The neural organization of discourse: An H215O-PET study of narrative production in English and American sign language

TLDR

The study compared English and American Sign Language, which differ maximally in mode of expression yet share core linguistic properties, to differentiate stages of discourse production. The authors aimed to identify brain regions essential for discourse production. H₂¹⁵O‑PET scans were acquired during spontaneous autobiographical narrative generation in hearing subjects native in both languages. Common activations were found in widespread left‑hemisphere language areas and extrasylvian regions in both hemispheres, with posterior perisylvian and basal temporal regions integral to spontaneous language formulation, and distinct anterior‑posterior roles suggesting a progression from bilateral to left‑lateralized activation during discourse generation, a pattern not predicted by the standard Wernicke‑Geschwind model.

Abstract

In order to identify brain regions that play an essential role in the production of discourse, H2 15O-PET scans were acquired during spontaneous generation of autobiographical narratives in English and in American Sign Language in hearing subjects who were native users of both. We compared languages that differ maximally in their mode of expression yet share the same core linguistic properties in order to differentiate the stages of discourse production: differences between the languages should reflect later, modality-dependent stages of phonological encoding and articulation; congruencies are more likely to reveal the anatomy of earlier modality-independent stages of conceptualization and lexical access. Common activations were detected in a widespread array of regions; left hemisphere language areas classically related to speech were also robustly activated during sign production, but the common neural architecture extended beyond the classical language areas and included extrasylvian regions in both right and left hemispheres. Furthermore, posterior perisylvian and basal temporal regions appear to play an integral role in spontaneous self-generated formulation and production of language, even in the absence of exteroceptive stimuli. Results additionally indicate that anterior and posterior areas may play distinct roles in early and late stages of language production, and suggest a novel model for lateralization of cerebral activity during the generation of discourse: progression from the early stages of lexical access to later stages of articulatory-motor encoding may constitute a progression from bilateral to left-lateralized activation. This pattern is not predicted by the standard Wernicke-Geschwind model, and may become apparent when language is produced in an ecologically valid context.