Lexicon and Grammar in Bilingual Individuals with Alzheimer’s Disease and Parkinson’s Disease: A Comparative Review

Abstract

Given the number of bilingual individuals worldwide, many of patients with Alzheimer’s disease (AD) or Parkinson’s disease (PD) are bilinguals. Yet little is known about the consequences of the two neurodegenerative diseases on the language of bilingual patients. In this paper, we review the available data in the bilingual literature, specifically the decline of language in patients with AD and PD at the lexical and grammatical levels. Our literature search of three electronic databases identified nine articles on bilingual patients with AD and five on those with PD that analyzed the lexicon and grammar of these patients. The findings of these studies are inconsistent but suggest that AD and PD should affect both languages in bilingual patients. They also show a trend that AD results in greater difficulties with lexicon and L2 grammar, while PD affects L1 grammar to a greater extent. This pattern is as expected by the declarative/procedural model that each disease affects a distinct memory system.