People with more developed language skills as young adults may be better able to stay sharp well into old age, even if they develop Alzheimer's-like abnormalities in their brains, new research in the journal Neurology shows.
The findings, which come from autopsies of 38 nuns' brains, also suggest that this may be in part because their remaining brain cells become extra large to compensate, study co-author Dr. Juan C. Troncoso of Johns Hopkins University in Baltimore and his colleagues say.
Scientists have long wondered why some people with plaques and tangles in their brains characteristic of Alzheimer's have intact mental faculties their whole lives. Troncoso and his team have dubbed this condition asymptomatic Alzheimer's disease.
In two previous studies of deceased Baltimore Longitudinal Study of Aging participants, most of whom were men, the researchers found that individuals with asymptomatic Alzheimer's had larger cells in many areas of the brain, as well as bigger cell structures called nuclei and nucleoli, than people with mild cognitive impairment.
To confirm the findings in a totally different population, Troncoso and his team examined the brains of 38 Catholic sisters. Ten of the women had asymptomatic Alzheimer's when they died, five had mild cognitive impairment, and 10 had Alzheimer's, while another 13 women had no cognitive problems and no brain lesions and served as a control group.
The researchers found that the women with asymptomatic Alzheimer's did indeed have larger neurons, nuclei, and nucleoli than the women with mild cognitive impairment, while the cells in the brains of women with Alzheimer's had shrunk compared to the cells in the control women's brains.
The researchers were able to look at essays that 14 of the women had written in their late teens or early 20s, when they entered the convent. They analyzed their "idea density," or the average number of ideas expressed for every ten words, as well as their grammatical complexity.
The early writings of the eight women in the group who had no cognitive deficits when they died were significantly denser in ideas than the essays written by the six who had either Alzheimer's or mild cognitive impairment. But there was no difference between the two groups in the degree of grammatical complexity.
The findings show that people's brains can adapt and change — a phenomenon known as plasticity — well into an individual's 80s and 90s, Troncoso and his colleagues say. It's possible that neurons get bigger to compensate for damage done by the toxic proteins produced in Alzheimer's disease, they add, while the cell nuclei and nucleoli may be enlarged because they are making more DNA and RNA to repair this damage.
Even though the study was small, "it remains a fascinating observation that an intellectual ability measured in the early 20s can predict the likelihood of remaining cognitively normal 5 or 6 decades later, even in the presence of substantial AD pathology," Troncoso and his team write.
"Perhaps mental abilities at age 20 are indicative of a brain that will be better able to cope with diseases later in life," the researcher says in an American Academy of Neurology press release accompanying the study.
SOURCE: Neurology, July 9, 2009.