White matter pathway supporting phonological encoding in speech production: a multi-modal imaging study of brain damage patients

Abstract

In speech production, an important step before motor programming is the retrieval and encoding of the phonological elements of target words. It has been proposed that phonological encoding is supported by multiple regions in the left frontal, temporal and parietal regions and their underlying white matter, especially the left arcuate fasciculus (AF) or superior longitudinal fasciculus (SLF). It is unclear, however, whether the effects of AF/SLF are indeed related to phonological encoding for output and whether there are other white matter tracts that also contribute to this process. We comprehensively investigated the anatomical connectivity supporting phonological encoding in production by studying the relationship between the integrity of all major white matter tracts across the entire brain and phonological encoding deficits in a group of 69 patients with brain damage. The integrity of each white matter tract was measured both by the percentage of damaged voxels (structural imaging) and the mean fractional anisotropy value (diffusion tensor imaging). The phonological encoding deficits were assessed by various measures in two oral production tasks that involve phonological encoding: the percentage of nonword (phonological) errors in oral picture naming and the accuracy of word reading aloud with word comprehension ability regressed out. We found that the integrity of the left SLF in both the structural and diffusion tensor imaging measures consistently predicted the severity of phonological encoding impairment in the two phonological production tasks. Such effects of the left SLF on phonological production remained significant when a range of potential confounding factors were considered through partial correlation, including total lesion volume, demographic factors, lesions on phonological-relevant grey matter regions, or effects originating from the phonological perception or semantic processes. Our results therefore conclusively demonstrate the central role of the left SLF in phonological encoding in speech production.

White matter tracts lesions and decline of verbal fluency after deep brain stimulation in Parkinson's disease

“…Additionally, we found that the electrode impacted the three (Schmahmann et al, 2007). This tract has been found to be associated with language articulation (Han et al, 2016;Johnson et al, 2015), processing speed (Kerchner et al, 2012), and working memory (Vestergaard et al, 2011). For instance, the superior longitudinal fasciculus has been identified to contribute to VF performance in schizophrenia (Peters et al, 2012) since reduced integrity of the superior longitudinal fasciculus correlated with poorer VF.…”

“…SLF II links caudal part of the inferior parietal lobule and various dorsolateral and ventrolateral frontal regions whereas the more ventral component, SLF III, connects the supramarginal gyrus with the ventral premotor and prefrontal cortex (Schmahmann et al, ). This tract has been found to be associated with language articulation (Han et al, ; Johnson et al, ), processing speed (Kerchner et al, ), and working memory (Vestergaard et al, ). For instance, the superior longitudinal fasciculus has been identified to contribute to VF performance in schizophrenia (Peters et al, ) since reduced integrity of the superior longitudinal fasciculus correlated with poorer VF.…”

Semantic representation in the white matter pathway

“…The dissimilarity between images was computed by 1 minus Jaccard similarity. For the phonological RDM, the dissimilarity of two-item names was measured by 1 minus the proportion of shared sub-syllabic units (onset or rhyme), regardless of position (e.g., [ 57 ]). The sub-syllabic units for a given syllable were defined based on the phonetic transcript of Chinese characters (the “pinyin” system), which transcribes each syllable with an onset consonant (“shengmu”) and a rhyme vowel or vowel-consonant (“yunmu”).…”

Multifunctional Roles of the Ventral Stream in Language Models: Advanced Segmental Quantification in Post-Stroke Aphasic Patients

“…The dorsal pathway consists of the superior longitudinal fascicle (SLF) and arcuate fascicle (AF), and is responsible for sound-to-motor mapping ( 13 , 14 ). Stroke involving these bundles can lead to dysfunction in speech production and a decreased aphasia quotient (AQ) ( 15 – 18 ). The dorsal route was once considered the dominant pathway in linguistic processing, until higher-level language comprehension was found to be mediated by the ventral stream ( 19 ), which consists of the inferior fronto-occipital fascicle (IFOF), uncinate fascicle (UF), and inferior longitudinal fascicle (ILF).…”