It is a privilege to present the introduction to this new volume of The Cambridge Handbook of Language and Brain. The chapters in this volume represent important trends, methods, and central questions in research on brain and language that encompasses perspectives that include a spectrum of studies in methodology that range from healthy subjects that use one or multiple languages to neurodiversity and neurological disorders. A reader looking to come up to speed on a particular topic in language and the brain need look no further than thorough the list of contributions in this book.
The researchers who have authored chapters for this volume represent an extraordinary group of international scholars representing the multiple disciplines that are critical to the study of language and brain. The chapters represent critical findings from key international research institutes, laboratories, and universities. The clinical and research faculties which have authored contributions come from neuroscience, cognitive neuroscience, brain sciences, neuropsychology, neurolinguistics, neuroimaging, neurosurgery, bilingualism and second language acquisition, language development, specialists in autism spectrum, stroke, and dementias.
The volume is divided into five primary sections: neuroimaging studies of brain and language; language and cognitive development; brain and languages (encompassing building cognitive brain reserve, aphasia and autism spectrum disorders, memory and cognitive-communication disorders); and brain, language, music, and cross-modalities.
Section II Neuroimaging Studies of Brain and Language
In Section II, three chapters review different methodologies to map the brain. The first chapter by Gallo and Abutalebi (“Neuroimaging of Cognitive Reserve in Bilinguals”) explores in detail the importance of use of multiple languages in order to change trends in cognitive aging and cognitive reserve. The authors give recent empirical research results from behavioral studies and neuroimaging studies that focus on cognitive mechanisms of the bilingual brain that can produce cognitive reserve, which can delay and diminish the onset of symptoms of dementias and provide special attention to the differences in brain reserve, neural reserve, and neural compensation. Conclusions include modeling of the mechanisms of bilingualism-induced reserve, the ubiquitous and equitable nature of bilingualism in the general population worldwide, the socioeconomic consequences of cognitive reserve on successful aging and quality of life.
In the second chapter, Andrews and Rammell (“Networks and Multimodalities Underlying Language Processing in the Brain: Evidence from Structural and Functional Neuroimaging”) review a range of studies focusing on language and languages using invasive and noninvasive neuroimaging techniques, including CSM (cortical stimulation mapping), PET (positron emission tomography), structural (DTI) and functional MRI (including task-based and resting state), challenges in interpreting activation results across studies, and the increasing attention to including proficiency measurements to understand neural differences in processing by low vs. higher proficiency users. The role of embodied cognition and multimodalities in language processing and cognitive brain reserve is also examined.
In the third chapter of this section, Kaur, Grant, and Baumer (“TMS as a Tool for Mapping the Dynamic Properties of Language in the Brain”) present the neurosurgical clinical perspective on language mapping techniques, including CSM (cortical stimulation mapping), WADA testing, MEG (magnetoencephalography), fMRI and TMS (transcranial magnetic stimulation). The primary focus of the discussion is on TMS mapping procedures, especially language mapping with rTMS and error analysis. The final sections compare TMS with all the above mentioned techniques and both questions of safety and the limitations of comparative approaches.
Section III Language and Cognitive Development
Section III deals with several chapters that review the neural regions implicated in language processing in the brain. Among these chapters, several further our understanding of how recent methodological approaches have improved our understanding of language development and language disorders in adults. Also, for the first time, dedicated chapters in this book review applications of resting state fMRI analysis and resting state functional connectivity MRI (rsfc-MRI) specifically to language and brain.
In the first chapter in this section, Bitan (“Functional Connectivity and Recovery from Aphasia”) examines the normalization of functional connectivity and, by inference, language processing in individuals with post-stroke aphasia. The effect of stroke and brain lesions has a devastating effect on brain processing, and contrary to old literature that belied any recovery, recent neuroimaging work has highlighted the potential for recovery and reorganization in the adult stroke brain. This chapter first explains the different methodological approaches that have addressed brain connectivity in the context of language processing in aphasia, that is, studies that have examined individuals with aphasia at single time points and those that have examined longitudinal changes in individuals. The author summarizes a convergent finding across all the studies, that after a stroke, the language network tends to normalize its functional connectivity, especially within the left hemisphere and there is concurrent evidence of compensatory connectivity within the right hemisphere and across hemispheres.
