A lack of emotion or interest during older age could signal a decrease in brain volume—and possibly be an early sign of dementia.

In a new study, published April 16 in the journal Neurology, researchers found that older people with apathy had smaller brain volumes than those without. The study involved 4,354 participants without dementia, with an average age of 76.

“Just as signs of memory loss may signal brain changes related to brain disease, apathy may indicate underlying changes,” said study author Lenore J. Launer, a neuroepidemiologist with the National Institute on Aging at the National Institutes of Health, in a press release. “Apathy symptoms are common in older people without dementia. And the fact that participants in our study had apathy without depression should turn our attention to how apathy alone could indicate brain disease.”

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Researchers used brain volume, measured by an MRI scan, as an indication of advanced brain aging. While brain volume normally decreases as one ages, a larger loss can indicate the presence of certain types of dementia, such as Alzheimer’s disease.

In addition to measuring brain volume, researchers asked the participants several questions to determine whether they showed signs of either apathy or depression. Symptoms of apathy include lack of interest or emotion, giving up favorite activities, preferring to stay home, and decreased energy.

Compared with people who didn’t have apathy, those who reported two or more symptoms of apathy had 1.4 percent smaller volume of gray matter—the area of the brain where learning occurs and memories are stored. In addition, their white matter—which connects different areas of the brain—was 1.6 percent smaller.

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“Apathy is something that is well known to result after things like stroke or brain injuries, but in the context of dementia, the interest has been more recent,” says Dr. Joe Verghese, a neurologist at Montefiore Medical Center, who was not associated with this study. “One of the reasons is that, as the paper points out, people often mix up depression and apathy because some of the symptoms overlap.”

This study provides support for the independence of apathy and depression. When the researchers excluded people with depression, the results remained strong. So symptoms of apathy may be signaling changes in the brain that are missed when doctors look only for depression.

Although more-detailed questionnaires are available for diagnosing apathy, the researchers used three questions from a diagnostic tool for depression. This provided them with a quick snapshot of a person’s level of apathy.

“Nonetheless,” says Verghese, “the symptoms they picked are ones that people would generally agree are more apathy than depression.”

This study showed that areas of the brain affected in people with apathy were similar to the parts of the brain changed by dementia.

“What they find,” says Verghese, “is that many of the areas where there’s shrinkage of brain volume are the same areas that you might expect to see in early Alzheimer’s disease—the hippocampus, the seat of memory in the brain, was relatively shrunken in people with apathy symptoms compared to those who did not have apathy symptoms.”

However, the changes were not just typical of Alzheimer’s disease, but also included areas affected in many types of dementia.

Even though brain changes in people with apathy resembled those that occur in dementia patients, the study wasn’t set up to look at whether everyone with apathy will eventually develop dementia.

“This study doesn’t really say that apathy is a feature of early dementia,” says Verghese. “It just shows a cross-sectional association. It just might be there’s some common underlying processes that result in apathy at early stages and then cognitive impairment.”

More research is needed, but if there is a common cause of apathy and dementia, doctors might be able to use lack of interest or energy as early warning signs to target people with an increased risk of cognitive impairment.

“So potentially you could intervene by getting these older individuals to exercise, to have a healthier lifestyle, and by improving their diet,” says Verghese. “You’d think that’s all common sense and good recommendations, and things that every one should practice, but the reality is that most people don’t. In some ways it’s better to identify who’s at higher risk and target these interventions to those people than to just give broad recommendations.”