Tracking the microstructural properties of the main white matter pathways underlying speech processing in simultaneous interpreters

Abstract

Due to the high linguistic and cognitive demands placed on real-time language translation, professional simultaneous interpreters (SIs) have previously been proposed to serve as a reasonable model for evaluating experience-dependent brain properties. However, currently it is still unknown whether intensive language training during adulthood might be reflected in microstructural changes in language-related white matter pathways contributing to sound-to-meaning mapping, auditory-motor integration, and verbal memory functions. Accordingly, we used a fully automated probabilistic tractography algorithm and compared the white matter microstructure of the bilateral inferior longitudinal fasciculus (ILF), uncinate fasciculus (UF), and arcuate fasciculus (AF, long and anterior segments) between professional SIs and multilingual control participants. In addition, we classically re-evaluated the three constitutional elements of the AF (long, anterior, and posterior segments) using a deterministic manual dissection procedure. Automated probabilistic tractography demonstrated overall reduced mean fractional anisotropy (FA) and increased radial diffusivity (RD) in SIs in the fiber tracts of the left hemisphere (LH). Furthermore, SIs exhibited reduced mean FA in the bilateral AF. However, according to manual dissection, this effect was limited to the anterior AF segment and accompanied by increased mean RD. Deterministic AF reconstruction also uncovered increased mean FA in the right and RD in the left long AF segment in SIs compared to controls. These results point to a relationship between simultaneous interpreting and white matter organization of pathways underlying speech and language processing in the language-dominant LH as well as of the AF.

Neurocognitive signatures of phonemic sequencing in expert backward speakers

“…www.nature.com/scientificreports/ Finally, as stated earlier, our study indicates that similar forms of language expertise may recruit differential neural mechanisms. Although the majority of the studies on language-related neuroplasticity have favored averaged reports across multiple samples, thus masking potential individual differences within their samples 90,92,93,96 , our results align with few studies using difficult artificial language learning tasks in healthy subjects that report individual variability in the integrity of dorsal and ventral white matter tracts associated to successful learning 22,112 . Crucially, a recent study 116 has also provided evidence on individual variability in auditory-motor integration abilities, potentially related to the adoption of different cognitive strategies during linguistically demanding tasks.…”

“…Third, our design did not include online measures of the functional activity during backward speech neural correlates of backward expertise. Even though the results converge with those from task-related fMRI research on spontaneous backward speech 31 , and despite the validity of off-line assessments to detect neural correlates of language expertise 90,93,96 , further investigations involving online and offline neuroscientific measures are needed. Fourth, our cross-sectional design did not allow us to determine whether the neural patterns observed are the result of experience-dependent plastic changes due to training, or if they reflect pre-existing individual differences.…”

“…Indeed, professional simultaneous interpreters and phoneticians, who exhibit elevated phonemic processing abilities, also show grey matter volumetric (or thickness) increases [89][90][91] (but see 92 ) and distinctive microstructural white matter properties. In fact, both higher and lower diffusivity in relevant pathways are frequent findings in studies of expert auditory-motor abilities [93][94][95][96] . The observed MD adjustments in task-relevant tracts may be attributed to greater efficiency of these networks, Figure 2.…”

The beauty of language structure: a single-case fMRI study of palindrome creation

“…Interestingly, the involvement of the dorsal frontoparietal language circuit agrees with recent evidence from a neuroimaging study of two language experts in "backward speech", which consist in the production of utterances by reversing the order of phonemes (e.g., at the word level, from mesaasem or at syllable level, same) (Torres-Prioris et al, 2020). Structural MRI analysis in these experts indicated increased grey matter volume, greater integrity of white matter and functional connectivity along dorsal language stream regions mediating phonological encoding and audio-motor integration and supporting short-term storage and manipulation of verbal information, which also converges with structural changes in this dorsal fronto-temporal parietal network previously observed in simultaneous interpreters (Elmer & Kühnis, 2016;Elmer et al, 2019) and expert phoneticians (Vandermosten, Price & Golestani, 2016).…”

Structural Connectivity in Ventral Language Pathways Characterizes Nonverbal Autism

“…Finally, artefactual bers, if present in any of the tracts / hemispheres, were removed using exclusion ROIs, as is standard practice in manual reconstructions (Elmer et al 2019;Vaquero et al 2021). Tract volume and Fractional Anisotropy (FA) values were extracted in every participant for each tract and hemisphere.…”