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.
Those tests ask, for instance, how many words beginning with W a patient can list, and how many breeds of dogs he can name, rather than have patients speak spontaneously. The latter "is too hard to score," said neuropsychologist Sterling Johnson, of the University of Wisconsin, who studies brain function in Alzheimer's disease. "But everyday speech is definitely a way of measuring cognitive decline. If people are noticing [a change in Trump's language agility], that's meaningful."
Although neither Johnson nor other experts STAT consulted said the apparent loss of linguistic fluency was unambiguous evidence of mental decline, most thought something was going on.
John Montgomery, a psychologist in New York City and adjunct professor at New York University, said "it's hard to say definitively without rigorous testing" of Trump's speaking patterns, "but I think it's pretty safe to say that Trump has had significant cognitive decline over the years."
No one observing Trump from afar, though, can tell whether that's "an indication of dementia, of normal cognitive decline that many people experience as they age, or whether it's due to other factors" such as stress and emotional upheaval, said Montgomery, who is not a Trump supporter.
Even a Trump supporter saw and heard striking differences between interviews from the 1980s and 1990s and those of 2017, however. "I can see what people are responding to," said Dr. Robert Pyles, a psychiatrist in suburban Boston. He heard "a difference in tone and pace. … What I did not detect was any gaps in mentation or meaning. I don't see any clear evidence of neurological or cognitive dysfunction."
Johnson cautioned that language can deteriorate for other reasons. "His language difficulties could be due to the immense pressure he's under, or to annoyance that things aren't going right and that there are all these scandals," he said. "It could also be due to a neurodegenerative disease or the normal cognitive decline that comes with aging." Trump will be 71 next month.
Northwestern University psychology professor Dan McAdams, a critic of Trump who has inferred his psychological makeup from his public behavior, said any cognitive decline in the president might reflect normal aging and not dementia. "Research shows that virtually nobody is as sharp at age 70 as they were at age 40," he said. "A wide range of cognitive functions, including verbal fluency, begin to decline long before we hit retirement age. So, no surprise here."
Researchers have used neurolinguistics analysis of past presidents to detect, retrospectively, early Alzheimer's disease. In a famous 2015 study, scientists at Arizona State University evaluated how Presidents Ronald Reagan and George H.W. Bush spoke at their news conferences. Reagan's speech was riddled with indefinite nouns (something, anything), "low imageability" verbs (have, go, get), incomplete sentences, limited vocabulary, simple grammar, and fillers (well, basically, um, ah, so) — all characteristic of cognitive problems. That suggested Reagan's brain was slipping just a few years into his 1981-1989 tenure; that decline continued. He was diagnosed with Alzheimer's disease in 1994. Bush showed no linguistic deterioration; he remained mentally sharp throughout his 1989-1993 tenure and beyond.