ABSTRACT
The corticoreticular pathway (CRP) is a major motor tract that provides volitional input to the reticular formation motor nuclei and may be an important mediator of motor recovery after central nervous system damage. However, its cortical origins, trajectory and laterality are incompletely understood in humans. This study aimed to map the human CRP and generate an average CRP template in standard MRI space. Following recently established guidelines, we manually delineated the primary reticular formation motor nucleus (gigantocellular reticular nucleus [GRN]) using several group-mean MRI contrasts from the Human Connectome Project (HCP). CRP tractography was then performed with HCP diffusion-weighted MRI data (N=1,065) by selecting diffusion streamlines that reached both the frontal cortex and GRN. Corticospinal tract (CST) tractography was also performed for comparison. Results suggest that the human CRP has widespread origins, which overlap with the CST across most of the motor cortex and include additional exclusive inputs from the medial and anterior prefrontal cortices. The estimated CRP projected through the anterior and posterior limbs of the internal capsule before partially decussating in the midbrain tegmentum and converging bilaterally on the pontomedullary reticular formation. Thus, the CRP trajectory appears to partially overlap the CST, while being more distributed and anteromedial to the CST in the cerebrum before moving posterior to the CST in the brainstem. These findings have important implications for neurophysiologic testing, cortical stimulation and movement recovery after brain lesions. We expect that our GRN and tract maps will also facilitate future CRP research.
HIGHLIGHTS
The corticoreticular pathway (CRP) is a major tract with poorly known human anatomy
We mapped the human CRP with diffusion tractography led by postmortem & animal data
The CRP appears to originate from most of the motor cortices and further anterior
The estimated CRP had distributed and bilateral projections to the brainstem
These findings have important implications for motor recovery after brain lesions
Competing Interest Statement
The authors have declared no competing interest.
ABBREVIATIONS
- ALIC
- anterior limb of internal capsule
- aPFC
- anterior prefrontal cortex
- CReST
- cortico-reticulo-spinal tract
- CRP
- corticoreticular pathway
- CST
- corticospinal tract
- DEC
- direction-encoded color
- DLPFC
- dorsolateral prefrontal cortex
- EPI
- echo-planar imaging
- FA
- fractional anisotropy
- FSL
- FMRIB software library
- GRN
- gigantocellular reticular nucleus
- HCP
- human connectome project
- M1
- primary motor cortex
- MNI
- Montreal Neurologic Institute
- mPFC
- medial prefrontal cortex
- PLIC
- posterior limb of internal capsule
- PMd
- dorsal premotor cortex
- PMv
- ventral premotor cortex
- QA
- quantitative anisotropy
- SDF
- spin distribution function
- SMA
- supplementary motor area
- RST
- reticulospinal tract