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. fMRIsare extremely common in modern neuroscience studies, and with good reason. This tech can give us information about whatkind of activity is happening in different parts of the brain in response to differenttasks 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 haveused fMRI, but the journalism surrounding the actual results of these studies can get,well, sensational. Media coverage about a specific study from2008 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 fromvolunteers as they jumped out of an airplane. They also collected saliva before and afterthe jump to try and detect the stress hormone, cortisol. Then on a separate day, they had participantsrun on a treadmill and collected sweat and saliva again. The idea was that skydiving invoked a fearbased stress response while the treadmill invoked a non-fear based stress response whichacted as a control. There were multiple components to the study,but one involved placing separate participants in an fMRI, exposing them to a vaporized solutionwhich included either sweat collected from the skydiving conditions, sweat from exercise,or just air and scanning their brains. When the participants were exposed to theskydiver sweat, the researchers saw increased activation of their amygdalas, the so calledfear center of the brain. So if you were a journalist reporting on thisstudy, you could reasonably make the connection that people could smell something in thatsweat sample that indicated fear, right? That’s a heck of a stretch. Regions associated with vision, goal-directedbehavior, and motor control also lit up, not just the amygdala. fMRIs work by showing us where blood is flowingin the brain, but they can’t tell you what someone is thinking. A more accurate headline would be that a studysuggested that humans can signal emotional stress. “Fear is contagious” is a bit sensational. So today, we’re going to learn the regionsof the brain, what happens in each one, and how to correctly interpret a headline thatmakes a claim about your brain. As we learned in the last video, the brainis one of the key pieces in our central nervous system, along with the spinal cord. It has to interpret and process informationit receives from the outside world, and then come up with responses for it. When we look at the brain from the side, wecan see three big structures. The first of which is the cerebrum, this enormousround part. We’re going to go in depth on the differentpieces 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 toremember this structure. Because on the back side is a structure calledthe cerebellum, which literally translates to the little brain. This is where your body takes in certain sensoryinformation and regulates movements like balance and coordination, although more recent researchshows that the cerebellum might process emotions and social behavior too. All in all, about half of your brain’s neuronslive in this part of the brain. Below the cerebrum and cerebellum is the brainstem. I personally used to think of the brainstemas 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 interestedin which region of the brain does what, they’re looking at the big brain, the cerebrum. Alright, check this thing out, this is thestandard view of your cerebrum. Right now, we’re looking at the outermostlayer called the cerebral cortex, but if we were to slice it in half, we’d see deeperstructures called subcortical structures, literally meaning underneath the cortex. Among all those subcortical structures arebig players like the limbic system which helps you express emotions and the pituitary glandwhich pumps out a bunch of different hormones. It also includes a structure that connectsthe two sides of the brain called the corpus callosum, a thick band of nerve fibers thatlets 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 brainis 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 dealswith language differently, but past that, we’re talking about minor differences atmost. Importantly though, we can say definitivelythat the left half of the brain interprets signals from the right half of the body andvice versa. So the left hand is controlled by the rightside of the brain — that kind of thing. Knowing that, we can finally look at whatthe different parts of the cerebral cortex do. First thing, look at all those different dipsand ridges, also known as sulci and gyri respectively. By having all those folds, you increase thesurface area available and thus, shove more brain into your brain. Those squiggly lines might seem like randombumps, but they help us divide the cerebral cortex further into different functional centers,or lobes. The biggest one is the frontal lobe, whichis, as you guess, in the front part of our brain. This is where we find a bunch of the structuresthat make us uniquely human, most notably our enormous prefrontal cortexes which handlehigher order functioning and cognition. Other animals have prefrontal cortexes, butwe’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, theprimary motor cortex. The primary motor cortex is a long regionthat extends over both halves of your brain like over-ear headphones. And each moving body part is represented witha 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 somatosensorycortex which is split up to represent different body parts, so the area that represents theface 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 amountof 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 ofthe brain that processes hearing, called the auditory cortex. And that makes enough sense, the ears arelike, right there. The temporal lobe also has a special areacalled Wernicke’s area that helps it interpret speech. Well, I should say “Vern-ick-ee’s” areasince it’s German. Now, harkening back to the days before fMRIstudies, 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 multiplenetworks 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 backof your head would interpret signals from the front of your head, but it be like thatsometimes. Now, here’s where I want to introduce someasterisks to the conversation. The primary visual cortex, the main spot wherewe process vision is in the occipital lobe. But, if we follow an image from the momentit hits our eyes until it’s processed, we see that it’s not that straightforward. After light passes through our eyes, it hitsspecial photoreceptor cells in the back of our eyes called rod cells and cone cells. Each of those cells contains light sensitivepigment 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 yourTimotheé Chalamet wallpaper, that image is processed in part by the eye itself. From there, different aspects of vision getprocessed 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 primaryvisual cortex while some crosses the optic chiasma, a little bridge between the opticnerves that connects the left and right pathways. Then, we have pathways in the brain that tiethat visual information with the coinciding audio information, or smell, or touch. After all is said and done, after the visualcortex processes the image, it still relays that information elsewhere. I’m going into so much detail because Ifind it so fascinating that all this prep work has to be done to process one of themain ways we interpret the world, our sight. It’s a great reminder that the brain isthe most complicated piece of anatomy that exists. Yes, that skydiving sweat fMRI experimentI mentioned at the beginning showed increased activity in the amygdala. But be careful. When you’re listening to the results ofan fMRI study, whether it’s on the news or if you go the extra mile and find the primarysource, 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 specificjob to a whole lobe of the brain. Earlier we mentioned Broca’s area, an areanamed after French surgeon Pierre Broca after he noticed that two men lost their abilityto speak after both of the patients suffered injuries to the sides of their heads. To him, that seemed like pretty good evidencethat 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.