Laura Barron-Lopez:

Following verbal stumbles on the campaign trail, polls have consistently shown voters are concerned about the mental fitness of both leading presidential contenders.

In a recent poll, an NBC News survey found that 76 percent of voters had major concerns about President Biden's physical and mental health. Meanwhile, 48 percent of voters had the same major concerns about former President Trump.

To help us understand more about what happens to our brains as we age and for some perspective on these lapses from both men, I'm joined by two experts in memory and cognition.

Dr. Dan Blazer is a professor emeritus of psychiatry and behavioral studies at Duke University. Charan Ranganath is a professor of psychology and neuroscience at the University of California, Davis. He's also the author of a new book releasing next week called "Why We Remember: Unlocking Memory's Power to Hold on to What Matters."

Thank you both so much for joining us.

Professor Ranganath, I want to start with you.

As we know, President Biden is 81 years old. Former President Donald Trump is 77. Help us sort through what we know about what happens to cognition, brain function, and memory as we age, particularly once we get over the age of 75.

Charan Ranganath, University of California, Davis: Yes, there's actually — it's fascinating because the work has really been evolving.

But the basic story is, on average, memory goes down with age. I don't think that's a surprise for many viewers. But if you actually look at different individuals, it really varies. Some people, if you track them over time, they can go into their old age and they're super agers and they're fine, and other people do have a decline over time.

And so you really need to ask yourself what's going on with an individual person.

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