Syntax-sensitive regions of Broca's area and the posterior temporal lobe are differentially recruited by production and perception

Abstract

Neuroimaging studies of syntactic processing typically result in similar activation profiles in Brocas area and the posterior temporal lobe (PTL). However, substantial functional dissociations between these regions have been demonstrated with respect to lesion-symptom mapping in aphasia. To account for this, Matchin & Hickok (2020) proposed that both regions play a role in syntactic processing, broadly construed, but attribute distinct functions to these regions with respect to production and comprehension. Here we report an fMRI study designed to test this hypothesis by contrasting the subvocal articulation and comprehension of structured jabberwocky phrases (syntactic), sequences of real words (lexical), and sequences of pseudowords (phonological). We defined two sets of language-selective regions of interest (ROIs) in individual subjects for Brocas area and the PTL using the contrasts [syntactic > lexical] and [syntactic > phonological]. We found robust significant interactions of comprehension and production between these two regions at the syntactic level, for both sets of language-selective ROIs. This suggests a core difference in the function of these regions: language-selective subregions of Brocas area play a role in syntax driven by the demands of production, whereas language-selective subregions of the PTL play a role in syntax driven by the demands of comprehension.