRI.

We can also look at correlated activity across the brain. While we're just at rest sitting in a scanner because different areas of our brain, which normally communicate, which are normally well connected, will change their blood flow spontaneously at about the same time. So these are great techniques for learning about brain function during development because they're completely safe for children.

There's a basic structure that we're born with, but these structures are shaped by our experiences. They are shaped into distinct modules. Language modules for example.

The group of language areas which have to connect together and work together to perform language - and these modules are highly distinct and within the modules they're highly integrated. So they talk within a module to each other, but they're separate from other modules.

Functional activity through development changes so that the brain becomes more modular and it becomes more efficient. So in functional MRI scans of language in young children, we see that there is a great deal of diffuse activity across the brain.

It's in both the left hemisphere and in the right hemisphere, and it's, pretty big.

When we compare the same language tasks to young adults, we see the same brain regions, but now, it's mostly centered in the left side of the brain in the MRI world.

Left is right and right is left. It's more specialized and we also see that less tissue is dedicated to it, because what has happened is these modules have become specialized and used solely for language without any of this extra stuff. This extra stuff would have been stuff that will have been pruned away by the time we get to adulthood, and that is really the process of brain matter that helps to support these functional networks.

When and How the Brain Develops: Part Two

There are other things that we could learn about with functional MRIs: developmental disabilities, developmental disorders, using this kind of brain connectivity technique. There is a study of children who are typically developing and children with autism when they're exposed to rewards, and in this case the reward would be simply seeing a smiling face.

Most of us respond very nicely to a smiling face and we have a reward center in the brain that does that. With this kind of brain scanning, we can see that the reward network, while fully intact in a typically developing kid, is not working as well in the children with autism, and this is the difference between groups suggesting to us that there is a problem in the reward Network of the brain of children with autism.

Environmental exposures can also have a very major effect on brain development.

There is prenatal exposure to alcohol at the top. A child can develop sapote by being severely exposed to alcohol prenatally, and I think the first thing we see right off the bat is that there is no corpus callosum at all, so the big major connecting fibers that connect the right and left sides of the brain is simply missing and when we look inside the brain, we see a similar pattern. A lack of connectivity - some abnormalities in several different parts of the brain. So environmental exposures can have a profound effect upon brain development.

When and How the Brain Develops: Part Two

Adolescence is a time of great rapid brain change.

With the influx of hormones, the brain becomes very sensitive to new experiences, it becomes very reward sensitive and it becomes driven towards novelty and also, in particular, to social experiences.

This makes a lot of sense because, when kids grow up and become adolescents, they need to find a way to launch and they can't do that unless they become interested in new things and in new people.

Of course, their emotion networks also become very active, and yet there's a problem, because the area of the brain that helps to regulate and control these emotional experiences and these impulses does not come online until at least the 20s, and sometimes quite late.

In the 20s, so we have this situation where there's a lot of impulsive impulsivity and a lot of emotional arousal. Without the ability to regulate that arousal, that's why teens are the way they are and that's why it's so difficult for teens, because they get exposed to novel experiences which can have negative consequences and they don't have quite the regulation that is built into the brain to calm that down and to control it.

When and How the Brain Develops: Part Two

There is so much more that we do not know about brain development. In fact, we're, really just starting to scratch the surface.

  • How does the human connectome develop over time?

  • How do individual differences in connections relate to behavior to cognitive strengths, to cognitive weaknesses?

  • How do our individual experiences affect the development of this connectome and...

  • What are the effects of things that we are exposed to?

  • And particularly our kids today are exposed to like video games and social media and things like that? How does that affect brain development?

  • What are the effects of environmental exposures? Toxins and drugs? Things like that? What are the effects of these on our brain connections?

There's, so much that we still don't know, and these are questions that we at UCLA are trying to answer with research.

When and How the Brain Develops: Part Two

There are a few research projects. We're doing right now, and one is the human connectome development project where we are bringing children in from the ages of 5 through 21 and scanning their brains to look at the functional connections and the structural connections, and also doing a series of tests on cognition how they solve problems and what kinds of things they've been exposed to, and also their emotional experiences, to try to understand brain development, the adolescent brain and cognitive development.

ABCD is a study of 10,000 children across the Country 1,000, in Los Angeles County alone. they are recruited from select schools in Los Angeles County at the ages of nine and ten and followed for ten years to see what is happening exactly in adolescence.

During that very critical adolescent period, we're, also studying the human connectome in older folks between 35 and a hundred to find out what makes a brain age well and gracefully. What makes people healthy throughout their life and what are some of the changes that can affect that brain development over time?

There are a number of differences that we see in the brains of children with autism and we're doing many studies right now on on children with autism, young adults with autism and even infants, who are at high risk for developing autism.

We believe that autism is a problem of the development of these connections that are set on a wrong trajectory very, very early in life. We are getting better at identifying what some of these problems are and trying to intervene early so that these children will have the best outcomes, but in general, just as in the learning disabilities, when we look at a brain of a child with autism, we don't see anything wrong. There is not damage to the brain. It's merely developing in a different trajectory, forming different kinds of connections that the brains of children with autism will sometimes form. A lot of local connections, but the long range connections may not be as intact.

So this is something that we're beginning to learn more and more about and hope to be able to have more answers for you as the years go by...

I would like to thank you so much for your attention and have a great day, thank you.

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