Family members remember some of the early signs of Alzheimer’s in their loved ones quite well. This type of dementia often begins with struggles in communication, lapses in memory, and confusion around everyday problem-solving.
But scientists are now uncovering evidence of another early signal — mood disorders, like depression and bipolar disorder, that begin later in life. While a link between these conditions and Alzheimer’s has long been suspected, what’s been missing is a clear understanding of how the two connect in the brain.
That’s starting to change. A research team from Japan’s National Institutes for Quantum Science and Technology (QST) recently found significant amounts of tau protein — a hallmark of Alzheimer’s — in the brains of people with late-life mood disorders (LLMDs). Their study, published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, suggests that these psychiatric symptoms might serve as a warning sign for neurodegenerative disease.
Alzheimer’s and Mood Changes
Memory loss may be the most widely known symptom of Alzheimer’s, but it’s not the only one. Depending on which parts of the brain are affected, the disease can present in other ways — especially as changes in behavior.
Friends and relatives of people with Alzheimer’s often report personality shifts, moodiness, anxiety, and even uncharacteristic aggression or depression. These symptoms point to damage in brain regions responsible for emotional regulation. While they usually show up in the middle or late stages of Alzheimer’s, researchers have long wondered: Could these mood changes also be among the earliest signs?
Read More: Annual Dementia Cases Are Anticipated to Double in the U.S. by 2060
Comparing Brain Imaging
To investigate, the QST team used brain imaging to examine 52 people diagnosed with LLMDs and compared them to 47 healthy controls. They conducted positron emission tomography (PET) scans with two types of tracers to detect abnormal protein buildup — specifically tau and amyloid beta, both tied to Alzheimer’s and other forms of dementia.
The study found tau accumulation in the brains of about 50 percent of people with LLMDs, while only 15 percent of healthy participants showed the same pattern. Additionally, close to 29 percent of the mood disorder group also had amyloid deposits, while only two percent of the control group did.
To back up these results, the researchers analyzed 208 autopsy cases and found the same trend: Individuals who had experienced late-life depression or mania were significantly more likely to have tau-related pathologies.
“Because most of the participants with LLMDs in our study had no or mild cognitive decline, these results support the evidence that neurodegenerative diseases, including Alzheimer’s and non-Alzheimer’s tau-related pathologies, can initially manifest as psychiatric symptoms,” said lead author Shin Kurose in a press statement.
One notable pattern was the location of tau deposits. Many participants showed buildup in the frontal lobes — the region tied to decision-making, personality, and emotion. Just as importantly, these deposits could be detected well before cognitive symptoms emerged. Based on the autopsy data, mood changes tended to precede memory or motor problems by an average of 7.3 years.
Early Identification, Faster Intervention
“Overall, our findings strongly suggest that tau-PET scans can detect diverse tau pathologies that underlie dementia in patients with LLMDs,” said co-author Keisuke Takahata in the news statement.
The implications could be profound. Some cases of late-life depression or bipolar disorder might actually be the earliest phase of a neurodegenerative illness — one that’s currently misdiagnosed as purely psychiatric.
If doctors can identify these conditions earlier, it opens the door to disease-modifying therapies while they can still make a difference. The study also underlines the value of the PET scan tracers as potential biomarkers, which could guide diagnosis and treatment years before traditional symptoms arise.
Read More: Alzheimer's Disease Blood Test Could Lead to Earlier, More Effective Treatment
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Alzheimer's & Dementia: The Journal of the Alzheimer's Association: Diverse tau pathologies in late-life mood disorders revealed by PET and autopsy assays
UCSF Weill Institute for Neurosciences Memory and Aging Center: Behavior & Personality Changes
Having worked as a biomedical research assistant in labs across three countries, Jenny excels at translating complex scientific concepts – ranging from medical breakthroughs and pharmacological discoveries to the latest in nutrition – into engaging, accessible content. Her interests extend to topics such as human evolution, psychology, and quirky animal stories. When she’s not immersed in a popular science book, you’ll find her catching waves or cruising around Vancouver Island on her longboard.
