Plasticity of white matter connectivity in phonetics experts.

Maaike Vandermosten,Cathy J Price,Narly Golestani

doi:10.1007/s00429-015-1114-8

Abstract

Phonetics experts are highly trained to analyze and transcribe speech, both with respect to faster changing, phonetic features, and to more slowly changing, prosodic features. Previously we reported that, compared to non-phoneticians, phoneticians had greater local brain volume in bilateral auditory cortices and the left pars opercularis of Broca’s area, with training-related differences in the grey-matter volume of the left pars opercularis in the phoneticians group (Golestani et al. 2011). In the present study, we used diffusion MRI to examine white matter microstructure, indexed by fractional anisotropy, in (1) the long segment of arcuate fasciculus (AF_long), which is a well-known language tract that connects Broca’s area, including left pars opercularis, to the temporal cortex, and in (2) the fibers arising from the auditory cortices. Most of these auditory fibers belong to three validated language tracts, namely to the AF_long, the posterior segment of the arcuate fasciculus and the middle longitudinal fasciculus. We found training-related differences in phoneticians in left AF_long, as well as group differences relative to non-experts in the auditory fibers (including the auditory fibers belonging to the left AF_long). Taken together, the results of both studies suggest that grey matter structural plasticity arising from phonetic transcription training in Broca’s area is accompanied by changes to the white matter fibers connecting this very region to the temporal cortex. Our findings suggest expertise-related changes in white matter fibers connecting fronto-temporal functional hubs that are important for phonetic processing. Further studies can pursue this hypothesis by examining the dynamics of these expertise related grey and white matter changes as they arise during phonetic training.Electronic supplementary materialThe online version of this article (doi:10.1007/s00429-015-1114-8) contains supplementary material, which is available to authorized users.

Highlights

A growing number of studies show brain structural differences in grey (Richardson and Price 2009; Mechelli et al 2004; Elmer et al 2013; Bermudez et al 2009) and white matter (Roberts et al 2013; Elmer et al 2011; Bengtsson et al 2005) between expert and non-expert individuals, in linguistic, musical, and other domains (Golestani 2014)
We find evidence for reduced fractional anisotropy (FA) in the white matter fibers arising from the bilateral auditory cortices in the phoneticians compared to controls
This group difference may have arisen from training-related plasticity in the auditory cortex in this expert group, and/or from pre-existing structural differences in the phoneticians compared to the non-expert individuals

Summary

Introduction

A growing number of studies show brain structural differences in grey (Richardson and Price 2009; Mechelli et al 2004; Elmer et al 2013; Bermudez et al 2009) and white matter (Roberts et al 2013; Elmer et al 2011; Bengtsson et al 2005) between expert and non-expert individuals, in linguistic, musical, and other domains (Golestani 2014). In light of the proposed distinction between the dorsal audio-motor interface and the ventral meaning integration interface (Rodriguez-Fornells et al 2009; Lopez-Barroso et al 2013; Aboitiz 2012; Hickok and Poeppel 2007), it can be expected that especially pathways which form part of the dorsal system such as AF_long might be different in phonetics experts Indirect support for this hypothesis is given by the fact that AF_long connects, among other regions, the auditory and frontal regions for which Golestani and colleagues (2011) reported structural grey matter differences in phoneticians. AF_long has not been investigated in phoneticians, and especially the fibers within this language tract that connect with the auditory cortex have not been investigated in this expert group (Fig. 1, lower left panel). Group and training-related differences in the fractional anisotropy (FA) of these tracts were evaluated (see Supplementary Information for analyses on axial and radial diffusivity)

Participants

Results

Discussion