That Neuroscience Guy - Q&A: Brain Disorders and Stroke

Episode Date: May 17, 2021

In a special That Neuroscience Guy Q&A, I discuss various types of nervous system disorders and injuries, and how they affect your brain. 

Hi, my name is Olof Kergolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm That Neuroscience Guy. Welcome to the podcast. Today, I'll be answering your questions again. Remember that if you have a question, you can email me a question at thatneuroscienceguy at gmail.com, or you can post one on me a question at thatneuroscienceguy at gmail.com, or you can post one on my Twitter feed at thatneuroscienceguy. Today's first question is, what is aphasia? There are actually two principal types of aphasia.

There is Wernicke's aphasia and Broca's aphasia. Wernicke's aphasia is due to neural damage in the left temporal lobe, and it impacts your ability to understand words. Someone with Wernicke's aphasia will hear noise when you speak, but they won't be able to translate those sounds into words with meaning. So auditory information comes into the brain and is processed in early auditory processing areas, and eventually it arrives in Wernicke's area. And Wernicke's area plays a crucial role in translating that sound and the neural representation of that sound into meaning. So people with Wernicke's aphasia hear sound, but they can't translate it into something that they can understand. Importantly, they still understand the meaning of these words, so they haven't lost their representation for things. For instance, if you said the word hammer, they wouldn't know you

had said the word hammer because they wouldn't be able to translate that pattern of sound into something that has meaning, but they would understand what a hammer is. Broca's aphasia is due to neural damage in the left frontal lobe, just below the key motor regions. And people with Broca's aphasia have trouble producing spoken language. So in other words, they understand what you're saying when you speak to them because they don't have damage to Wernicke's area. But when they go to reply and generate speech, they have trouble encoding language into a motor command or motor output. In some instances, Broca's aphasia can be quite minor and really is just seen as stuttering. In other instances, Broca's aphasia in its strongest form, which is true aphasia, basically means an inability to generate written language. What's interesting about both Wernicke's and Broca's aphasia is that they impact language as

a whole. So, for instance, someone with Wernicke's aphasia has trouble understanding language, whether they're reading something or listening to you speak. And someone with Broca's aphasia has trouble speaking and writing. How does a stroke impact you? There are three main types of strokes, ischemic strokes, hemorrhagic strokes, and transient ischemic attacks. strokes and transient ischemic attacks. Ischemic strokes are by far the most common type of stroke and they occur when blood throws through an artery that provides oxygenated blood to the brain becomes blocked, most typically by a blood clot. This will lead to an ischemic stroke. Hemorrhagic strokes occur when an artery in the brain leaks blood or ruptures. Typically,

this is a result of high blood pressure or an aneurysm, and you get a bulge in the actual artery that stretches and bursts, and this leads to a hemorrhagic stroke. Transient ischemic attacks are basically a mini-stroke. They typically last a short duration, no more than five minutes. They are an important warning sign that the blood flow within the brain is compromised or impaired. In terms of how it impacts you, when you have a stroke, essentially you're damaging neural tissue. So if there is a lack of oxygenated blood flow near a neural tissue, that tissue dies and becomes damaged, or in the case of a rupture, the blood on the brain can damage the tissue itself. And when neural tissue dies, the story is quite simple. It doesn't work anymore. If you had neural damage in a part of the brain that controlled the movement of your left arm, then you would have trouble moving your left arm.

of your left arm, then you would have trouble moving your left arm. In a similar manner, if a stroke occurs towards the back of the brain, for instance, in the occipital cortex, you'll have trouble seeing as a result of that stroke. The amount of reduction in brain function, if you will, is dependent on the amount of tissue damage. Because the brain is wired left to right and right to left, if you have a stroke on the right side of the brain, you typically get impact on the left side of the body. And conversely, if you have a stroke on the left side of the brain, you typically get impact on the right side of the body. In addition to paralysis of the left side of the body, right brain strokes are typically associated with vision problems, a change in behavior to sort of a quick nature, and memory loss. Conversely, left brain strokes, in addition to paralysis on the right side of the body, typically result in speech and language problems, a more slow and cautious

behavioral style, and memory loss. What is apraxia? Apraxia is a motor disorder which is caused by damage to the posterior parietal cortex, and there are many different types of apraxia. Ideational apraxia, for instance, means that the person with it has trouble putting together a complex series of actions. If you ask them to make some toast, they might put butter on the toast before they put it in the toaster as opposed to after, or they might put their shoes on before they put their socks on. So they have trouble with the movement sequence they need to do to perform a complex action. In some extreme cases, someone might pick up a screwdriver and try to write with it, thinking it's a pen.

People with idiomotor apraxia can perform an action. For instance, they can brush their teeth or they can hammer in a nail. But if you ask them to mimic that action, imagine doing it without the tool in your hand. So for instance, if I asked you to brush your teeth, you might move your index finger slowly back and forth in front of your teeth. People with ideomotor apraxia can't imagine that type of action without the actual object in their hand. For my last question today, what is the Capgras delusion? People that experience the Capgras delusion have an interesting clinical presentation. Typically, when they think about their significant other and they're in the room with them, they believe that their significant other is an imposter. For instance, someone with a Capcraw delusion might believe that their husband or wife is not actually their husband or wife, but it's an imposter. In one case,

someone even thought that their dog was no longer their but it's an imposter. In one case, someone even thought that their dog was no longer their dog, but an imposter dog. What causes the Capgras delusion? The Capgras delusion is caused by a disconnect between emotional processing and visual processing. Normally, when we see a significant other, our visual system recognizes them, but there's also an emotional response. And that emotional response gives emotional meaning to the visual recognition. It's not quite the warm fuzzy feeling that you feel, but it plays an important role in visual recognition. People with the Capgras delusion see their significant other, but without that emotional response, their brain's forced to come to a new conclusion, and that conclusion is that person is an imposter.

It's actually kind of rational when you think about it. They see someone that looks exactly like their significant other, but there's no underlying emotional response, so their brain is forced to come up with an explanation. emotional response, so their brain is forced to come up with an explanation. What's interesting about people with the Capgras delusion is if they talk to their significant other on the phone, they have no trouble recognizing them. My name is Olive Krigolson, and I'm That Neuroscience Guy. Remember, you can ask me questions by emailing me at thatneuroscienceguy at gmail.com or by posting them on my Twitter feed at thatneuroscienceguy. Thanks for listening, and I'll see you on the next episode.