This combination of photos show then-President Donald Trump, left, and former Vice President Joe Biden during the first presidential debate on Sept. 29, 2020, in Cleveland, Ohio. (Patrick Semansky/The Associated Press)

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The connection between “cognitive decline” and “the president’s age” has attracted increasing attention. In February, special counsel Robert Hur’s report highlighted President Joe Biden’s “significantly limited” memory, intensifying the debate over whether the two leading presidential contenders are too old for another term. On June 4, the Wall Street Journal reported more alarming signs of President Biden’s slipping mental acuity, observed behind closed doors by more than 45 Republicans and Democrats.

In the highly polarized political theater, pundits on both sides fiercely defend their geriatric candidates, arguing that aging afflicts only the opposing party’s candidate. Politicizing this vital discussion clouds what is at stake. Voters may soon see “cognitive impairment” and “the president” in the same sentence.

Nikki Haley, the former Republican presidential candidate, called for mandatory cognitive tests for politicians over 75. It is highly doubtful that politicians can agree on which tests disqualify the other party’s candidates.

Cognitive tests are routinely administered to evaluate brain functions. For example, can you recite the months of the year backward from December? While easy for most, individuals in the early stages of dementia often struggle with this task. The patient may answer, “December, November, October, um, September, um, um, October, November, December.” A feeble brain has difficulty resisting the temptation of reciting the months forward.

This test quickly assesses how well the brain works, especially the frontal cortex, which sits behind the forehead. The frontal cortex is the brain’s commander-in-chief. One of its essential functions is impulse control. It whispers, “Don’t do it, or you will regret it,” steering us toward following rules and social norms.

Building a healthy frontal cortex is a lengthy, arduous undertaking lasting over two decades. The frontal cortex’s immaturity is on full display during the teenage years when adults frown upon teens’ impulsivity. It is no coincidence that one can become president only after turning 35 instead of 15. Handing a teen control of the country’s nuclear weapons isn’t a brilliant idea.

Worse than immaturity, impairment of the frontal cortex has more threatening consequences. Drugs, alcohol and brain injury diminish its functions. About 1 in 5 death-row inmates has suffered concussive trauma to this vital brain structure.

How does advanced aging impact the frontal cortex and its ability to rein back impulses? The outlook is rather heartbreaking. Observing elderly individuals suffering from dementia reveals that each day can be an eternal struggle. Aging doesn’t cripple the brain overnight, but once troubling signs appear, improvement is rare.

When a man past his 70s sniffed young women’s hair multiple times in public, read teleprompter script instructions out loud, “Four more years, pause,” and joked about his craving for ice cream right before speaking about the mass shooting in Nashville, were those merely benign senior moments?

When another man in his 70s fired off hundreds of random, insulting tweets a day, told a young female journalist, “You are a nasty person,” during a televised town hall, and spewed numerous lies in the face of indisputable facts, did he simply lack integrity?

No, such aberrant behaviors are much more disturbing. They are consistent with decreasing impulse control, a strong indicator of deteriorating frontal cortex functions in old age. The two men knew their actions were inappropriate. However, the temptation to do the easy thing is so irresistible that the weakened frontal cortex can’t tap on the brake on time.

Examining such deviant behaviors through the lens of science doesn’t give us much confidence about either party’s presumed nominee. Confusion mounts when partisan hacks jump into the debate about mental competency and aging to score cheap points.

Aging-induced cognitive decline and impairment are not an isolated incident but a progression. The critical question is: Are both men getting worse? Unfortunately, the answer is definitely yes.

For Biden to yell at the nation for over an hour during his most recent State of the Union address doesn’t dispel concerns about his sinking cognition. On the contrary, it demonstrates failing frontal cortical functions in tamping down his angry impulses.

For Trump to repeatedly refuse to comply with a judge’s gag orders during his criminal trial is not a show of defiance. Instead, it is consistent with what we already know about his impulsivity, which is only worse this time.

No need to go behind closed doors to witness each presidential contender’s frontal cortex losing its grip. Simply watching C-SPAN or the news will confirm why 55% of voters don’t look forward to the high-stakes rematch between two grumpy old men.

Not every gaffe and stumble can be chalked up to cognitive decline. But it’s equally reckless to ignore glaring, persistent patterns of erratic conduct in those aspiring to the world’s most mentally demanding job. The 2024 election is no place for neurodegenerative optimism and negligence.

Advanced aging can debilitate the brain regardless of political affiliation. The president is our nation’s frontal cortex. Dysfunctions have unthinkable consequences. Our next leader is shuffling toward a finish line for which few Americans are prepared.

The frontal cortex makes its first grand appearance when a child is potty-trained. Overriding the urge for immediate release symbolizes a big step forward. Diapers become a thing of the past. When the frontal cortex crumbles due to aging-induced dementia, that desire for instant release becomes impossible to control. Diapers may sneak a return for patients bidding a long goodbye.

The urgent question in this election seems to be: Which elderly candidate is the real fit for the White House?

In reality, voters face a more stinking question: Is our country about to choose a leader to depend on or with Depends on?

Terry Wu, of Plymouth, is a neuroscientist, leadership speaker and consultant. A version of this article was published previously by the San Francisco Chronicle.