The Cortical Maps of Hierarchical Linguistic Structures during Speech Perception

Abstract

The hierarchical nature of language requires human brain to internally parse connected-speech and incrementally construct abstract linguistic structures. Recent research revealed multiple neural processing timescales underlying grammar-based configuration of linguistic hierarchies. However, little is known about where in the whole cerebral cortex such temporally scaled neural processes occur. This study used novel magnetoencephalography source imaging techniques combined with a unique language stimulation paradigm to segregate cortical maps synchronized to 3 levels of linguistic units (i.e., words, phrases, and sentences). Notably, distinct ensembles of cortical loci were identified to feature structures at different levels. The superior temporal gyrus was found to be involved in processing all 3 linguistic levels while distinct ensembles of other brain regions were recruited to encode each linguistic level. Neural activities in the right motor cortex only followed the rhythm of monosyllabic words which have clear acoustic boundaries, whereas the left anterior temporal lobe and the left inferior frontal gyrus were selectively recruited in processing phrases or sentences. Our results ground a multi-timescale hierarchical neural processing of speech in neuroanatomical reality with specific sets of cortices responsible for different levels of linguistic units.

Sentence processing: How words generate syntactic structures in the brain

“…Subsequent EEG and MEG studies using this paradigm have replicated this main finding [41][42][43], also extending it to delta-band phase [41,42], confirming the robustness and replicability of this effect.…”

“…Several studies using (time-)frequency analyses seem to converge on the key role of oscillations in the delta band (< 4 Hz) in structure-based processing of linguistic information. This evidence is derived most notably from delta-band (power and phase) effects selectively modulated by grouping words into particular syntactic structures (frequency-tagging paradigm: [40][41][42][43]; single-sentence paradigm: [44,46]). These recent findings from two different paradigms provide important and promising advancements in our understanding of the neural dynamics underlying syntactic processing.…”

No evidence for functional distinctions across fronto-temporal language regions in their temporal receptive windows

“…The current results are inconsistent with a division of linguistic labor across the core language network that is topographically organized by integration timescales (cf. Lerner et al, 2011;DeWitt and Rauschecker, 2012;Bornkessel-Schlesewsky et al, 2015;Hasson et al, 2015;Chen et al, 2016;Baldassano et al, 2017;Yeshurun et al, 2017a;Sheng et al, 2018). Instead, they support the hypothesis that temporal and inferior frontal core language regions form a unified whole that occupies a unique stage within a broader cortical hierarchy of temporal integration.…”

“…Further posterior and anterior temporal regions could only track lists of sentences or paragraphs (but not words), indicative of sensitivity to phraseor sentence-level information. And, finally, some inferior frontal regions exhibited this same pattern of sensitivity to phrase/sentence information, with yet others reliably tracking only paragraph (but not sentence) lists, indicative of sensitivity to information above the sentence level (a long TRW).This hierarchy of integration timescales is an appealing organizing principle of the core language network (DeWitt and Rauschecker, 2012;Bornkessel-Schlesewsky et al, 2015;Hasson et al, 2015;Chen et al, 2016;Baldassano et al, 2017;Yeshurun et al, 2017a;Sheng et al, 2018). Nevertheless, there are several reasons to question the putative correspondence between this hierarchy and the set of language-selective cortical regions.…”

“…This hierarchy of integration timescales is an appealing organizing principle of the core language network (DeWitt and Rauschecker, 2012;Bornkessel-Schlesewsky et al, 2015;Hasson et al, 2015;Chen et al, 2016;Baldassano et al, 2017;Yeshurun et al, 2017a;Sheng et al, 2018). Nevertheless, there are several reasons to question the putative correspondence between this hierarchy and the set of language-selective cortical regions.…”