Moving on to adult language processing, the next chapter in this section, by Meier and Sandberg (“Recent Developments in Psycholinguistics and Neurolinguistics through the Lens of Aphasia”), reviews recent theories and models of language processing that have emerged from extensive research on the neurobiology of language. For instance, our understanding of semantic processing in the brain has shifted significantly from recent work that describes semantic processing as opposing views on hub-and-spoke processing versus convergent zones. Likewise, the notion of semantic control, a relatively new concept, has been substantiated by a large amount of neuroimaging research. The authors systematically cover other aspects of language processing (phonology, syntax) to bring us up to speed on the latest theoretical frameworks emergent in the research.
The next chapter in this section, addresses a slightly similar topic. Duncan, Pradeep, Kidwai, and Buchwald extend our understanding of brain connectivity beyond the language network and review the existing literature on the default mode network (DMN). Historically, the DMN has been considered a task-independent modality-free network in the brain. Duncan and colleagues review the latest evidential relationship, or the lack thereof, between the default mode network and language processing. Through studies of the healthy brain and also in aging adults as well as in individuals with stroke and neurodegenerative disease, such as dementia and primary progressive aphasia, the chapter highlights the consistent finding that connectivity in the DMN is reduced or impaired in neurological disorders and even though evidence about the link between DMN and language processing is mixed at this time, it may be a promising avenue for interventions.
Expanding beyond language processing, Villard, Zipse, and Vallila-Rohter, review recent evidence on cognitive processes such as attention, memory, working memory, and executive function. Of note, existing neuroimaging evidence has further underscored the link between cognitive and language processing and this chapter tries to link these seemingly disparate processes that also overlap with language processing through evidence from studies on aphasia. For instance, semantic memory, a form of declarative memory, relies on processing the relationship between words and their meanings. As the authors summarize cognitive functions such as memory, working memory and executive function are interconnected to language processing and impact future work on this topic.
In the final chapter of this section, Traxler and Swaab (“Predictive Processing in Language”) examine the processing of “real-time” language production and comprehension through a wide range of methodological approaches. Complexities arise because of the ambiguous and multifaceted aspects of linguistic processing and the important role of different contextual outcomes. These complexities require a more robust model of ecologically valid processing and realization of speech acts. The authors challenge models of “pure bottom-up” processing and explore modeling that requires a broader range of processing, including top-down processing and hybridity.
Section IV Brain and Languages: Building Cognitive Brain Reserve and the Importance of Proficiency
Section IV deals with studies that deepen our understanding of lifelong bi/multilingualism and linguistic variation, including cross-modalities and multi-modalities. In the first chapter of this section, Pliatsikas (“Bilingualism as a Dynamic Experience and Its Effects on Brain Structure, Function, and Metabolism”) brings together a significant body of data that support the view that bilingualism affects domain general cognition and directly impacts both structural and functional aspects of brain function. The author explains the shift in describing bilingualism as a spectral, multivariate experience by using a dynamic restructuring model (DRM) and multiple stages in the bilingual experience. The result is new research that shows additional variability in empirical outcomes that were previously unknown. Topics include healthy subject research, developmental perspectives and both healthy aging and neurodegenerative diseases in aging. Structural changes are noted in gray matter and white matter regions. Functional changes are discussed in the context of resting state networks using hemodynamic and electrophysiological imaging techniques.
In the second chapter, Birdsong (“Factors in Variable Outcomes in Second Language Acquisition” (L2A)) focuses specifically on the range of multiple factors that impact second language learning outcomes, the role of working memory in L2A, learner attitudes, musical training, genetics, age of acquisition, and their interactions. Other topics include language dominance relationships and the instability of L1A and L2A learning outcomes.
In the next chapter, Andrews and Swaine (“Longitudinal fMRI Analyses of Second Language Acquisition: Expanding the Repertoire of Imaging Techniques and Proficiency Measures in Future Studies”) provide a full analysis of longitudinal fMRI studies of second language acquisition conducted from 2010 to the present. All of the six existing studies use BOLD fMRI task-based protocols, and the results of these studies are compared with cross-sectional studies in order to develop methodologies and new strategies for improving research design and empirical methods used in fMRI. The authors identify important theoretically supported dynamic modeling and use variation in L1/L2 language processing to provide the basis for the understanding of a broader array of structural and functional imaging technologies (resting state fMRI, functional connectivity, structural DTI, and fractional anisotropy measures). This study calls for more recognition of the importance of including internationally recognized proficiency measurements to enhance diversity in subject selection and improve overall research design.
