So! You want to study brain activity? In order to get accurate and precise data,
we’ll need a piece of technology like functional magnetic resonance imaging, or fMRI. fMRIs
are extremely common in modern neuroscience studies, and with good reason. This tech can give us information about what
kind of activity is happening in different parts of the brain in response to different
tasks or just at rest. If you’ve heard that a region of the brain
“lit up” or was “activated” in response to being shown an image or hearing a sound,
that news probably came from an fMRI study. Thousands and thousands of experiments have
used fMRI, but the journalism surrounding the actual results of these studies can get,
well, sensational. Media coverage about a specific study from
2008 claimed that scientists proved we can smell fear. Not only that, but fear is contagious. Let’s dig into that, shall we? The actual study collected sweat samples from
volunteers as they jumped out of an airplane. They also collected saliva before and after
the jump to try and detect the stress hormone, cortisol. Then on a separate day, they had participants
run on a treadmill and collected sweat and saliva again. The idea was that skydiving invoked a fear
based stress response while the treadmill invoked a non-fear based stress response which
acted as a control. There were multiple components to the study,
but one involved placing separate participants in an fMRI, exposing them to a vaporized solution
which included either sweat collected from the skydiving conditions, sweat from exercise,
or just air and scanning their brains. When the participants were exposed to the
skydiver sweat, the researchers saw increased activation of their amygdalas, the so called
fear center of the brain. So if you were a journalist reporting on this
study, you could reasonably make the connection that people could smell something in that
sweat sample that indicated fear, right? That’s a heck of a stretch. Regions associated with vision, goal-directed
behavior, and motor control also lit up, not just the amygdala. fMRIs work by showing us where blood is flowing
in the brain, but they can’t tell you what someone is thinking. A more accurate headline would be that a study
suggested that humans can signal emotional stress. “Fear is contagious” is a bit sensational. So today, we’re going to learn the regions
of the brain, what happens in each one, and how to correctly interpret a headline that
makes a claim about your brain. As we learned in the last video, the brain
is one of the key pieces in our central nervous system, along with the spinal cord. It has to interpret and process information
it receives from the outside world, and then come up with responses for it. When we look at the brain from the side, we
can see three big structures. The first of which is the cerebrum, this enormous
round part. We’re going to go in depth on the different
pieces of the cerebrum in a moment, but for now, you can think of this as the big brain. And overall, that isn’t a terrible way to
remember this structure. Because on the back side is a structure called
the cerebellum, which literally translates to the little brain. This is where your body takes in certain sensory
information and regulates movements like balance and coordination, although more recent research
shows that the cerebellum might process emotions and social behavior too. All in all, about half of your brain’s neurons
live in this part of the brain. Below the cerebrum and cerebellum is the brain
stem. I personally used to think of the brainstem
as just an interface for the spinal cord and brain, but it’s so much more than that. Overall, it can regulate heart rate and breathing,
as well as sleeping. It also connects most of the cranial nerves,
which are involved in everything from facial sensation to swallowing. But most of the time when people are interested
in which region of the brain does what, they’re looking at the big brain, the cerebrum. Alright, check this thing out, this is the
standard view of your cerebrum. Right now, we’re looking at the outermost
layer called the cerebral cortex, but if we were to slice it in half, we’d see deeper
structures called subcortical structures, literally meaning underneath the cortex. Among all those subcortical structures are
big players like the limbic system which helps you express emotions and the pituitary gland
which pumps out a bunch of different hormones. It also includes a structure that connects
the two sides of the brain called the corpus callosum, a thick band of nerve fibers that
lets the two sides of the brain communicate with each other. Each side of the cerebrum is called a hemisphere,
the good old left brain and right brain. Now, you might’ve heard that the left brain
is your analytical and logic oriented side while your right side is the creative side,
and that you can be a right vs left brained person. Sorry, but that’s not actually a thing. There’s some evidence that each half deals
with language differently, but past that, we’re talking about minor differences at
most. Importantly though, we can say definitively
that the left half of the brain interprets signals from the right half of the body and
vice versa. So the left hand is controlled by the right
side of the brain — that kind of thing. Knowing that, we can finally look at what
