Bulut, T. | bioRxiv Science

bioRxiv2022

Domain-general and domain-specific functional networks of Broca's area underlying language processing

Despite abundant research on the role of Brocas area in language processing, there is still no consensus on language specificity of this region and its connectivity network. The present study employed the meta-analytic connectivity modeling procedure to identify and compare domain-specific (language-related) and domain-general (non-language) functional connectivity patterns of three subdivisions within the broadly defined Brocas area: pars opercularis (IFGop), pars triangularis (IFGtri) and pars orbitalis (IFGorb) of the left inferior frontal gyrus. The findings revealed a left-lateralized frontotemporal network for all regions of interest underlying domain-specific linguistic functions. The domain-general network and its conjunction with the domain-specific network, however, spanned frontoparietal regions that overlap with the multiple-demand network. The findings suggest that language-specificity of Brocas area emerges within a left-lateralized frontotemporal network, and that domain-general resources are garnered from the frontoparietal network when required by task demands.

neuroscience↗

bioRxiv2022

Functional connectivity of the inferior frontal gyrus: A meta-analytic connectivity modeling study

BackgroundNeurocognitive models of language processing highlight the role of the left inferior frontal gyrus (IFG) in the functional network underlying language. Furthermore, neuroscience research has shown that IFG is not a uniform region anatomically, cytoarchitectonically or functionally. However, no previous study explored the language-related functional connectivity patterns of different IFG subdivisions using a meta-analytic connectivity approach. PurposeThe present meta-analytic connectivity modeling (MACM) study aimed to identify language-related coactivation patterns of the left and right IFG subdivisions. MethodSix regions of interest (ROIs) were defined using a probabilistic brain atlas corresponding to pars opercularis (BA44), pars triangularis (BA45) and pars orbitalis (Fo6&7) of IFG in both hemispheres. The ROIs were used to search the BrainMap functional database to identify neuroimaging experiments with healthy, right-handed participants reporting language-related activations in each ROI. Activation likelihood estimation analyses were then performed on the foci extracted from the identified studies to compute functional convergence for each ROI, which was also contrasted with the other ROIs within the same hemisphere. In addition, a behavioral analysis was conducted to determine functional specificity for language subdomains within each ROI. ResultsA primarily left-lateralized functional network was revealed for the left and right IFG subdivisions. The left IFG ROIs exhibited a more robust coactivation pattern than the right IFG ROIs. In particular, the left posterior-dorsal IFG (BA44) was associated with the most extensive coactivation pattern involving bilateral frontal, bilateral parietal, left temporal, left subcortical (thalamus and putamen), and right cerebellar regions, while the left anterior-ventral IFG (BA45 and Fo6&7) revealed a predominantly left-lateralized involvement of frontotemporal regions. ConclusionThe findings align with the neurocognitive models of language processing that propose a division of labor among the left IFG subdivisions and their respective functional networks. Also, the opercular part of left IFG (BA44) stands out as a major hub in the language network with connections to diverse cortical, subcortical and cerebellar structures.

neuroscience↗