Big Question 2
(last update 2019-06-18)
What are the characteristics and consequences of internal brain organization for language?
The human brain provides a neurobiological infrastructure that allows us to acquire and process language, and that co-determines the characteristics of spoken (and sign) and written language. The internal organization of the brain and its cognitive architecture both determine and constrain the space of possibilities for human language. This internal organization can be called the Kantian brain for language. It has resulted in a language-readiness of the human brain that is found nowhere else in the animal kingdom. The big question is to characterize the Kantian brain for language.
Currently BQ2 is in the process of building links between the various sub-projects. Each sub-project has had the opportunity to present their most recent work/ideas/questions of interest, and BQ2 is now in a phase of bridging the sub-projects to try to define new research questions based on collaborations between sub-themes. To foster such collaborations, meetings are planned where pairings of sub-projects will present ideas that culminate from joint brainstorm sessions about potential links between one another’s work and expertise. In the long run the hope is that such combinations of expertise and perspectives will lead to innovative and cutting-edge projects that address the overarching goal of how the human brain supports language processing.
Highlight 1: Anatomical and Connectopic Adaptations to Language
Team members: Freches, Beckmann, and Mars
The purpose of this project is to develop a large-scale comparative approach to studying the architecture of connections across the brains of a range of different primates that differ in their communicative abilities and strategies. The project utilizes measures of functional and structural connectivity to shed light on underlying building blocks that support the features for the connectome of language. The pipeline for connectopic mapping using white matter tractography data has been developed. Thus far the pipeline has been used for mapping the connectopies in Brodmann areas 44/45, V1, and Temporal Lobe in humans and primates. In BA44/45, two overlapping modes of connectivity were disentangled: the first mode (G1) showing gradual connectivity change when moving along the BA44/45 posterior-anterior axis; the second mode (G2) highlighting separate contribution of dorsal and ventral tracts towards this region’s connectivity fingerprint. Preliminary results on the temporal lobe show that humans and chimpanzees share the first mode of connectivity, but start to diverge on their connectivity fingerprints when higher order gradients are explored. Differences seem to be driven by expansion of the arcuate fasciculus towards the anterior temporal lobe in humans.
First two overlapping gradients of white matter connectivity present in BA 44/45 for each hemisphere. G1 (first gradient) separates BA44 from BA45. G2 (second gradient) separates contributions from dorsal and ventral white matter tracts. Colours indicate relative similarity in patterns of connectivity
This project is at the forefront of methods development with a strong focus on brain connectivity across species.
It directly addresses a core question of the BQ2: what characteristics of human brains support our unique abilities to acquire/use language.
This project brings together expertise from neuroimaging, specifically related to novel approaches to mapping functional and structural connectivity, and a cross-species comparative perspective. Such a large-scale cross-species comparative project would not be possible without extensive sharing of data (especially primate) and expertise.
Highlight 2: The Role of Basal Ganglia Mediated Inhibition in Producing Inflections
Team members: Ferreira, Roelofs, and Piai
This project investigates the role of basal ganglia in language. In particular, inflectional encoding is studied as a proxy for inhibition mediated by the basal ganglia. Dual-system theory proposes that regular forms (walk – walked) are constructed by rule, while irregulars (swim – swam) are stored and retrieved from memory. During retrieval of irregular forms, rule application is assumed to be inhibited.
When speakers switch between tasks, an asymmetrical switch-cost is obtained which has been attributed to overcoming previous inhibition of the predominant response. Capitalizing on this, participants in the experiment alternated between producing regular and irregular past tense forms. Results displayed no difference in reaction time between regulars and irregulars, offering no support for the proposal that the production of irregulars involves (basal ganglia mediated) inhibition of the regular rule. A control experiment showed clear switch-costs when switching between reading and inflecting, suggesting that the paradigm had sufficient power to detect switch-costs. These findings challenge the assumption that inhibition is the mechanism by which rule application is blocked in producing the past tense of irregular verbs.
Mean naming response time (RT) for each participant and group-level mean RT (M) and mean error percentage (E%) for the inflect and read tasks grouped by regularity (regular, irregular) and type of trial
The task-switching paradigm being developed has potential to be used as a comparative measure of inhibition during language function in controls and patients. Specifically, it could be used in combination with fMRI to probe basal ganglia circuits responsible for hypothesized inhibition.
This project combines expertise in cognitive modelling, language production, task switching and inhibition, neuroimaging, and patient studies. This unique combination of expertise/knowledge is essential for developing novel paradigms to assess understudied sub-cortical structures in the context of language processing.
Synergy with other Big Questions
Once there is clarity on future directions for collaborative projects within BQ2, the plan is to try to find points of contact with other related BQs in the consortium and potentially foster cross-BQ collaborations on particular aspects of projects where such links present themselves. For instance, neuroimaging data to be collected can be used to evaluate models developed by BQ1. Some of the analysis methods from BQ2 can be further utilized in BQ4 and BQ5.
More concretely, the BQ2 team members Piai (Tenure) and Janssen (PhD) have developed a neuropsychological measure in collaboration with De Swart (CLS): the SynTest. The SynTest is a sentence-to-picture matching task that assesses sentence comprehension with increasing grammatical complexity. It is specifically developed to aid in the differentiation between logopenic and non-fluent primary progressive aphasia (PPA) patients and data collection for validation has now started in multiple Dutch hospitals. A computerized version of this test is being implemented in the BQ4 test battery by Menks (Postdoc).
Hans Rutger Bosker
Guilherme Blazquez Freches
Floris de Lange