Vincent DeLuca

Bilingualism research sits at the intersection of linguistics, cognitive neuroscience, and psychology, yet these disciplines often operate in relative isolation, limiting explanatory power and theoretical progress. This paper argues that deeper, more purposeful cross-fertilization among these fields is both possible and necessary to address some of the most pressing questions in the study of bilingualism. After establishing a shared foundation through a concise history of mind–brain–language inquiry, we outline the componential architecture of language — spanning phonology, syntax, morphology, semantics, and pragmatics — to underscore the linguistic sophistication required for meaningful neuroscientific investigation. We then review the neuroanatomical substrates of language representation, processing, and cognitive control, emphasizing distributed network models over classical localizationist accounts. The contribution of electroencephalography (EEG) is examined, including event-related potentials, oscillatory dynamics, and resting-state measures, highlighting their capacity to capture how bilingual experience reshapes linguistic processing and neural function over time and at the individual level. Two exemplars operationalize our convergence argument. Exemplar 1 demonstrates how early brain states measured via EEG can predict individual differences in bilingual linguistic developmental trajectories, offering prospective, mechanistic insights that retrospective adult studies cannot. Exemplar 2 illustrates how linguistically principled formalization of relative linguistic typological distance (RLTD) is indispensable for studies seeking to link cross-language structural differences to bilingualism-induced neurocognitive adaptations. Together, these cases show that linguistics needs neuroscience to ground its constructs in neural mechanisms, while neuroscience needs linguistics to properly characterize what is being processed. Genuine interdisciplinary integration, not parallel inquiry, is the path forward for bilingualism research.

Individual differences in using multiple languages are thought to differentially affect brain structure and function. The present study assessed the neuroanatomical predictions of an emerging theory, the Unifying the Bilingual Experience Trajectories framework, which provides the most comprehensive set of predictions of how individual differences in bilingual experiences lead to specific neural and cognitive adaptations. A total of 140 young adults with variable language experiences were scanned using magnetic resonance imaging and completed demographic questionnaires. Brain structure measures implicated in predictions of the Unifying the Bilingual Experience Trajectories model were extracted and regressed against the model’s experiential factors. Consistent with the model’s predictions, greater intensity and diversity of bilingual language use resulted in changes in gray matter volume in cortical regions involved in executive control (including inferior frontal gyrus, middle temporal gyrus, angular gyrus, and medial frontal gyrus), indicating adaptations toward handling increased executive control demands. Conversely, duration of bilingual engagement resulted in changes within white matter microstructure (bilateral superior longitudinal fasciculus) and increases in subcortical gray matter (left caudate), indicative of adaptations toward increased efficiency of control. Overall, this research enhances our understanding of how bilingual experiences influence brain structure and provides the first direct empirical evidence for the predictions made by the Unifying the Bilingual Experience Trajectories framework.

Recent advances in our understanding of the neural bases of the brain’s structure(s) have critically shaped research on second language (L2) and bilingualism. The emergence and wider-scale use of neuroimaging methods in the last 30 years has increasingly enabled investigating the structural brain changes, revealing a high level of neuroplasticity for the bilingual brain. This chapter describes the neuroimaging methods that enable the analysis of the structural changes that occur in response to bilingualism and L2 acquisition. First, the chapter describes the most used methods, including techniques to study the brain’s gray and white matter, and the neurostructural adaptations that occur in the face of L2 language acquisition and bilingualism. Then each technique is exemplified through key research articles. Finally, the chapter concludes by offering some potential developments for future research and discussing how new structural neuroimaging techniques may further our understanding of neurophysiological effects of bilingualism.

Modern Generative Second Language Acquisition (GenSLA) examines many aspects of acquisition and processing that transcend access to Universal Grammar in adulthood, though the connections between GenSLA and neurolinguistics are limited. Notwithstanding, formal and neurolinguistic inquiry inform one another meaningfully, particularly in the domain of second language (L2) acquisition and processing. This chapter discusses the L2 acquisition and processing of grammatical gender and non-local dependencies by examining the history of GenSLA and its modern turn, including pertinent neurolinguistic methods and questions. In so doing, the chapter addresses questions such as ultimate attainment and the tenability of a critical period for L2 acquisition.

The earliest investigations of the neural implementation of language started with examining patients with various types of disorders and underlying brain damage

Herein, we contextualize, problematize, and offer some insights for moving beyond the problem of monolingual comparative normativity in (psycho) linguistic research on bilingualism. We argue that, in the vast majority of cases, juxtaposing (functional) monolinguals to bilinguals fails to offer what the comparison is supposedly intended to do: meet the standards of empirical control in line with the scientific method. Instead, the default nature of monolingual comparative normativity has historically contributed to inequalities in many facets of bilingualism research and continues to impede progress on multiple levels. Beyond framing our views on the matter, we offer some epistemological considerations and methodological alternatives to this standard practice that improve empirical rigor while fostering increased diversity, inclusivity, and equity in our field.

Bilinguals have often, but not always, been found to outperform monolinguals on domain-general attentional control. Inconsistent findings have been argued to stem, at least partly, from treating bilingualism as a uniform category and from not considering how neural adaptations to bilingual experiences modulate behavioural outcomes. The present study investigated how patterns of language experience, including language switching behaviour, duration and intensity/diversity of bilingual language use, influence the brain processes underlying cognitive control, and how these in turn translate to cognitive control performance. We examined reaction times and spectral dynamics of the electroencephalograms (EEG) of two-hundred-and-thirty-nine participants (about 70% bilinguals) with diverse language experiences during two cognitive control paradigms testing interference suppression (flanker and Simon task). Using structural equation modelling, we found that different bilingual experience factors were related with neurocognitive measures, which in turn were related with behavioural interference effects, for the flanker but not the Simon task. More specifically, increased frequency of language switching and intensity / diversity of bilingual language usage was negatively related to induced top-down control measures (especially midline-frontal theta), which in turn was beneficial for interference control. In contrast, duration of bilingual engagement correlated negatively with evoked bottom-up control measures (especially P3) and was therefore detrimental to interference control. We demonstrate here for the first time how the different factors of bilingual experience lead to different neural adaptations which impact behavioural outcomes. Significance statement: Like other intensive experiences, bilingualism leads to brain adaptations. It results in structural changes in language areas, and, due to demands on language control, in brain areas associated with domain-general cognitive control. Related to this, bilinguals often outperform monolinguals on cognitive control tasks. But what is often ignored is that bilingualism is a multi-dimensional phenomenon, with variations such as diversity of language usage and duration of language use. The present large-scale study of neural functioning in bilingualism revealed for the first time how individual differences in bilingual experience lead to adaptations to brain functioning which in turn affect cognitive control behaviour. It exemplifies how the complexity of individual experiences plays a fundamental role in brain function.