Despite the fact that the Heschl gyrus (HG) is a crucial brain structure as it contains the primary auditory cortex (PAC), relatively few structural MRI studies have concentrated upon it. We propose that this may be attributed in part to the considerable variability of this structure and, most importantly, to the lack of unified criteria for defining the extent of the PAC along the MRI-determined landmarks of the HG, which ultimately affects the reliability and reproducibility of these studies. This review highlights three aspects: first, the standard and variant anatomy of the HG and PAC with particular focus on MRI definition of these regions; second, the importance of studying the HG and PAC in health and disease using structural MRI; and, third, the problem of MRI localization of the PAC. The scientific community should be aware that the HG and its included PAC are not synonyms. Additionally, owing to the great complexity and variability of these regions, future MRI studies should be cautious when using single brain-based atlas or maps generated by simply averaging across individuals to localize these regions. Instead, and while waiting for future in vivo microstructural localization of the PAC, the use of probabilistic and functional maps is advantageous but not without shortcomings. THE HESCHL GYRUS (HG) HAS EXCITED neuroscientists who study it as it contains a very crucial region, the primary auditory cortex (PAC). Tremendous interhemispheric and interindividual variations have been reported in this gyrus by both postmortem (1,2) and MRI studies (3,4). Adding more complexity is the finding that the extent of the cytoarchitectonic PAC along the HG are also subjected to interhemispheric and interindividual variations (2,5). These facts would greatly question both the validity of structural MRI studies concentrating on these regions and the use of single brain-based atlas in localizing them. This is especially true for the PAC as it, unlike the HG, lack MR-defined macroanatomical landmarks. This may, in part, explain why the HG (and its included PAC) has not been studied as extensively as other regions of the superior temporal gyrus (STG) such as the planum temporale (PT). Consequently, these difficulties will also affect interpretation of functional MRI findings. Therefore, the need for adequate knowledge of the standard and variant anatomy of these regions and particularly the PAC seems to be of extreme importance. Equally important is to correlate these anatomical variations with the diverse results obtained by previously published structural MRI studies of these regions and to suggest unified definitions and criteria that future studies can make reference to. To our knowledge, these issues have not been addressed previously.The review is divided into three main parts: in the first, the standard and variant anatomy of the HG and its included PAC is discussed, paying particular attention to MRI definition of these regions. This is followed by highlighting the previously published morphometric/volumetric st...

This work was conducted to study the plasticity of superior (SCP) and middle (MCP) cerebellar peduncles in musicians. The cerebellum is well known to support several musically relevant motor, sensory and cognitive functions. Previous studies reported increased cerebellar volume and grey matter (GM) density in musicians. Here, we report on plasticity of white matter (WM) of the cerebellum. Our cohort included 10/10 gender and handedness-matched musicians and controls. Using diffusion tensor imaging, fibre tractography of SCP and MCP was performed. The fractional anisotropy (FA), number of streamlines and volume of streamlines of SCP/MCP were compared between groups. Automatic measurements of GM and WM volumes of the right/left cerebellar hemispheres were also compared. Musicians have significantly increased right SCP volume (p = 0.02) and number of streamlines (p = 0.001), right MCP volume (p = 0.004) and total WM volume of the right cerebellum (p = 0.003). There were no significant differences in right MCP number of streamlines, left SCP/MCP volume and number of streamlines, SCP/MCP FA values, GM volume of the right cerebellum and GM/WM volumes of the left cerebellum. We propose that increased volume and number of streamlines of the right cerebellar peduncles represent use-dependent structural adaptation to increased sensorimotor and cognitive functional demands on the musician's cerebellum.

Purpose: To compare manual volumetry of gray matter (GM) / white matter (WM) of Broca's area subparts: pars opercularis (POP) and pars triangularis (PTR) in both hemispheres between musicians and nonmusician, as it has been shown that these regions are crucial for musical abilities. A previous voxel-based morphometric (VBM) study conducted in our laboratory reported increased GM density in Broca's area of left hemisphere in male orchestral musicians. Functional segregation of POP/PTR justified separate volumetric analysis of these parts. Materials and Methods:We used the same cohort for the VBM study. Manual morphometry (stereology) was used to compare volumes between 26/26 right-handed orchestral musicians/nonmusicians.Results: As expected, musicians showed significantly increased GM volume in the Broca's area, specifically in the left POP. No significant results were detected in right POP, left/right PTR GM volumes, and WM volumes for all regions. Results were positively correlated with years of musical performance (r ¼ 0.7, P ¼ 0.0001). Conclusion:This result corroborates the VBM study and is in line with the hypothesis of critical involvement of POP in hearing-action integration being an integral component of frontoparietotemporal mirror neuron network. We hypothesize that increased size of musicians' left POP represent use-dependent structural adaptation in response to intensive audiomotor skill acquisition.

Purpose: To investigate whether scanning at different field strengths and pulse sequences would influence reproducibility of corpus callosum (CC) morphometric measurements as variations in scanning parameters may result in differences in contrast properties between resulting images that are independent of the underlying tissue but rather reflect the physics of the imaging process. Materials and Methods:Ten subjects were scanned twice at 3T using magnetization-prepared rapid gradient-echo imaging (MPRAGE) and modified driven equilibrium Fourier transform (MDEFT) sequences and once at 1.5T using MPRAGE. Cross-sectional area measurements of four callosal regions were performed on midsagittal magnetic resonance imaging (MRI) sections.Results: Repeated measures analysis of variance with four regions as dependent variables and three scanning protocols (1.5T MPRAGE, 3T MPRAGE and 3T MDEFT) as independent variables revealed no significant region by protocol interaction: F(6,54) ¼ 0.69, P ¼ 0.52. Reliability measures for (3T MPRAGE/3T MDEFT) and (1.5T MPRAGE/3T MPRAGE; 1.5T MPRAGE/3T MDEFT) comparisons were high, ranging between 0.90 and 0.97. Conclusion:Based on our results, combining and comparing CC morphometric data obtained at different field strengths and/or with different pulse sequences appears possible.