Some stints of memory lapse in older adults may be due to silent strokes, tiny spots of dead cells inside the brain that bring on undetectable stroke symptoms, according to a study published Wednesday in the journal Neurology.
Nearly a quarter of older adults have experienced a silent stroke, according to the study. Silent stroke is one type of ischemic stroke, which is characterized by a blood clot in a vessel that supplies blood to the brain. Ischemic strokes account for 87 % of all stroke cases, according to the American Stroke Association.
While symptoms may not be outwardly detectable, research suggests the condition could cause damage to parts of the brain and long-term memory loss.
"Typically people think of a lot of memory decline as an early indicator of Alzheimer-like changes," said Adam Brickman, assistant professor of neuropsychology at Columbia University's Taub Institute for Research on Alzheimer's Disease and the Aging, and co-author of the study.
Brickman and his colleagues looked at 658 participants with an average age of 79 who had no history of dementia. They were administered a test that gauged their memory, language skills and thinking abilities. Researchers also measured the size of the participants' hippocampus, crucial to the regulation of memory and emotion, and they also administered an MRI brain scan.
A smaller hippocampus has been previously associated with cognitive decline.
The brain scans showed that 174 of the participants had experienced silent strokes, and those participants did not perform as well on their memory tests, independent of their hippocampus size.
"We showed that above and beyond size, stroke also contributed to the memory loss and could be a potential indicator for Alzheimer's development," said Brickman.
Study findings suggest that Alzheimer symptoms may be due both to the size changes in the hippocampus and the vascular changes in the brain, Brickman said.
Risk factors for silent stroke include high blood pressure, obesity and high cholesterol.
According to Dr. Shazam Hussain, director of the stroke program at Cleveland Clinic, many people are suffering strokes at earlier ages in adulthood.
"Over time these strokes accumulate damage," said Hussain. "Unfortunately, stroke is a problem that's not reversible."
Brickman said it's unrealistic to use MRIs as a screening method to check for silent strokes in older adults, but it would be beneficial to monitor those who are at high risk for the condition.
"By controlling vascular symptoms, we can prevent stroke, which may be a viable way of preventing cognitive changes of aging," he said.
While the study suggests some connection between silent strokes and memory decline, it's unclear whether silent strokes are a potential marker for later development of Alzheimer's disease. Researchers are now following participants over a longer period of time to see whether some will develop Alzheimer's.
"I think what's emerging is a story in which vascular disease contributes to the symptoms of Alzheimer's disease," said Brickman.