1 Cognition and Brain Plasticity Group, Bellvitge Biomedical Research Institute, L'Hospitalet de Llobregat, 08097, Barcelona, Spain; Division Neuropsychology, Department of Psychology, University of Zurich, Zurich, Switzerland. Electronic address: s.elmer@psychologie.uzh.ch.
2 Division Neuropsychology, Department of Psychology, University of Zurich, Zurich, Switzerland. Electronic address: j.haenggi@psychologie.uzh.ch.
3 Cognition and Brain Plasticity Group, Bellvitge Biomedical Research Institute, L'Hospitalet de Llobregat, 08097, Barcelona, Spain; Department of Cognition, Development and Education Pychology, University of Barcelona, Passeig de la Vall d'Hebron, 171, 08035, Barcelona, Spain; Laboratory of Motor learning and Neural Plasticity, Concordia University, 7141 Rue Sherbrooke West, H4B 1R6, Montreal, QC, Canada. Electronic address: lucia.vaquero.z@gmail.com.
4 Department of Cognition, Development and Educational Psychology, Campus Bellvitge, University of Barcelona, L'Hospitalet de Llobregat, 08097, Barcelona, Spain. Electronic address: golivec95@gmail.com.
5 Cognition and Brain Plasticity Group, Bellvitge Biomedical Research Institute, L'Hospitalet de Llobregat, 08097, Barcelona, Spain; Department of Cognition, Development and Educational Psychology, Campus Bellvitge, University of Barcelona, L'Hospitalet de Llobregat, 08097, Barcelona, Spain; Institut de Recerca Pediàtrica Hospital Sant Joan de Déu, Barcelona, Spain; Aix Marseille University, CNRS, LPL, Aix-en-Provence, France. Electronic address: fclement24@hotmail.com.
6 Cognition and Brain Plasticity Group, Bellvitge Biomedical Research Institute, L'Hospitalet de Llobregat, 08097, Barcelona, Spain; Department of Cognition, Development and Educational Psychology, Campus Bellvitge, University of Barcelona, L'Hospitalet de Llobregat, 08097, Barcelona, Spain; Institució Catalana de Recerca i Estudis Avançats, ICREA, 08010, Barcelona, Spain. Electronic address: arfornells@gmail.com.

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.