Bilingualism 101: The Bilingual Brain

Foreword

Child bilingualism constitutes a significant global phenomenon which implies that many societies worldwide are multilingual. Thus, children encounter many languages which play a crucial role in shaping their thoughts and minds. If on one hand children may hear two (or more) languages from birth, they could also be reared bilingually despite not living in a bilingual family. This series of articles is therefore focused on bilinguals’ development and the mechanisms involved in the mastery of a plurality of linguistic codes.

The Bilingualism 101 series will be divided into the following chapters of content:

1. Bilingualism 101: Bilingualism in Early Childhood

2. Bilingualism 101: Biological Basis of Bilingualism

3. Bilingualism 101: The Bilingual Brain

4. Bilingualism 101: Bilingualism and Society

5. Bilingualism 101: Bilingualism in Immigrants

6. Bilingualism 101: Language Delay in Bilingualism

The Bilingual Brain

Both linguistic researchers and common people seem to think that learning a second language positively affects human thinking, more specifically lending people higher cognitive flexibility. The European Union Commission for Multilingualism (2008) sustains that

The ability to communicate in several languages […] enhances creativity, breaks cultural stereotypes, encourages thinking “outside the box” and can help develop innovative products and services. (p. 3)

The increased demand for performance adapts to within-brain networks.

Nowadays research focuses on demonstrating why and how the brain of a — simultaneous or sequential — bilingual is affected by the mastery of two or more languages. It is crucial to keep in mind the difference between simultaneous and sequential bilinguals: the first ones are bilinguals who have been adequately exposed to two or more languages since birth; the second ones are either early or late bilinguals (between 2 and 9 years old and after 10 years old, respectively), depending on how long they have been exposed to the second language. Mastering two or more languages requires additional neurocomputation, which can result in changes in the neural substrates. Thus, a higher-demanding performance is needed, leading to increased efficiency of brain networks. The adaptive changes that can be required by those processes might then be detected in the structural properties of the tissue — e.g. grey matter density. According to Paradis (2004) and Green (2008), the neural representation for each language should be interleaved in the bilingual brain, consequently allowing the subject to easily switch and select one language or another.

Considering both monolingual and bilingual speakers, language-control processes prove to be crucial. As said in De Zubicaray et al. (2019),

by ‘control processes’ we refer broadly to processes that allow individuals to perform a range of language tasks (e.g., naming a picture rather than describing it), making a request or issuing a command, and speaking one language rather than another. (p. 262)

The ‘language network’ and the ‘control network’ are brain regions connected by several fiber bundles.

Control processes are needed for several reasons: according to Green and Abutalebi (2013), they play a pivotal role in inhibiting and regulating the interferences from the non-target language, thus implementing the intention to speak one specific language and not the other. Control processes are moreover involved in the ability to code-switch between different languages in the same conversational turn. Nowadays literature indicates a network of cortical, subcortical and cerebellar regions which seem to organize these processes. Green and Abutalebi (2007) consider the dorsal anterior cingulate cortex (dACC), the pre-supplementary motor area (pre-SMA), the left prefrontal cortex, the left caudate and the inferior parietal lobules bilaterally to be the primary regions involved in the language-control network. Moreover, Green and Abutalebi (2013, 2016) have revealed the importance of the control input from the right prefrontal cortex, the thalamus, the putamen of the basal ganglia and the cerebellum. More specifically on the subcortical structures (left caudate, putamen and thalamus), Aron et al. (2007) considered that a specialised neural network for the analysis of salient cues (meaning salient features) in the language would be important to ensure sensitivity to the language context and to initiate a switch in language. Smith et al. (2011) affirmed that the regions of the right inferior frontal cortex connect to the thalamus, which in turn connects two subcortical regions which are crucial for language control, the left head of the caudate and the putamen. Furthermore, the thalamus has a crucial role in attention shifting and action selection and according to Ford (2013), it connects the anterior to the posterior inferior frontal gyrus (IFG). Therefore, De Zubicaray and Schiller (2019, p. 265) suppose that the thalamus is also likely to play a role in language production in bilinguals, “by aiding the selection of the intended lexical and semantic representations, especially in the weaker or less exposed language in highly proficient bilingual speakers”.

