What is a typical degree of cognitive ability for a person in their 80s?

CNN —

Concerns about age and mental fitness have been a recurring theme through the past two presidencies and are set to only mount in 2024 with two frontrunner candidates nearing or exceeding the age of 80.

If re-elected in November, President Joe Biden would remain in the White House until he is 86. Former President Donald Trump would be 82 at the end of his second term.

Both men have a history of speaking blunders. In a speech this week, Biden referenced dead European leaders and confused the presidents of Mexico and Egypt. And Trump stumbled in a January speech when he mixed up Republican presidential candidate Nikki Haley and former House Speaker Nancy Pelosi.

An NBC News poll in January found that 76% of registered voters say they have major or moderate concerns about Biden’s mental and physical fitness for a second term. About 48% say they have major or moderate concerns about Trump’s mental and physical fitness for a second term.

But what does science tell us about aging and what typical cognition looks like at 80?

How we change as we age

A decline in cognitive abilities is a normal part of healthy aging, said Dr. Emily Rogalski, Rosalind Franklin Professor of Neurology at the University of Chicago. Overall, cognition peaks in our 30s and gradually declines over time.

Common changes in thinking as people age include slower word and name recall, difficulty with multitasking and mild decreases in attention span, according to the UCSF Memory and Aging Center. These skills are part of what scientists call fluid abilities, which decline steadily throughout our lifetimes.

“Fluid abilities are things like processing speed, attention, working memory. This stuff requires cognitive efficiency,” said Dr. Molly Mather, an assistant professor of psychiatry and behavioral sciences at Northwestern University’s Feinberg School of Medicine. “It’s thought that general wear and tear happens as we get older and chips away at cognitive efficiency.”

Natural changes happen in the brain as someone ages. Certain parts that are important to learning and other complex mental activities shrink, connectivity between neurons may become less effective, blood flow may decrease, and inflammation may increase, according to the National Institute on Aging.

“Mixing up names or having difficulty retrieving names, especially if the names are similar in their structure or if you’re linking two people together in your mind, is not necessarily unusual as we get older,” said Dr. Angela Roberts, an assistant professor of communication sciences and computer science at Western University who researches aging and speech signatures that detect cognitive decline.

Although these “tip of the tongue” experiences can be frustrating, they do not necessarily indicate a broader problem with cognition or memory on their own if they happen occasionally, Roberts said.

Even from day to day, our thinking abilities can change drastically, and they’re influenced by factors other than age: Illness, stress, distraction and lack of sleep are all reasons why our thinking abilities might be worse one day and better the next, Roberts added.

A diagnosis of mild cognitive impairment is made clinically when cognitive difficulties become frequent and fall outside what is considered normal aging. If these difficulties become so pronounced that they affect everyday abilities like getting dressed or going to the bathroom, then a clinical diagnosis of dementia can be made, according to the UCSF Memory and Aging Center. There are many causes of dementia, but Alzheimer’s disease is the most common.

In contrast to “fluid abilities,” certain “crystallized abilities” improve with age. This comprises knowledge that comes from learning and experiences, such as vocabulary and knowledge of how to do things, Roberts said.

“There’s not a whole lot of good evidence that there’s anything special about age 80 that leads to a drop-off” in cognitive abilities, Mather said.

How cognition is tested

Assessing cognition can be difficult, even for doctors.

They can employ a few different methods to determine whether someone has cognitive problems that fall outside the realm of normal aging. Ideally, they already have a clinical relationship with their patient, so they can assess any unusual changes or ask close relatives or friends whether they have noticed changes.

They order brain imaging and other medical tests, such as blood work, to rule out other factors that could lead to worsening cognition, such as infections or vitamin deficiencies. And they use cognitive tests, such as the Mini Mental Status Exam (MMSE) or Montreal Cognitive Assessment (MOCA), to assess performance in different cognitive areas.

The 11-question MMSE asks patients to recall the date and where they are, and they get three words to learn and recall after a few minutes. Their attention is assessed by asking them to spell “world” backward. Additional tasks test language skills, including following commands, repeating words, reading and writing.

The MOCA exam is slightly more complex and tests additional cognitive domains such as abstraction, the process of generalizing from specific examples.

“We’re not able to [assess cognition] just by observing someone speaking in public. That would require a very thorough investigation,” Mather said.

Neither Biden nor Trump has released recent medical results that would offer more information about their cognitive functioning. Under federal health care laws, they are not obligated to disclose personal medical information.

Different aging trajectories

There is vast variation in how people age, experts said.

“Chronological age does not necessarily reflect biological age,” said Dr. Nir Barzilai, director of the Institute for Aging Research at the Albert Einstein College of Medicine and scientific director of the American Federation for Aging Research.

Although population-level data associates aging with cognitive decline, the actual manifestation of aging is very diverse on an individual level, Rogalski said.

“Several decades ago, we used to think that there was really only one trajectory for aging,” she said. “We’ve learned that there are different trajectories of aging: There are pathologic trajectories of aging associated with disease, then there’s normal aging, and there are people who seem to be defying that average trajectory.”

Rogalski leads a research study that collects data on superagers, people in their 80s who have brains as sharp as those 30 years younger.

Researchers have been studying superagers to try to understand genetic and environmental protective factors that could help stave off aging.

They have found on brain scans that superagers have more gray matter volume than typical older adults in areas of the brain responsible for cognitive functioning and memory. They also on average have bigger, healthier cells in the entorhinal cortex, one of the first areas of the brain affected by Alzheimer’s disease.

In terms of lifestyle, superagers tend to report strong social relationships, live active lifestyles and continue to challenge themselves.

Publicly available medical data is not enough to conclude whether Biden – or Trump in a few years – would qualify as a superager, but Barzilai says they might both have a genetic advantage.

“Both Biden and Trump had parents that lived over 90. When it comes to exceptional longevity, there is a genetic component,” he said. “It means to me that their aging is a little bit slower than people who don’t have longevity in their family.”

Assumptions about age

“It is valid for voters to be concerned about people who have large amounts of power having intact cognitive functioning. As people age, probabilistically, the risk for certain types of decline do increase,” Mather said. “But there is really such variability as people age. I think it’s unfair in many ways to assume the worst.”

A special counsel report on Biden’s handling of classified documents, released Thursday, mentioned apparent memory lapses, which Biden and his lawyer later rejected as inappropriate and incorrect. Roberts described the report’s claims as “very troubling” and not rooted in science.

“It’s not the comments I have concern with; it’s the attributing it to age and what that does from an ageist perspective in society,” she said.

Get CNN Health's weekly newsletter

She also said that trouble with word recall is not automatically indicative of memory problems.

“We have a special counsel describing this as a memory issue, and it may or may not be a memory issue. It may be that, in that moment when the question was asked, the individual just had difficulty retrieving the word or didn’t retrieve it fast enough,” Roberts said. “Whether or not it’s a memory issue is really a clinical judgment.”

Society has spent a lot of time shifting how we talk about one another from a racial, cultural or gender perspective, Roberts said, but ageism remains very much codified.

“Ageism is not just what people do to each other. Ageism is also a mindset that you carry within yourself,” she said. “It actually impacts your health negatively.”