Older people who have "mental lapses流逝，失效," or times when their thinking seems disorganized or illogical or when they stare into space, may be more likely to have Alzheimer's disease than people who do not have these lapses, according to a study published in the January 19, 2010, print issue of Neurology®, the medical journal of the American Academy of Neurology. These mental lapses, also called cognitive认知的，认识的 fluctuations起伏，变动, are common in a type of dementia痴呆 called dementia with Lewy bodies路易氏体失忆症, but researchers previously did not know how frequently they occurred in people with Alzheimer's disease and, equally important, what effect fluctuations might have on their thinking abilities or assessment scores.

The study involved 511 people with an average age of 78. Researchers interviewed the participant and a family member, evaluated the participants for dementia and tested their memory and thinking skills.

People with three or four of the following symptoms met the criteria标准，条件 for having mental lapses:
Feeling drowsy昏昏欲睡的，沉寂的 or lethargic昏睡的，冷漠的 all the time or several times per day despite getting enough sleep the night before
Sleeping two or more hours before 7 p.m.
Having times when the person's flow of ideas seems disorganized, unclear, or not logical
Staring into space for long periods

A total of 12 percent of the people with dementia in the study had mental lapses. Of 216 people with very mild or mild dementia, 25 had mental lapses. Of the 295 people with no dementia, only two had mental lapses.

Those with mental lapses were 4.6 times more likely to have dementia than those without mental lapses. People with mental lapses also tended to have more severe Alzheimer's symptoms and perform worse on tests of memory and thinking skills than people who did not have lapses.

"When older people are evaluated for problems with their thinking and memory, doctors should consider also assessing them for these mental lapses," said senior study author James E. Galvin, MD, MPH, of Washington University School of Medicine in St. Louis, who is a member of the American Academy of Neurology.