Elsevier

Neuropsychologia

Volume 98, April 2017, Pages 212-219
Neuropsychologia

Cortical thickness increases after simultaneous interpretation training

https://doi.org/10.1016/j.neuropsychologia.2017.01.008Get rights and content

Highlights

  • We carried out a longitudinal investigation on simultaneous interpretation training.

  • Trainee interpreters showed cortical thickening in multiple regions.

  • These regions are implicated in audio-motor and phonological processing.

  • Thickening was also seen in regions linked to executive and attentional control.

  • Interpreter training may also confer some protection against normal, age-related thinning.

Abstract

Simultaneous interpretation is a complex cognitive task that not only demands multilingual language processing, but also requires application of extreme levels of domain-general cognitive control. We used MRI to longitudinally measure cortical thickness in simultaneous interpretation trainees before and after a Master's program in conference interpreting. We compared them to multilingual control participants scanned at the same interval of time. Increases in cortical thickness were specific to trainee interpreters. Increases were observed in regions involved in lower-level, phonetic processing (left posterior superior temporal gyrus, anterior supramarginal gyrus and planum temporale), in the higher-level formulation of propositional speech (right angular gyrus) and in the conversion of items from working memory into a sequence (right dorsal premotor cortex), and finally, in domain-general executive control and attention (right parietal lobule). Findings are consistent with the linguistic requirements of simultaneous interpretation and also with the more general cognitive demands on attentional control for expert performance in simultaneous interpreting. Our findings may also reflect beneficial, potentially protective effects of simultaneous interpretation training, which has previously been shown to confer enhanced skills in certain executive and attentional domains over and above those conferred by bilingualism.

Introduction

There is growing interest in understanding the brain's structural changes, or plasticity, arising from bilingualism (García-Pentón et al., 2014, Klein et al., 2014, Li et al., 2014, Mechelli et al., 2004, Ressel et al., 2012, et al., 2012) and from training in language-specific domains, such as phonetics (Golestani et al., 2011, Vandermosten et al., 2015) and simultaneous interpreting (Elmer et al., 2014, Elmer et al., 2011). A growing number of cross-sectional (Klein et al., 2014, Li et al., 2014, Mechelli et al., 2004, Olulade et al., 2015, Ressel et al., 2012) as well as some longitudinal (Schlegel et al., 2012, et al., 2012) studies on bilingualism have reported structural findings in regions including the left inferior parietal cortex, the auditory cortex, the inferior frontal gyri bilaterally and in regions involved in polyglot language control (Abutalebi and Green, 2007, Abutalebi and Green, 2008, Hervais-Adelman et al., 2011). However, the results are relatively heterogeneous and diverse (Golestani, 2014), perhaps due to differences in populations, brain imaging sequences and brain imaging analysis approaches across studies (et al., 2015, Higby et al., 2013).

Beyond work on language acquisition and bilingualism, previous work on language expertise has shown grey (Golestani et al., 2011) and white matter (Vandermosten et al., 2015) differences between phonetics experts and controls in the auditory cortices bilaterally and in the left pars opercularis. These regions belong to the dorsal, audio-motor stream that subserves audio-motor mapping of sounds onto articulatory-based representations, rather than to the ventral meaning integration interface (Golestani, 2015, Golestani and Pallier, 2007, Hickok and Poeppel, 2004, Hickok and Poeppel, 2007, Rodriguez-Fornells et al., 2009, Saur et al., 2008). Moreover, among the phoneticians there was a correlation between years of phonetics transcription training and grey and white matter properties of these regions, suggesting experience-dependent plasticity in relation to this relatively low-level form of linguistic expertise (Golestani et al., 2011, Vandermosten et al., 2015).

Simultaneous interpreting (SI), by contrast, is a linguistic task that involves higher-level (i.e. phonetic but also semantic, syntactic and prosodic) linguistic processing and extensively taps cognitive control mechanisms that are not specifically linguistic in nature. Listening to continuous prose in one language while simultaneously converting and producing the narrative in another language requires real-time processing of a source input, whilst simultaneously transposing the content of that input to a target language, monitoring production of that output, whilst maintaining access to and control over the relevant phonetic, semantic, syntactic and prosodic rules of both source and target languages. Interpreters listen to source language input while producing target language output for an average of 65% of their time on task. In order to monitor their output in the target language interpreters need to listen to it, while simultaneously listening to newly arriving input in the source language. Thus, success at simultaneous interpretation depends not only on outstanding processing speed and excellent verbal working memory skills, but also on the ability to simultaneously comprehend and produce speech in two oftentimes structurally very dissimilar languages, while also monitoring one's output and continuously translating it in real-time (Moser-Mercer et al., 1997). Consistent with this, a recent functional magnetic resonance imaging (fMRI) study has shown that simultaneous interpretation recruits brain networks associated with speech comprehension and production such as the left inferior frontal gyrus, auditory and posterior temporal and temporo-parietal regions, alongside regions involved in more domain-general functions such as task-switching, conflict resolution, and inhibition; functions that have previously been implicated in language control. These latter regions included the anterior cingulate cortex and a thalamo-striatal-cerebellar network (Hervais-Adelman et al., 2015b).

