Picture a high school math teacher on a free period. She’s been forgetting things lately, so she slips out to get an MRI. Later that day, the doctor calls with “bad news”: the scan shows amyloid plaques, the classic marker doctors look for when they diagnose Alzheimer’s.
She’s shaken, but she still has a class to teach. She walks in, works through every formula on the board, and answers every question the kids throw at her. By every measure that actually matters, she’s still fully herself.
Now flip it. Same teacher, same free period, same MRI. This time the doctor calls with “good news”: a clean scan, no plaques, no tangles, no dementia diagnosis. Relieved, she heads to class. A student asks her to walk through a formula, and she stares back blankly. “What’s a formula?” The kids remind her gently that she’s their teacher. She can’t answer a single question for the rest of the period.
Who actually has dementia here? Not the version the paperwork says.
This is the question at the heart of a new book on dementia economics by Robert J. Brent, Professor of Economics Emeritus at Fordham University: what if the entire medical field has been measuring the wrong thing?
The scan isn’t the disease
For decades, a dementia diagnosis has hinged on brain pathology plaques on the outside of neurons, tangled tau fibers on the inside, lesions from restricted blood flow. If the scan shows it, you’re labeled. If it doesn’t, you’re cleared. Case closed.
Except it isn’t. Plaques and tangles can sit quietly in someone’s brain for years, sometimes decades, before any symptoms show up, and some people never develop symptoms at all. Meanwhile, plenty of people struggle to function day-to-day without the “textbook” scan to explain why.
Brent’s book makes the case bluntly: brain pathology is neither necessary nor sufficient for a dementia diagnosis. It’s not a reliable yes/no test, because the actual disease isn’t happening on a scan; it’s happening in a life. Dementia, at its core, is the loss of the ability to carry out ordinary daily activities: managing money, following a conversation, remembering an appointment, cooking dinner safely. The image on the screen is a clue. It was never supposed to be the verdict.
So how do you actually measure it?
If a scan can’t reliably tell you who has dementia, something else has to. That something is the Clinical Dementia Rating scale, or CDR, a tool used worldwide that scores six areas of daily life: memory, orientation, judgment and problem-solving, community involvement, hobbies and home life, and personal care. Each area gets rated from “none” to “severe,” and the totals combine into a single number that reflects how much dementia is actually interfering with someone’s world, not what a picture of their brain looks like.
It sounds almost too simple. But that’s the point. A functional measure asks the only question that actually matters to a patient and their family: can this person still live their life? A pathology measure asks a different question entirely, and for years the two have been treated as if they’re interchangeable. They aren’t.
Why this isn’t just semantics
This distinction isn’t an academic quibble; it changes what counts as progress. If dementia is defined purely by brain pathology, then the only “real” treatment is one that erases plaques and tangles, a cure that, frankly, doesn’t exist yet. That leads to a bleak and, it turns out, false conclusion: that nothing meaningful can be done for people living with dementia today.
But once you define dementia by function by whether someone can still manage their own life the picture changes completely. Suddenly, things that have nothing to do with brain plaques start to matter enormously: whether someone can hear well enough to stay socially connected, whether they can see well enough to read a bill, whether they have access to decent healthcare, whether they’re stuck in an under-resourced nursing home. None of these fix a single tangle in the brain. All of them can measurably reduce the symptoms of the disease.
That reframe is the foundation for everything that follows in Brent’s research: a rigorous, data-driven look at which interventions for people with dementia genuinely help, which ones look helpful but aren’t, and which ones, surprisingly, do more harm than good. It starts with getting the definition right. Everything else follows from there.
