The study was carried out on nuns
People with superior language skills early in life may be less likely to develop Alzheimer's disease decades later, research suggests.
A team from Johns Hopkins University studied the brains of 38 Catholic nuns after death.
They found those with good language skills early in life were less likely to have memory problems - even if their brains showed signs of dementia damage.
The study appears online in the journal Neurology.
Dementia is linked to the formation of protein plaques and nerve cell tangles in the brain.
But scientists remain puzzled about why these signs of damage produce dementia symptoms in some people, but not others.
The researchers focused on nuns who were part of an ongoing clinical study.
They divided the women into those with memory problems and signs of dementia damage in the brain, and those whose memory was unaffected regardless of whether or not they showed signs of dementia damage.
And they also analysed essays that 14 of the women wrote as they entered the convent in their late teens or early 20s, assessing them for complexity of language and grammar.
The study showed that language scores were 20% higher in women without memory problems than those with signs of a malfunctioning memory.
The grammar score did not show any difference between the two groups.
Lead researcher Dr Juan Troncoso said: "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."
Brain cell growth
The study also found that brain cells were largest in women who retained a normal memory despite showing signs of disease in their brains.
The researchers said this suggested that a growth in brain cells might be part of the body's early response to the onset of dementia, and this might help to prevent memory impairment.
Dr Troncoso said: "Perhaps mental abilities at age 20 are indicative of a brain that will be better able to cope with diseases later in life."
Dr Susanne Sorensen, head of research at the Alzheimer's Society, said: "It is interesting that the nuns in the study with better language skills in their youth avoided memory problems in later life.
"However, the research is in a very small, select group and it would be difficult to say at this stage if language skills could really predict dementia."
Rebecca Wood, chief executive of the Alzheimer's Research Trust, said: "One possible implication of this study is that an intellectual ability test in the early 20s may predict the likelihood of remaining cognitively normal five or six decades later.
"However, prominent exceptions exist, including authors like Terry Pratchett and Iris Murdoch, who developed dementia despite their linguistic brilliance."