the different parts of the cerebral cortex do. First thing, look at all those different dips
and ridges, also known as sulci and gyri respectively. By having all those folds, you increase the
surface area available and thus, shove more brain into your brain. Those squiggly lines might seem like random
bumps, but they help us divide the cerebral cortex further into different functional centers,
or lobes. The biggest one is the frontal lobe, which
is, as you guess, in the front part of our brain. This is where we find a bunch of the structures
that make us uniquely human, most notably our enormous prefrontal cortexes which handle
higher order functioning and cognition. Other animals have prefrontal cortexes, but
we’re the freaks with massive ones. The frontal lobe also houses Broca’s area,
one of our language processing centers, and another big deal center of the brain, the
primary motor cortex. The primary motor cortex is a long region
that extends over both halves of your brain like over-ear headphones. And each moving body part is represented with
a little strip of this cortex — parts like your ankles or toes getting very little space,
but pieces with complex motions like your individual fingers get a lot of space. Behind the frontal lobe is the parietal lobe,
which processes information coming in from the body’s senses. It has another cortex called the somatosensory
cortex which is split up to represent different body parts, so the area that represents the
face is next to the area that represents the eyes, and eyelids, and so on. We see another cool phenomenon in this cortex
— our fingertips, tongue, lips which all have lots of nerve endings get a huge amount
of space dedicated to processing their sensory input. Below the parietal lobe is the temporal lobe,
which literally means “near the temples”. This is where we’ll find the main area of
the brain that processes hearing, called the auditory cortex. And that makes enough sense, the ears are
like, right there. The temporal lobe also has a special area
called Wernicke’s area that helps it interpret speech. Well, I should say “Vern-ick-ee’s” area
since it’s German. Now, harkening back to the days before fMRI
studies, experiments made it seem like we had two speech centers:
Broca’s area for speech production and Wernicke’s area for speech comprehension. In reality, language is handled in multiple
networks around the brain. Behind the parietal lobe is our final lobe,
the occipital lobe, the area where we process most of our vision. I know it seems weird that a lobe in the back
of your head would interpret signals from the front of your head, but it be like that
sometimes. Now, here’s where I want to introduce some
asterisks to the conversation. The primary visual cortex, the main spot where
we process vision is in the occipital lobe. But, if we follow an image from the moment
it hits our eyes until it’s processed, we see that it’s not that straightforward. After light passes through our eyes, it hits
special photoreceptor cells in the back of our eyes called rod cells and cone cells. Each of those cells contains light sensitive
pigment that kicks off a chemical reaction that converts light into a nervous signal. Even before your eyes have decoded those photons
— whether its a notification on your phone, or the words in your text message, or your
Timotheé Chalamet wallpaper, that image is processed in part by the eye itself. From there, different aspects of vision get
processed on different pathways. One of them carries information about shape,
motion, and brightness while another carries information about color and detail. Then some information goes towards the primary
visual cortex while some crosses the optic chiasma, a little bridge between the optic
nerves that connects the left and right pathways. Then, we have pathways in the brain that tie
that visual information with the coinciding audio information, or smell, or touch. After all is said and done, after the visual
cortex processes the image, it still relays that information elsewhere. I’m going into so much detail because I
find it so fascinating that all this prep work has to be done to process one of the
main ways we interpret the world, our sight. It’s a great reminder that the brain is
the most complicated piece of anatomy that exists. Yes, that skydiving sweat fMRI experiment
I mentioned at the beginning showed increased activity in the amygdala. But be careful. When you’re listening to the results of
an fMRI study, whether it’s on the news or if you go the extra mile and find the primary
source, consider exactly what part of the brain is being reported on. Be sure to differentiate not just the lobe,
but individual parts, because as you can see, it’s really hard to isolate one specific
job to a whole lobe of the brain. Earlier we mentioned Broca’s area, an area
named after French surgeon Pierre Broca after he noticed that two men lost their ability
to speak after both of the patients suffered injuries to the sides of their heads. To him, that seemed like pretty good evidence
that that part of the brain handled speech, and while it was more complicated than that,
we call that area on the brain Broca’s area in his honor. Thanks for watching this episode of Seeker
Human, I’m Patrick Kelly
