From StatNews comes this alarming investigative look into Donald Trump's collapsing cognition:
Research has shown that changes in speaking style can result from cognitive decline. STAT therefore asked experts in neurolinguistics and cognitive assessment, as well as psychologists and psychiatrists, to compare Trump’s speech from decades ago to that in 2017; they all agreed there had been a deterioration, and some said it could reflect changes in the health of Trump’s brain.
In interviews Trump gave in the 1980s and 1990s (with Tom Brokaw, David Letterman, Oprah Winfrey, Charlie Rose, and others), he spoke articulately, used sophisticated vocabulary, inserted dependent clauses into his sentences without losing his train of thought, and strung together sentences into a polished paragraph, which — and this is no mean feat — would have scanned just fine in print. This was so even when reporters asked tough questions about, for instance, his divorce, his brush with bankruptcy, and why he doesn’t build housing for working-class Americans.
Trump fluently peppered his answers with words and phrases such as “subsided,” “inclination,” “discredited,” “sparring session,” and “a certain innate intelligence.” He tossed off well-turned sentences such as, “It could have been a contentious route,” and, “These are the only casinos in the United States that are so rated.” He even offered thoughtful, articulate aphorisms: “If you get into what’s missing, you don’t appreciate what you have,” and, “Adversity is a very funny thing.”
Now, Trump’s vocabulary is simpler. He repeats himself over and over, and lurches from one subject to an unrelated one, as in this answer during an interview with the Associated Press last month:
“People want the border wall. My base definitely wants the border wall, my base really wants it — you’ve been to many of the rallies. OK, the thing they want more than anything is the wall. My base, which is a big base; I think my base is 45 percent. You know, it’s funny. The Democrats, they have a big advantage in the Electoral College. Big, big, big advantage. … The Electoral College is very difficult for a Republican to win, and I will tell you, the people want to see it. They want to see the wall.”
For decades, studies have found that deterioration in the fluency, complexity, and vocabulary level of spontaneous speech can indicate slipping brain function due to normal aging or neurodegenerative disease. STAT and the experts therefore considered only unscripted utterances, not planned speeches and statements, since only the former tap the neural networks that offer a window into brain function.
...The reason linguistic and cognitive decline often go hand in hand, studies show, is that fluency reflects the performance of the brain’s prefrontal cortex, the seat of higher-order cognitive functions such as working memory, judgment, understanding, and planning, as well as the temporal lobe, which searches for and retrieves the right words from memory. Neurologists therefore use tests of verbal fluency, and especially how it has changed over time, to assess cognitive status.