The role of the arcuate and middle longitudinal fasciculi in speech perception in noise in adulthood

Abstract

In this article, we used High Angular Resolution Diffusion Imaging (HARDI) with advanced anatomically constrained particle filtering tractography to investigate the role of the arcuate fasciculus (AF) and the middle longitudinal fasciculus (MdLF) in speech perception in noise in younger and older adults. Fourteen young and 15 elderly adults completed a syllable discrimination task in the presence of broadband masking noise. Mediation analyses revealed few effects of age on white matter (WM) in these fascicles but broad effects of WM on speech perception, independently of age, especially in terms of sensitivity and criterion (response bias), after controlling for individual differences in hearing sensitivity and head size. Indirect (mediated) effects of age on speech perception through WM microstructure were also found, after controlling for individual differences in hearing sensitivity and head size, with AF microstructure related to sensitivity, response bias and phonological priming, and MdLF microstructure more strongly related to response bias. These findings suggest that pathways of the perisylvian region contribute to speech processing abilities, with relatively distinct contributions for the AF (sensitivity) and MdLF (response bias), indicative of a complex contribution of both phonological and cognitive processes to age‐related speech perception decline. These results provide new and important insights into the roles of these pathways as well as the factors that may contribute to elderly speech perception deficits. They also highlight the need for a greater focus to be placed on studying the role of WM microstructure to understand cognitive aging.

New Insights Into the Anatomy, Connectivity and Clinical Implications of the Middle Longitudinal Fasciculus

“…Merging this anatomical substrate with the results from speech and neuropsychological tests (impaired learning, memory, and concentration), we may reinforce our hypothesis regarding the functional network supported by the pMdLF. Acoustic information would be processed within the aTTG and subsequently redirected by the pMdLF to SPL and LOC, while the AF would support the phonological processing of verbal information, word flow, and verbal working memory through its terminations within the temporo-parietal and frontal regions (Wang et al, 2013;Fernández-Miranda et al, 2015;Bernard et al, 2019;Tremblay et al, 2019). The language impairment identified in this patient confirms the functional evidence regarding the AF and its close anatomical relationship with the primary auditory cortex.…”

“…Indeed, an associative bundle between TP/STG and IPL was initially described in monkeys (Seltzer and Pandya, 1984), and more recently in humans using in vivo virtual dissection, DTI-based, techniques (Makris et al, 2009). However, the absence of cortical terminations to the IPL (AG and/or SG) is probably the most striking dissonance between pure virtual dissection studies (Makris et al, 2009(Makris et al, , 2013b(Makris et al, , 2017Menjot de Champfleur et al, 2013;Suzuki et al, 2018;Tremblay et al, 2019) and white matter dissection studies, including the present one. Indeed, our fiber dissection and high resolution fiber tracking study could not document the presence of MdLF terminations at IPL.…”

“…According to Tremblay et al (2019), MdLF connectivity between the STG and parietal lobe suggests a role for this tract in supporting speech processing, possibly through changes in attentional biases. Other studies, owing to MdLF connectivity with parietal regions, suggest a role of the MdLF in attentional functions through a correlation between poor attention and the micro-structure of MdLF in patients with schizophrenia (Steffens et al, 2017).…”

The frontotemporal organization of the arcuate fasciculus and its relationship with speech perception in young and older amateur singers and non‐singers

“…Several hypotheses have been proposed to account for the age‐related SPiN decline, but a consensus about the underlying mechanisms is still lacking. Several studies have suggested that normal aging of the peripheral auditory system, called presbycusis , is the main contributing factor to SPiN difficulties in aging (e.g., Akeroyd, 2008; Divenyi & Haupt, 1997; Humes & Christopherson, 1991; Humes & Roberts, 1990; Jerger, Jerger, & Pirozzolo, 1991; Souza & Turner, 1994), but evidence suggesting that SPiN decline cannot be explained solely by presbycusis is accumulating (Bilodeau‐Mercure, Lortie, Sato, Guitton, & Tremblay, 2015; Fostick, Ben‐Artzi, & Babkoff, 2013; Jin, Liu, & Sladen, 2014; Tremblay et al, 2019).…”

“…The arcuate fasciculus (AF) forms the white matter scaffolding of the dorsal speech stream. A recent study from our group using High Angular Resolution Diffusion Imaging (HARDI) techniques has found that the structure of the bilateral AF is related to SPiN performance in young and older adults (Tremblay et al, 2019), particularly in terms of sensitivity to phonetic details.…”