"Silent" strokes, which are strokes that don't result in any noticeable symptoms but cause brain damage, are common in people over 60, and especially in those with high blood pressure, according to a study published in the July 28, 2009, print issue of Neurology®, the medical journal of the American Academy of Neurology.

"These strokes are not truly silent, because they have been linked to memory and thinking problems and are a possible cause of a type of dementia," said study author Perminder Sachdev, MD, PhD, of the University of New South Wales in Sydney, Australia. "High blood pressure is very treatable, so this may be a strong target for preventing vascular disease."

The study involved 477 people age 60 to 64 who were followed for four years. At the beginning of the study 7.8 percent of the participants had the silent lacunar infarctions, small areas of damage to the brain seen on MRI that never caused obvious symptoms. They occur when blood flow is blocked in one of the arteries leading to areas deep within the brain, such as the putamen or the thalamus. By the end of the study, an additional 1.6 percent of the participants had developed "silent" strokes.

People with high blood pressure were 60 percent more likely to have silent strokes than those with normal blood pressure. Also, people with another type of small brain damage called white matter hyperintensities were nearly five times as likely to have silent strokes as those without the condition.

The study was supported by the National Health and Medical Research Council of Australia.