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Picture a brain in your brain.
That’s wild.
So your mind’s eye is probably showing you a pink wrinkly thing,
and that wrinkly outer layer is called the neocortex.
For a long time, scientists considered the neocortex
the brainiest part of the human brain,
an obvious candidate for the thing that makes us unique.
It’s the biggest part of our brain, and it has those
lovely wrinkles that many smaller mammals just don’t have.
But in some ways, it’s not actually that different from other mammals’ brains.
So researchers have started looking at other places
to figure out what makes us distinctly human.
Move over, neocortex, it’s time to talk about the underrated cerebellum.
Now, there are good reasons why scientists thought our neocortex was
a major thing that made us stand out as a species.
It takes up about 80% of the human brain’s mass.
Plus, it's divided into about 200 areas that are specialized for different functions.
For comparison, early mammals probably had about 20.
Those 200-ish areas are responsible for a lot of functions
we think of as characteristically human, like making plans,
speaking, and understanding language.
But as scientists dug deeper, they found some things that weren’t all that unique.
Like, many specialized regions in our neocortex
perform functions we do share with other primates.
For example, the prefrontal cortex is in charge of planning and inhibitory control.
And the insula is involved in gut reactions.
In fact, some functions seem to be shared across nearly all mammals,
like visual and auditory systems, and areas for sensory and motor control.
And even though our overall brains are 238% bigger
than you’d expect for a primate of our size,
our neocortex isn’t out of proportion to the rest of our brain.
Which is what you would expect if it was what made it special.
I mean, even a mouse lemur has a frontal cortex
that's about the size you’d expect based on their overall brain.
And humans like to fancy ourselves as, well, fancier than a mouse lemur.
All of this means our neocortex might not be particularly exceptional.
And it might not be the only thing that contributes to human intelligence.
So scientists have started to look at the second biggest part of the brain.
It's called the cerebellum, and it's located at the back of your skull,
just above your spinal cord.
The word cerebellum means “little brain.”
But even though it’s small, it contains four times more neurons than the neocortex.
In humans, the cerebellum is largely responsible for
fine motor control and implicit memory.
That's the kind of procedural memory you don't memorize so much as practice,
like riding a bike, playing an instrument, or navigating home.
Among vertebrates, we actually see the greatest
size variation in the cerebellum, not the neocortex.
As humans and other apes evolved, the cerebellum expanded
much more rapidly than the neocortex,
resulting in a cerebellum that is outsized compared to the rest of the brain.
And when you look deeper, you find even more differences.
In 2021, researchers published a study that looked at
methylation of DNA in human and primate brains.
Methylation basically means your DNA gets some
chemical hop-ons that can change how genes are expressed.
They found different levels of methylation between humans and primates.
But the difference was bigger in samples
taken from the cerebellum than from the neocortex.
What’s more, the genes that were likely to have more methylation seemed to be
related to neuronal growth, plasticity and learning.
If those genes are being fine-tuned through methylation, our brain’s growth
and evolution might depend more on the cerebellum than we thought.
When we look at the evolution of other animals, we tend to see an
enlarged cerebellum associated with more elaborate motor skills.
Like, when primates and squirrels get more practice
using their forelimbs to climb trees, that can favor a bigger cerebellum.
Which further enhances their motor skills.
As humans evolved, the expansion of our cerebellum likely
increased our technical capabilities, like our skill in making tools.
That’s crucial, because a hallmark of human intelligence is that
we make tools better than any other animal.
And we couldn’t do that without an advanced cerebellum
helping us plan and coordinate complex sequences of actions.
In addition, our cerebellum-fueled technical skills may have
driven the development of language and syntax.
Speech itself is an extreme fine motor skill, and we do have neural connections
between the cerebellum and areas of the cortex involved in language.
Research suggests that the human cerebellum expanded
at the same time our language and verbal memory abilities emerged.
Which makes sense, because scientists think human language may have evolved
largely to help us teach each other how to create tools from stones and plants.
The more scientists investigate the cerebellum,
the more central it seems to human abilities.
It helps us perform complex actions in a smooth and coordinated way,
whether those actions are crafting cooking tools
or engaging in cognition and conversation.
And it’s considered a “learning machine” capable of
predicting outcomes and adapting after making errors.
Now that’s not to say the neocortex isn’t really important.
The neocortex and cerebellum are densely linked,
and they closely coordinate to produce thoughts and behaviors.
So, to discover how humans operate, we need to look at the whole brain.
And remember that when it comes to the neocortex, size is not everything.
The more we understand how our brains work,
the more we can use that knowledge in our everyday lives.
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