[Music] >> ARMIN RAZNAHAN, M.D., Ph.D.: Does the brain
scale-up like Photoshop?
Just like a linear expansion?
Or is it a case that in larger brains some regions become notably large and others fail
to get as they should, essentially.
So what you see here is a spinning human brain, with a map that ansers that question.
Where you see red, those regions expand prominently, as a function of brain size.
in contrast, where you see blue, these regions expand, but not as much as the red regions.
They become more expanded than the blue regions in larger brained individuals.
This does not enable a large brained person to say "My brain is better then a small brain
person."
So our question is about bigger individuals compared to smaller individuals.
The two other routes to a big primate brain are evolving one -- i.e. the difference between
humans and non-human primates.
Or growing one.
The difference between adult brain size and the size of a child's.
This map that we found very strongy aligns with both of those maps.
And what this is telling us is we seem to detecting some sort of blueprint -- an architectural
blueprint, if you like -- with the primate brain, given that all three routes to a bigger
brain induce this sort of shift in brain organization.
Which was really very striking for us and suggests that its a sort of deeply ingrained
biological signature.
So one metaphor is: If you think about making a garden shed as big as the white house, you
can't build it the same way.
It has to be differently proportioned to be able to stand up.
And it seems somehow that bigger primate brains need to construct themselves a different way
to operate, relative to smaller primate brains.
What was prominent for these red regions, is that they seem to bear functional and cellular
signatures of integration.
They specialize in combining information from lower order systems within the brain.
In contrast, these blue regions that don't expand as much tend to be involved in what
are called lower order sensory motor tasks.
Basic vision, sensation, motion.
So genes that were involved in the long processes of neurons that are important for connecting
with other neurons, are particularly highly expressed in these red regions.
These red regions have high levels of expression of genes that have to do with mitochondria,
that have to do with energy consumption and generation.
So a hint that these regions might be potentially expensive, requiring more energy than the
blue regions.
At rest, we found that these red regions consume a lot more energy than the blue regions do.
So altogether, this seems to suggest that there's a very basic architectural plan by
which having a larger primate brain consistently seems to require making some parts that are
important for integration and hungry for energy, disproportionately, or more notably large
in bigger brains.
The brain is spending its money differently.
If you know that brain shape changes as a function of brain size, it's going to help
us more accurately detect smaller sub regions of brain differ as a function of age, between
males and females, potentially between patients and controls, patients and typically-developing
individuals.
All of these things are associated with brain size differences.
It's a signal biological investment.
These red regions have another signature in that they seem to be consistently impacted
by a whole range of neurodevelopmental disorders.
So they may actually be a kind of important key to understanding how a whole range of
gene and environmental changes can impact higher mental functions.
Planning, processing difficult tasks in humans.
That larger brains are kind of constructed more differently than smaller brains.
And that different construction presumably is there to perfectly suit each brain size.
So evolution doesn't sort of spend its money unwisely.
So we're not suggesting that having larger areas in these red regions smaller area in
these blue regions is necessarily good.
But they are a clue about how the brain is having to optimize its configuration at different
sizes.
And that give us some insight into how the brain is operating.
So we already know from prior work that within humans, there's a subtle relationship between
general cognitive ability, or IQ, and brain size -- such that there's an association that
larger brained individuals, on average, tend to have a slightly higher IQ than smaller
brained individuals.
To the extent that there are functional differences between large brains and small brains -- and
that's not something our study directly addresses -- what our study shows is that there are
also consistent organizational changes between large brains and small brains.
And that knowledge that observing that the brain needs to consistently configure itself
differently as a function of its size is an important clue into the how the brain functions
in health.
And it's potentially a clue into how the brain has difficulties in disease states.
What is clear from our findings is that the red vs. blue regions seem to have a different
biological cost, from a number of perspectives.
One, it costs money to grow tissue.
And the core of our finding is that the red regions grow more than the blue regions as
a function of increasing total brain size.
So there's biological money being spent to build that extra tissue.
The second signature of cost comes from direct measures of energy consumption at rest.
And at rest, we know that these red regions seem to be a bit greedier -- to receive more
oxygenated blood than the blue regions.
And we interpret that as making the assumption that nature spends its money very wisely.
That there must be a kind of functional reason for that differential investment.
This is one of the most comprehensive maps detailing how the brain spends its money.
It gives us leads regarding which brain regions we need to focus on and how we need to study
them.
And that's real advantage, because the brain's a big place and there are lots of questions
you could ask.
And having leads like this to help you know where to dig is a very, sort of, powerful,
potentially powerful, step.
For us, because we study patients that often have alterations in their total brain size,
by having these maps, we can do a better job of pinpointing which sub regions of the brain
seem to be disproportionately altered in those patients.
And that is important, because if we can understand the map of altered brain organization in patients,
that might being us one step forward, ultimately, in the future, to potentially helping them.
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