While most of my work focuses on language processing in healthy aging, I have recently started dabbling in the field of language (and cognition in general) in neurodegenerative diseases, such as Alzheimer’s Disease and Parkinson’s Disease. We just got word that the first paper from a really neat project on Lexicon and Grammar in native speakers of Farsi was accepted for publication in the journal Neuropsychology. In this paper, we link right-side hypokinesia (which reflects the degeneration of the left basal-ganglia, which causes the motor deficits associated with Parkinson’s Disease) to specific difficulties with regular (but not irregular) verb morphology. Interestingly, this effect was much stronger for men than for women (who might be able to compensate for deficits with regular inflection with the help of their (usually) better memory). Congrats to my co-authors Karim Johari (University of South Carolina & Tabriz University of Medical Sciences, Tehran), Matt Walenski (Northwestern), Farzad Ashrafi (Shahid Beheshti University of Medical Sciences, Tehran), and Michael Ullman (Georgetown).
Here is the abstract:
Objective: Parkinson’s disease (PD), which involves the degeneration of dopaminergic basal-ganglia neurons, appears to affect language. We investigated which aspects of language are impaired in PD, and what moderates these impairments. Our predictions were based on the declarative/procedural model of language, which links grammar, including in regular inflection, to procedural memory and left-lateralized basal-ganglia dopaminergic circuits, but links lexical memory, including irregulars, to declarative memory. Since females tend to show declarative memory advantages as compared to males, the model predicts that females rely more on this system for regulars, which can be stored as chunks.
Methods: We probed regular/irregular Farsi past-tense production in 40 Farsi-speaking patients with moderate-to-severe non-demented PD (half female) and 40 normal controls (half female).
Results: Consistent with our predictions, we found that male but not female PD patients showed greater deficits at regular than irregular past-tense production. The females’ impairment was mildest for regulars, likely from compensatory storage, as revealed by regular past-tense frequency effects only in females. Right-side hypokinesia (linked to left basal-ganglia degeneration), correlated negatively with accuracy of regulars but not irregulars. Similarly, the levodopa equivalent dose of patients’ last medication correlated only with regulars.
Conclusions: The results suggest that language is impaired in PD, but the impairments are moderated by multiple factors, including the type of linguistic knowledge, the degree of left basal-ganglia degeneration, dopamine, and sex. The findings underscore the impact of sex on the neurocognition of language, and the roles of left basal ganglia dopaminergic circuits in aspects of rule-governed grammar.
We were awarded a Partners in Research grant from the Dean of Research at Georgetown University Medical Center: "How does aging affect our ability to remember words?". We live in a rapidly aging society, so the impact of age-related problems is increasing dramatically. Word finding and word learning (e.g., the names of medications to be taken) appear to be the greatest language problems in older adults. This study is designed to reveal just what specific aspects of word use and word learning decline during aging and why such declines take place. The highly interdisciplinary project uses a rigorous behavioral and brain experimental approach, and tests the innovative novel hypothesis that the word problems experienced by older people can be at least partly explained by underlying declines in declarative memory, a general-purpose learning and memory system rooted in the hippocampus. The findings should advance our understanding of word difficulties in aging, and may lead to therapeutic approaches for these problems in healthy aging as well as in age-related disorders such as Alzheimer’s disease. I am one of the co-investigator on this project, with Michael Ullman as the principal investigator, and Peter Turkeltaub and Gheorghe Luta at Georgetown as fellow co-investigators. Collaborators David Balota (Washington University in St. Louis), Marcus Meinzer (University of Queensland, Brisbane), Loraine Obler (City University of New York), and Michael Rugg (UT Dallas) will also contribute to the project.