Two recent structural brain imaging studies have investigated grey (Elmer et al., 2014) and white matter (Elmer et al., 2011) in professional simultaneous interpreters. Unlike the trainee interpreters studied by Hervais-Adelman et al., 2015a, Hervais-Adelman et al., 2015b described above, these two studies featured highly experienced professionals. Elmer and colleagues (Elmer et al., 2014) revealed lower grey matter volumes in the interpreters compared to control participants in the left pars opercularis and supramarginal gyrus (SMG), in the middle-anterior cingulate gyrus, and bilaterally in the pars triangularis and middle-anterior insula. Within the interpreters groups, the grey matter volume in a subset of these regions (the left pars triangularis, right pars opercularis and middle-anterior cingulate gyrus) and in the bilateral caudate nucleus was negatively correlated with the cumulative number of interpreting hours. These findings likely reflect experience-dependent structural plasticity in these language-related and cognitive control regions, although some of the differences may have predated the training (Elmer et al., 2014) and may thus reflect possibly innate, domain-specific aptitudes (c.f. Golestani et al., 2011).

In the present study, we examined cortical thickness changes arising from simultaneous interpretation training longitudinally, before and after our participants undertook a Master's program in conference interpreting. The longitudinal nature of our design allows for greater sensitivity to training-related changes, and mitigates against many confounding effects of cohort (Fitzmaurice et al., 2011). Due to the fact that many studies have reported positive relationships between behavioural measures and regional measures of thickness and/or volume (Blackmon et al., 2010, Foster and Zatorre, 2010, Golestani, 2014, Li et al., 2014, Wong et al., 2010), we predicted that we would find training-related increases in cortical thickness in brain regions responsible for speech production and comprehension, in ones involved in language and cognitive control, and in attentional regions. These include fronto-temporo-parietal regions, motor and premotor regions, the anterior cingulate gyrus and subcortical regions, and right superior parietal attentional regions. We expected structural modifications to at least partly converge in terms of localisation with brain regions previously found to be functionally involved in simultaneous interpreting (Hervais-Adelman et al., 2015b) and in language control (Hervais-Adelman et al., 2011), and in regions found to differ structurally between interpreters and controls by others (Elmer et al., 2014, Elmer et al., 2011).

Section snippets

Participants

Sixty-seven individuals participated in the study. Of these, 34 were trainee interpreters, and 33 constituted a control group. For logistical reasons, participants were scanned at either of two imaging centres (see below), but all scans for a given individual always took place on the same scanner / at the same centre. The trainee interpreters were enrolled in the Master's program in conference interpreting at the Faculty of Translation and Interpreting at the University of Geneva, Switzerland.

Results

Results revealed group differences in the change in cortical thickness in three posterior peri-Sylvian regions of the left-hemisphere, namely, the posterior superior temporal gyrus, the supramarginal gyrus and the planum temporale within the posterior lateral (or Sylvian) fissure. Group differences in the change in cortical thickness were also found in the right hemisphere, in the superior parietal lobule, in the angular gyrus of the inferior parietal cortex, in the intraparietal sulcus and in

Discussion

Our results revealed cortical thickness changes, arising from approximately 14 months of simultaneous interpretation training, in a number of regions across both cerebral hemispheres. Increases in cortical thickness were observed in left perisylvian regions generally associated with speech processing, ones that have previously been found to be functionally implicated in SI. Training-related cortical thickness changes in the right hemisphere were not confined to regions functionally implicated

Author contributions

N.G. conceived and supervised the study. A.H.-A. carried out the analyses. A.H.-A and N.G. collected data and wrote the paper, and B.M.M and M.M. contributed to the paper.

Acknowledgments

We wish to thank Professor Stephanie Clarke and Professor Reto Meuli for assistance in facilitating access to the scanner at the Centre for Biomedical Imaging (CIBM) at the Centre Hospitalier Universitaire Vaudois (cohort 1). We also wish to thank the Brain and Behaviour Lab at the University of Geneva for access to the scanner for cohort 2, as well as two anonymous reviewers for their helpful comments and suggestions for the paper. This work was supported by Swiss National Science Foundation

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