Inter‐individual variability in dorsal stream dynamics during word production. (30th August 2022)

• Record Type: Journal Article
• Authors: Liégeois‐Chauvel, Catherine; Dubarry, Anne‐Sophie; Wang, Irene; Chauvel, Patrick; Gonzalez‐Martinez, Jorge A.; Alario, F.‐Xavier
• Is Part Of: European journal of neuroscience. Volume 56:Number 7(2022)
• Page Start: 5070
• Page End: 5089
• Publication Date: 2022-08-30
• Subjects: fronto‐parietal network -- HGA -- iERP -- speech production -- stereotactic electroencephalography; Nervous system -- Periodicals; 612.8
• DOI: 10.1111/ejn.15807
• Languages: English
• ISSNs: 0953-816X

Abstract

Abstract: The current standard model of language production involves a sensorimotor dorsal stream connecting areas in the temporo‐parietal junction with those in the inferior frontal gyrus and lateral premotor cortex. These regions have been linked to various aspects of word production such as phonological processing or articulatory programming, primarily through neuropsychological and functional imaging group studies. Most if not all the theoretical descriptions of this model imply that the same network should be identifiable across individual speakers. We tested this hypothesis by quantifying the variability of activation observed across individuals within each dorsal stream anatomical region. This estimate was based on electrical activity recorded directly from the cerebral cortex with millisecond accuracy in awake epileptic patients clinically implanted with intracerebral depth electrodes for pre‐surgical diagnosis. Each region's activity was quantified using two different metrics—intra‐cerebral evoked related potentials and high gamma activity—at the level of the group, the individual and the recording contact. The two metrics show simultaneous activation of parietal and frontal regions during a picture naming task, in line with models that posit interactive processing during word retrieval. They also reveal different levels of between‐patient variability across brain regions, except in core auditory and motor regions. The independence and non‐uniformity of cortical activity estimated through the two metrics push the current model towards sub‐second and sub‐region explorations focused on individualized language speech production. Several hypotheses are considered for this within‐region heterogeneity. Abstract : Standard models of language processing involve a dorsal stream connecting temporal, parietal and frontal regions, each linked to particular aspects of word production—for example, phonological processing or articulatory programming. Most theories imply that the same network should be identifiable across individuals. This hypothesis was tested by quantifying the variability of activation observed across speakers within each region. Two metrics of brain activity recorded intra‐cerebrally in awake epileptic patients revealed diverse levels of variability. Several hypotheses are considered for this within‐region heterogeneity.