How multicultural inputs interact with the brain and the behavioural consequences that follow are still poorly understood matters. Notably, they are of great importance for health, educational, team management, and legal purposes, especially given that cultural admixture has been increasing. The aim of the present work is to provide a multidisciplinary review on the subject, in which behavioural data is linked to brain imaging research whenever possible. The focus lies on bicultural individuals, as they represent the simplest form of the phenomenon to be analysed. This task comprises a journey through cultural priming and cultural frame switching; migration and personality shifts; and cultural metacognition.
In the globalised World, it can be a benefit to understand better how the internalization of a second culture occurs in the brain, as well as the behavioural outcomes to expect both during the initial period of the acculturation process and throughout the lifespan of an individual. In other words, to unravel brain plasticity towards culture and its consequences. The current cross-cultural research comprising neural and behavioural aspects suggests that there are differences between cultures regarding cognitive biases, perceptions of the self, language and music processing, neural recruitment on numerical and visuospatial tasks [1, 2], among others. However, such accounts are almost exclusive to comparisons between the so-called Western and East Asian cultures. Still, they are relevant to consider, because they indicate that culture is somehow wiring our brain , as the existence of a sensible period for acculturation also supports . Noteworthy, Han and Ma  advanced the culture-behaviour-brain loop model, which posits that, by contextualizing behaviour, culture shapes the brain, which, in turn, may fit or modify culture through the voluntary behaviours it guides. Remains the question: how are inputs from a second culture kept in the loop? – and this is precisely what the present work seeks to answer. Strangely, very few efforts have been made to test contrasts between monocultural X and Y with bicultural XY individuals , which is a paramount piece to understand the mentioned cultural contrasts.
A final clarification must be made: biculturalism is not, by any means, a straightforward phenomenon. One may be bicultural only regarding some particular trait, or a restricted set of traits. Moreover, the level of bicultural identity integration (BII) increases its complexity: whereas people low on BII integrate separately two, probably conflicting, cultural identities, those high on BII are told to have a single blended cultural identity . Additionally, specific behavioural outcomes can be expected depending on the BII score . Before proceeding, it is worth to cite Ambady and Barucha’s  description of the relation between culture and the brain:
“Cultural practices adapt to neural constraints, and the brain adapts to cultural practice. Other circuits are wired as a result of learning, particularly implicit learning. In this latter respect, the brain is a cultural sponge – indeed, possibly, the organ of culture. It internalizes the structural regularities of its environment within the parameters of innate and developmental constraints, and it employs these internalized representations to facilitate interaction with the physical and social world.”
Can cultural priming dissect brain-wiring?
There are behavioural paradigms attributed to the individualist Western cultures, which contrast with those of the collectivistic East Asian ones. For instance, when interpreting a given social event, the first group tends to focus on internal attributions, while the latter relies more on external aspects . Hong, Morris, Chiu, and Benet-Martínez  proposed the term cultural frame switching in a revision of experiments documenting that bicultural individuals store different behavioural patterns, ready to respond to stimuli from specific cultures. This concept followed assumptions from the cultural constructivist approach: rather than being internalized as a general mentality, culture is a dispersed system of meanings; which can be fed with information from distinct cultures, even if that may generate internal conflicts. One of the studies they mention  consisted of several experiments with bicultural Hong Kong Chinese students, who were randomly exposed to one of three primes: pictures of American icons, of Chinese icons, and six drawings of geometric pictures (control). Then, when processing a common image, participants in the American-prime condition engaged in less external attributions than those in the Chinese-prime condition, as expected. Importantly, the control group showed intermediate levels of the behavioural measure. Furthermore, neuroimaging research seems to support the dual response capacity of bicultural individuals ; while at the same time indicating that to the between-cultures behavioural differences corresponds a characteristic pattern of brain activation . “The reported research makes it very tempting to conclude that internalizing a second culture produces alterations in the brain, which will determine disparate behavioural pathways, whose activation depends on specific cultural cues within the surrounding environment”. However, several issues must be taken into account…
First: the described priming effect is not straightforward. It was shown that individuals low on BII were cultural reactant, exhibiting a contrast effect, as opposed to the assimilation effect; meaning they behaved American-like when exposed to the Chinese primes, and vice versa . However, when the cultural primes were negative stereotypic words, the pattern inverted – with the low BII group responding congruently and the high BII one incongruently . Hence, it is possible that these contrast effects can be explained by general cognitive processes, such as seeking distance from cues perceived as antagonistic , rather than culture-specific wiring causes. Second: cultural variation in functional and structural brain arrangements may be partially due to genetic factors . Finally, there are meta-analysis studies suggesting that the reported cross-cultural differences may not be as large and systematic as assumed . In fact, a study from Chiao and colleagues  gave further support to this claim. They presented a sample of native Japanese and American Caucasian participants in which, during a self-judgement task, 70% of those who behaved individualistically were Japanese, while around 64% of Caucasians fell into the collectivistic group, contrarily to what would be expected from the supposedly cultural-characteristic behaviours. The reported neuroimaging results revealed main effects of collectivism and individualism at the individual level, but not from cultural affiliation.
Unfortunately, data gathered so far in this framework are hardly comparable due to contrasting methodologies, poor descriptions of the populations sampled, lack of knowledge regarding causality, and possible confounding effects on stimuli endorsement . Nevertheless, cultural priming assimilation effects on bicultural individuals have also been described in aesthetic judgments  and memory tasks regarding faces from different ethnicities [20, 21]. Importantly, the latter found clear behavioural differences between mono- and bicultural participants, as the priming technique sorted no effect on the monocultural group Thus, despite being difficult to draw safe conclusions on the current ground, there are pieces of evidence pointing to the existence of a complex brain plasticity towards culture.
