Diversity of Grammars and Their Diverging Evolutionary and Processing Paths: Evidence From Functional MRI Study of Serbian

Abstract

We address the puzzle of “unity in diversity” in human languages by advocating the (minimal) common denominator for the diverse expressions of transitivity across human languages, consistent with the view that early in language evolution there was a modest beginning for syntax and that this beginning provided the foundation for the further elaboration of syntactic complexity. This study reports the results of a functional MRI experiment investigating differential patterns of brain activation during processing of sentences with minimal versus fuller syntactic structures. These structural layers have been postulated to represent different stages in the evolution of syntax, potentially engaging different brain networks. We focused on the Serbian “middles,” analyzed as lacking the transitivity (vP) layer, contrasted with matched transitives, containing the transitivity layer. Our main hypothesis was that transitives will produce more activation in the syntactic (Broca's–Basal Ganglia) brain network, in comparison to more rudimentary middles. The participants (n = 14) were healthy adults (Mean age = 33.36; SD = 12.23), native speakers of Serbo-Croatian. The task consisted of reading a series of sentences (middles and transitives; n = 64) presented in blocks of 8, while being engaged in a detection of repetition task. We found that the processing of transitives, compared to middles, was associated with an increase in activation in the basal ganglia bilaterally. Although we did not find an effect in Broca's area, transitives, compared to middles, evoked greater activation in the precentral gyrus (BA 6), proposed to be part of the “Broca's complex.” Our results add to the previous findings that Broca's area is not the sole center for syntactic processing, but rather is part of a larger circuit that involves subcortical structures. We discuss our results in the context of the recent findings concerning the gene-brain-language pathway involving mutations in FOXP2 that likely contributed to the enhancement of the frontal-striatal brain network, facilitating human capacity for complex syntax.

Neural Correlates of Syntax and Proto-Syntax: Evolutionary Dimension

“…The reason for the difficulty of using the insights about the nature of syntactic representations and computation to inform our knowledge about functional organization of the brain and vice versa was said to lie in the inherent mismatch in conceptual granularity as well as ontological incompatibility between the concrete biological units of neuroscience and the abstract syntactic postulates (Poeppel and Embick, 2005). We propose that the considerations of the evolution of syntax, as outlined in Progovac (2015, 2016), provide a way of bringing together the postulates from Theoretical Syntax and Cognitive Neuroscience (see also Progovac et al, 2018). This framework, by contrasting modern structures (syntax) with ancestral structures (proto-syntax), introduces linguistic constructs of the granularity commensurate with the tools used in neuroscience to probe the neural correlates of syntactic computation.…”

“…Furthermore, it may be possible to isolate certain brain networks that are specialized for processing structures of different degrees of syntactic elaboration, as reflected in the stages of language evolution. The rationale behind this proposal is that complex, uniquely human, grammatical patterns require more support by the most recently evolved/enhanced neural networks than do their flatter proto-syntactic counterparts, which in turn may show a less streamlined and more diffuse distribution across the brain, as well as more individual variability (Progovac et al, 2018).…”

“…For further findings correlating an increase in syntactic complexity to an increase in neural activation in certain specific areas of the brain, the reader is referred to Just et al (1996), Caplan (2001), Indefrey et al (2001), Pallier et al (2011), and Brennan et al (2012). In an fMRI experiment, Progovac et al (2018) found that the basal ganglia showed increased activation, both on the left and on the right, with the processing of Serbian transitive sentences (instantiating a vP layer), in contrast to matched “middle” sentences (analyzed as lacking the vP layer) 6 .…”

Natural/sexual selection: What’s language (evolution) got to do with it?

“…We hypothesized that the processing of Serbian middles, relative to (phonologically and semantically) matched transitive accusative counterparts, would result in reduced activation in the Broca's-basal ganglia network (Progovac et al 2018a). We found that the processing of transitives, compared to middles, indeed showed an increase in activation in the basal ganglia bilaterally.…”

“…Especially noteworthy is the contrast between absolutive-like middles (a,b examples below), which exhibit animacy effects, and the (default) accusative grammars, illustrated in the (c) Consistent with this analysis, absolutive-like se structures seem to be processed differently by the brain, in comparison to transitive accusative struc-tures. Progovac et al (2018a) report the results of an fMRI experiment which was designed to test the processing of vP-less se middles in Serbian, in comparison to their semantically matched accusative counterparts with vP. We specifically looked at the differential role played by the Broca's-basal ganglia network in processing ancestral versus more modern types of structures because several recent findings suggest that this network has been bolstered relatively recently in evolution, through selection, by increased synaptic plasticity and neuronal connectivity (e.g.…”