The relative pitch of harmonic complex sounds, such as instrumental sounds, may be perceived by decoding either the fundamental pitch (f0) or the spectral pitch (fSP) of the stimuli. We classified a large cohort of 420 subjects including symphony orchestra musicians to be either f0 or fSP listeners, depending on the dominant perceptual mode. In a subgroup of 87 subjects, MRI (magnetic resonance imaging) and magnetoencephalography studies demonstrated a strong neural basis for both types of pitch perception irrespective of musical aptitude. Compared with f0 listeners, fSP listeners possessed a pronounced rightward, rather than leftward, asymmetry of gray matter volume and P50m activity within the pitch-sensitive lateral Heschl's gyrus. Our data link relative hemispheric lateralization with perceptual stimulus properties, whereas the absolute size of the Heschl's gyrus depends on musical aptitude.

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Leftward volume asymmetry of the pars opercularis and pars triangularis may exist in the human brain, frequently referred to as Broca's area, given the functional asymmetries observed in this region with regard to language expression. However, post-mortem and magnetic resonance imaging (MRI) studies have failed to consistently identify such a volumetric asymmetry. In the present study, an analysis of the asymmetry of sulco-gyral anatomy and volume of this anterior speech region was performed in combination with an analysis of the morphology and volume asymmetry of the planum temporale, located within the posterior speech region, in 50 healthy subjects using MRI. Variations in sulcal anatomy were documented according to strict classification schemes and volume estimation of the grey matter within the brain structures was performed using the Cavalieri method of stereology. Results indicated great variation in the morphology of and connectivity between the inferior frontal, inferior precentral and diagonal sulci. There were significant inter-hemispheric differences in the presence of (1) the diagonal sulcus within the pars opercularis, and (2) horizontal termination of the posterior Sylvian fissure (relative to upward oblique termination), both with an increased leftward incidence. Double parallel inferior precentral sulci and absent anterior rami of the Sylvian fissure prevented stereological measurements in five subjects. Therefore volumes were obtained from 45 subjects. There was a significant leftward volume asymmetry of the pars opercularis ( P = 0.02), which was significantly related to the asymmetrical presence of the diagonal sulcus ( P < 0.01). Group-wise pars opercularis volume asymmetry did not exist when a diagonal sulcus was present in both or neither hemispheres. There was no significant volume asymmetry of the pars triangularis. There was a significant leftward volume asymmetry of the planum temporale ( P < 0.001), which was significantly associated with the shape of the posterior Sylvian fissure as a unilateral right or left upward oblique termination was always associated with leftward or rightward volume asymmetry respectively ( P < 0.01). There was no relationship between volume asymmetries of the anterior and posterior speech regions. Our findings illustrate the extent of morphological variability of the anterior speech region and demonstrate the difficulties encountered when determining volumetric asymmetries of the inferior frontal gyrus, particularly when sulci are discontinuous, absent or bifid. When the intrasulcal grey matter of this region is exhaustively sampled according to strict anatomical landmarks, the volume of the pars opercularis is leftward asymmetrical. This manuscript illustrates the importance of simultaneous consideration of brain morphology and morphometry in studies of cerebral asymmetry.

We provide neurobehavioral evidence supporting the transferable benefit of music training to alter brain function and enhance cognitive performance in a nonmusical visuospatial task in professional orchestral musicians. In particular, orchestral musicians' performance on a three-dimensional mental rotation (3DMR) task exhibited the behavioral profile normally only attained after significant practice, supporting the suggestion that these musicians already possessed well developed neural circuits to support 3DMR. Furthermore, functional magnetic resonance imaging revealed that only orchestral musicians showed significantly increased activation in Broca's area, in addition to the well known visuospatial network, which was activated in both musicians and nonmusicians who were matched on age, sex, and verbal intelligence. We interpret these functional neuroimaging findings to reflect preferential recruitment of Broca's area, part of the neural substrate supporting sight reading and motor-sequence organization underpinning musical performance, to subserve 3DMR in musicians. Our data, therefore, provide convergent behavioral and neurofunctional evidence supporting the suggestion that development of the sight-reading skills of musical performance alters brain circuit organization which, in turn, confers a wider cognitive benefit, in particular, to nonmusical visuospatial cognition in professional orchestral musicians.

Our results suggest that such neural changes may represent neural origins for tinnitus or consequences of tinnitus and its associations.