A team from Johns Hopkins University studied the brains of 38 Catholic nuns after death and found that those with good language skills early in life were less likely to have memory problems, even if their brains showed signs of dementia damage.
"A puzzling feature of Alzheimer's disease is how it affects people differently," said study author Juan C. Troncoso, MD, with Johns Hopkins University in Baltimore.
"One person who has severe plaques and tangles, the telling signs of Alzheimer's disease in their brains, may show no symptoms affecting their memory. Another person with those same types of plaques and tangles in the same areas of the brain might end up with a full-blown case of Alzheimer's disease. We looked at how language ability might affect the onset of symptoms," Troncoso added.
In the study, scientists determined two groups: women with memory problems and Alzheimer's disease hallmarks in the brain and women with normal memory with or without signs of Alzheimer's disease in the brain.
The researchers analyzed essays that 14 participants wrote as they entered the convent in their late teens or early 20's.
They studied the average number of ideas expressed for every 10 words. The analysis also measured how complex the grammar was in each essay.
The study found that language scores were 20 percent higher in the women without memory problems compared to those with memory problems. The grammar score, however, did not show any difference between the two groups.
"Despite the small number of participants in this portion of the study, the finding is a fascinating one.
Our results show that an intellectual ability test in the early 20s may predict the likelihood of remaining cognitively normal five or six decades later, even in the presence of a large amount of Alzheimer's disease pathology," Troncoso said.
The study has been published in the July 9, 2009, online issue of Neurology.