Abstracts

Rationale: The motor fibers from the pre-central gyrus pass through the anterior portion of the posterior limb of the internal capsule (PLIC) to reach the brain stem. Within the PLIC, the lateral to medial regions of the pre-central gyrus (PG) have an anterior to posterior pattern of topographical projection through the PLIC. We studied this projection pattern using probabilistic tractography.Methods: Diffusion MRI (with 55 gradients) was obtained in 20 healthy volunteers (age: mean=19 5.1 (SD) years; range=14-32 years; 10 males). In each person, bilateral PG was segmented into four subregions medio-laterally (medial-parasagittal, superior-medial, superior-lateral, inferior-lateral), and PLIC was segmented antero-posteriorly into six subregions (1-6, from anterior to posterior) of equal size in a single transaxial plane. Probabilistic tractography was performed from each of the PG subregions, and their connectivity to each PLIC subregion was estimated.Results: Our objective analysis showed a specific topographical pattern of projection of motor fibers from the pre-central gyrus passing through the PLIC (chi square = 39.7, p = 0.0005). In this group of 20 subjects, the inferior-lateral pre-central gyrus had the maximum connection to the anterior part (subregion 2) of the PLIC. The superior-lateral pre-central gyrus had the maximum connection to the intermediate part (subregion 3) of the PLIC, while both the superior-medial and medial parasagittal pre-central gyrus had the maximum connection to the posterior portion (subregion 4) of the PLIC.Conclusions: Objective MRI with probabilistic tractography can demonstrate the detailed topographical projection pattern of motor fibers from the pre-central gyrus through the posterior limb of the internal capsule. Tractographic evaluation of this topographical distribution of the motor pathway within the internal capsule is of significant clinical value in neurosurgery and in assessing brain injury.