Neuropathologies of language and cognition relationship

neuropathologies of language and cognition relationship

Keywords: bilingualism, language learning, cognitive aging, healthy aging, . It was concluded that research broadly supports a relation between improves the brain's resistance to neuropathology is not understood. Recent. The relation between bilingualism and cognition is informative about the connection . Bilingual language production: The neurocognition of language Personality and resilience to Alzheimer's disease neuropathology: a. Neuropathology and Cognitive Impairment in Alzheimer Disease: A Complex but Coherent Research on CP correlation in AD has been active for sev- eral decades, and .. skills, language, executive function, etc.). As if factoring in both the.

Speed of processing had the highest heritability in this particular study. This is an efficiency model, rather than a threshold model, and it implies that the task is processed using less resources and in a way that makes errors unlikely to occur.

While studies have shown that certain education, socio-economic status, and lifestyle factors provide cognitive reserve, pathological studies of human brains donated to science have shown few correlations with brain damage and cognitive reserve.

In a study of normal aging, education was found to be related to levels of cognitive functioning but unrelated to rates of cognitive change, suggesting that cognitive reserve reflects the persistence of earlier differences in cognitive functioning rather than differential rates of age-associated cognitive declines.

Cognitive reserve - Wikipedia

This is true even when education and IQ are controlled for. This suggests that differences in lifestyle may increase cognitive reserve by making the individual more resilient. One subject showing reduced neocortical plaques survived with mild deficits, despite or due to low brain weight. Global reserve[ edit ] In spite of the differences in approach between the models of brain reserve and cognitive reserve, there is evidence that both might be interdependent and related.

This is where the computer analogy ends, as with the brain it seems that hardware can be changed by software. Neurotrophic effect of knowledge[ edit ] Exposure to an enriched environmentdefined as a combination of more opportunities for physical activity, learning and social interaction, may produce structural and functional changes in the brain and influence the rate of neurogenesis in adult and senescent animal model hippocampi.

Similarly, while acquiring a second language requires extensive and sustained cognitive activity, it does not appear to reduce dementia risk compared to those who have not learned another language.

The theory of cognitive reserve explains this phenomenon. People with high reserve go undiagnosed until damage is severe, then rapid decline ensues. Cognitive reserve can be estimated clinically as it is effectively general cognitive ability and knowledge. The variables that are associated with cognitive reserve include: IQbrain sizeeducation, professional attainment, leisure activities, and familial history of diagnosed dementia.

It is important to note that cognitive reserve and the variables associated with it do not "protect" from Alzheimer's disease as a disease process—the definition of cognitive reserve is based exactly on the presence of disease pathology. This means that the traditional idea that education protects from Alzheimer's disease is false, albeit that cognitive reserve is protective of the clinical manifestations of disease. Conversely anyone who has used these instruments clinically knows that they can yield false positives in people with very low reserve.

From this point of view the concept of "adequate level of challenge" easily emerges. Conceivably one could measure cognitive reserve and then offer specifically tailored tests that would pose enough level of challenge to accurately detect early cognitive impairment both in individuals with high and low reserve.

  • Cognitive reserve
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Bilinguals have higher white matter integrity than monolinguals in the corpus callosum extending to the superior and inferior longitudinal fasciculi, and also stronger anterior to posterior functional connectivity Luk et al. Aging bilinguals outperformed monolinguals on the Flanker task, and had increased gray matter in the anterior cingulate cortex, whereas monolinguals showed decreased gray matter in the dorsolateral prefrontal cortex Abutalebi et al. Further, brain regions that support executive control significantly overlap with brain regions recruited for language control Abutalebi and Green, There is also evidence that bilingual brains are better able to accommodate anatomical and physiological brain changes and deterioration without exhibiting the expected increase in behavioral symptoms.

Bilingual patients also showed substantially greater impairment of glucose uptake in frontotemporal and parietal regions Brodmann areas 9, 47, 40, and 21 and in the left cerebellum relative to monolingual patients Kowoll et al.

This evidence supports the view that lifelong bilingualism may benefit the brain by making use of efficient or alternative neural networks in the event of age-related decline and that greater amounts of brain atrophy are required before the disease manifests, which may possibly delay the incidence of dementia. Does Bilingualism Protect Against Dementia? The evidence for a protective effect of bilingualism on the incidence of dementia is considerable.

Numerous studies have examined dementia incidence in hospital records and concluded that bilingualism exerts a protective effect. The first such study by Bialystok et al. Similarly, Craik et al. Additionally, Woumans et al. Looking at specific dementia subtypes, bilingualism delayed the age at onset in the behavioral but not in the aphasic variants of Frontotemporal Dementia Alladi et al.

Indeed the effects of bilingualism on language functions are not always beneficial e. Further, a similar study by Alladi et al. Moreover, Atkinson reviewed nine papers and concluded that frequent use of two languages over a lifetime may be protective against dementia, and that inconsistencies arise due to study design or definitions of bilingualism.

