Bilingualism and Cognitive Reserve: A Critical Overview and a Plea for Methodological Innovations

Over ninety years old: Does high cognitive reserve still help brain efficiency?

Nonagenarians and centenarians, also called oldest-old, are a very heterogeneous population that counts a limited number of individuals as it is a real challenge to reach this goal. Even if it is well known that cognitive reserve can be considered a factor in maintaining good cognitive functioning in ageing, only very few studies have been carried out on the role of cognitive reserve (CR) in the oldest-old people. The aim of this study is to investigate the relationship between cognitive reserve and cognitive functioning in a population living in a specific region of Italy, the Blue Zone in Sardinia. This population is characterised by extreme longevity and distinctive historical, geographic, social, linguistic and nutritional features. The cognitive Reserve Index questionnaire (CRIq) and the short cognitive Esame Neuropsicologico Breve-2 (ENB-2, Brief Neuropsychological Examination) were administered to 67 participants, all aged between 90 and 105 years old. The CRIq was a predictor of neuropsychological performance for the global score of the battery of tests, ENB-2 (ENB-tot) and also for 7 out of 16 of its sub-tests. All except one (Token) tapped executive functions (Interference memory at 10 and 30 s, TMT-B, Overlapping figures, Abstraction, Fluency). Results highlight that also in the oldest-old population CR has a positive effect on cognition, especially on executive functioning.

Bilingual neurocognitive resiliency, vulnerability, and Alzheimer's disease biomarker correlates in Latino older adults enrolled in the Health and Aging Brain Study - Health Disparities (HABS-HD)

INTRODUCTION

The effects of bilingualism on neuropsychological test performance in bilinguals with and without cognitive impairment are not well-understood and are relatively limited by small sample sizes of Latinos.

METHODS

Using analysis of covariance (ANCOVA), we explored patterns of cognitive performance and impairment across a large sample of community-dwelling bilingual and monolingual Latino older adults with (n = 180) and without (n = 643) mild cognitive impairment (MCI) enrolled in HABS-HD.

RESULTS

Bilinguals demonstrated cognitive resiliency in the form of significantly better performance on the Trail Making Test and Digit Symbol Substitution Test, observed across the cognitively unimpaired and MCI groups. In contrast, bilinguals demonstrated cognitive vulnerability in the form of significantly poorer performance and higher impairment rates on phonemic fluency in the MCI phase, only. Follow-up analyses revealed less balanced bilinguals demonstrated poorer performance and higher impairment rates on this measure, supported by lower levels of plasma Aβ 42/40.

DISCUSSION

Patterns of cognitive performance and impairment differ as a function of bilingualism. Bilingualism must be considered when evaluating cognitive and biomarker outcomes in Latino older adults.

Highlights

Latino bilinguals perform better on measures of processing speed and coding.Latino bilinguals with MCI demonstrate cognitive vulnerability in verbal fluency.Less balanced bilinguals demonstrate greatest vulnerability anchored by Aβ 42/40.

Does Language Distance Modulate the Contribution of Bilingualism to Cognitive Reserve in Seniors? A Systematic Review

We report a systematic review and exploratory meta-regression investigating the hypothesis that the effects of bilingualism on cognitive reserve are modulated by the distance between the pair of languages a bilingual uses. An inclusive multiple database search was performed in order to identify all relevant published research conducted in bilingual seniors. A combination of qualitative and quantitative synthesis methods were used in order to investigate our research questions. Results suggest that healthy bilingual seniors speaking more distant language pairs show improved monitoring performance on cognitive tasks. Evidence regarding a modulatory influence of language distance (LD) on the age of dementia diagnosis was inconclusive due to the small number of published studies meeting our inclusion criteria. We recommend more detailed reporting of individual differences in bilingual experience to assess the impact of LD and other variables on typical cognitive aging and the development of dementia. Linguistic differences in samples should also be considered as a constraint on bilingual advantages in future studies. Preregistration: PROSPERO CRD42021238705; OSF DOI 10.17605/OSF.IO/VPRBU.

Bilingual Primary Progressive Aphasia: A Scoping Review of Assessment and Treatment Practices

BACKGROUND

Primary progressive aphasia (PPA) is a neurodegenerative syndrome characterized by speech and/or language impairment with relatively spared cognition. Research investigating behavioral speech-language intervention and methods for cognitive-linguistic assessment in PPA has predominantly centered around monolingual speakers. This gap hinders the widespread adoption of evidence-based approaches and exacerbates the inequities faced by culturally and linguistically diverse populations living with PPA.

OBJECTIVE

This scoping review synthesizes the current evidence for assessment and treatment practices in bilingual PPA as well as the operationalization of bilingualism in PPA.

METHODS

Arksey & O'Malley's scoping review methodology was utilized. Information was extracted from each study and entered into a data-charting template designed to capture information regarding operationalization of bilingualism in PPA and assessment and treatment practices.

RESULTS

Of the 16 identified studies, 14 reported the results of assessments conducted in both languages. Three studies reported positive naming treatment outcomes. Thirteen studies included English-speaking participants, revealing linguistic bias. Most studies reported age of acquisition, proficiency, and patterns of language use rather than providing an operational definition for bilingualism.

CONCLUSIONS

Neither formal assessment measures nor clear guidelines for assessment of bilingual PPA currently exist; however, language-specific measures are emerging. Speech-language intervention in bilingual PPA has been relatively unexplored, representing a significant gap in the literature. In order to improve diagnostic and treatment options for bilingual PPA, targeted efforts to increase representation of bilinguals from various sociocultural contexts, as well as those who speak a variety of language pairs, is necessary.

