Department of Psychiatry, University of California, San Diego, La Jolla, CA, 92093, USA.
Department of Linguistics, Northwestern University, Evanston, IL, 60208, USA.
Neuropsychologia. 2024 Sep 9;202:108948. doi: 10.1016/j.neuropsychologia.2024.108948. Epub 2024 Jul 4.
Theories of bilingual language production predict that bilinguals with Alzheimer's disease (AD) should exhibit one of two decline patterns. Either parallel decline of both languages (if decline reflects damage to semantic representations that are accessed by both languages), or asymmetrical decline, with greater decline of the nondominant language (if decline reflects reduced ability to resolve competition from the dominant language with disease progression). Only two previous studies examined decline longitudinally with one showing parallel, and the other asymmetrical, decline. We examined decline over 2-7 years (3.9 on average) in Spanish-English bilinguals (N = 23). Logistic regression revealed a parallel decline pattern at one year from baseline, but an asymmetrical decline pattern over the longer decline period, with greater decline of the nondominant language (when calculating predicted probabilities of a correct response). The asymmetrical decline pattern was significantly greater for the nondominant language only when including item-difficulty in the model. Exploratory analyses across dominance groups looking at proportional decline relative to initial naming accuracy further suggested that decline of the nondominant language may be more precipitous if that language was acquired later in life, but the critical interaction needed to support this possibility was not statistically significant in a logistic regression analysis. These results suggest that accessibility of the nondominant language may initially be more resilient in early versus more advanced AD, and that AD affects shared semantic representations before executive control declines to a point where the ability to name pictures in single-language testing block is disrupted. Additional work is needed to determine if asymmetrical decline patterns are magnified by late age of acquisition of the nondominant language, and if more subtle impairments to executive control underlie impairments to language switching that occur in the earliest stages of AD (even preclinically).
双语语言产生理论预测，患有阿尔茨海默病 (AD) 的双语者应该表现出两种衰退模式之一。一种是两种语言同时衰退（如果衰退反映了对两种语言都能访问的语义表示的损伤），另一种是不对称衰退，非主导语言的衰退更为严重（如果衰退反映了随着疾病的进展，从主导语言中解决竞争的能力下降）。只有两项之前的研究在纵向检查中发现了一种模式，一种显示出平行，另一种显示出不对称。我们检查了西班牙语-英语双语者在 2-7 年内（平均 3.9 年）的衰退情况（N=23）。逻辑回归显示，从基线开始一年后呈现平行衰退模式，但在较长的衰退期间呈现不对称衰退模式，非主导语言的衰退更为严重（在计算正确反应的预测概率时）。只有当在模型中包括项目难度时，非主导语言的不对称衰退模式才更为显著。在优势群体中进行的探索性分析，观察相对于初始命名准确性的比例下降，进一步表明，如果非主导语言是在生命后期习得的，那么该语言的衰退可能更为突然，但在逻辑回归分析中，支持这种可能性的关键交互作用并不具有统计学意义。这些结果表明，在早期而非更晚期的 AD 中，非主导语言的可及性可能最初更为稳健，并且 AD 会影响共享的语义表示，直到执行控制下降到足以干扰单语言测试块中图片命名的程度。需要进一步的工作来确定非主导语言的习得年龄较晚是否会放大不对称衰退模式，以及执行控制的更微妙损伤是否是 AD 早期（甚至在临床前）发生的语言转换损伤的基础。
