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Can a simple brain scan determine how old your brain is? Your brain is as old as you are in chronological years, of course, but what about in wear-and-tear years? It would be an exciting prospect if it were possible. Countless people might be eager to "check their brain age" to find out if it's aging prematurely. They might be especially interested if they have a family history of , for example, or if they carry the apoE4 genotype, which raises the risk of .

The authors of a recent study claim that it's possible to do exactly that, using existing SPECT technology (a type of brain scan that uses a radioactive tracer and measures blood flow throughout the brain). The researchers analyzed data from more than 60,000 brain scans—a huge sample size—and found that as we age, there is less blood flow in specific parts of the brain like the anterior cingulate, parts of the prefrontal cortex, and other regions (as other studies have found). Less blood flow is consistent with less brain activity in these areas.

They then used these correlations between blood flow and age to assess whether certain conditions like and are consistent with increased age in the brain. Their results suggested that some of the conditions they looked at did indeed show patterns of blood flow in the brain that were consistent with increased brain age. For example, the brains of individuals with looked 4 years older than their actual age, and users' brains looked nearly 3 years older.

At the end of the paper the authors conclude:

"This has implications for using a simple brain SPECT scan to predict brain age and, by comparing it to chronological age, determine if a patient’s brain is undergoing accelerated aging. Such information is actionable for patients to further enroll them earlier in programs for prevention and of .”

These conclusions suggest that brain scans may be offered to consumers for the purpose of determining their "brain estimated age." The big question for those considering getting such a scan is whether it actually provides useful information related to brain aging.

There are multiple reasons to think very carefully before paying for one of these scans; I recently spoke with a reporter from Healthline about this article, and his write-up does a very good job of summarizing the study and some of the controversy related to it. The following points offer additional context in which to interpret these findings.

Blood Flow Varies Based on All Kinds of Conditions Besides Age

One of the most basic concepts in research is that the measures have to be valid—that is, the researchers must show that they're indeed measuring what they say they're measuring. In this study that would mean showing that differences in blood flow to the brain necessarily tell us anything about a person's brain age.

Instead, the researchers found that blood flow to certain areas of the brain can vary as a function of all kinds of condition that have little to nothing to do with age—like cannabis use, ADHD, and . They did not show that we should take decreases in blood flow as necessarily indicating aging in the brain. Again, they showed the opposite—that all kinds of things can decrease blood flow to the brain, and these other conditions may not have anything to do with aging.

By analogy, we could look at hours of sleep and see if it changes over the lifespan. In fact it does—like blood flow to the brain, amount of sleep decreases from when we’re babies through , , and adulthood. There are also conditions like that are associated with less sleep. Does that mean that being depressed and too little means you’ve prematurely aged? Not necessarily. It might just mean that lots of things can affect our sleep. Aging is one of them, as are depression, , and .

Dementia Was Associated with a "Younger Brain"

If the researcher's technique were a good measure of brain age, dementia is the one condition they examined in which we would most expect to see an increase in estimated brain age. But that’s not what they found—and in fact they found the opposite. This finding is probably the most revealing as to the usefulness of this study.

In their sample of more than 1600 people with dementia, including Alzheimer’s Disease, their brains looked four years younger than their actual age. The average age in the people with dementia was 54 years, but they had the brains of 50-year-olds. Should we conclude that having dementia is good for our brains, shedding an average of four years from our brain age? Certainly not. Thus it is hard to make the argument that data from this study can be used to estimate brain age, particularly in the context of possible dementia.

Brain Scans Are Not Useful for Diagnosis

As I and others have written, brain scans can be very useful in certain contexts. For example, they can reveal what parts of the brain might be involved in a specific diagnosis like schizophrenia. In a typical study, the average size or activity in a certain brain region is different when comparing a group with schizophrenia to a control group without schizophrenia.

However, that does not mean we can get meaningful information about a psychiatric diagnosis by looking at a single person's brain, for many reasons. One of the main reasons is that there's a lot of overlap between the brain measures of people with and without a specific diagnosis. It's like height and —the average man is taller than the average woman, but knowing a person's height isn't a very good predictor of whether the person is a man or a woman. Someone 5'9", for example, could be an average-sized man or a tall woman.

In a similar way, it's unlikely that we can derive interpretable information about a person's "brain age" from looking at their SPECT scan results. Group-level analyses like those done in this recent study don't allow us to make precise determinations for individuals. (For more on these issues, see this previous post: Using Brain Scans to Diagnose Mental Disorders.)

The Psychiatric Community Has Come Out Against This Use of SPECT Imaging

The American Psychiatric Association published a consensus statement on the use of brain imaging in psychiatry. Based on existing research, they concluded that there is inadequate scientific basis for the use of SPECT and other types of brain imaging in psychiatric diagnosis. The committee concluded:

"The hope is that the continued growth of knowledge will eventually have practical applications in guiding psychological and pharmacologic treatments, but the general consensus is that SPECT and other kinds of neuroimaging are not yet recommended for diagnostic evaluation and treatment monitoring in individual patients." [emphasis added]

They go on to state that the only valid use of brain imaging like SPECT for diagnosis is limited to "ruling out the presence of known neurological illnesses." Specifically, SPECT analysis of blood flow in the brain may be useful for "the diagnosis of cerebral , certain kinds of dementia, strokes, seizure disorders, and brain tumors, in which characteristic patterns of perfusion abnormalities are detectible." Additionally, SPECT may be used to assess "cerebrovascular diseases, dementias, epilepsy, , malignant brain tumors, movement disorders, and Gilles de la ." Note that these conditions are neurological, not psychiatric, meaning they have well-established markers in the brain.

The Bottom Line

Unfortunately the hope of determining brain age based on a SPECT scan appears to be premature. A final consideration for someone considering getting one of these scans is that SPECT exposes the body and the brain to radioactive substances, which is a concern for anyone and particularly for children and adolescents.

However, don't be surprised if in the near future you see certain companies offering brain scans to determine your brain age. After all, multiple clinics are already offering scans for psychiatric diagnosis, despite the widespread consensus in the scientific community that such scans have very little to offer.

For more on these issues: