THE CORTICAL ORGANIZATION OF SYNTAX
I am currently developing a neurobiological framework for syntax and semantics in the brain, centered on the posterior superior temporal sulcus (pSTS/MTG as a core region for hierarchical syntactic representations (Matchin & Hickok, 2019 - Cerebral Cortex) (Figure 1). The PTL is well-positioned to connect sensory brain systems to conceptual brain systems. Our model posits a second fundamental organizing principle for semantics and syntax that places the pSTS/MTG in an appropriate cortical location. This principle takes inspiration from vision research regarding two fundamental streams of processing: the dorsal stream (how to interact with an object) and the ventral stream (what an object is) (Goodale & Milner, 1992). The pSTS/MTG connects these two systems for processing meaning to each other, allowing for people to create complex new thoughts.
Our model also contributes to our understand of aphasia, and makes the prediction that syntactic deficits in fluent aphasia, paragrammatism, will be localizable to the pSTS/MTG. For more information, you can watch a talk I gave at the Center for the Study of Aphasia Recovery (C-STAR).
Neuroimaging studies of sentence processing reliably activate a set of brain regions in the frontal and temporal lobes (Mazoyer et al., 1993; Pallier et al., 2011). However, the specific role each region plays in sentence processing, particularly with respect to syntax, remains unclear. Using parallel fMRI and MEG experiments, we have shown that posterior temporal areas are involved in predictive abstract syntactic processing, while anterior temporal areas are involved in conceptual-semantic processing (Matchin et al., 2017, Cortex; Matchin et al., 2018, Human Brain Mapping) (Figure 2).
fMRI studies of sentence/phrase comprehension reveal structural effects in several classic language-related areas (Matchin et al., 2019 - Neuropsychologia) (Figure 3). However, new data comparing syntacftic processing with phonological processing in both comprehension AND production reveal that certain areas are more sensitive to the demands of production generally, rather than syntactic processing (IFG pars opercularis) while other areas are more sensitive to the demands of syntactic processing generally, regardless of production or comprehension (IFG pars triangularis, posterior STS/MTG) (Matchin & Wood, in prep) (Figure 4).