Linguistic Sequence Processing and the Prefrontal Cortex

Since language necessarily unfolds over time, language comprehension involves the processing of a sequentially ordered input. In this paper, we review neuroimaging findings on syntactic processing and word order variations in order to shed light on the neural bases of linguistic sequencing, focusing particularly on the role of prefrontal cortex (including Broca's region). On the basis of the full range of available data from several languages, we argue that different types of sequencing cues correlate with activation along an anterior-posterior gradient in frontal cortex, with highly local sequencing cues eliciting activation in the most posterior frontal regions (premotor cortex and the cytoarchitectonically corresponding frontal operculum) and less local sequencing cues (requiring relational comparisons between the current input element and the current sentence or discourse context, respectively) engendering activation in successively more anterior regions of the left inferior frontal gyrus. We argue that this neurocognitive gradient of linguistic sequence processing can be associated with a more general hierarchy of cognitive control in prefrontal cortex, which has also been shown to vary along an anterior-posterior gradient (1). We conclude that the processing of linguistic sequences and the concomitant extraction of information (e.g. semantic relations) from them, as an essential component of language processing, follows more general principles of neurocognitive organisation in prefrontal cortex.