Bilingualism and creativity: Benefits from cognitive inhibition and cognitive flexibility

Bilingualism has been shown to be associated with creativity, but the mechanisms of this association are not very well understood. One possibility is that the skills that bilinguals use in switching back and forth between languages also promote the cognitive processes associated with creativity. We hypothesized that high-proficient Chinese-English bilinguals would show higher convergent and divergent thinking than low-proficient bilinguals, with the differences being mediated by cognitive inhibition and cognitive flexibility, respectively. Chinese university students (N = 54) were classified as high-proficient (n = 27) and low-proficient (n = 27) bilinguals based on their performance on the National English Test for College Students. As expected, group comparisons showed that the high-proficient group had higher scores on the Remote Associates Test (RAT, convergent thinking) and the Torrance Test of Creative Thinking (TTCT, divergent thinking). Also as expected, the association between bilingualism and convergent thinking was mediated by scores on a Stroop task (cognitive inhibition), and the association between bilingualism and divergent thinking was mediated by scores on a More-odd shifting task (cognitive flexibility). These findings suggest that bilingual learning can promote the development of different components of creativity through stronger cognitive inhibition and cognitive flexibility. The results provide empirical evidence for the relationship and mechanism between bilingual learning and creativity.

The effect of acculturation on cognitive performance among older Hispanics in the United States

The effect of acculturation on cognition was examined among 142 older Hispanics: cognitively normal [CN; n = 70], Mild Cognitive Impairment, amnestic [aMCI; n = 27], and Dementia [D; n = 45]. Acculturation levels (high vs. low) were determined using the Short Acculturation Scale for Hispanics (SASH). ANCOVAs used a wide variety of neuropsychological tests as independent variables controlling for age and education. Among CN subjects, the highly acculturated group performed better on Logical Memory delayed recall (LM-II) [F(1, 56) = 9.26, p < .001, η p 2 = 0.14], Digit Span Forward [F(1, 56) = 4.37, p < .05, η p 2 = 0.07], Trail Making Test A [F(1, 56) = 7.74, p < .05, η p 2 = 0.12], and Trail Making Test B [F(1, 56) = 4.66, p = .03, η p 2 = 0.08], indicating that high acculturation was associated with a better performance on tests of episodic memory, auditory attention, working memory, cognitive flexibility, and processing speed among CN Hispanics. ANCOVA analyses were not significant among the other groups. In the absence of acculturation scales in clinical practice, caution should be exerted when interpreting neurocognitive results.

The neuroanatomical consequences and pathological implications of bilingualism

In recent years, there has been a rise in the number of people who are able to speak two or more languages. This has been paralleled by an increase in research related to bilingualism. Despite this, much of the neuroanatomical consequences and pathological implications of bilingualism are still subject to discussion. This review aims to evaluate the neuroanatomical structures related to language and to the acquisition of a second language as well as exploring how learning a second language can alter one's susceptibility to and the progression of certain cerebral pathologies. A literature search was conducted on the Medline, Embase, and Web of Science databases. A total of 137 articles regarding the neuroanatomical or pathological implications of bilingualism were included for review. Following analysis of the included papers, this review finds that bilingualism induces significant gray and white matter cerebral changes, particularly in the frontal lobes, anterior cingulate cortex, left inferior parietal lobule and subcortical areas, and that native language and acquired language largely recruit the same neuroanatomical structures with however, subtle functional and anatomical differences dependent on proficiency and age of language acquisition. There is adequate evidence to suggest that bilingualism offsets the symptoms and diagnosis of dementia, and that it is protective against both pathological and age-related cognitive decline. While many of the neuroanatomical changes are known, more remains to be elucidated and the relationship between bilingualism and other neurological pathologies remains unclear.

Bilingualism, Executive Function, and the Brain: Implications for Autism

Autism spectrum disorder (ASD) is associated with marked heterogeneity with respect to the development of executive function abilities. The bilingual advantage refers to the observation that individuals who speak two languages perform better on executive function tasks than monolinguals under some circumstances. There is not yet consensus, however, as to whether this advantage can be reliably demonstrated, nor is there consensus regarding under which conditions it emerges. Bilingual and monolingual children with ASD have comparable developmental outcomes, particularly in the areas of core ASD symptoms, cognitive function, and language. Still, despite the potential advantages that bilingualism may confer, clinicians commonly advise against providing a bilingual environment for children with ASD. The purpose of the present review is to provide an up-to-date assessment of the limited literature on bilingualism in children with ASD in order to inform evidence-based practice. Studies suggest a potential bilingual advantage in ASD in the areas of nonverbal intelligence quotient, adaptive functioning, and expressive vocabulary. A limited yet growing literature provides preliminary evidence for enhanced executive function ability in some children with ASD. Taken together, current evidence suggests that although a bilingual advantage may not be universally present in typical development, it may manifest under specific circumstances, conferring advantage for populations in which executive function is compromised. Further work is needed to develop consistent, evidence-based guidelines around language recommendations for families of children with ASD and to better understand the cognitive and brain mechanisms giving rise to the bilingual advantage in clinical developmental populations.

