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

Yang Liu; Chenyang Gao; Peng Wang; Angela D Friederici; Emiliano Zaccarella; Luyao Chen

doi:10.3389/fpsyg.2023.1151518

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

Front Psychol. 2023 May 23:14:1151518. doi: 10.3389/fpsyg.2023.1151518. eCollection 2023.

Authors

Yang Liu^#¹, Chenyang Gao^#², Peng Wang^{3

4

5}, Angela D Friederici⁶, Emiliano Zaccarella⁶, Luyao Chen^{1

6

7}

Affiliations

¹ Max Planck Partner Group, School of International Chinese Language Education, Beijing Normal University, Beijing, China.
² School of Global Education and Development, University of Chinese Academy of Social Sciences, Beijing, China.
³ Method and Development Group (MEG and Cortical Networks), Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
⁴ Institute of Psychology, University of Greifswald, Greifswald, Germany.
⁵ Institute of Psychology, University of Regensburg, Regensburg, Germany.
⁶ Department of Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
⁷ Institute of Educational System Science, Beijing Normal University, Beijing, China.

^# Contributed equally.

Abstract

Introduction: Human 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.

Methods: This 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.

Results: Behavioral 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.

Discussion: Taken 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.

Keywords: Broca’s area; Merge; fMRI; natural language comprehension; syntactic processing.

Grants and funding

This work was supported by the National Social Science Foundation of China (No. 22CYY017).