U.S. President Joe Biden speaks as he visits Garage Grill and Fuel Bar in Northville, Michigan, U.S., July 12, 2024. / REUTERS/Elizabeth Frantz

As Joe Biden's verbal gaffes, shaky voice and other troubling signs have brought an intense focus on the US president's mental acuity, health experts are calling on him and rival Donald Trump to pass additional cognitive tests, even while warning against leaping to conclusions.

Such tests, experts said, could either help repudiate speculation that the 81-year-old president's mental state is in worrying decline—or else confirm it—and could enlighten voters on the mental abilities of Trump, who has had his own share of verbal lapses. But reliable diagnoses, they caution, cannot be made from afar.

Since Biden's disastrous performance in his debate with Trump two weeks ago, the Democrat's campaign has faced fierce opposition. A growing number of officials in his own party are questioning his ability to lead the country for four more years. And it didn't help when at a summit in Washington earlier this week, Biden mistakenly introduced Ukrainian President Volodymyr Zelensky as his foe Vladimir Putin, before quickly correcting himself.

Dennis Selkoe, a neurologist at Harvard Medical School, said the fundamental issue is whether Biden is suffering from "a normal age-related process" or "something that represents a neurologic disease." "Making a mistake with a name is not automatically a sign of dementia or of Alzheimer's," he told AFP.

But Selkoe, who sees many patients with neurodegenerative problems, said Biden does seem to have the "appearance of an early Parkinson"patient"—including his slow, stiff gait and his low, sometimes barely audible voice, which could be a condition known as hypophonia.

Detailed tests 

In February, Biden underwent a complete physical exam. A published summary of its results indicated that an "extremely detailed neurologic exam" had ruled out Parkinson's. But no detail was provided on the exact nature of the tests or their results.

Could a neurological illness have taken root over just the past five months? If the exams in February had been comprehensive, Selkoe said, there should have been early signs of a nascent condition.

In an editorial in March, the scientific journal Lancet called for standardized procedures to examine the health of sitting and prospective presidents so as to insulate American voters from a "pestilence of speculation, misinformation and slander."

Absent such reliable testing, "the US public remains beholden to voluntarily released reports from politicians' personal physicians," the journal said.

Jay Olshansky, an expert in aging at the University of Illinois at Chicago, sounded a similar note, saying, "We think the time has arrived for complete transparency." He urged both major presidential candidates to pass a cognitive test, something former president Trump has frequently challenged Biden to do.

Several such exams, including those known as the MMSE and the MoCA, are available either for an initial screening or as part of a more comprehensive battery of tests.

Biden has said that he effectively passes a cognitive test every day, simply by carrying out his presidential duties.

But "I don't think it's the same," Selkoe said. Being able to conduct familiar tasks one has done for years is one thing, he said, while being able to repeat a list of words heard five minutes earlier, as some tests require, is another.

At a news conference Thursday, the president said he would be willing to take a new neurological exam if his doctors recommended it, but that "no one is suggesting that to me now."

Stereotypes on aging

Aging changes one's brain, said Allison Sekuler, president of the Baycrest Academy, a hospital specializing in elderly care. "Garbage is basically building up in the brain," she told AFP, adding that parts of the brain atrophy, or shrink, including parts important to memory.

An early phase known as "mild cognitive impairment" can sometimes develop into Alzheimer's or some other form of dementia, she said.

During their recent debate, both Biden and Trump, who is 78, "exhibited some sort of issues in terms of being able to stay on track with a question," Sekuler said, recommending that both men undergo testing. But, she added, "we're really only talking about one of them right now because that aligns with our stereotype of what aging is."

Olshansky also denounced what he called "raging" ageism, citing a recent magazine cover that used a walker as a symbol of the Biden-Trump race. He noted that while there is a lower age limit for would-be US presidents—they must be at least 35—there is no upper limit.

What he called "crystallized intelligence," or the ability to use past experience to improve one's reasoning skills, "gets stronger and stronger" with age.

Olshansky co-authored a 2020 study that gave Biden a 95 percent chance of surviving a first term, based on average life expectancy for someone of his age plus personal risk factors.

But a similar calculation four years later, on a man now four years older, gave Biden a much lower probability of survival: just 75 percent.