Interhemispheric transcallosal connectivity between the left and right planum temporale predicts musicianship, performance in temporal speech processing, and functional specialization.

Currently, there is strong evidence showing that musicianship favours functional and structural changes of the left planum temporale (PT), and that these cortical reorganizations facilitate the discrimination of temporal speech cues. Based on the proposition of a division of labour between the left and right PT, here we postulated that the musicians' advantage in processing temporal speech cues and PT specialization origin, at least in part, from increased white matter connectivity between the two auditory-related cortices. In particular, we assume that increased transcallosal PT connectivity might promote functional specialization and asymmetry of homotopic brain regions. With this purpose in mind, we applied diffusion tensor imaging and compared axial diffusivity (AD), radial diffusivity (RD), and fractional anisotropy (FA) of the interhemispheric connection between the left and right PT in thirteen musicians and 13 nonmusicians. Furthermore, in the form of an addendum, we integrated cortical surface area values and blood oxygenation level dependent (BOLD) responses of the left PT that were collected in the context of two previous studies conducted with the same sample of subjects. Our results indicate increased connectivity between the left and right PT in musicians compared to nonmusicians, as indexed by reduced mean RD. We did not find significant between-group differences in FA and AD. Most notably, RD was related to the performance in the phonetic categorization task, musical aptitudes, as well as to BOLD responses in the left PT. Hence, we provide first evidence for a relationship between PT connectivity, musicianship, and phonetic categorization.