Bilinguals stay cognitively healthy longer
Craik, F. I., Bialystok, E., & Freedman, M. (2010). Delaying the onset of Alzheimer disease Bilingualism as a form of cognitive reserve. Neurology, 75(19), 1726-1729.
Bilingual patients had been diagnosed 4.3 years later and had reported the onset of symptoms 5.1 years later than the monolingual patients. The groups were equivalent on measures of cognitive and occupational level, there was no apparent effect of immigration
status, and the monolingual patients had received more formal education. There were no gender differences.
The present data confirm results from an earlier study, and thus we conclude that
lifelong bilingualism confers protection against the onset of AD. The effect does not appear to be attributable to such possible confounding factors as education, occupational status, or immigration. Bilingualism thus appears to contribute to cognitive reserve, which acts to compensate for the effects of accumulated neuropathology
Bialystok, E., Craik, F. I., & Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia, 45(2), 459-464.
The sample was selected from the records of 228 patients referred to a Memory Clinic with cognitive complaints. The final sample consisted of 184 patients diagnosed with dementia, 51% of whom were bilingual. The bilinguals showed symptoms of dementia 4 years later than monolinguals, all other measures being equivalent. Additionally, the rate of decline in Mini-Mental State Examination (MMSE) scores over the 4 years subsequent to the diagnosis was the same for a subset of patients in the two groups, suggesting a shift in onset age with no change in rate of progression
Bilinguals have greater neuroplasticity and stay cognitively healthy in spite of greater brain damages
Schweizer, T. A., Ware, J., Fischer, C. E., Craik, F. I., & Bialystok, E. (2012). Bilingualism as a contributor to cognitive reserve: evidence from brain atrophy in Alzheimer’s disease. Cortex, 48(8), 991-996.
Bilingualism may be one factor contributing to ‘cognitive reserve’ (CR) and therefore to a delay in symptom onset. If bilingualism is protective, then the brains of bilinguals should show greater atrophy in relevant areas, since their enhanced CR enables them to function at a higher level than would be predicted from their level of disease. We analyzed a number of linear measurements of brain atrophy from the computed tomography (CT) scans of monolingual and bilingual patients diagnosed with probable AD who were matched on level of cognitive performance and years of education.
Bilingual patients with AD exhibited substantially greater amounts of brain atrophy than monolingual patients in areas traditionally used to distinguish AD patients from healthy controls, specifically, the radial width of the temporal horn and the temporal horn ratio. Other measures of brain atrophy were comparable for the two groups. Bilingualism
appears to contribute to increased CR, thereby delaying the onset of AD and requiring the presence of greater amounts of neuropathology before the disease is manifest.
Gold, B. T., Johnson, N. F., & Powell, D. K. (2013). Lifelong bilingualism contributes to cognitive reserve against white matter integrity declines in aging. Neuropsychologia, 51(13), 2841-2846.
Results indicated significantly lower microstructural integrity in the bilingual group in several WM tracts. In particular, compared to their monolingual peers, the bilingual group showed lower fractional anisotropy and/or higher radial diffusivity in the inferior longitudinal fasciculus/inferior fronto-occipital fasciculus bilaterally, the fornix, and multiple portions of the corpus callosum. There were no group differences in GM volume. Our results suggest that lifelong bilingualism contributes to CR against WM integrity declines in aging.
Experience modifies brain structure and brain function
Bialystok, E., Craik, F. I., & Luk, G. (2012). Bilingualism: consequences for mind and brain. Trends in cognitive sciences, 16(4), 240-250.
Bilingualism is different from other types of cognitive training
Fine motor skills, gaming, professional careers (arts, music etc.) The context for how bilingualism affects cognitive ability is functional neuroplasticity, the study of how experience modifies brain structure and brain function. Such modifications have been found following experiences as diverse as juggling [Draganski B, et al. Neuroplasticity: changes in grey matter induced by training. Nature. 2004; 427:311–312.], video-game playing [Green CS, Bavelier D. Exercising your brain: a review of human brain plasticity and traininginduced learning.
Psychol. Aging. 2008; 23:692–701], careers in architecture [Salthouse TA, Mitchell DRD. Effects of age and naturally occurring experience on spatial visualization performance. Dev. Psychol. 1990; 26:845–854] taxi-driving [Maguire EA, et al. Navigation-related structural change in the hippocampi of taxi drivers. Proc. Natl. Acad. Sci. U. S. A. 2000; 97:4398–4403], and musical training [Schellenberg EG. Music lessons enhance IQ. Psychol. Sci. 2004; 15:511–514; Elbert T, et al. Increased cortical representation of fingers of the left hand in string players. Science. 1995; 270:305–307].
Bilingualism is different from all of these: like juggling and playing video games it is intense, and like architecture and driving taxis in London it is sustained, but unlike these experiences, bilinguals are not typically pre-selected for talent or interest. Although bilinguals undoubtedly differ from monolinguals in certain ways, they generally did not choose bilingualism.
Old thought: bilingualism harms children cognitive development
It has long been assumed that childhood bilingualism affected developing minds but the belief was that the consequences for children were negative: learning two languages would be confusing [Hakuta, K. Mirror of language: the debate on bilingualism. New York: Basic Books; 1986]. A study by Peal and Lambert [Peal E, Lambert W. The relation of bilingualism to intelligence. Psychol. Monogr. 1962; 76:1–23] cast doubt on this belief by reporting that children in Montreal who were either French-speaking monolinguals or English-French bilinguals performed differently on a battery of tests.
The authors had expected to find lower scores in the bilingual group on language tasks but equivalent scores in nonverbal spatial tasks, but instead found that the bilingual children were superior on most tests, especially those requiring symbol manipulation and reorganization. This unexpected difference between monolingual and bilingual children was later explored in studies showing a significant advantage for bilingual children in their ability to solve linguistic problems based on understanding such concepts as the difference between form and meaning, that is, metalinguistic awareness [Bialystok E. Factors in the growth of linguistic awareness. Child Dev. 1986; 57:498–510; Cromdal J. Childhood bilingualism and metalinguistic skills: analysis and control in young Swedish–English bilinguals. Appl. Psycholinguist. 1999; 20:1–20] and nonverbal problems that required participants to ignore misleading information [Bialystok E, Majumder S. The relationship between bilingualism and the development of cognitive
processes in problem-solving.
Appl. Psycholinguist. 1998; 19:69–85; Mezzacappa E. Alerting, orienting, and executive attention: developmental properties and sociodemographic correlates in an epidemiological sample of young, urban children. Child Dev. 2004; 75:1373–1386].
Bilinguals at all ages demonstrate better executive control than monolinguals matched in age and other background factors. Executive control is the set of cognitive skills based on limited cognitive resources for such functions as inhibition, switching attention, and working memory [Miyake A, et al. The unity and diversity of executive functions and their contributions to complex “frontal lobe” tasks: a latent variable analysis. Cogn. Psychol. 2000; 41:49–100].