In the brains of all subjects, PTs were found to originate from the primary sensori-motor cortex (SM1, anterior boundary: precentral sulcus, posterior boundary: postcentral sulcus, medial boundary: midline, lateral boundary: lateral sulcus), and descended through the corona radiata, the posterior limb of the internal capsule, the cerebral peduncle of the midbrain, the anterior pons, and the anterior medulla along the known pathway of the PT. By contrast, in thirty-four (18.3%, right hemisphere: 20, left hemisphere: 14) of the 186 hemispheres, APTs separated from the PT at the upper midbrain level, descended through the medial lemniscus from the midbrain to the pons, and then rejoined with the PT at the upper medulla. Nine (26.5%) of the 34 APTs were found to originate from the primary somatosensory cortex (anterior boundary: central sulcus, posterior boundary: postcentral sulcus, medial boundary: midline, lateral boundary: lateral sulcus) without a primary motor cortex (anterior boundary: precentral sulcus, posterior boundary: central sulcus, medial boundary: midline, lateral boundary: lateral sulcus) origin.
Mean values of fractional anisotropy (FA), mean diffusivity (MD), tract volume (the number of voxels), and incidence of the APT are summarized in table . FA value and tract volume of the APT were lower than those of the PT. There were significant differences in terms of FA (t = 11.86, p < 0.001) value and tract volume (t = 11.28, p < 0.001) between the PT and the APT in the independent t-test, (P < 0.05). Likewise, we found significant difference in FA (Pearson's correlations: r = -0.163, P = 0.015) value between the PT and the APT in one-way analysis of covariance (ANCOVA; age) (P <0.05). However, no difference in MD (Pearson's correlations: r = 0.146, P = 0.03) value was observed in both the independent t-test and ANCOVA (P >0.05). We did not observe any differences in the values of FA (PT: t = -0.84, p = 0.40 APT: t = -0.49, p = 0.62), MD (PT: t = 1.23, p = 0.22 APT: t = 1.63, p = 0.11, tract volume (PT: t = -0.83, p = 0.41 APT: t = -0.12, p = 0.90), and incidence of the APT between the right and left hemispheres in either the PT or the APT (P > 0.05).
Results of diffusion tensor imaging parameters and incidence of the pyramidal tract and aberrant pyramidal tract.