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

Abstract

Background: Neurocognitive 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. Purpose: The present meta-analytic connectivity modeling (MACM) study aimed to identify language-related coactivation patterns of the left and right IFG subdivisions. Method: Six 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. Results: A 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. Conclusion: The 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.

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

“…Given that a functional network identified during language tasks may still involve domain-general processes such as working memory and cognitive control, directly exploring divergence (through contrast analyses) and convergence (through conjunction analyses) between the functional network identified for language tasks and that identified for non-language tasks may help disentangle domain-specific and domain-general neural circuitry of Broca’s area. Against this background, the present study builds on and extends a previous MACM study on the functional connectivity of IFG for language tasks (Bulut, 2022). Thus, the present research aims to contrast domain-specific and domain-general coactivation patterns of the left IFGop, IFGtri and IFGorb by utilizing the MACM method and the BrainMap functional neuroimaging database.…”

“…Against this background, the present study builds on and extends a previous MACM study on the functional connectivity of IFG for language tasks (Bulut, 2022). Thus, the present research aims to contrast domain-specific and domain-general coactivation patterns of the left IFGop, IFGtri and IFGorb by utilizing the MACM method and the BrainMap functional neuroimaging database.…”

“…Given that a large database of experiments with various tasks and designs are utilized, MACM can produce highly generalizable findings (Samartsidis et al, 2020). Recent MACM investigations of IFG revealed a language network spanning largely left-lateralized frontal, temporal and parietal regions as well as several subcortical structures (Bernal et al, 2015; Bulut, 2022). Furthermore, striking differences in the language-related functional connectivity patterns were observed amongst IFG subdivisions, with the left IFGop coactivating with a broad network of cortical, subcortical and cerebellar structures (Bulut, 2022).…”

“…Although MACM has been employed to identify functional connectivity of the left IFGop for language tasks (Bernal et al, 2015) and to parcellate distinct clusters within the left IFGop and identify their connectivity for different functional domains including language (Clos et al, 2013), no previous meta-analytic connectivity study directly compared domain-specific (language-related) and domain-general (non-language) functional connectivity of subdivisions of the broadly defined Broca’s area or complex including the left IFGop, IFGtri and IFGorb. Although a recent study investigated language-related functional connectivity of bilateral IFGop, IFGtri and IFGorb using MACM (Bulut, 2022), these connectivity patterns were not compared with domain-general connectivity patterns of the relevant regions. Given that a functional network identified during language tasks may still involve domain-general processes such as working memory and cognitive control, directly exploring divergence (through contrast analyses) and convergence (through conjunction analyses) between the functional network identified for language tasks and that identified for non-language tasks may help disentangle domain-specific and domain-general neural circuitry of Broca’s area.…”

“… 1 The left-hemispheric ROIs and the neuroimaging experiments included in the domain-specific analyses in the present research were the same as a previous study on language-specific connectivity of bilateral IFG (Bulut, 2022). However, differently from that study, the present study included a domain-general contrast and compared domain-general and domain-specific networks of the left IFG subdivisions in contrast and conjunction analyses.…”