Localization of orofacial representation in the corona radiata, internal capsule and cerebral peduncle inMacaca mulatta

Abstract

Subcortical white matter injury is often accompanied by orofacial motor dysfunction, but little is known about the structural substrates accounting for these common neurological deficits. We studied the trajectory of the corticobulbar projection from the orofacial region of the primary (M1), ventrolateral (LPMCv), supplementary (M2), rostral cingulate (M3) and caudal cingulate (M4) motor regions through the corona radiata (CR), internal capsule (IC) and crus cerebri of the cerebral peduncle (ccCP). In the CR each pathway was segregated. Medial motor area fibers (M2/M3/M4) arched over the caudate and lateral motor area fibers (M1/LPMCv) curved over the putamen. At superior IC levels, the pathways were widespread, involving the anterior limb, genu and posterior limb with the M3 projection located anteriorly, followed posteriorly by projections from M2, LPMCv, M4 and M1, respectively. Inferiorly, all pathways maintained this orientation but shifted posteriorly, with adjacent fiber bundles overlapping minimally. In the ccCP, M3 fibers were located medially and M1 fibers centromedially, with M2, LPMCv, and M4 pathways overlapping in between. Finally, at inferior ccCP levels, all pathways overlapped. Following CR and superior IC lesions, the dispersed pathway distribution may correlate with acute orofacial dysfunction with spared pathways contributing to orofacial motor recovery. In contrast, the gradually commixed nature of pathway representation inferiorly may enhance fiber vulnerability and correlate with severe, prolonged deficits following lower subcortical and midbrain injury. Additionally, in humans these findings may assist in interpreting orofacial movements evoked during deep brain stimulation, and neuroimaging tractography efforts to localize descending orofacial motor pathways.

Bundle-Specific Axon Diameter Index as a New Contrast to Differentiate White Matter Tracts

“…This is usually neglected the aspect of CC topology, albeit already shown by tracer injections in the CC of the cat (Nakamura and Kanaseki, 1989 ), and is compatible with the ordering of CC connections already described with DW-MRI (Hofer et al, 2015 ). Also, anteroposteriorly organized bundles of streamlines connect the sectors of PIC to anteroposterior cortical territories, compatible with the topology shown by tracer injections and DW-MRI in monkeys (Morecraft et al, 2017 ) and DW-MRI in humans (Archer et al, 2018 ).…”

Patients with chronic migraine without history of medication overuse are characterized by a peculiar white matter fiber bundle profile

“…Overall, most of the tracts found to exhibit abnormal WM diffusive metrics in the present study form parts of the widespread WM bundle fiber system of the brain that conveys information about somatosensory, cognitive, and/or emotional components of orofacial pain discrimination [33]. Other tracts, like the superior LF, seem to be involved in endogenous pain modulatory mechanisms and multisensory integration [34].…”

Holographic Reconstruction of Axonal Pathways in the Human Brain

“…The general process of importing histological results and developing streamline approximations for each pathway was repeated for the posterior limb of internal capsule (Morecraft et al, 2017; Figure 3A), anterior limb of internal capsule (Safadi 3B), and hyperdirect pathway (Haynes and Haber, 2013;Coudé et al, 2018;Figure 4). However, the available anatomical results for these pathways were derived from the non-human primate experiments, so direct co-registration with the CIT168 MRI slices was not explicit but inferred from expert knowledge.…”

“…The control point locations were selected such that there was a somatopic organization of the projections from primary motor cortex (face, upper ex., lower ex.) (Figure 3A; Morecraft et al, 2017). In addition, we imposed an anterior-posterior organization within the internal capsule of first the SMA fibers, then the premotor fibers, and finally the primary motor cortex projections (Figure 3A; Morecraft et al, 2017).…”