Exploring the neurobiology of Merge at a basic level: insights from a novel artificial grammar paradigm

Abstract

IntroductionHuman language allows us to generate an infinite number of linguistic expressions. It’s proposed that this competence is based on a binary syntactic operation, Merge, combining two elements to form a new constituent. An increasing number of recent studies have shifted from complex syntactic structures to two-word constructions to investigate the neural representation of this operation at the most basic level.MethodsThis fMRI study aimed to develop a highly flexible artificial grammar paradigm for testing the neurobiology of human syntax at a basic level. During scanning, participants had to apply abstract syntactic rules to assess whether a given two-word artificial phrase could be further merged with a third word. To control for lower-level template-matching and working memory strategies, an additional non-mergeable word-list task was set up.ResultsBehavioral data indicated that participants complied with the experiment. Whole brain and region of interest (ROI) analyses were performed under the contrast of “structure > word-list.” Whole brain analysis confirmed significant involvement of the posterior inferior frontal gyrus [pIFG, corresponding to Brodmann area (BA) 44]. Furthermore, both the signal intensity in Broca’s area and the behavioral performance showed significant correlations with natural language performance in the same participants. ROI analysis within the language atlas and anatomically defined Broca’s area revealed that only the pIFG was reliably activated.DiscussionTaken together, these results support the notion that Broca’s area, particularly BA 44, works as a combinatorial engine where words are merged together according to syntactic information. Furthermore, this study suggests that the present artificial grammar may serve as promising material for investigating the neurobiological basis of syntax, fostering future cross-species studies.

Transcranial Photobiomodulation on the Left Prefrontal Cortex Enhances Mandarin Chinese L1 and L2 Complex Sentence Processing Performances

“…In addition, the activation of LIFG directly correlates with the syntactic complexity as shown by the studies focusing on the processing of noncanonical sentences involving word scrambling, syntactic movement, and multiple syntactic embeddings (e.g., Ben-Shachar et al, 2004;Caplan et al, 2008;Friederici et al, 2006b;Makuuchi et al, 2009Makuuchi et al, , 2013Meyer et al, 2012;Röder et al, 2002;Santi & Grodzinsky, 2010). Evidence of artificial hierarchical grammar processing from Chen et al (2021a) and Liu et al (2023) further indicated that LIFG engages in the build-up process of syntactic hierarchies.…”

“…Moreover, word frequencies and the frequencies of collocation between two nouns/verbs or a noun and a verb were carefully controlled so that participants were unable to process the sentences or make judgements with any possible strategies unrelated to language processing. Following Xu et al (2020) and Liu et al (2023), a probing statement of thematic relation (i.e., the relation of "who did what to whom") was attached to each sentence trail for the correctness judgement to detect participants' performance of syntactic processing (Figure 2A). The probing sentences were also controlled regarding the collocation frequencies between words and the frequencies of probing verbs with respect to their location (i.e., in main clauses or relative clauses), with half being correct/incorrect.…”

“…The processing of sentences is proposed to be based on the fundamental operation of merge, a process defined by the Generative Linguistics to combine two syntactic objects into a larger new constituent (Chomsky, 1995;Friederici, 2017;Miyagawa et al, 2013;Zaccarella & Friederici, 2015). Such a computational ability to build up the syntactic hierarchies is believed to play an essential role in human language faculty, which was found to be largely dependent on the functions of the left inferior frontal gyrus (LIFG) within the ventral part of LPFC (e.g., Chen et al, 2021aChen et al, , 2023Friederici, 2017;Friederici et al, 2006b;Jeon, 2014;Liu et al, 2023;Makuuchi et al, 2009;Meyer et al, 2012;Santi & Grodzinsky, 2010;Zaccarella et al, 2015Zaccarella et al, , 2017a; see also Zaccarella et al, 2017b for the meta-analysis on the neurobiology of merge). Zaccarella et al (2015) provided evidence that Brodmann Area (BA) 44, a relatively posterior part of LIFG, played the primary supporting role for merge when processing syntactic phrases compared to word-list sequences.…”

“…In addition, the activation of LIFG directly correlates with the syntactic complexity as shown by the studies focusing on the processing of noncanonical sentences involving word scrambling, syntactic movement, and multiple syntactic embeddings (e.g., Ben-Shachar et al, 2004; Caplan et al, 2008; Friederici et al, 2006b; Makuuchi et al, 2009, 2013; Meyer et al, 2012; Röder et al, 2002; Santi & Grodzinsky, 2010). Evidence of artificial hierarchical grammar processing from Chen et al (2021a) and Liu et al (2023) further indicated that LIFG engages in the build-up process of syntactic hierarchies. In particular, for the first time, Liu et al (2023) found a significant correlation between the signal intensity of the relatively posterior part of LIFG as identified in their artificial merge grammar processing and the behavioral performances of natural complex sentence processing.…”

“…Evidence of artificial hierarchical grammar processing from Chen et al (2021a) and Liu et al (2023) further indicated that LIFG engages in the build-up process of syntactic hierarchies. In particular, for the first time, Liu et al (2023) found a significant correlation between the signal intensity of the relatively posterior part of LIFG as identified in their artificial merge grammar processing and the behavioral performances of natural complex sentence processing. These studies, thus, converge on and underly the critical role of LIFG within the ventral LPFC in merge during sentence processing as a syntactic engine.…”