Functional and anatomical correlates of language expertise

Abstract

A number of previous studies have shown that intensive training and expertise in a particular domain are associated with functional and structural changes of the human brain. Exactly these altered brain characteristics as a function of intensive training have previously well been documented in cross-sectional (Bangert & Schlaug, 2006; Baumann, Meyer, & Jancke, 2008; Elmer, Meyer, & Jäncke, 2011; Pantev, Roberts, Schulz, Engelien, & Ross, 2001) and longitudinal (Bangert & Altenmuller, 2003; Bezzola, Merillat, Gaser, & Jancke, 2011; Draganski et al., 2004; Hyde et al., 2009) studies by using different methodologies. In this context, an abundance of work dedicated to investigate the influence of intensive training in professional musicians, found convergent evidence for an altered brain architecture, most notably in auditory (Jancke, 2009; Munte, Altenmuller, & Jancke, 2002; Schlaug, Jancke, Huang, & Steinmetz, 1995), somatosensory, and motor brain regions (Amunts et al., 1997; Bangert et al., 2006; Elbert, Pantev, Wienbruch, Rockstroh, & Taub, 1995). Furthermore, previous work performed with musicians not only showed that brain functions and structures can change as a function of training, but notably also that these architectural changes can indeed favour cognitive and perceptual abilities in domains which were not explicitly trained (Aleman, Nieuwenstein, Bocker, & de Haan, 2000; Bilhartz, Bruhn, & Olson, 1999; Brochard, Dufour, & Despres, 2004; Gromko & Poorman, 1998; Magne, Schon, & Besson, 2006; Marie, Magne, & Besson, 2011; Schlaug, Norton, Overy, & Winner, 2005).
Basing on this previous evidence for neuroplasticity and transfer effects in professional musicians, the present work was dedicated to systematically address functional and structural neuronal reorganization in language experts. In particular, the present work aimed at uncovering the effect of intensive language training as experience by simultaneous interpreters (SIs) on 1) lexical processing within and across the languages intensively trained, 2) on structural white matter adaptations in regions supporting articulation, sensory-to-motor coupling mechanisms, and cognition, and 3) on functional and behavioural transfer effects originating from language training. With these purposes in mind, and by adopting cross-sectional designs, I postulated that neuronal reorganisation and transfer effects may originate as a consequence of the processing demands necessary for translating a source language into a target language.
The aim of study A (EEG), entitled “Simultaneous Interpreters as a Model for Neuronal Adaptation in the Domain of Language Processing”, was to examine the impact of language training as experienced by SIs on lexical processing within and across the native (L1) and non-native (L2) languages. With this purpose in mind,
eleven native German SIs and controls matched in L2 proficiency and age of acquisition were asked to judge whether auditory presented disyllabic noun pairs
were either semantically congruent or incongruent. In terms of electrophysiological responses, we observed an earlier negative deflection of the N400 component in the
SIs group, in comparison to the controls, while detecting incongruent trials within the native (L1) and non-native (L2) languages, as well as during the incongruent
German-English condition (GE). These earlier negative responses were interpreted as indicating a training-related altered sensitivity to lexical processing within L1 and L2 as a function of language expertise. Otherwise, the tonic increased N400 responses we observed in the SIs while processing semantic congruent noun pairs which were presented in the opposite direction as usually trained (i.e., from L1 to L2) were interpreted as reflecting the engagement of additional cognitive resources necessary for accomplishing an untrained and therefore unusual language task.
In study B (DTI), entitled “Differential Language Expertise Related to White Matter Architecture in Regions Subserving Sensory-Motor Coupling, Articulation and Interhemispheric Transfer”, we investigated white matter alterations as a function of long-term language training. Basing on the assumption that simultaneous interpreting places high demands on articulation and sound-to-motor mapping mechanisms, as well as on cognitive functions which are vital for executing fast interpretations, we expected to provide evidence for an altered white matter architecture in brain regions involved in the motor control of speech and cognition. In line with our hypothesis, we found evidence for an altered white matter architecture in the SIs group, in comparison to the controls, in the left anterior insula and in the head of the right caudate nucleus, both structures previously shown to be involved in supporting articulation and sensory-to-motor coupling mechanisms. Furthermore, we revealed a differential white matter architecture in the SIs group in the most anterior part of the corpus callosum, a structure being composed of fibre bundles connecting the two frontal lobes. These training-related white matter adaptations we revealed in the anterior part of the corpus callosum are supposed to optimise the interplay between the two frontal lobes which are strongly involved in controlling executive functions during interpreting.
In study C (fMRI), entitled “Intensive Language Training and Attention Modulate the Involvement of Fronto-Parietal Regions During a Non-Verbal Auditory Discrimination Task”, we investigated behavioural and functional transfer effects originating from language training. In particular, we explored whether the intensively trained attention functions of SIs may facilitate the discrimination of non-verbal stimulus attributes. With this purpose in mind, we used the fMRI technique and compared brain activation maps in SIs and control subjects while the subjects performed a non-verbal pitch discrimination task which strongly relies on auditory attention and categorization functions. Whereas the two groups did not differ in terms of correct responses, results showed an expertise-related modulation of fronto-parietal brain regions while performing the task. This expertise-related modulation was manifested by increased brain responses in the left angular gyrus in conjunction with reduced brain activity in the right frontal operculum. The anterior to posterior displacement of brain responses we observed in the SIs group was interpreted as being particularly advantageous for relieving the functional capacity of the frontal lobe, which is indeed strongly involved in supporting executive functions during interpreting, from additional cognitive loads.