The National Institute on Aging and the Alzheimer's Association have made changes to the research definition of Alzheimer's disease dementia. The changes include criteria to define what Alzheimer's disease dementia is and who has it. But the changes apply only to clinical trials and research. The changes don't affect how a person is diagnosed in a health care provider's office.

Previously, Alzheimer's disease dementia was diagnosed based on symptoms such as memory loss and changes in thinking and cognition. And that's still the case when a provider makes a diagnosis.

The research definition calls for a biological definition of Alzheimer's disease dementia that can be made during life. It's determined by detecting the presence of biomarkers — a buildup of plaques and tangles in the brain. Biomarkers can be seen on imaging scans of the brain. They also can be identified in samples of cerebrospinal fluid and in the fluid part of blood.

This definition change allows researchers to better design clinical trials and include the right people to be part of the trials. As a result, researchers learn more about the disease in its earlier stages.

Here's why it's important: The classic symptoms that are used to diagnose Alzheimer's disease dementia are a complication of the changes in the brain that define the disease. These brain changes can occur long before symptoms show up. Changing the research definition may lead to earlier diagnosis, which will hopefully lead to delayed disease progression and better treatments.