The Cortical Organization of Syntax

Abstract

Syntax, the structure of sentences, enables humans to express an infinite range of meanings through finite means. The neurobiology of syntax has been intensely studied but with little consensus. Two main candidate regions have been identified: the posterior inferior frontal gyrus (pIFG) and the posterior middle temporal gyrus (pMTG). Integrating research in linguistics, psycholinguistics, and neuroscience, we propose a neuroanatomical framework for syntax that attributes distinct syntactic computations to these regions in a unified model. The key theoretical advances are adopting a modern lexicalized view of syntax in which the lexicon and syntactic rules are intertwined, and recognizing a computational asymmetry in the role of syntax during comprehension and production. Our model postulates a hierarchical lexical-syntactic function to the pMTG, which interconnects previously identified speech perception and conceptual-semantic systems in the temporal and inferior parietal lobes, crucial for both sentence production and comprehension. These relational hierarchies are transformed via the pIFG into morpho-syntactic sequences, primarily tied to production. We show how this architecture provides a better account of the full range of data and is consistent with recent proposals regarding the organization of phonological processes in the brain.

Dissociation between Frontal and Temporal-Parietal Contributions to Connected Speech in Acute Stroke

“…This work provides the first evidence in acute stroke of a functional and anatomical dissociation between temporal-parietal and frontal focal brain regions for lexically and syntactically driven processes required for spontaneous connected speech. These results are consistent with predictions from models of syntactic processing based primarily on evidence from language comprehension (Friederici et al, 2017;Hagoort, 2019;Matchin and Hickok, 2019;cf. Wilson et al, 2016;Fedorenko et al, 2018;Rogalsky et al, 2018).…”

“…Thothathiri et al, 2012;Magnusdottir et al, 2013;Blank et al, 2016;Wilson et al, 2016;Fedorenko et al, 2018;Rogalsky et al, 2018). Matchin and Hickok (2019) propose that the inherently different processing requirements for language production and comprehension account for the differences in syntactic processing related neural substrates. In production as well as comprehension, the generation of lexicalsemantic structure is required both to understand the relationship between words during comprehension, as well specify relationships between words to accurately reflect the message to be produced.…”

“…During initial stages of connected speech, a speaker generates a message she wishes to convey and activates the concepts associated with that message (Levelt, 1989;Levelt et al, 1999). As Fromkin (1971) and Garrett (1975;1980) originally formulated based on speech errors and others further developed (Dell, 1986;Levelt, 1989;Bock and Loebell, 1990;Bock and Levelt, 1994;Bock, 1995;Vigliocco and Hartsuiker, 2002;Matchin and Hickok, 2019), subsequent stages orchestrate word selection and the organization of words into larger multiword utterances. During functional encoding, a speaker must select the words associated with the concepts that form part of the intended message, potentially along with associated information like the word's grammatical class (Levelt et al, 1999;cf.…”

Agrammatism and paragrammatism: a cortical double dissociation revealed by lesion-symptom mapping

“…We identified patients' grammatical deficits through a perceptual rating of patients' speech samples. According to the hypothesis presented in Matchin & Hickok (2019), we expected a double dissociation: paragrammatism would be associated with damage to the pMTG (and not IFGtri) while agrammatism would be associated with damage to IFGtri (and not the pMTG). Because neuroimaging studies have also identified syntactic effects in neighboring tissue (see Matchin & Hickok, 2019 for a review), and the difficulty of straightforwardly interpreting the localization in lesion-symptom mapping (Wilson, 2016), we created broader regions of interest (ROIs) encompassing these regions in order to maximize our ability to detect effects.…”

“…An important issue concerning research into syntactic deficits in aphasia is the question of how syntax is organized in the healthy brain. While prominent models of syntax in the brain posit a primary syntactic function to different subregions of the inferior frontal gyrus (Friederici 2017;Hagoort 2014), Matchin and Hickok (2019) recently hypothesized a new model of syntax in the brain, with two primary cortical zones responsible for distinct aspects of syntactic processing. The first is a hierarchical lexical-syntactic system in the left posterior middle temporal gyrus (pMTG), including the ventral bank of the superior temporal sulcus (STS).…”