Comprehension of ambiguous sentences in Alzheimer's disease: A study with Brazilian older adults

Introduction: Language impairment is an early marker in Alzheimer's disease (AD), manifesting in both semantic memory and syntactic comprehension. The comprehension of lexical (LAS) and syntactic (SAS) ambiguous sentences requires the integrity of both systems and is particularly challenging for patients with probable AD. The study aimed to investigate differences in performance on ambiguous sentence comprehension between healthy older adults and patients with probable AD, and to identify which type of ambiguity posed the greatest difficulty for each group. Methods: A cross-sectional observational study with 118 participants (60 patients with probable AD and 58 healthy controls) underwent an experimental task of comprehending 12 ambiguous sentences (6 LAS and 6 SAS). Multiple linear regression models were adjusted for age, sex, and education. Results: Patients with probable AD performed significantly worse in LAS (β = -4.664; 95% CI: -5.827 to -3.502; p < 0.001), SAS (β = -3.259; 95% CI: -4.294 to -2.225; p < 0.001), and TAS (β = -7.776; 95% CI: -9.624 to -5.927; p < 0.001). Both groups interpreted LAS significantly better than SAS. Education was associated with better performance in all three models (p < 0.05). Age and sex were not significantly associated. Conclusion: Patients with probable AD present significantly impaired comprehension of ambiguous sentences, with syntactic ambiguity posing the greatest challenge. Education proved to be a protective factor. These findings reinforce the multifactorial nature of linguistic deficits in probable AD and suggest that the ambiguous sentences task is a useful tool for assessing linguistic impairment.