One of the most remarkable factors that separate human beings from other species is the ability to communicate through the sophisticated tool of language. It is also true that one of the most extraordinary characteristics of the computational machine in which language is developed, the brain, is modified and structurally influenced by the environment and the experiences we have in our daily life. Interestingly, the process of learning two different languages, whether this be from birth (early or simultaneous bilingualism) or later in adulthood (late or sequential bilingualism), results in structural and functional modifications of the brain. In the last two decades many disciplines have started to investigate these neurostructural changes and the benefits of being bilingual, an example being potentially delayed dementia onset. Here you can find described the last studies and more interesting research outcomes.
NEUROSTRUCTURAL AND NEUROFUNCTIONAL MODIFICATIONS
The best way to study whether the assimilation of a second language modifies (at some level) the brain structure is to obtain brain images through Magnetic Resonance Imaging (MRI), and observe if any difference in bilinguals’ brain exist. Indeed, Klein D. et al, did this. In 2013, they compared the thickness of the inferior frontal gyrus (IFG), (Figure 1)- (the area of the frontal lobe which is involved in language articulation) in monolinguals and different types of bilinguals. The study showed that the left pars reticularis and pars orbitalis (the most anterior parts of IFG), are significantly thicker in late bilinguals (age of acquisition from 4 to 13) than in monolinguals. This finding may show that the acquisition of a second language after the most sensitive period of language learning (early childhood), causes quantifiable alterations in brain regions involved in this new task learning. These adaptations are comparable to the acquisition of complex motor tasks such as juggling (Klein D. et al, 2013).
Furthermore, the study illustrated a positive correlation between age of language acquisition and thickness of the aforementioned area, which means that the later the second language is learnt, the thicker the IFG is. This result would suggest that, the highest level of structural modifications are greatly enhanced when the sensitive period for language acquisition is chronologically as far away as the second language is learnt.
Interestingly, this hypertrophic effect of the left IFG is completely reversed in individuals that developed simultaneously two languages since birth. In these type of bilinguals the left IFG is thinner than in monolinguals and the right IFG is thicker. It is widely known that the language is a “lateralised” function of the brain, in simple words: the left hemisphere is responsible for that function. So why do we find an increased structural development in the opposite hemisphere in this case? Well, the most intuitive answer to this phenomenon is that the exposure of these children to two languages since birth probably, not only causes structural brain modifications but also leads to a reorganisation of these areas functionalities.
Figure 1. The Inferior Frontal Gyrus in the frontal lobe is anatomically divided in three subregions (from rostral to caudal): pars orbitalis, pars triangularis and opercular pars.
Notle J., Angevine J.B., 2013
Berken A.J. et al, in 2016, studied the correlation between the neural connectivity -the connection between populations of neurons linking the right hemisphere and left hemisphere IFG-, against the level of activation of these areas when producing the same speech in early and late bilinguals.
This comparison used functional MRI, and demonstrated that simultaneous bilinguals, have a higher functional connectivity between the homologous structures (IFG) of both sides. In simple terms, the stronger the neural connection between the left and right structures, the lower the activation of the neurons required to produce the same sentence in the second language (Figure 2). This amazing finding not only demonstrates that the assimilation of two languages since birth leads to enhanced neural connectivity, but it is also a great example of brain functional reorganisation in response to a stimuli received in in early childhood.
Figure 2. Graph showing the negative correlation between the neural activation (% BOLD) in simultaneous and sequential bilinguals, against neural connectivity (Fischer’s Z).
Berken J.A. et al, 2016
BILINGUALISM AND DEMENTIA ONSET
By determining the neurostructural and neurofunctional modifications that occur in bilinguals’ brain, scientists have generated controversy regarding the general beneficial effects that bilingualism seems to provide. In particular, the greatest beneficial effect that has been identified is the delay in dementia onset in individuals fluently speaking two languages.
