In a May 23 story, the health website Stat posted a report that, on the surface, shows something alarming about the cognitive and verbal skills of President Donald Trump.

"Trump wasn’t always so linguistically challenged. What could explain the change?" is the headline of Sharon Begley's story, for which she reviewed dozens of interviews Trump gave over the last three decades. She found that the president's vocabulary, sentence structure, speed of speaking, and ability to carry one answer from start to finish had all noticeably declined.

To make sense of her conclusions, Begley interviewed a number of linguists, neuroscientists, and psychologists. She reported that "all agreed there had been a deterioration, and some said it could reflect changes in the health of Trump’s brain."

Going back to interviews Trump gave in the 1980s, Begley observed that the future president "fluently peppered his answers with words and phrases such as “subsided,” “inclination,” “discredited,” “sparring session,” and “a certain innate intelligence." In addition, "He tossed off well-turned sentences .... He even offered thoughtful, articulate aphorisms." 

Now, Trump's language is simpler, full of repeated words and phrases, and includes dramatic shifts from subject to subject, often within the same sentence. 

There have been a number of amateur diagnoses of Trump as suffering from various cognitive illnesses. Dementia and Alzheimer's are the two most frequently mentioned, with Trump's verbal decline, mental lapses, and lashing out over Twitter attributed to the stress of the presidency worsening whatever mental condition he might have. 

But it's important to recognize that Trump has never been diagnosed with a cognitive impairment, and no expert quoted in the Stat article diagnoses him with any disease.

One psychologist who is quoted, Ben Michaelis in New York, allows that while "there are clearly some changes in Trump as a speaker” since the 1980's, this could be a result of his age. "In fairness to Trump, he’s 70, so some decline in his cognitive functioning over time would be expected.”

Researchers haven't been able to pin down one particular age where cognitive decline begins for everyone. A long-term British study published in 2012, involving 10,000 government employees, found that while the oldest participants had the steepest declines in verbal and cognitive ability, "even for the youngest participants, aged 45-49 in 1997-99, average skills declined with age in every one of the test categories except vocabulary," according to Time Magazine.

This was a sharp change from previous research, which found that there was little mental decline in people younger than 60, likely because the tests being administered were too easy for younger subjects. 

If cognitive decline at 45 isn't frightening enough, another long-term study found that mental decline can began even younger. A 2009 study from the University of Virginia found that cognitive ability peaks at age 22, with a slow decline that has its first glimmers in one's late 20s. But the study also found that "accumulated knowledge skills, such as improvement of vocabulary and general knowledge, actually increase at least until the age of 60."

To confuse the matter even more, another study, this one done with nearly three million subjects playing a series of internet games, found that vocabulary skills only improve with age. In fact, the MIT study found that word knowledge actually hits its highest point in the late 60's and early 70's. 

"The researchers believe this may be a result of better education, more people having jobs that require a lot of reading, and more opportunities for intellectual stimulation for older people," MIT News reported. 

The Virginia study's lead investigator was quick to point out that cognitive ability varies greatly from person to person, and that it's common for people to function at a highly effective level well into advanced age. So this might not mean much as far as Trump's brain goes.

As one psychologist told Begley, without rigorous in-person testing it's impossible to tell if the vocabulary decline is "an indication of dementia, of normal cognitive decline that many people experience as they age, or whether it’s due to other factors” including the stress of the office, anger over the scandals his administration is facing, and the amount of reading Trump needs to do as president.

But the researchers interviewed by Stat all saw evidence that something had changed with the president. And at a time when, at least according to this research, his vocabulary should be its strongest, Trump's vocabulary is getting simpler and being expressed less clearly.