How Aphasia Causes Difficulty Speaking
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Today’s topic moves beyond language and into language disorders, and the kinds of things we can learn from them. Language impairment is often caused by tragic conditions like aphasia, a type of brain damage. This condition can teach us a lot about how language works. To begin to understand such a complex, fascinating, and ever-changing field, we will first talk about the human brain and the field devoted to its study.
What Is Neurolinguistics?
Neurolinguistics is a branch of neuroscience whose goal is to understand the neural aspects of language, such as how the brain processes language. To do research in neurolinguistics, neuroscientists depend largely on impaired language data, not normal language data. In other words, analyzing the patterns in the abnormal speech of someone who has suffered from an event like a stroke, or from someone who has a medical condition like dementia, provides information for scientists that normal speech cannot provide.
The Basic Components of Our Brains
The brain consists of more than 100 billion nerve cells—called “neurons”—which are connected with fibers. The brain’s surface is called the cortex, or “gray matter,” and is responsible for making decisions, storing memories, initiating action, and, of course, for our knowledge of language and grammar. (2) One of the coolest things about the brain is how it’s wrinkled and folded up, because if it weren’t, our heads would be enormous! The cortex is thin, but quite large in surface area, and we need for all of that surface area somehow to fit into the skull—it’s like taking a sheet of newspaper and crumpling it into a ball to fit inside a small bowl. (4) In proportion to our bodies, human brains are larger and more intricate than any other living creature. (6)
You may have learned that the brain has two halves, which are known as its hemispheres (“hemi” is a prefix that means “half”). They are connected by the “corpus callosum”—a network of 200 million fibers. Incredibly, some patients with severe epilepsy need to have this connection surgically removed, and they are still able to function normally! You may also have heard that brain function is “contralateral,” which means that the left side of the brain controls the right side of the body, and vice versa.
Lots of Language Processing Happens in the Left Side of the Brain
The answer to this question is complicated. You may have heard that the left hemisphere is “responsible for language,” and that is mostly true: It’s called “lateralization” when a brain function is localized to one hemisphere (“lateral” means “side”).
Scientists have figured this out using technology such as CT scans and PET scans, which show the areas of the brain that light up when subjects are given various types of language stimuli, and the areas that light up when they get non-linguistic stimuli, too.
Furthermore, those epileptic patients with the separated-hemisphere surgery provide a dramatic illustration of this language-on-the-left idea, because although those patients function just fine after the operation, controlled experiments show that separating the hemispheres results in some odd language changes.
For example, one experiment blindfolded the patients, and placed simple objects like keys and pens into one hand at a time. These subjects were able to easily name objects in their right hand, because the left hemisphere—where language is located—operates the right hand. However, in the left hand, they recognized the objects but were unable to name them, because the right hemisphere operates the left hand, but does not process language, and more importantly, they are blindfolded, and their right hemispheres can no longer communicate with their left hemispheres! (4)
Language Isn’t Limited to the Left Side of the Brain Though
So, it seems pretty clear that language lives on the left side of our brains, right? Well, it’s not that simple. Research, including that same brain-scan research, shows that small amounts of language processing are found in the right side of the brain, too, and that the amount varies from person to person. (4) Remarkably, left-handed people are less lateralized for language, in that they have significant language representation in both of their hemispheres. Left-handed people also recover from language loss after strokes better than right-handed people, because they have language spread out more evenly. In fact, this quicker recovery is also observed in right-handed people who have left-handed people in their family! (3)