Early signs of Alzheimer's disease may be hidden in the way a person speaks, but it's not yet clear which details of our diction are most critical for diagnosis.
A study from 2023 suggests that as we age, how we say something may matter more than what we say. Researchers at the University of Toronto think the pace of everyday speech may be a better indicator of cognitive decline than difficulty finding a word.
"Our results indicate that changes in general talking speed may reflect changes in the brain," said cognitive neuroscientist Jed Meltzer when the research was published.
"This suggests that talking speed should be tested as part of standard cognitive assessments to help clinicians detect cognitive decline faster and help older adults support their brain health as they age."
Watch the video below for a summary of the study:
Lethologica, also known as the 'tip of the tongue' phenomenon, is experienced by young and old alike. But as we grow older, finding the names for things can become more challenging, especially after age 60.
To explore why that is, researchers asked 125 healthy adults, aged 18 to 90, to describe a scene in detail.
Next, the participants were shown pictures of everyday objects while listening to audio that was designed to confirm or confuse them.
For instance, if participants were shown a picture of a broom, the audio might say 'groom', which helps them recall the word through rhyme. But on the flip side, the audio might also offer a related word like 'mop', which can momentarily lead the brain astray.
The faster a person's natural speech in the first task, the more quickly they came up with answers in the second task.
The findings align with the 'processing speed theory', which argues that a general slowdown in cognitive processing lies at the very center of cognitive decline, not a slowdown in memory centers specifically.
"It is clear that older adults are significantly slower than younger adults in completing various cognitive tasks, including word-production tasks such as picture naming, answering questions, or reading written words," explained a team led by University of Toronto psychologist Hsi T. Wei.
"In natural speech, older adults also tend to produce more dysfluencies such as unfilled and filled pauses (e.g., "uh" and "um") in between speech and have a generally slower speech rate."
In a 2024 piece for The Conversation, dementia researcher Claire Lancaster said that the study from Toronto "has opened exciting doors… showing that it's not just what we say but how fast we say it that can reveal cognitive changes."
Recently, some AI algorithms have used speech patterns to predict an Alzheimer's diagnosis with an accuracy of 78.5 percent.
Other studies have found that patients with more signs of amyloid plaque in their brains are 1.2 times more likely to show speech-related problems.
Amyloid plaques are a hallmark of Alzheimer's disease, as are tau tangles.
In 2024, researchers at Stanford University led a study that found longer pauses and slower speech rates were associated with higher levels of tangled tau proteins.
Neuroimaging records of 237 cognitively unimpaired adults suggest that those with greater tau burdens tended to have a slower speech rate, longer pauses between speech, and more pauses overall.
Interestingly, participants with greater evidence of tau in their brains did not have greater difficulty producing the correct answer on memory recall tests.
Perhaps participants dealing with early memory issues are still finding the right answer; they are just taking longer to get there, leading to slower speech with more pauses.
If that's true, then speech patterns during memory recall tests could provide whole new intel on a person's neurological state, not captured by traditional tests.
"This suggests that speech changes reflect development of Alzheimer's disease pathology even in the absence of overt cognitive impairment," the authors of the 2023 study conclude.
"It may be especially fruitful to examine speech during delayed recall of a story memory task," the team writes.
Longer-term studies are now needed to follow up with participants who perform more slowly on memory recall tests, to see if they really do go on to develop dementia or cognitive issues down the road.
After all, just because someone shows signs of having elevated tau tangles or amyloid plaques in their brain, doesn't mean they are doomed to develop Alzheimer's.
Related: Blood Test 'Clock' Can Predict Alzheimer's Symptoms Before They Emerge
While there is still work to be done, scientists are getting closer to decoding the nuances of human speech to figure out what our words are saying about our brains.
The 2023 study was published in Aging, Neuropsychology, and Cognition.
An earlier version of this article was published in July 2025.