Investigations of the syntax-brain relationship

This dissertation critically examines extant hypotheses on the syntax-brain relationship, particularly proposals concerning Broca's area, and presents empirical data in efforts to localize syntactic operations in the brain. Chapter 2 of the dissertation reviews arguments for and against a role for Broca's area in syntax, and presents an fMRI experiment using a construction called backward anaphora in which the activity in the pars triangularis of Broca's area is shown to pattern with how sentences are processed (i.e., whether the construction involves active processing), and not their syntactic properties (i.e., activity is not contingent on Movement constructions). Chapter 3 extends Dehaene & Cohen's neuronal recycling hypothesis (Dehaene & Cohen, 2007) to language function in Broca's area to account for sentence-selective activations in this region of cortex (Fedorenko et al., 2012). In particular, the discussion in Chapter 3 focuses on language- or sentence-specific working memory (Caplan & Waters, 1999), and how language-specific working memory may develop out of domain-general working memory. Chapter 4 presents an fMRI experiment aimed at uncovering the neural basis of syntax using a "syntactic perturbation" technique during overt sentence production. In addition, the experiment specifically examined the response profile of Broca's area and another region classically implicated in structural processing, the anterior temporal lobe (ATL), to our novel manipulation targeting syntactic structure. The results, when compared to perturbation in a control condition of unstructured word lists, revealed preferential activation for syntactic perturbation in networks previously implicated in motor control (Tourville et al., 2008) and action inhibition (Aron et al., 2014), including the basal ganglia, thalamus, and right inferior frontal gyrus, suggesting that (i) sentence production allows greater phonological/articulatory planning than list production, and (ii) syntax may rely on networks similar to basic motor control. However, effects at the syntax level are conflated with effects at lower motor levels in our experiment. Broca's area and the ATL did not exhibit effects consistent with syntactic processing, although our results extended the basic finding of increased activation to sentences compared to word lists previously found in the ATL (Mazoyer et al., 1993). Finally, Chapter 5 concludes the dissertation