Bilingualism Appears to be Protective Against Cognitive Decline Related to Cerebral Tau in Mexican Americans: An HABS‐HD Study

Abstract

AbstractBackgroundBilingualism is thought to provide protective effects from neurodegeneration and age‐related diseases such as Alzheimer’s Disease (AD). The protective effect is considered to be due to differences in grey and white matter between monolingual and bilinguals; however, no work to date has looked at differences in additional AD brain pathology. The aim of this study was to examine among Mexican Americans the impact of cerebral tau levels on cognitive functioning stratified by language status.MethodData were analyzed on a combined sample of n=44 Mexican American (n=15 Monolingual [n=9 Cognitively Normal; n=6 Cognitively Impaired {Mild Cognitive Impairment/Dementia}]; n=29 Bilingual [n=19 Cognitively Normal; n=10 Cognitively Impaired]) participants. One outlier case (Cognitively Impaired, Monolingual participant) was removed from subsequent analyses. All participants underwent cognitive testing and PET tau imaging using Siemens Biograph Vision 450 PET/CT scanner with PI‐2620. PET scans were co‐registered with 3T MRI scans (Siemens Vida). PET tau scans were processed using FreeSurfer‐defined regions of interest (ROIs) focused on the medial temporal lobe (average across entorhinal, hippocampus and amygdala), posterior cingulate cortex (isthmus cingulate and posterior cingulate) and lateral parietal cortex (inferior parietal, superior parietal and supramarginal). Linear regression models were generated for each language status group (monolingual, bilingual) examining the impact of each ROI on cognitive outcomes covarying for age, sex, and education.ResultAmong monolingual Mexican Americans, higher Medial Temporal SUVR was significantly related to poorer performance across measures of global cognition (MMSE p<0.001), processing speed (DSST p=0.038), episodic learning and memory (WMS‐III LM I p<0.001; WMS‐III LM II p<0.001) as well as rote verbal learning (SEVLT Immediate Recall p=0.004). Posterior Cingulate and Lateral Parietal SUVRs were not found to be significantly related to cognitive functioning among monolinguals. Additionally, among bilinguals, cerebral tau (derived from select ROIs) was not found to be significantly related to cognition.ConclusionHigher cerebral tau, specifically in the Medial Temporal ROI, was found to be related to poorer cognitive functioning across multiple domains but only among those who were monolingual. Results provide further support for the protective effect of bilingualism.