Left posterior temporal cortex is sensitive to syntax within conceptually matched Arabic expressions

Suhail Matar,Liina Pylkkänen,Alec Marantz,Julien Dirani

doi:10.1038/s41598-021-86474-x

Suhail Matar, Liina Pylkkänen + Show 2 more

Open Access

https://doi.org/10.1038/s41598-021-86474-x

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Abstract

During language comprehension, the brain processes not only word meanings, but also the grammatical structure—the “syntax”—that strings words into phrases and sentences. Yet the neural basis of syntax remains contentious, partly due to the elusiveness of experimental designs that vary structure independently of meaning-related variables. Here, we exploit Arabic’s grammatical properties, which enable such a design. We collected magnetoencephalography (MEG) data while participants read the same noun-adjective expressions with zero, one, or two contiguously-written definite articles (e.g., ‘chair purple’; ‘the-chair purple’; ‘the-chair the-purple’), representing equivalent concepts, but with different levels of syntactic complexity (respectively, indefinite phrases: ‘a purple chair’; sentences: ‘The chair is purple.’; definite phrases: ‘the purple chair’). We expected regions processing syntax to respond differently to simple versus complex structures. Single-word controls (‘chair’/‘purple’) addressed definiteness-based accounts. In noun-adjective expressions, syntactic complexity only modulated activity in the left posterior temporal lobe (LPTL), ~ 300 ms after each word’s onset: indefinite phrases induced more MEG-measured positive activity. The effects disappeared in single-word tokens, ruling out non-syntactic interpretations. In contrast, left anterior temporal lobe (LATL) activation was driven by meaning. Overall, the results support models implicating the LPTL in structure building and the LATL in early stages of conceptual combination.

Highlights

During language comprehension, the brain processes word meanings, and the grammatical structure—the “syntax”—that strings words into phrases and sentences
We focused on four left-hemispheric cortical regions most commonly associated with syntactic processing (Fig. 2a): the left anterior temporal lobe (LATL)[4,9,18,19], the left
We found clusters in right posterior temporal lobe (RPTL) (121–138 ms), right anterior temporal lobe (RATL) (192–215 ms), and right inferior frontal cortex (RIFC: 382–394 ms), but the Monte Carlo simulation revealed no significant effects (RPTL, RATL, RIFC: p = 0.547)

Summary

Introduction

The brain processes word meanings, and the grammatical structure—the “syntax”—that strings words into phrases and sentences. The neural basis of reading comprehension is multi-faceted and comprises many different computations, including the composition of individual words to build more complex phrases and sentences This combinatory procedure involves processing syntax—i.e., the underlying hierarchical structure of a phrase or sentence. One popular approach that attempts to dissociate syntax from meaning uses word lists4,5—jumbled-up word sequences that discourage syntactic structure building (‘chased the the cat mouse’)—and pseudo-word stimuli6–9—i.e., well-formed tokens that are devoid of meaning (‘The fouse chaled the yat.’). Such unnatural stimuli may engage brain computations and processes that are extraneous to real language comprehension. We use a two-pronged approach to elucidate the neural basis of syntax: (i) magnetoencephalography (MEG) recordings, with the dual benefits of millisecond temporal resolution and a good ability to spatially trace signals back to their cortical origins, and (ii) a Standard Arabic minimally-contrastive, two-word composition

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