Can Machines Find the Bilingual Advantage? Machine Learning Algorithms Find No Evidence to Differentiate Between Lifelong Bilingual and Monolingual Cognitive Profiles

Bilingualism has been identified as a potential cognitive factor linked to delayed onset of dementia as well as boosting executive functions in healthy individuals. However, more recently, this claim has been called into question following several failed replications. It remains unclear whether these contradictory findings reflect how bilingualism is defined between studies, or methodological limitations when measuring the bilingual effect. One key issue is that despite the claims that bilingualism yields general protection to cognitive processes (i.e., the cognitive reserve hypothesis), studies reporting putative bilingual differences are often focused on domain specific experimental paradigms. This study chose a broader approach, by considering the consequences of bilingualism on a wide range of cognitive functions within individuals. We utilised 19 measures of different cognitive functions commonly associated with bilingual effects, to form a "cognitive profile" for 215 non-clinical participants. We recruited Welsh speakers, who as a group of bilinguals were highly homogeneous, as means of isolating the bilingualism criterion. We sought to determine if such analyses would independently classify bilingual/monolingual participant groups based on emergent patterns driven by collected cognitive profiles, such that population differences would emerge. Multiple predictive models were trained to independently recognise the cognitive profiles of bilinguals, older adults (60-90 years of age) and higher education attainment. Despite managing to successfully classify cognitive profiles based on age and education, the model failed to differentiate between bilingual and monolingual cognitive ability at a rate greater than that of chance. Repeated modelling using alternative definitions of bilingualism, and just the older adults, yielded similar results. In all cases then, using our "bottom-up" analytical approach, there was no evidence that bilingualism as a variable indicated differential cognitive performance - as a consequence, we conclude that bilinguals are not cognitively different from their monolingual counterparts, even in older demographics. We suggest that studies that have reported a bilingual advantage (typically recruiting immigrant populations) could well have confounded other key variables that may be driving reported advantages. We recommend that future research refine the machine learning methods used in this study to further investigate the complex relationship between bilingualism and cognition.

The Effect of Bilingualism on Cue-Based vs. Memory-Based Task Switching in Older Adults

Findings suggest a positive impact of bilingualism on cognition, including the later onset of dementia. However, it is not clear to what extent these effects are influenced by variations in attentional control demands in response to specific task requirements. In this study, 20 bilingual and 20 monolingual older adults performed a task-switching task under explicit task-cuing vs. memory-based switching conditions. In the cued condition, task switches occurred in random order and a visual cue signaled the next task to be performed. In the memory-based condition, the task alternated after every second trial in a predictable sequence without presenting a cue. The performance of bilinguals did not vary across experimental conditions, whereas monolinguals experienced a pronounced increase in response latencies and error rates in the cued condition. Both groups produced similar switch costs (difference in performance on switch trials as opposed to repeating trials within the mixed-task block) and mixing costs (difference in performance on repeat trials of a mixed-task block as opposed to trials of a single-task block), but bilinguals produced them with lower response latencies. The cognitive benefits of bilingualism seem not to apply to executive functions per se but to affect specific cognitive processes that involve task-relevant context processing. The present results suggest that lifelong bilingualism could promote in older adults a flexible adjustment to environmental cues, but only with increased task demands. However, due to the small sample size, the results should be interpreted with caution.

Sex and gender differences in cognitive and brain reserve: Implications for Alzheimer's disease in women

Women represent ⅔ of the cases of Alzheimer's disease (AD). Current research has focused on differential risks to explain higher rates of AD in women. However, factors that reduce risk for AD, like cognitive/brain reserve, are less well explored. We asked: what is known about sex and gender differences in how reserve mitigates risk for AD? We conducted a narrative review of the literature, with keywords: "sex/gender differences", "cognitive/brain reserve", "Alzheimer's Disease", and the following cognitive reserve contributors: "education", "IQ", "occupation", "cognitive stimulation", "bilingualism", "socioeconomic status", "physical activity", "social support". Sixteen papers disaggregated their data by sex. Those papers observed sex and gender differences in reserve contributors. There is also evidence that greater reserve may be more beneficial in lowering AD risk in women, although more research is needed. We discuss how traditional reserve contributors are gendered and may not capture factors that support cognition in aging women.

Lifelong Bilingualism Functions as an Alternative Intervention for Cognitive Reserve Against Alzheimer's Disease

Bilingualism has been reported to significantly delay the onset of dementia and plays an important role in the management of Alzheimer's disease (AD), a condition inducing impairment in the brain network and cognitive decline. Cognitive reserve is associated with the adaptive maintenance of neural functions by protecting against neuropathology. Bilingualism acts as a beneficial environmental factor contributing to cognitive reserve, although some potential confounding variables still need further elucidation. In this article, the relationship between bilingualism and cognitive reserve is discussed, interpreting the advantage of bilingualism in protecting against cognitive decline. In addition, the possible brain and biochemical mechanisms, supporting the advantageous effects of bilingualism in delaying the onset of dementia, involved in bilingualism are reviewed. Effectively, bilingualism can be considered as a pharmacological intervention with no side effects. However, the investigation of the pharmacological parameters of bilingualism is still at an early stage.

Cognitive and Neurocognitive Effects From the Unique Bilingual Experiences of Interpreters

For bilinguals, research suggests that both languages are constantly active and competing in the mind, even when only using one. However, this body of work has reported inconclusive results on the long-term effects of the constant parallel activation and use of more than one language on the brain. This has mostly been due to inconsistent comparisons between groups of bilinguals and monolinguals. Not all bilingualisms are the same. The investigation of the use of more than one language over a lifetime offers the opportunity to better understand the consequences of bilingualism on the brain. However, few studies have specifically looked at the long-standing effects of being an interpreter. In this paper, we review theories from the field of Translation and Interpreting Studies and provide a critical review of work that offers insight on the cognitive and neurocognitive effects that seem to arise from the unique, highly-cognitive-demanding practices experienced by interpreters.