Has acculturation changed me?
The adaptation to a second culture is psychologically challenging and the potential distress it can cause is called acculturative stress . Within the current literature it is possible to find examples of shifts concerning behavioural and psychological aspects, attributed to the acculturation process. Mesoudi  made a review showing a trend within migrant populations to approach, across generations, the host society’s patterns for several traits, such as religiosity, collectivism, trust, self-esteem, and social closeness. However, an essential piece of the puzzle is missing: there seems to be no study presenting comparisons between those who remain in the country of origin and the first-generation migrants. In other words, the origin of the axis is missing, making it very difficult to understand the extent to which acculturation can produce changes through the lifespan of an individual.
Still, studies of personality combining the Big Five Personality Traits  with language tests, can provide further clues. Chen and Bond  showed that Chinese-English bilinguals tended to place themselves between Cantonese and English native speakers across several personality dimensions, although closer to the former group, that of their origins. Furthermore, they presented an analysis relying on the ratings of external observers, while the participants were interacting with four different interlocutors. The experimental design consisted of Ethnicity (Chinese/Caucasian) x Language (Cantonese/English) and it revealed a significant interaction effect, suggesting that participants seek to adapt to the perceived prototypic personality of the interlocutor. Bringing back the mentioned priming technique, further evidence can be extracted for the occurrence of personality shifts in bicultural individuals. In an experiment run by Mok and Morris , bicultural East Asian-American participants with high BII, primed with Asian vignettes, scored lower on the self-reported need for uniqueness and extroversion than those in the American-prime condition. Meaning they reacted congruently to the stimulus. Contrastingly, low BII individuals exhibited the opposite patterns.
Are there any specific mental abilities related with multiculturalism?
One of the few comparisons between bicultural and monocultural individuals has pointed out that the former group tends to exhibit cultural representations with higher cognitive complexity . Further on, cultural metacognition is the capacity to consider how the cultural background may influence one’s behaviour. This mental ability proved to be paramount to make multicultural teams function properly, working as a social glue . Together with cultural frame switching, they constitute the cognitive elements underlying the bicultural competence, defined by Hong  as the:
“(…) bicultural’s ability to draw upon cultural knowledge and cross-cultural abilities (such as adapting one’s behavior [sic.] and communicating across cultures) to effectively switch cultural frames and apply cultural metacognition to disparate cultural contexts in order to work successfully with people from different cultural backgrounds toward [sic.] a desired organizational outcome.”
This author defends that, from the perspective of international management, across all the BII scale, bicultural individuals have unique positive contributions to give – namely, in conflict mediation and boundaries spanning. Interestingly, there are pieces of evidence suggesting that individuals with low BII have even more cognitively complex cultural representations than those high on BII . Furthermore, Maddux, Adam, and Galinsky  found a positive correlation between multicultural learning with both idea flexibility and creative insight in American and French university students, but only when they lived abroad. Nonetheless, other studies report mixed results with a series of pros and cons detected in several verbal and visual tasks, depending on the order of acquisition of the two cultures considered . Additionally, others argue that only when the two cultures are well blended the domain-general creativity enhancement does arise . According to Stahl, Maznevski, Voigt, and Jonsen , culturally diverse teams tend to be creative and satisfactory, though prone to conflict and social integration problems. The authors added that, while satisfaction depends on the team size, the risk of conflict is affected by the complexity of the task. Overall, this suggests that bicultural individuals are potentially exposed to an innovative and rewarding environment, in which social interactions may be quite cognitively demanding. It is in this ground of challenges and opportunities that cultural metacognition flourishes. Unfortunately, mostly because of the absence of brain imaging data, this mental faculty remains poorly understood.
There are many pieces of evidence suggesting that learning a second culture has a broad impact on Human psychology. In fact, our personality seems to present a certain cultural flexibility. For example, bicultural individuals seem to adjust to the perceived prototypical personality of a given interlocutor, according to the language being spoken . Additionally, it is known that behavioural shifts occur across generations, with the descendants of migrants successively approaching the patterns of the receiving population . Unfortunately, the extension of this effect through the lifespan of a single individual is poorly understood. Having a certain psychological malleability is paramount to navigate between distinct cultural worlds, and bicultural individuals seem to exhibit the capacity to store distinct behavioural pathways. Because these patterns are triggered by cultural-specific cues, this mental ability has been designated cultural frame switching. Accordingly, brain imaging research points out that cultural frame switching translates into disparate brain activation patterns [11, 12]. Thus, multiculturalism seemingly affects brain function as well. Together with cultural metacognition, this psychological feature constitutes the bicultural competence – which international management research denotes to be an essential skill to make multicultural teams function properly . These characteristics probably cannot be developed merely through studying other cultures. Rather, they may require a complete exposure to a different cultural environment, as documented when testing the advantages on idea flexibility and creativity originated from multicultural learning .
Worth noting, enculturation effects have also been detected in aesthetic judgement  and facial memory [20, 21]. Interestingly, the latter case presents one of the few direct, behavioural contrasts found between mono- and bicultural participants – in which the cultural priming technique sorted effects exclusively regarding the second group. Another important comparison concerns cultural metacognition: monocultural individuals seem to have less cognitively complex cultural representations than their bicultural peers . Still, future research should focus on further dissecting behavioural differences between these two groups. Additionally, because not all combinations of cultures may produce equal results, a wider range of cultures should be included in the battery of analyses. Overall, all the mentioned information should be considered carefully, as it is frequently made in the bases of pre-established cultural patterns of behaviour – which do not always prove to be consistent [16, 17]. Also, there might be confounding effects derived from genetic factors . Finally, mechanisms such as the cultural frame switching are not linear, as they dramatically change depending on how the individuals have integrated both cultures [6, 13].
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