Abstract
We applied Surface-Based Morphometry to assess the variations in cortical thickness (CT) and cortical surface area (CSA) in relation to the occurrence of Heschl's gyrus (HG) duplications in each hemisphere. 430 healthy brains that had previously been classified as having a single HG, Common Stem Duplication (CSD) or Complete Posterior Duplication (CPD) in each hemisphere were analyzed. To optimally align the HG area across the different groups of gyrification, we computed a specific surface-based template composed of 40 individuals with a symmetrical HG gyrification pattern (20 single HG, 10 CPD, 10 CSD). After normalizing the 430 participants' T1 images to this specific template, we separately compared the groups constituted of participants with a single HG, CPD, and CSD in each hemisphere. The occurrence of a duplication in either hemisphere was associated with an increase in CT posterior to the primary auditory cortex. This may be the neural support of expertise or great abilities in either speech or music processing domains that were related with duplications by previous studies. A decrease in CSA in the planum temporale was detected in cases with duplication in the left hemisphere. In the right hemisphere, a medial decrease in CSA and a lateral increase in CSA were present in HG when a CPD occurred together with an increase in CSA in the depth of the superior temporal sulcus (STS) in CSD compared to a single HG. These variations associated with duplication might be related to the functions that they process jointly within each hemisphere: temporal and speech processing in the left and spectral and music processing in the right.
Highlights
Heschl’s gyrus (HG), which hosts the Primary Auditory Cortex (PAC), exhibits very high anatomical variability in its size and gyrification across both individuals and hemispheres (Penhune et al, 1996; Leonard et al, 1998; Abdul-Kareem and Sluming, 2008; Marie et al, 2015)
In cases with a Common Stem Duplication (CSD) in the right hemisphere, a small cluster of high variability was observed in the sulcus intermedius of Beck (Figure 2B), similar to that on the left, which corresponded to a variation in the width of the mid-part of the second sulcus
A larger cortical thickness (CT) was observed in the medial part of the second HG in both hemispheres in the Complete Posterior Duplication (CPD) group compared to the single HG group, but it was more medially situated on the right
Summary
Heschl’s gyrus (HG), which hosts the Primary Auditory Cortex (PAC), exhibits very high anatomical variability in its size and gyrification across both individuals and hemispheres (Penhune et al, 1996; Leonard et al, 1998; Abdul-Kareem and Sluming, 2008; Marie et al, 2015). Three configurations of HG can be observed: a single HG, a Common Stem Duplication (CSD), Surface-Based Morphometry of Duplications of Heschl’s Gyri corresponding to a partial split of the lateral part of the gyrus by the sulcus intermedius of Beck, and a Complete Posterior Duplication (CPD) that is a double HG (Abdul-Kareem and Sluming, 2008). MRI methods that provide estimates of myelination have demonstrated a highly myelinated area running over the medial two-thirds of HG in single gyrus and over the aHG in duplications (Dick et al, 2012). This myelinated area likely corresponds to the location of the PAC, primary areas being more heavily myelinated than the associative areas (Glasser and Van Essen, 2011). Post-mortem probabilistic maps of acoustic radiations further confirmed Pfeifer’s pioneering observations (Rademacher et al, 2002)
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