Subcortical Role in Figurative Processing by Persian- speaking Alzheimer and Parkinson’s Patients

Introduction: The production of figurative expressions, particularly idioms, and proverbs, is negatively affected by damage to the left hemisphere and subcortical area of the brain. Alzheimer patients, thanks to the preservation of basal ganglia, can produce these expressions. In contrast, compared to Alzheimer’s patients, Parkinson’s patients cannot produce these expressions due to the malfunction of the basal ganglia. This study attempts to compare the linguistic and cognitive performance of Persian-speaking patients with Alzheimer’s disease, Parkinson’s disease, and healthy counterparts regarding the production and comprehension of these figurative expressions. Materials and Methods: In doing so, by selecting a sample  of participants  composed  of  10 Alzheimer’s patients, 10 Parkinson’s patients, and 10 healthy individuals matched with each other regarding age and education. Then, different tests, including Arizona battery for communication disorders of dementia, famous names, and face test, structured conversation, figurative expression completion, elicitation of response based on situational context, Northridge evaluation of idioms and proverbs in situational context, conventional and figurative expression evaluation were condcuted to analyze their performance. Results: The results of Arizona battery for communication disorders of dementia indicated that Alzheimer’s patients were in the middle stage of the disease while Parkinson’s participants were classified as non-dementia patients. Although the result of the Renown face and name recognition test demonstrated a significant difference between Alzheimer’s patients and the healthy group regarding cognition and confidence levels, the same result was not observed between healthy control and Alzheimer’s patients. Furthermore, in the test of structured conversation, the proportion of produced words by Alzheimer’s patients was more than that of Parkinson’s patients. However, the results of sentence and figurative expression completion tests corroborated the weaker performance of Alzheimer’s patients compared to their Parkinson and healthy counterparts. Furthermore, notwithstanding in the test of Elicitation of response based on Situational Context, Parkinson’s patients performed more poorly than their Alzheimer and healthy counterparts, in the tests of conventional and figurative expression evaluation, Alzheimer’s patients’ pattern of performance was different from that of other groups as they performed more weakly than Parkinson patients. Conclusion: The observed dissociation in the performance of Alzheimer as well as Parkinson’s patients in the linguistic production and comprehension tests shed light on the significant role of the subcortical area of the brain in the production of idioms and proverbs.