Moderation-Mediation Effects in Bilingualism and Cognitive Reserve

We first provide a critical review of the existing findings on bilingualism as a contributor to cognitive reserve from moderator-mediator warranting cause-effect research conclusions. We next address the question of direct or indirect effects between bilingualism and neurocognitive protective factors influencing the associated age-related mental deficits. The existing findings support bilingualism as a predictor and as a moderator. Third, we propose cognitive reserve models of bilingualism describing analytical approaches that allow testing of these models and hypotheses related to path strength and causal relationships between predictors, moderators, and mediators. Lastly and most importantly, we suggest using large datasets available via open repositories. This can aid in the testing of theoretical models, clarifying the roles of moderators and mediators, and assessing the research viability of multi-causal paths that can influence cognitive reserve. Creating collaborative datasets to test these models would greatly advance our field and identify critical variables in the study of the bilingual aging brain.

Effects of bilingualism on age at onset in two clinical Alzheimer's disease variants

INTRODUCTION

The effect of bilingualism on age at onset has yet to be examined within different clinical variants of Alzheimer's disease.

METHODS

We reviewed the research charts of 287 well-characterized participants with either amnestic Alzheimer's dementia or logopenic variant primary progressive aphasia (lvPPA) and identified bilingual speakers based on regular use of two or more languages and/or ability to communicate with native speakers in two or more languages. We evaluated whether bilingual speakers demonstrated a delay in age of symptom onset relative to monolingual speakers while controlling for other variables known to influence cognitive reserve.

RESULTS

A 5-year delay in age at symptom onset was observed for bilingual relative to monolingual speakers with lvPPA. This delay in onset was not observed in the amnestic Alzheimer's dementia cohort.

DISCUSSION

Bilingualism may serve as a unique cognitive reserve variable in lvPPA, but not in amnestic Alzheimer's dementia.

Beyond Alzheimer's disease: Can bilingualism be a more generalized protective factor in neurodegeneration?

Bilingualism has been argued to have an impact on cognition and brain structure. Effects have been reported across the lifespan: from healthy children to ageing adults, including clinical (ageing) populations. It has been argued that active bilingualism may significantly contribute to the delaying of the expression of Alzheimer's disease symptoms. If bilingualism plays an ameliorative role against the expression of neurodegeneration in dementia, it is possible that it could have similar effects for other neurodegenerative disorders, including Multiple Sclerosis, Parkinson's and Huntington's Diseases. To date, however, direct relevant evidence remains limited, not least because the necessary scientific motivations for investigating this with greater depth have not yet been fully articulated. Herein, we provide a roadmap that reviews the relevant literatures, highlighting potential links across neurodegenerative disorders and bilingualism more generally.

Does bilingualism influence neuropsychological test performance in older adults? A systematic review

OBJECTIVE

Using standardized tests which have been normed on monolinguals for the assessment of bilinguals presents challenges to the accurate characterization of cognitive profile as the literature provides compelling evidence for the influence of bilingualism on cognitive abilities. However, little is known about the generalizability of these findings to clinical neuropsychology. The aim of this review was to address this gap by summarizing current evidence on the performance of bilingual older adults on standardized tests routinely used in clinical practice.

METHOD

A systematic search of Web of Science, PsycINFO and PubMed was conducted. 27 cross-sectional and longitudinal studies which use at least one standardized neuropsychological test for cognitive impairment were included in the review. Potential demographic (cultural/linguistic background of the participants, immigrant status), clinical (diagnostic status), and methodological confounders (language of test administration, components of bilingualism) were also examined. The review protocol was registered at the PROSPERO International Prospective Register of Systematic Review with registration number CRD42018114658.

RESULTS

The results of this review revealed some bilingual advantage on measures of inhibitory control and bilingual disadvantage on measures of verbal fluency in cross-sectional studies. Bilingualism status was not associated with test performance in longitudinal studies. However, findings lack consistency due to demographic variables and methodological differences across studies.

CONCLUSION

Neuropsychological tests assessing language domains and, to some extent executive function act as clinically relevant features of bilingualism for neuropsychological evaluation. However, immigration status, acculturation level and language of test administration needs to be taken into account when assessing bilingual older adults.

Active bilingualism delays the onset of mild cognitive impairment

Lifelong bilingualism may contribute to cognitive reserve (CR) in neurodegenerative diseases as shown by a delay of the age at symptom onset in bilinguals with Alzheimer's disease (AD) and Mild Cognitive Impairment (MCI). However, some studies have failed to show this bilingual advantage, suggesting that it might depend on the type and degree of bilingualism. In the present study, we tested the hypothesis that active bilingualism, defined as the continuous use of the two languages as opposed to second language exposition only, may protect against cognitive decline. Moreover, we investigated whether bilingualism as a CR factor may be explained by an advantage within the executive control (EC) system. To do so, we collected clinical measures (age at onset of cognitive symptoms, age at the first medical visit for cognitive impairments, and age at diagnosis) in patients with MCI and patients with AD with different degrees of language experience and usage of Catalan and Spanish. Additionally, all participants were tested on four EC tasks and one long-term memory recognition task. First, results from multiple regression analyses showed that active bilingualism was a significant predictor of delay in the age at onset for all the clinical measures in MCI, but not AD patients. Second, the effect of active bilingualism was independent of occupation, educational level and job attainment across the individuals' lifespan. Finally, although we did not find an effect of active bilingualism across all EC tasks, we did find an effect for conflict resolution. These results are discussed in the context of CR hypotheses, suggesting that compensatory mechanisms may play a role in protecting against cognitive decline.

