Abstract
The core human capacity of syntactic analysis involves a left hemisphere network involving left inferior frontal gyrus (LIFG) and posterior middle temporal gyrus (LMTG) and the anatomical connections between them. Here we use magnetoencephalography (MEG) to determine the spatio-temporal properties of syntactic computations in this network. Listeners heard spoken sentences containing a local syntactic ambiguity (e.g., “… landing planes …”), at the offset of which they heard a disambiguating verb and decided whether it was an acceptable/unacceptable continuation of the sentence. We charted the time-course of processing and resolving syntactic ambiguity by measuring MEG responses from the onset of each word in the ambiguous phrase and the disambiguating word. We used representational similarity analysis (RSA) to characterize syntactic information represented in the LIFG and left posterior middle temporal gyrus (LpMTG) over time and to investigate their relationship to each other. Testing a variety of lexico-syntactic and ambiguity models against the MEG data, our results suggest early lexico-syntactic responses in the LpMTG and later effects of ambiguity in the LIFG, pointing to a clear differentiation in the functional roles of these two regions. Our results suggest the LpMTG represents and transmits lexical information to the LIFG, which responds to and resolves the ambiguity.
Highlights
Over the last 150 years substantial efforts have been made to understand the brain bases of human language
We have consistently found that L BA 45 and left posterior middle temporal gyrus (LpMTG) are implicated in syntactic analysis, together with the white matter tracts that directly connect them – the arcuate fasciculus and the extreme capsule fiber bundles
We focus on two regions of interest (ROIs: left inferior frontal gyrus (LIFG) (BA 45/47) and LpMTG) and their RH homologs, functionally defined from a previous fMRI study in which listeners heard a set of stimuli all of which were included in the present MEG study (Tyler et al, 2011)
Summary
Over the last 150 years substantial efforts have been made to understand the brain bases of human language. Recent attempts to integrate these disparate findings into a coherent framework have placed renewed emphasis on the bi-hemispheric foundations of human language, taking into account data on the neurobiology of auditory processing in non-human primates and human studies on brain and language (Rauschecker and Tian, 2000; Jung-Beeman, 2005; Tyler and Marslen-Wilson, 2008; Bozic et al, 2010) This bi-hemispheric model claims that human language is subserved by two main processing networks: one involving a bilateral temporal-parietal system which supports the semantic/pragmatic aspects of language, and a second left hemisphere (LH) frontotemporal system which supports syntactic computations (Tyler and Marslen-Wilson, 2008). The arcuate fasciculus, one of the direct fronto-temporal connecting white matter tracts, is not wellestablished either in non-human primates (Rilling et al, 2008) or in young children (Brauer et al, 2011), neither of which have well-developed syntactic capacities
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