Differences between the somatotopic corticospinal tract for the fingers and toes in the human brain.

The corticospinal tract (CST) is the most important motor tract in the human brain. The authors compared CST fibers of the fingers and toes using diffusion tensor imaging. Eleven normal healthy subjects were recruited for this study. Functional MRI stimulation was performed using finger grasp-release movements and toe flexion-extension movements (1 Hz). CST fibers of the fingers and toes were determined by selecting fibers passing through seed (the CST portion in the pons) and target regions of interest (the activation areas of the cerebral cortex during active finger and toe movements, respectively). No significant differences were observed between CST fibers of the fingers and toes in terms of fractional anisotropy, mean diffusivity, or tract volume (P> 0.05), and no differences were observed between the connectivities of CST fibers of the fingers and toes and the dorsal premotor cortex or the supplementary motor area (P>0.05). However, the connectivities between CST fibers of legs and the contralateral primary motor cortex were greater than those of CST fibers of the fingers (P< 0.05). It was found that somatotopic CST fibers of the fingers and toes did not differ in terms of diffusion tensor imaging characteristics, but that transcallosal fibers to the contralateral motor cortex were more frequent for CST fibers of the toes than for CST fibers of the fingers.