A cross-sectional and longitudinal study on the protective effect of bilingualism against dementia using brain atrophy and cognitive measures

Background

Evidence from previous studies suggests that bilingualism contributes to cognitive reserve because bilinguals manifest the first symptoms of Alzheimer’s disease (AD) up to 5 years later than monolinguals. Other cross-sectional studies demonstrate that bilinguals show greater amounts of brain atrophy and hypometabolism than monolinguals, despite sharing the same diagnosis and suffering from the same symptoms. However, these studies may be biased by possible pre-existing between-group differences.

Methods

In this study, we used global parenchymal measures of atrophy and cognitive tests to investigate the protective effect of bilingualism against dementia cross-sectionally and prospectively, using a sample of bilinguals and monolinguals in the same clinical stage and matched on sociodemographic variables.

Results

Our results suggest that the two groups did not differ in their cognitive status at baseline, but bilinguals had less parenchymal volume than monolinguals, especially in areas related to brain atrophy in dementia. In addition, a longitudinal prospective analysis revealed that monolinguals lost more parenchyma and had more cognitive decline than bilinguals in a mean follow-up period of 7 months.

Conclusion

These results provide the first prospective evidence that bilingualism may act as a neuroprotective factor against dementia and could be considered a factor in cognitive reserve.

Bilingualism for Dementia: Neurological Mechanisms Associated With Functional and Structural Changes in the Brain

As the number of older adults increases, the prevalence of dementias, such as Alzheimer's dementia (AD), vascular dementia, dementia with Lewy bodies, and frontotemporal dementias, also increases. Despite research into pharmacological approaches for treating diverse diseases, there is still no cure. Recently, novel non-pharmacological interventions are attracting attention. Non-pharmacological approaches include cognitive stimulation, alterations in diet, physical activity, and social engagement. Cognitive stimulating activities protect against the negative effects of cognitive decline caused by age-related neurogenerative diseases. Bilingualism is one form of cognitive stimulation that requires multiple aspects of brain activity and has been shown to delay the onset of dementia symptoms in patients by approximately 4-5 years as compared with monolingual patients through cognitive reserve. The purpose of this review was to bilingualism protects against cognitive decline associated with AD and other dementias. We discuss potential underlying neurological mechanisms, including: (1) stimulating adult neurogenesis, (2) enhancing synaptogenesis, (3) strengthening functional connectivity that bilingualism may delay clinical AD symptoms, (4) protecting white matter integrity, and (5) preserving gray matter density.

In the Long Run: Physical Activity in Early Life and Cognitive Aging

A certain degree of age-related cognitive decline is normal; however, some people retain more cognitive function than others. Cognitive impairment is associated with an increased risk of dementia. Thus, understanding the factors that contribute to cognitive reserve is crucial, so effective strategies for the prevention of dementia can be developed. Engaging in physical activity can delay cognitive decline and reduce the risk of dementia and a number of early life conditions have been shown to have long-lasting effects on cognition. This mini-review combines these two observations to evaluate the evidence from both animal models and epidemiological studies for physical activity in early life (≤30 years) delaying cognitive decline in later life (cognition tested ≥60 years). Three epidemiological studies were found; two showed a positive association and one found none. The latter was deemed to have an unreliable method. A review of animal studies found none that analyzed the effect of physical activity in early life on cognition in later life. However, in rodent models that analyzed mid-life cognition, runners showed improved cognition and enhanced adult hippocampal neurogenesis, changes which were preserved across the life span. Currently, there is insufficient evidence to conclude whether physical activity in early life may delay cognitive decline in later life, but these results indicate that further studies are warranted. Future human research should be in the form of longitudinal studies that begin below ≤15 years and assess sex differences. Crucially, the physical activity data must define type, quantity and intensity of exercise.

Cognitive Advantages in Adult Turkish Bilingual Immigrants - a Question of the Chicken or the Egg

A number of studies suggest both cognitive disadvantages and advantages of bilingualism. In the current study, it is attempted to provide an account of the cognitive advantages associated with bilingualism in a Turkish immigrant population in Denmark.The total sample consisted of 71 middle-aged and older adults born and raised in Turkey who had migrated to Denmark in their teenage years or later. All participants were assessed with a neuropsychological test battery and degree of Turkish-Danish bilingualism was estimated via rater assessment according to a three-point scale. Associations between bilingualism and cognitive function were established for five cognitive domains: executive function, memory, language, visuospatial function and speed. Analysis of covariance was used to estimate the independent association between bilingualism and cognitive function for each cognitive domain. Covariates included education, gender, ethnicity, and proportion of life lived in Denmark. In unadjusted analyses, greater degree of bilingualism was associated with better executive functioning (p < .001), visuospatial functioning (p = .002) and speed (p < .001). However, in analyses adjusted for covariates only executive functioning (p = .01) and task switching ability (p = .01) remained significant, while a trend for better memory function was found in those with a high degree of bilingualism (p = .07).The current study indicates that bilingual Turkish immigrants have better executive functioning and episodic memory compared to Turkish immigrant monolinguals. Whether this is due to the effects of bilingualism or reflects inherent cognitive abilities in those able to acquire bilingualism in later life remains to be resolved.