Bilinguals select the adequate language for a conversation based on salient linguistic cues.

The so-called ‘language network’ is a set of regions in the left frontal and temporal cortices, together with the inferior parietal cortex. These regions are interconnected by several long fiber bundles of white matter. These bundles seem to support language comprehension production mechanism and, according to Friederici (2015), distinct ventral and dorsal pathways support syntactic, semantic and sensorimotor processes for language use. Nonetheless, the way these pathways manage to integrate sound, syntax and the meaning of language remains underdetermined at present. More precisely, research shows that ventral pathways mediate semantic processing, whereas dorsal pathways take care of sensorimotor and syntactic processing. Therefore, language processing in bilinguals requires language-control signals to operate the selection of the relevant structure in the target language, given that multiple languages in a bilingual’s brain compete to control output. This competing mechanism has been demonstrated by behavioural and event-related potential (ERP) studies such as Leckey and Fredermeier (2019). ERP can be defined as time-locked neural responses, meaning that this method is capable of recording brain responses from a very early stage. For instance, ERP studies demonstrated the existence of a very early brain response to semantic incongruence in native language comprehension tasks, which arises 600 milliseconds after the stimulus onset (see Chow and Phillips, 2013). The use of ERP indeed revolves around the current research interests for those neural events that immediately follow a stimulus leading to a behavioural response, even in terms of mere bloodstream variation.

Since the late 90s, it was suggested that bilingualism might influence — namely enhance — cognitive flexibility, thus upgrading thinking in non-linguistic functions (Bialystok, 1999). In her study, this last author demonstrated that bilingual children outperform monolingual peers. Arguably, monolingual and bilingual children could differ in their ability to conceptualize reality in their motor response during the execution of a task or in their ability to switch from one concept to another (e.g., the ability to switch from grammar to another when using language in the communication). Bialystok (2004), through a card sort task, observed that the only ability which showed remarkable differences between the two groups — i.e. monolinguals and bilinguals — was concept-switching, as bilinguals perform better when it comes to ignoring non-relevant stimuli. The difference in the whole way of thinking between bilinguals and monolinguals, as firstly suggested by Grosjean (1989), was also demonstrated in the experiment carried out by Athanasopoulos (2009). This study introduced a new variable, namely the Categorical Perception Index (CPI), which was assessed in the domain of colour for Greek-English bilinguals. As a result, cognition seems to be tightly linked to semantic memory for specific linguistic categories such as colours, and cultural immersion in the L2-speaking country as well — thus proving the effects of acculturation. Moreover, Pavlenko (2006) showed that bilinguals perceive themselves as different persons when using one of the languages they master as a function of linguistic and cultural differences between the languages themselves, the degree of language emotionality, the level of language proficiency and the language-learning context.

Bilingual life experience shapes cognition, based on general executive control.

In conclusion, even if we have no well-structured theory of the actual changes that seem to happen within the brain at present, there is evidence to state that non-linguistic performance is influenced by the mastery of two or more languages. The seemingly increased demand for the use of more than one language could drive the plastic changes within the bilingual brain. The use of more than one language seems to alter the structure of the language network compared to that of a monolingual, but the same holds true for the network which is involved in its control. The Oxford Handbook of Neurolinguistics by De Zubicaray et al. (2019) supposes that language control exploits the same neural regions which are involved in the control of action in general (also see Pliatsikas and Luk, 2016). It is important to consider that the language network and the control network are separated so that they imply a separate demand. Responding to increased demand might imply an increased efficiency in the networks’ patterns of connectivity. On the contrary, radically distinct brain areas could also become involved in the bilingual brain to perform the required neurocomputations. Nonetheless, according to Paz-Alonso et al. (2019), it seems that bilinguals exploit the same brain regions to process lexical, syntactic and prosodic information of all the languages they master, thus showing an overlapping activation of the regions involved in language processing. According to Pliatsikas and Luk (2016), “bilingual experience shapes cognition”, meaning that the interaction between task-related functional networks and resting-state networks must be considered too. Such interaction is crucial for bilingual language control, which relies on domain-general executive control — i.e. a set of skills sustaining goal-directed behaviours such as inhibition of non-relevant inputs, updating and attention shifting.

Bibliographical references

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