Dementia comprises a wide range of brain disorders that manifest themselves with symptoms that mainly concern progressive and irreversible cognitive decline. The cognitive functions initially affected are generally memory, orientation in space and events and impaired ability to perform everyday tasks ( Argonin M. E., 2008). Bialystok E. et al in 2006 studied 184 patients diagnosed with dementia, of which half ( 51 %) were bilinguals. The amazing finding was that, bilingual individuals developed the first symptoms of dementia on average 4.1 years later than the monolinguals.
One of the major critiques raised to these types of studies, is that the population tested often included immigrated populations and thus the delay in dementia onset could be due other environmental or biological factors rather than the use of two languages. However, a more recent study (Alladi Suvrana D.M. et al 2013), addressed this issue by studying the dementia onset of the indian population, which is mainly bilingual for historical reasons and not for immigration causes. Furthermore, the study compared the monolingual and bilingual groups subdividing further the population based on different variables such as level of education, occupation and severity of dementia. The result of this study showed a delay in dementia onset in bilinguals individuals of 4.5 years, and for three types of dementia: Alzheimer’s, frontotemporal dementia and vascular dementia. However, speculation surrounds the theory of bilingualism delaying dementia onset. The reason being is that, ultimately, not enough information is known about the pathway through which this effect is brought about.
However, it is important to understand that, if bilingualism is responsible for this great delay in dementia onset not only it would be absolutely beneficial for the individual, but it also would represent a great advantage under a socio-economical point of view, and learning a second language should be highly encouraged. For instance, it has been calculated that a delay in dementia onset of 2 years in USA would decrease the prevalence of the disorder of 1.94 millions in 50 years. (Brookmeyer R et al., 1998 as cited in Bialystok E. et al, 2006).
It is important to take into account the fact that cognitive, structural and functional benefits of bilingualism could widely vary in relation to the type of bilingualism, proficiency and age of learning. It is not possible to state for definite that whoever speaks fluently two languages will undoubtedly preserve his/her cognitive functions better than monolinguals in their lifetime. Furthermore a variety of other environmental, biological and educational factors can support and synergically contribute to the protective effects against many types of dementia. However, there is supporting evidence that infers to bilingualism as being a protective factor. Also, one of the most important benefits of speaking more than one language is without any doubts the ability to communicate and exchange information with more people. and the opportunity to discover new cultures…so, why not give it a try?
If you cannot visualise the IFG from the diagram then take a look at this interesting animation.
- Argonin E.M., 2008, Alzheimer disease and other dementias, second edition, Philadelphia, Lippincot Williams & Wilkins
- Berken A., Chai X., Chen J.K., Gracco V.L., Klein D., 2016, Effects of Early and Late Bilingualism on Resting-State Functional Connectivity, The Journal of Neuroscience, 36(4): 1165-1172
- Hickok G., Small S.L., 2016, Neurobiology of Language, USA, Elsevier Sanders
- Klein, Mok K. , Chen J.A., Watkins K.E., 2013, Age of language learning shapes brain structure: A cortical thickness study of bilingual and monolingual individuals, Brain & Language, 131 (2014) 20–24
- Notle J., Angevine J.B., 2013, The Human brain in Photographs and Diagrams, 4th Edition, Philadelphia USA, Elsevier Sanders
- Stephen, Does bilingualism delay dementia?, 2015, CMAJ Canadian Medical Association Journal, Volume 187(7), 21 April 2015, p E209–E210
- Suvarna , Thomas H.B., Vasanta D., Bapiraju S., Mekala S., Kumar S. A.,; Jaydip Ray C., Subhash K., 2013, Bilingualism delays age at onset of dementia, independent of education and immigration status, Neurology, Volume 81 (22), p1938-1944
- Bialystok E., Craik F.I.M., Freedman M., 2006, Bilingualism as a protection against the onset of symptoms of dementia, Volume 42 Issue 2, Pages 459–464
Author: Cristina Cabassi
Editor: Molly Campbell