A Systematic Review on the Possible Relationship Between Bilingualism, Cognitive Decline, and the Onset of Dementia

A systematic review was conducted to investigate whether bilingualism has a protective effect against cognitive decline in aging and can protect against dementia. We searched the Medline, ScienceDirect, Scopus, and ERIC databases with a cut-off date of 31 March, 2019, thereby following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) protocol. Our search resulted in 34 eligible studies. Mixed results were found with respect to the protective effect of bilingualism against cognitive decline. Several studies showed a protective effect whereas other studies failed to find it. Moreover, evidence for a delay of the onset of dementia of between 4 and 5.5 years in bilingual individuals compared to monolinguals was found in several studies, but not in all. Methodological differences in the set-up of the studies seem to explain these mixed results. Lifelong bilingualism is a complex individual process, and many factors seem to influence this and need to be further investigated. This can be best achieved through large longitudinal studies with objective behavioral and neuroimaging measurements. In conclusion, although some evidence was found for a cognitive reserve-enhancing effect of lifelong bilingualism and protection against dementia, to date, no firm conclusions can be drawn.

Rethinking the Neural Basis of Prosody and Non-literal Language: Spared Pragmatics and Cognitive Compensation in a Bilingual With Extensive Right-Hemisphere Damage

Above and beyond the critical contributions of left perisylvian regions to language, the neural networks supporting pragmatic aspects of verbal communication in native and non-native languages (L1s and L2, respectively) have often been ascribed to the right hemisphere (RH). However, several reports have shown that left-hemisphere activity associated with pragmatic domains (e.g., prosody, indirect speech, figurative language) is comparable to or even greater than that observed in the RH, challenging the proposed putative role of the latter for relevant domains. Against this background, we report on an adult bilingual patient showing preservation of pragmatic verbal skills in both languages (L1: Spanish, L2: English) despite bilateral damage mainly focused on the RH. After two strokes, the patient sustained lesions in several regions previously implicated in pragmatic functions (vast portions of the right fronto-insulo-temporal cortices, the bilateral amygdalae and insular cortices, and the left putamen). Yet, comparison of linguistic and pragmatic skills with matched controls revealed spared performance on multiple relevant tasks in both her L1 and L2. Despite mild difficulties in some aspects of L2 prosody, she showed no deficits in comprehending metaphors and idioms, or understanding indirect speech acts in either language. Basic verbal skills were also preserved in both languages, including verbal auditory discrimination, repetition of words and pseudo-words, cognate processing, grammaticality judgments, equivalent recognition, and word and sentence translation. Taken together, the evidence shows that multiple functions of verbal communication can be widely spared despite extensive damage to the RH, and that claims for a putative relation between pragmatics and the RH may have been overemphasized in the monolingual and bilingual literature. We further discuss the case in light of previous reports of pragmatic and linguistic deficits following brain lesions and address its relation to cognitive compensation in bilingual patients.

Effects of Bilingualism on Verbal and Nonverbal Memory Measures in Mild Cognitive Impairment

OBJECTIVES

Maintaining two active languages may increase cognitive and brain reserve among bilingual individuals. We explored whether such a neuroprotective effect was manifested in the performance of memory tests for participants with amnestic mild cognitive impairment (aMCI).

METHODS

We compared 42 bilinguals to 25 monolinguals on verbal and nonverbal memory tests. We used: (a) the Loewenstein-Acevedo Scales for Semantic Interference and Learning (LASSI-L), a sensitive test that taps into proactive, retroactive, and recovery from proactive semantic interference (verbal memory), and (b) the Benson Figure delayed recall (nonverbal memory). A subsample had volumetric MRI scans.

RESULTS

The bilingual group significantly outperformed the monolingual group on two LASSI-L cued recall measures (Cued A2 and Cued B2). A measure of maximum learning (Cued A2) showed a correlation with the volume of the left hippocampus in the bilingual group only. Cued B2 recall (sensitive to recovery from proactive semantic interference) was correlated with the volume of the hippocampus and the entorhinal cortex of both cerebral hemispheres in the bilingual group, as well as with the left and right hippocampus in the monolingual group. The memory advantage in bilinguals on these measures was associated with higher inhibitory control as measured by the Stroop Color-Word test.

CONCLUSIONS

Our results demonstrated a superior performance of aMCI bilinguals over aMCI monolinguals on selected verbal memory tasks. This advantage was not observed in nonverbal memory. Superior memory performance of bilinguals over monolinguals suggests that bilinguals develop a different and perhaps more efficient semantic association system that influences verbal recall. (JINS, 2019, 25, 15-28).

Measuring the Timing of the Bilingual Advantage

Empirical evidence has supported the idea that the bilingual advantage is a question of nuanced differences between bilinguals and monolinguals. In this article, I review findings from studies using eye tracking, mouse tracking, and event-related potentials (ERPs) which are particularly suited to measure time. Understanding the timing of the processes underlying executive function is crucial in evaluating the intricacies of the bilingual mind. Furthermore, I provide recommendations on how to best use these timing techniques to compare bilinguals and monolinguals. Temporal differences can characterize ongoing discussions of the bilingual advantage and help explain conflicting findings. Methodological and analytical innovations to better investigate the timing of the cognitive processes at play will inform a wide range of areas in cognitive science.

