In-vivo analysis of the human planum temporale (PT): does the definition of PT borders influence the results with regard to cerebral asymmetry and correlation with handedness?

The aim of our study was to examine whether the degree of planum temporale (PT) asymmetry and the possible correlation of morphological PT asymmetries with handedness are influenced by the definition of PT borders. For this r eason, we applied three different anatomical PT definitions formerly used i n the literature. The PT total (with the end of the Sylvian fissure (SF) as its posterior border) was separated into anterior and posterior regions. T he border between anterior and posterior PT was set according to the follow ing definitions: at the end of Heschl's gyrus (Ist definition); at the star t of the ascending SF ramus according to the 'knife-cut' method (2nd defini tion); and at the bifurcation of the SF (3rd definition). Thirty right-hand ed healthy men were recruited. MRI data sets analyzed with the software pro gram BRAINS were used for in vivo PT volumetry. The Edinburgh Handedness In ventory (EHI) and the Hand Dominance Test were used to determine the degree of handedness. In summary, we detected that the type and the degree of asy mmetry between left and right PT were strongly dependent on the definition used for PT borders: a left > right asymmetry was found in all PT regions, except a right > left asymmetry of the anterior PT according to our Ist PT definition (lateral to Heschl's gyrus) and a symmetry of the posterior PT a ccording to our 3rd PT definition (posterior to SF bifurcation). In additio n, a significant correlation was found between the degree of handedness mea sured by the EHI and the right posterior PT (3rd definition). We conclude t hat the influence of the definition of PT borders on the investigated varia bles may explain some of the variances between former investigations on PT asymmetry and handedness. The possible implications of the correlation betw een handedness and the extension of the right parietal PT are discussed and have to be elucidated by further studies. (C) 2001 Elsevier Science Irelan d Ltd. All rights reserved.