Older adults with mild cognitive impairment characterized by impaired memory exhibit selective language deterioration, new research shows - a finding that could lead to earlier detection and ultimately more effective treatment of Alzheimer's disease.
Individuals with mild cognitive impairment of the amnestic type (aMCI) are more likely than those with healthy cognitive aging to go on to develop Alzheimer's. The researchers found that individuals with aMCI could appreciate the basic structure of sentences (syntax) and their meaning (semantics), but struggled with processing certain ambiguous sentences in which pronouns referred to people not named in the sentences. This deficit is independent of the memory deficit that characterizes this group.
"Previous research has looked most often at single words and vocabulary," said Barbara Lust, professor emerita in Cornell's Department of Psychology and lead author of "Disintegration at the Syntax-Semantics Interface in Prodromal Alzheimer's Disease: New Evidence From Complex Sentence Anaphora in Amnestic Mild Cognitive Impairment (aMCI)," published in the Journal of Neurolinguistics. "We looked at a more complex level of language knowledge. When we process a sentence, we have to both grasp its syntax and construct a meaning. We found a breakdown at that higher level where you're integrating form and meaning."
The paper's co-authors are Suzanne Flynn, professor of linguistics and philosophy at the Massachusetts Institute of Technology; Janet Cohen Sherman, an associate professor of psychology in the Department of Psychiatry at Massachusetts General Hospital and director of the MGH Psychology Assessment Center; and, posthumously, the scholars James Gair and Charles Henderson of Cornell.
The focus on such subtleties in language processing, in relation to aMCI and its potential transition to dementia such as Alzheimer's disease, is novel, the researchers said.
"These results are among the first to deal with complex syntax and really get at the abstract computation that's involved in processing these linguistic structures," Flynn said.
To conduct the study, the scholars ran experiments comparing the cognitive performance of individuals with aMCI to cognitively healthy individuals in separate younger and older control groups. The research involved 61 aMCI patients of Massachusetts General Hospital, with control group research conducted at Cornell and MIT.
The study pinpointed how well people process and reproduce sentences involving anaphora, or the use of one word to replace or refer to another - for example, the use of "his" in the sentence, "The electrician repaired his equipment." Ultimately, aMCI patients performed significantly worse than the control groups when producing sentences with "anaphoric coreference," the ones with ambiguity about the identity of the person referred to by a pronoun.
"It's not that aMCI patients have lost the ability to process syntax or put complex sentences together, or lost words. It's that they're showing a deficit when the mind has to figure out whether to stay in the sentence or go outside it, to figure out who we're talking about," Lust said. "When they didn't have to go outside the sentence for context, sentence production was preserved in the individuals with aMCI whom we studied."
The paper is part of an ongoing series of studies by Lust, Flynn, Sherman and their colleagues. The findings may encourage neuroscientists investigating MCI and other forms of cognitive impairment to further examine the regions of the brain that process language. The study may also help inform linguistic theory concerning various forms of anaphora.
Looking ahead, the scholars say they would like to increase the size of the studies as part of an effort to continue to define how diseases progress and how language may be a predictor of that.
"Our data is from a small population but very richly theoretically guided," Lust said. "You need hypotheses that are linguistically informed to make advances in neurolinguistics. There's so much interest in the years before Alzheimer's disease is diagnosed, to see if it can be caught and its progression stopped."
Support for the research was provided by the Cornell University Podell Award, Somashekar and Apple Corporation, Federal Formula Funds, Brad Hyman at Massachusetts General Hospital, the Cornell Bronfenbrenner Center for Translational Research, the Cornell Institute for Translational Research on Aging, the Cornell Institute for Social Science Research and the Cornell Cognitive Science Program.
Emily Groff is assistant director of communications for the College of Human Ecology.