The Protective Effect of Cantonese/Mandarin Bilingualism on the Onset of Alzheimer Disease

BACKGROUND

Several studies have found that bilingualism can delay the age of onset of Alz-heimer disease (AD). The interpretation of these findings is that switching between two languages can enhance cognitive reserve. However, some studies have provided inconsistent results. Diverse language pairs used by the bilinguals in different studies may contribute to the discrepancies. Cantonese and Mandarin are widely used in southern China, and regarded as bilingualism. The present study aims to determine if Cantonese/Mandarin bilingualism can delay the onset of AD.

METHODS

The data of 129 patients diagnosed with probable AD, including 48 Cantonese monolinguals, 20 Mandarin monolinguals, and 61 Cantonese/Mandarin bilinguals were analyzed.

RESULTS

Cantonese/Mandarin bilinguals were found to have an older age at AD onset, and older age at the first clinic visit than Mandarin monolinguals and Cantonese monolinguals. Both Mandarin monolinguals and Cantonese/Mandarin bilinguals had a higher education level and higher occupation status than the Cantonese monolinguals. Mandarin monolinguals did not differ from Cantonese/Mandarin bilinguals significantly in years of education and occupation status. The multiple linear regression analyses indicated that Cantonese/Mandarin bilingualism can delay the onset of AD independently.

CONCLUSION

Constantly speaking both Cantonese and Mandarin from at least early adulthood can delay the onset of AD.

Evidence against a cognitive advantage in the older bilingual population

Recent evidence has challenged long-standing claims that multi-language acquisition confers long-term advantages in executive function and may protect against age-related cognitive deterioration. We assessed evidence for a bilingual advantage in older monolingual and bilingual residents matched on age, gender, and socioeconomic status. A comprehensive battery of tests was administered to measure non-verbal reasoning, working memory capacity, visuo-spatial memory, response inhibition, problem solving, and language proficiency. Analyses, including Bayes factors, revealed comparable performance in both groups, with no significant differences on any task (and the only trend, found for the Tower of London task performance, indicated a monolingual advantage). Overall, therefore, our findings run counter to the bilingual advantage hypothesis. We consider the implications of our study and offer suggestions for future work in this area.

The language and social background questionnaire: Assessing degree of bilingualism in a diverse population

Research examining the cognitive consequences of bilingualism has expanded rapidly in recent years and has revealed effects on aspects of cognition across the lifespan. However, these effects are difficult to find in studies investigating young adults. One problem is that there is no standard definition of bilingualism or means of evaluating degree of bilingualism in individual participants, making it difficult to directly compare the results of different studies. Here, we describe an instrument developed to assess degree of bilingualism for young adults who live in diverse communities in which English is the official language. We demonstrate the reliability and validity of the instrument in analyses based on 408 participants. The relevant factors for describing degree of bilingualism are: (1) the extent of non-English language proficiency and use at home, and (2) non-English language use socially. We then use the bilingualism scores obtained from the instrument to demonstrate their association with: (1) performance on executive function tasks, and (2) previous classifications of participants into categories of monolinguals and bilinguals.

Neuroplasticity across the lifespan and aging effects in bilinguals and monolinguals

Evidence that bilingualism protects against age-related neurocognitive decline is mixed. One relatively consistent finding is that bilingual seniors have greater grey matter volume (GMV) in regions implicated in executive control (EC) and language processing. Here, we compare the neuroplastic effects of bilingual experience on the EC network of young and aging populations directly, and for the first time we evaluate the extent to which such effects may predict executive control performance across age. We used GMV as an index of neural reserve and response time (RT) performance on the Flanker task for measuring EC efficiency. In the presence of age-related widespread GM deterioration, bilinguals had greater GMV than monolinguals in key regions of interest across age. Moreover, whereas EC performance in monolingual seniors was strictly related to GMV, this was not observed for bilingual seniors or younger participants in either group. Interactions between expected effects-of-age and language group on the relationships between GMV and RT suggested that bilingualism affords differential benefits across the lifespan. In younger participants, greater GMV offered no behavioral benefit on EC performance, whilst it did for seniors. It thus appears that age-related cognitive decline following GMV loss in the EC network is delayed in bilinguals.

Mapping the Neural Dynamics of Korean-English Bilinguals With Medium Proficiency During Auditory Word Processing

Bilingualism is a worldwide phenomenon and provides an opportunity to understand how the brain represents language processing. Although many studies have investigated the neural mechanism of bilingualism, it still remain unclear how brain systems are involved in the second language processing. Here, we examined the neural dynamics of bilinguals with medium proficiency during auditory word processing. Korean–English (K–E) bilinguals were recruited for the study (L1: Korean and L2: English). They performed a word comprehension task on phonological and semantic aspects by hearing words. We compared their task performance, task-induced regional activity, and functional connectivity (FC) between L1 and L2 processing. Brain activation analyses revealed that L2 evoked more widespread and stronger activation in brain regions involved in auditory word processing and the increased regional activity in L2 was prominent during phonological processing. Moreover, L2 evoked up-regulation during semantic processing was associated with L2 proficiency. FC analyses demonstrated that the intra-network connectivity showed stronger in the language network (LN), dorsal attention network (DAN), and default mode network (DMN) in L2 than L1. For the L2 phonological processing, the increased FC within the DAN was positively correlated with individuals’ L2 proficiency. Also, L2 semantic processing induced the enhanced internetwork connectivity between the LN and DMN. Our findings suggest that L2 processing in K–E bilinguals induces dynamic changes in the brain at a regional and network-level and FC analysis can disentangle the different networks involvement in L2 auditory word processing according to two key features: phonology and semantics.

