Word meanings and sentence structure recruit the same set of fronto-temporal regions during comprehension

To understand what you are reading now, your mind retrieves the meanings of words from a linguistic knowledge store (lexico-semantic processing) and identifies the relationships among them to construct a complex meaning (syntactic or combinatorial processing). Do these two sets of processes rely on distinct, specialized mechanisms or, rather, share a common pool of resources? Linguistic theorizing and empirical evidence from language acquisition and processing have yielded a picture whereby lexico-semantic and syntactic processing are deeply inter-connected. In contrast, most current proposals of the neural architecture of language continue to endorse a view whereby certain brain regions selectively support lexico-semantic storage/processing whereas others selectively support syntactic/combinatorial storage/processing, despite inconsistent evidence for this division of linguistic labor across brain regions. Here, we searched for a dissociation between lexico-semantic and syntactic processing using a powerful individual-subjects fMRI approach across three sentence comprehension paradigms (n=49 participants total): responses to lexico-semantic vs. syntactic violations (Experiment 1); recovery from neural suppression across pairs of sentences differing in lexical items vs. syntactic structure (Experiment 2); and same/different meaning judgments on such sentence pairs (Experiment 3). Across experiments, both lexico-semantic and syntactic conditions elicited robust responses throughout the language network. Critically, no regions were more strongly engaged by syntactic than lexico-semantic processing, although some regions showed the opposite pattern. Thus, contra many current proposals of the neural architecture of language, lexico-semantic and syntactic/combinatorial processing are not separable at the level of brain regions – or even voxel subsets – within the language network, in line with strong integration between these two processes that has been consistently observed in behavioral language research. The results further suggest that the language network may be generally more strongly concerned with meaning than structure, in line with the primary function of language – to share meanings across minds.