This evidence supports the protective effect of bilingualism against the symptoms of dementia Bialystok et al. Bilingual individuals diagnosed with single-domain amnesic mild cognitive impairment demonstrated a later age of diagnosis than did monolinguals Ossher et al.

Furthermore, exposure to foreign language instruction during childhood and adolescence has been associated with lower risk of developing mild cognitive impairment in old age Wilson et al. Bilingualism has been associated with delayed onset of dementia and is also observed in illiterate patients Alladi et al. Taken together, this body of work suggests that bilingual experience delays the onset of neurodegenerative disease. However, an increasing number of studies have failed to detect a bilingual advantage in dementia incidence.

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

A cohort design with non-immigrant samples found no significant differences in the onset of dementia between mono- and bilingual subjects Lawton et al. In that study, non-native English speakers with at least 16 years of education had a fourfold increased risk for dementia compared to those with less education, which is an unusual finding and inconsistent with past literature on the protective effect of education.

Indeed, Clare et al. A recent meta-analysis concluded that bilingualism offers no protection against cognitive decline Mukadam et al. Note, however, that this meta-analysis has already been criticized as misleading and incomplete Woumans et al.

In sum, these studies have led to questions regarding the robustness or in some cases the validity of the bilingual dementia advantage.

In order to resolve the debate, attempts have been made to understand the role of any potential mediating factors and experimental confounds. Bak and Alladi highlight that although there exists support that bilingualism has a positive effect on cognition throughout the lifespan, common misconceptions concerning the nature of bilingualism persist, including that bilingualism is an unusual phenomenon, the holistic nature of bilingualism and its effects on cognition and bilingual diversity.

Bak and Alladi point out that it is necessary to study the effects of bilingualism separately from those of immigration and education, and to use data from both community-based approaches and memory clinics. Bak further highlights the importance of addressing confounding variables in bilingualism, aging and dementia research which include heterogeneity, migration, social factors, differences in general intelligence and the related issue of reverse causality. The above literature review has demonstrated that bilingualism yields executive functioning advantages, and these may contribute to building cognitive reserve, which may ultimately delay the onset of dementia.

The exact mechanisms are not agreed upon, and there exists counterevidence that limits the generalisability of these claims.

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

A possible fruitful avenue is the recent suggestion that sustained activation of noradrenergic signaling pathways associated with bilingualism could provide a possible mechanism linking current and previous results supporting a delayed onset of dementia in bilinguals Bak and Robertson, The following sections of this article are devoted to proposing additional possible explanations and mechanisms that may provide parsimonious explanations for the seemingly conflicting findings currently in the literature.

Age of Acquisition The majority of studies examining a bilingual advantage in cognitive aging have considered the effects of lifelong experience on cognitive function and decline. Consequently, very little attention has been paid to the age of acquisition of the second language.

neuropathologies of language and cognition relationship

Age of acquisition of the second language positively correlates with cortical thickness in the left inferior frontal gyrus and a thinner cortex in the right inferior frontal gyrus Klein et al.

Encouragingly, there is evidence of a positive effect of language experience on individuals who acquired their languages later in life. Both early and late bilinguals were found to have more efficient executive networks than monolinguals. Proficient late bilinguals showed the greatest advantage in conflict resolution, whereas early bilinguals showed enhanced monitoring processes Tao et al.

Interestingly, Abutalebi et al. Age of acquisition is a complex variable in that it not only represents the level of input experienced by a learner, where early age of acquisition results in more years of exposure, but also potentially differing patterns of language use between speakers who acquired their second language in early or in later life.

Such differences in language use may modulate the cognitive advantages associated with bilingualism. For instance, balanced bilinguals showed age-related decline in their inhibition abilities as indexed by the Simon taskwhereas dominant bilinguals showed no evidence of age-related decline Goral et al. Further, when looking purely at amount of input, age of acquisition may need to be evaluated differently in older adulthood than it is for younger adults.

For example, Tao et al. Although this difference in years of second language input might be marked for young adults, it is possible that this difference is negligible for those over the age of Additionally, age of acquisition may result in executive control differences, not because of biological or maturational constraints on language learning, but because age of acquisition may be a proxy for a set of environmental differences that are necessarily associated with early vs.

neuropathologies of language and cognition relationship

Indeed, those learning a language later due to migration will necessarily use their languages differently than someone learning a heritage language at an early age. Future longitudinal language training studies are needed to determine how age of acquisition modulates any cognitive improvements resulting from language learning, and whether it truly is never too late to begin language learning.

Neuroimaging Studies of Language Learning in Adults A large neuroscientific literature has demonstrated that lifelong bilingualism alters the structure of the brain. Foreign language training in students increased white matter including pathways in the right hemisphere, and correlated with gain in second language ability not observed in controls Hosoda et al. English natives who spent 5 months learning Swiss German showed structural changes in the left inferior frontal gyrus which correlated with increased second language proficiency Stein et al.