Likewise, Schwieter and Klassen (“Cognitive and Neural Aspects of the Multilingual Mental Lexicon”) focus on the central questions that define the research on the so-called mental lexical and neural representations in the multilingual brain. Key points include degrees and integration of lexical mental networks and how they may differ across languages. The authors consider different viewpoints of lexical-based neural processing as representations or patterns of neural activations, exploration of how this research may contribute to future knowledge about cognition, and implications for modeling the multilingual brain.
Gray and Bose contribute an important review of bilingual language processing and language control in healthy subjects. This study focuses on impairment and recovery interactions, as well as deepening understanding of how bilingual language control and cognitive control interact in general and in approaches to treatment.
In the final chapter, Pecukonis, Butler, Gaynor, and Tager-Flusberg provide a thorough review of different aspects of language processing in autism spectrum disorders (ASD). After first introducing the different methodological advances to study language processing in autism that include structural and functional imaging, the authors go on to review key findings of structural and functional differences in the brains of individuals with ASD compared to typically developing individuals. Critically, the authors summarize that ASD may be associated with reduced language connectivity and reduced volume in key frontal and posterior language regions. Finally, the authors present emerging but exciting evidence about atypical language development in infants with high-risk for ASD, when compared to their low-risk infant siblings. These early differences in reduced brain responses in key language regions and decreased functional connectivity could lead to future work on early diagnosis and early intervention.
Section V Brain, Language, and Music
Section V is devoted to the research focusing on the multi- and cross-modalities interactions between language and music and the examination of networks of regions involved in various aspects of language, music, and cognition.
The first and second chapters in this section (contributions by Bidelman and colleagues, and Van Hedger and Maheshwari) bring new perspectives to the field in a number of ways that amplify previous research on music and language, including their roles in neuroplasticity, cognitive-perceptual benefits, and specific comparative aspects of musical and linguistic structures.
First, Bidelman and colleagues focus on cross-sectional and longitudinal studies that examine the importance of music and musicianship on the languaging brain and potential bidirectional “transfer effects” across domains and modalities. Van Hedger and Maheshwari analyze major themes found in the research on music and language, providing compelling reasons to be cautious about overemphasis of what appear to be structural similarities between the two, and the significant differences in meaning generation in each. Van Hedger and Maheshwari present a general cognitive framework that can model both systems and includes both acquisition and maintenance at structural and functional neurological levels. Outcomes include elucidation of how training in one of these modalities can enhance the other at the domain-general system level while being distinct at the domain-specific level.
Section VI New Directions and Perspectives
This section focuses on new topics that intersect with the brain and language.
In the final chapter, Duff and Covington (“Hippocampal Dependent Memory Supports Communication and Language: Implications for Cognitive-Communication Disorders”) review the literature that links memory abilities and language processing. Through the lens of studies performed on individuals with hippocampal lesions, the authors review the literature that dissociates between memory issues that are not linked to language impairments and those that identify common deficits in memory and language processing. Perhaps the most interesting aspect of this chapter is the implementation of novel methodological approaches that elicit behaviors of natural language processing that tap into memory processing. Ultimately, the chapter highlights the observation that hippocampal contributions to language processing are not just restricted to the formation and retrieval of new memories but occur during routine language processing tasks as well.
Summary: Questions, Theory, Application
To summarize, this book identifies key new approaches to the study of language and the brain that sets it apart from previous broad reviews on this topic. Specifically, several technological advancements and theoretical shifts in cognitive neuroscience have allowed the understanding of: (a) Expansion of neural regions implicated in research on language and brain (including cortical, subcortical, brain stem, bilaterality); (b) Examination of networks of regions involved in various aspects of language, music and cognition; (c) Examination of the implications of applying principles of embodied cognition and multimodalities; (d) Applications of resting state fMRI analysis and resting state functional connectivity MRI (rsfc-MRI) specifically to language and brain; (e) Inclusion of research focusing on cognitive reserve (GM, WM - gray matter, white matter); understanding high-end sensory-motor advantages (bilingual, music, etc.); (f) Deepening the perspectives of lifelong bi/multilingualism and linguistic variation, including cross-modalities and multi-modalities; and (g) Reimagining the role of cortical stimulation mapping for neurosurgery and language mapping in pathology and how CSM will be relevant in future research in medical and academic research. All these new advancements situate the book in contemporary human and clinical neuroscience and encourage future work on these topics through further sophisticated and impactful questioning.
