Appendix:

Sentence processing is subserved by a large-scale network of brain structures, but contemporary models differ in the roles they ascribe to the left inferior frontal gyrus (IFG), and to BA44 in particular (Bornkessel-Schlesewsky & Schlesewsky, 2016, 2019; Friederici, 2016, 2017; Hagoort, 2014, 2016; Kemmerer, 2022; Matchin & Hickok, 2020; Murphy, 2021). For instance, Friederici’s (2016, 2017) model focuses on sentence comprehension and postulates that BA44 has the following functions: it supports simple syntactic computations, such as building local phrases, through its interactions with the frontal operculum and anterior superior temporal gyrus (STG); and it supports complex syntactic computations, such as building hierarchical configurations of nonadjacent elements, through its interactions with the posterior STG. Bornkessel-Schlesewsky and Schlesewsky’s (2016, 2019) model also focuses on sentence comprehension and emphasizes the dorsal pathway that connects BA44 with the posterior STG; however, it postulates that this pathway is not specialized for complex syntactic computations per se, but is instead critical for the more basic function of sentence-level sequential processing (i.e., tracking word order). Hagoort’s (2014, 2016) model applies to both sentence comprehension and sentence production, and it postulates that both BA44 and BA45 subserve syntactic unification, which involves assembling the sequential-hierarchical structures of phrases, clauses, and complex sentences based on the syntactic properties of lexical items stored in the lateral temporal cortex. Finally, Matchin and Hickok’s (2020) model postulates that BA44 does not contribute directly to syntax; instead, BA45 supports the sequential processing of sentences during production but not comprehension, via connections with lexical representations in the lateral temporal cortex.