![]() Research over the last decade suggests that speaking more than one language may provide cognitive benefits, specifically in executive functions involving cognitive control (for a review see Dong and Li, 2015). Although bilingualism is commonly defined as speaking more than one language (with most studies reporting participants who speak two languages), we use the term multilingualism when referring to our sample, as approximately half of our multilingual patients speak more than two languages. We will next briefly review the findings from each of these lines of evidence. The current study seeks to examine the above proposal by comparing cortical thickness and tissue density in LCC brain areas and areas known to atrophy in MCI and AD (referred to here as disease-related areas), in a sample of monolingual and multilingual MCI and AD patients, matched (within Diagnosis Group) on cognitive functioning. However, the predictions made by these two independent lines of evidence have not been concurrently evaluated in the same participants. Further, it has recently been proposed that the increased gray matter seen in older bilinguals may be one of a number of variables contributing to cognitive reserve seen in bilingual dementia patients (Gold, 2016). Secondly, research with patients with Alzheimer’s disease (AD) and mild cognitive impairment (MCI) suggests that bilingualism may contribute to cognitive reserve, similar to other enriching lifestyle factors, as evidenced by differences in age of symptom onset (Alladi et al., 2013, Bialystok et al., 2014), and medial temporal lobe atrophy (Schweizer et al., 2012). Firstly, research with healthy younger and older adults indicates that speaking more than one language is associated with increase gray matter volume or thickness in language and cognitive control (LCC) areas (e.g., Klein et al., 2014). Two independent lines of research provide evidence for bilingualism’s potential impact on brain structure. ![]() Our results suggest that being multilingual may contribute to increased gray matter in LCC areas and may also delay the cognitive effects of disease-related atrophy. Given that multilinguals and monolinguals were matched on memory functioning, this suggests that increased gray matter in these regions may provide support to memory functioning. Finally, multilingual patients showed a correlation between cortical thickness in LCC regions and performance on episodic memory tasks. Results were largely replicated in our native-born Canadian MCI participants, ruling out immigration as a potential confound. ![]() In areas related to language and cognitive control (LCC), both multilingual MCI and AD patients had thicker cortex than the monolinguals. In medial temporal disease-related (DR) areas, we found higher tissue density in multilingual MCIs versus monolingual MCIs, but similar or lower tissue density in multilingual AD versus monolingual AD, a pattern consistent with cognitive reserve in AD. ![]() We examined cortical thickness and tissue density in monolingual and multilingual MCI and AD patients matched (within Diagnosis Groups) on demographic and cognitive variables. Two independent lines of research provide evidence that speaking more than one language may 1) contribute to increased grey matter in healthy younger and older adults and 2) delay cognitive symptoms in mild cognitive impairment (MCI) or Alzheimer disease (AD). ![]()
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