Stable brain loci for the processing of complex syntax: A review of the current neuroimaging evidence

We conducted a retrospective review of fMRI studies of complex syntax, in order to study the stability of the neural bases of mechanisms engaged in syntactic processing. Our review set out rigorous selection criteria of studies which we discuss, including transparency and minimality of the contrasts between stimuli, and the presence of whole brain analyses corrected for multiple comparisons. Seventeen studies with 316 participants survived our sieve. We mapped the 65 resulting maxima onto JuBrain, a state-of-the-art cytoarchitectonic brain atlas (Amunts et al., 2020), and a sharp picture emerged: syntactic displacement operations (a k a MOVE) produce highly consistent results, activating left Broca's region across-the-board and unambiguously; to a somewhat lesser extent, maxima clustered in left posterior brain regions, including the STS/STG. The few studies of syntactic tree-building operations (a k a MERGE) produce a murkier picture regarding the involvement of the left IFG. We conclude that the extant data decisively point to the JuBrain-defined Broca's region as the main locus of complex receptive syntax in healthy people; the STS/STG also are involved, but to a lesser extent.