Modulation of hemispheric language dominance of left-handers according to musical experience: an fMRI study

Abstract

INTRODUCTION: Language processing is a function presenting a strong hemispheric leftdominance in the vast majority of population (94-96% of right-handers). Nonetheless, some conditions such as left-handedness have been associated with a higher incidence of atypical (right or bilateral) language dominance. Structural and functional asymmetry differences in primary auditory cortex (Heschl’s gyrus) and secondary auditory cortex (planum temporale) have been hypothesized as the underlying causal factor of this modulation by handedness. In this study, due to the differential development of Heschl’s gyrus previously described in musicians, we put to test if musicians could present a modulation of their hemispheric language dominance when compared to nonmusicians. EXPERIMENTAL PROCEDURES: We assessed hemispheric language dominance in musicians and nonmusicians (both right-handed and left-handed) using an fMRI language paradigm (verb generation task). Language dominance was established for each participant via the calculation of functional laterality indexes in the prefrontal region. RESULTS: Left-handed musicians were more likely to be right-dominant (34.5%) than lefthanded nonmusicians (5.3%). No differences were found among right-handed participants. DISCUSSION: Musical experience is related to a higher probability of presenting a rightdominance of language, but only in left-handed population. As musical training begins after language dominance is presumably already established, we interpret these results as an evidence of a common underlying factor linking both language dominance and the probability to undergo musical training. We propose the differential development of auditory cortex as this relating factor.