TABLE 2.
The alterations of radiological imaging in bilingualism.
| The age of L2 exposure | Subjects | Languages | Major findings | References | |||
| Age (Mono/Bi) | Number (Mono/Bi) | L1 | L2 | ||||
| Bilingualism related to dementia | 4 ∼ 6 | 78.8 ± 8.0/80.8 ± 6.9 | 49/37 | Welsh | English | Bilinguals outperformed monolinguals in the domain of response conflict and inhibition. There were no differences in executive function tests between monolinguals and bilinguals | Clare et al., 2016 |
| 6 ∼ 18a | 66.2 ± 26.0/66.2 ± 26.0 | 257/391 | Telugu Hindi | Dakkhini English | The onset of dementia was delayed by 4.5 years in bilingual patients as compared with that in monolinguals | Alladi et al., 2013 | |
| 9.3 ± 6.2 | 76.4 ± 8.5/77.9 ± 7.8 | 69/65 | Dutch | French | Bilingualism delayed AD onset and diagnosis by 4.6 and 4.8 years, respectively | Woumans et al., 2014 | |
| French | Dutch | ||||||
| 15 ∼ 24b | Non-immigrant 76.7 ± 7.8/77.6 ± 7.2 | 290/89, 19 | English | Different languages, French | Bilingualism did not protect against AD, but participants who spoke more than 3 languages were protected against AD | Chertkow et al., 2010 | |
| Immigrant | 66/28, 24 | French | Different languages, English | Bilinguals showed small protective effects of AD, and more than 3 languages delayed the diagnosis of AD by more than 5 years | |||
| – | 22/135 | Different languages | English | Two or more languages delayed the diagnosis of AD by more than 5 years | |||
| 20 ∼ 29c | 76.5 ± 10/80.8 ± 7.7 | 109/102 | Twenty-one different languages | English | AD diagnoses were delayed by 4.3 years in bilingual patients as compared with those in monolinguals patients | Craik et al., 2010 | |
| 20 ∼ 29c | 66.5 ± 12.3/70.0 ± 10.7 | 38/36 | English | Different languages | The onset of dementia and the first point of clinical visits were later in bilinguals than those in monolinguals | Bialystok et al., 2014 | |
| 74.2 ± 11.2/81.4 ± 8.4 | 35/40 | ||||||
| 20 ∼ 29c | 71.4 ± 9.6/75.5 ± 8.5 | 91/93 | Twenty-five different languages | English | Bilingualism delayed dementia by 4 years | Bialystok et al., 2007 | |
| 20 ∼ 29c | 74.9 ± 6.9/79.4 ± 6.3 | 49/19 | English | Different languages | In single-domain cases of amnestic mild cognitive impairment, bilinguals were diagnosed later than monolinguals | Ossher et al., 2013 | |
| <6, 6< | 52.8 ± 6.4/56.8 ± 6.5 57.6 ± 6.6 | 100/81, 97 | Spanish | Different languages | Bilingualism contributed to cognitive reserve and elevated visual-spatial and executive functions | Estanga et al., 2017 | |
| 59/55, 52 | Bilingualism alleviated cerebrospinal fluid AD-biomarkers (Aβ and tau) | ||||||
| – | 80.51 ± 6.50 | 27/54 | Spanish | English | There was no difference in diagnosis proportions for dementia between monolingual and bilingual users | Lawton et al., 2015 | |
| −/72.5 ± 9.4, 74.6 ± 7.8 | –/44 | Spanish | English | The age of diagnosis of AD delayed with increasing degree of proficiency in each language | Gollan et al., 2011 | ||
| Cognitive intervention of bilingualism | 16 ∼ 18 | – | –/10 | English | German | The GM in the left inferior frontal gyrus was increased in bilinguals (exchange students; 4 years) | Stein et al., 2012 |
| 20 | 20.1 ± 1.9/20.1 ± 1.9 | 27/16 | English | Chinese | The connectivity of the organization of WM was increased in bilinguals (nine times per week over 9 month) | Schlegel et al., 2012 | |
| 21 ∼ 27 | 24.9 ± 3.7/24.9 ± 3.7 | –/10 | English | French | L2 languages were related to an intrinsic functional interaction within the language processing area (French intensive training course; 6 h per day, 5 days per week over 12 weeks) | Chai et al., 2016 | |
| 23 | 23.2 ± 3.7/23.2 ± 3.7 | –/24 | English | Chinese | Activation in left superior parietal lobule and left inferior frontal gyrus region was increased in bilinguals (3 h per days, 5 days per week over 4 weeks) | Qi et al., 2019 | |
| 59 ∼ 79 | 65.7 ± 3.7/69.5 ± 5.3 | 12/14 | Italian | English | Global cognitive and functional connectivity was improved in the brains of bilinguals (long second language learning program; 2 h per week over 4 months) | Bubbico et al., 2019 | |
aSchool age. bYouth. cEarly adulthood age. Bi, bilingual; Mono, monolingual; L1, native language; L2, secondary language; WM, white matter.