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I was chatting about the Spring weather, which finally arrived in Boston, with a patient I saw in clinic this week. He appeared perfectly normal and mentioned how he was excited to get back out on the golf course. But when we began to discuss specifics of golf and other matters, it was clear that he was not able to understand many of the words I was using.
One common reason that people have difficulty understanding is due to hearing difficulties. But sometimes—particularly if the individual is also having memory or other cognitive difficulties—the problem is with comprehension, not hearing.
Comprehending language is a fundamental human trait. We learn language automatically, without effort, as we grow from infants to toddlers to children. Part of what we learn is the syntax and grammar of the language. But much of what we learn is vocabulary. In fact, learning vocabulary is such an essential part of our cognition that we have a special system devoted to it called semantic memory. The label “semantic” tells us that this memory system is related to the meaning of words. Thus, it is our semantic memory that puts together the sounds that make up the spoken word “apple” (or the image of the visual symbols of the word “apple” on the page) with the actual fruit that may be red, green, or yellow, have both a sweet and tart taste, and make a satisfying crunching sound when you bite into it.
A study published in 1996 provided compelling evidence that our semantic memories—our knowledge of words—are stored in the temporal lobes of the brain. The temporal lobes are next to your temples, just behind your eyes. The study found that patients with strokes that damaged the temporal lobe had trouble naming people and objects. Moreover, when the damage was in the front part of the temporal lobe, closest to the eyes, there was the greatest difficulty in naming persons. When the damage was in the back of the temporal lobe, near the back of the head, there was the most difficulty in naming tools—that is, man-made objects. Those who had damage in-between, in the middle of the temporal lobes, had the greatest difficulty naming animals. This study also examined which parts of the brain were activated when individuals were asked to name people or animals or tools. As you may have guessed, they found the same pattern of activation in the temporal lobe: Naming people activated the front, naming tools activated the back, and naming animals activated the middle.
Trouble coming up with people’s names is common, and it becomes more common as we age. This difficulty is likely related to the fact that most of us develop shrinkage in the front of our temporal lobes as we get older. So, a bit of trouble remembering the names of people is usually normal for an older adult.
What is not normal is to experience difficulty naming animals, tools, or other common words—or to have difficulty understanding what those words mean. Do you find yourself often filling in words for your mother or grandfather because you are so used to the word-finding pauses in their sentences? That is one common phenomenon that occurs when someone has significant word-finding difficulties—other family members automatically fill in the words. Do you find yourself using more simple words or describing things in more than one way when speaking to your father or grandmother? That often indicates that there has been some loss of comprehension—a loss of what some words mean—and so you have learned to compensate when you are speaking with them.
The most common disorder that leads to difficulty finding and comprehending words is Alzheimer’s disease. Although this disorder typically begins with difficulty remembering recent events, trouble with language is often the next symptom. Other disorders can also cause damage to semantic memory, leading to comprehension and word-finding difficulties. In addition to strokes and Alzheimer’s, there is a rare type of dementia that causes these language troubles as the first symptom. Appropriately enough, it is called semantic dementia.
When comprehension difficulties are present, we can still communicate effectively with our loved ones, either by using different words or by using non-linguistic and non-verbal communication. I will discuss these other forms of communication in future posts.
References
Damasio H, Grabowski TJ, Tranel D, Hichwa RD, Damasio AR. 1996. A neural basis for lexical retrieval. Nature 380: 499-505.
Budson AE, Solomon PR. Memory Loss, Alzheimer’s Disease, & Dementia: A Practical Guide for Clinicians, 2nd Edition, Philadelphia: Elsevier Inc., 2016.
Budson AE, O’Connor MK. Seven Steps to Managing Your Memory: What’s Normal, What’s Not, and What to Do About It, New York: Oxford University Press, 2017.