A core avenue for transcultural research on dementia: on the cross-linguistic generalization of language-related effects in Alzheimer's disease and Parkinson's disease

OBJECTIVE

Language is a key source of cross-cultural variability, which may have both subtle and major effects on neurocognition. However, this issue has been largely overlooked in two flourishing lines of research assessing the relationship between language-related neural systems and dementia. This paper assesses the limitations of the evidence on (i) the neuroprotective effects of bilingualism in Alzheimer's disease and (ii) specific language deficits as markers of Parkinson's disease.

DESIGN

First, we outline the rationale behind each line of research. Second, we review available evidence and discuss the potential impact of cross-linguistic factors. Third, we outline ideas to foster progress in both fields and, with it, in cross-cultural neuroscience at large.

RESULTS

On the one hand, studies on bilingualism suggest that sustained use of more than one language may protect against Alzheimer's disease symptoms. On the other hand, insights from the embodied cognition framework point to syntactic and action-verb deficits as early (and even preclinical) markers of Parkinson's disease. However, both fields share a key limitation that lies at the heart of cultural neuroscience: the issue of cross-linguistic generalizability.

CONCLUSION

Relevant evidence for both research trends comes from only a handful of (mostly Indo-European) languages, which are far from capturing the full scope of structural and typological diversity of the linguistic landscape worldwide. This raises questions on the external validity of reported findings. Greater collaboration between linguistic typology and cognitive neuroscience seems crucial as a first step to assess the impact of transcultural differences on language-related effects across neurodegenerative diseases. Copyright © 2017 John Wiley & Sons, Ltd.

Uncovering the Mechanisms Responsible for Why Language Learning May Promote Healthy Cognitive Aging

One of the great challenges facing humankind in the 21st century is preserving healthy brain function in our aging population. Individuals over 60 are the fastest growing age group in the world, and by 2050, it is estimated that the number of people over the age of 60 will triple. The typical aging process involves cognitive decline related to brain atrophy, especially in frontal brain areas and regions that subserve declarative memory, loss of synaptic connections, and the emergence of neuropathological symptoms associated with dementia. The disease-state of this age-related cognitive decline is Alzheimer's disease and other dementias, which may cause older adults to lose their independence and rely on others to live safely, burdening family members and health care systems in the process. However, there are two lines of research that offer hope to those seeking to promote healthy cognitive aging. First, it has been observed that lifestyle variables such as cognitive leisure activities can moderate the risk of Alzheimer's disease, which has led to the development of plasticity-based interventions for older adults designed to protect against the adverse effects of cognitive decline. Second, there is evidence that lifelong bilingualism acts as a safeguard in preserving healthy brain function, possibly delaying the incidence of dementia by several years. In previous work, we have suggested that foreign language learning programs aimed at older populations are an optimal solution for building cognitive reserve because language learning engages an extensive brain network that is known to overlap with the regions negatively affected by the aging process. Here, we will outline potential future lines of research that may uncover the mechanism responsible for the emergence of language learning related brain advantages, such as language typology, bi- vs. multi-lingualism, age of acquisition, and the elements that are likely to result in the largest gains.

Bilingualism as a strategy to delay the onset of Alzheimer's disease

The purpose of this study is to explore original studies which provide evidence about the effects of bilingualism on the delay of the onset of dementia, specifically Alzheimer’s disease (AD). A literature review was conducted in the world’s acknowledged databases: Web of Science, Scopus, and MEDLINE. Altogether, 14 original studies focusing on the research topic were detected. These included six prospective cohort studies and eight retrospective studies. Both types of studies suggest different conclusions. The findings from the prospective cohort studies state that there is no association between bilingualism and the delay of the onset of AD, while the retrospective studies claim the opposite. Despite the negative results of the prospective cohort studies, more research should be conducted on bilingualism and its impact on the delay of the onset of AD, since the brain studies have brought positive findings as far as the enhancement of cognitive reserve is concerned.

The relation of the number of languages spoken to performance in different cognitive abilities in old age

INTRODUCTION

Findings on the association of speaking different languages with cognitive functioning in old age are inconsistent and inconclusive so far. Therefore, the present study set out to investigate the relation of the number of languages spoken to cognitive performance and its interplay with several other markers of cognitive reserve in a large sample of older adults.

METHOD

Two thousand eight hundred and twelve older adults served as sample for the present study. Psychometric tests on verbal abilities, basic processing speed, and cognitive flexibility were administered. In addition, individuals were interviewed on their different languages spoken on a regular basis, educational attainment, occupation, and engaging in different activities throughout adulthood.

RESULTS

Higher number of languages regularly spoken was significantly associated with better performance in verbal abilities and processing speed, but unrelated to cognitive flexibility. Regression analyses showed that the number of languages spoken predicted cognitive performance over and above leisure activities/physical demand of job/gainful activity as respective additional predictor, but not over and above educational attainment/cognitive level of job as respective additional predictor. There was no significant moderation of the association of the number of languages spoken with cognitive performance in any model.

CONCLUSIONS

Present data suggest that speaking different languages on a regular basis may additionally contribute to the build-up of cognitive reserve in old age. Yet, this may not be universal, but linked to verbal abilities and basic cognitive processing speed. Moreover, it may be dependent on other types of cognitive stimulation that individuals also engaged in during their life course.