New Corticopontine Connections in the Primate Brain: Contralateral Projections From the Arm/Hand Area of the Precentral Motor Region

Abstract

The ipsilateral corticopontine projection (iCPP) represents a massive descending axon system terminating in the pontine nuclei (PN). In the primate, this projection is well known for its dominant influence on contralateral upper limb movements through the classical cerebrocerebellar circuity system. Although a much weaker contralateral corticopontine projection (cCPP) from motor cortex to the paramedian region has been reported in the non-human primate brain, we provide the first comprehensive description of the cCPP from the lateral motor cortex using high resolution anterograde tract tracing in Macaca mulatta. We found a relatively light cCPP from the hand/arm area of the primary motor cortex (M1), comparatively moderate cCPP from ventrolateral premotor cortex (LPMCv) and a more robust and widespread cCPP from the dorsolateral premotor cortex (LPMCd) that involved all nine contralateral PN. The M1 projection primarily targeted the dorsal pontine region, the LPMCv projection targeted the medial pontine region and LPMCd targeted both regions. These results show the first stage of the primate frontomotor cerebrocerebellar projection is bilateral, and may affect both ipsilateral and contralateral limbs. Clinically, the cCPP originating in the non-injured hemisphere may influence the recovery process of the more affected upper extremity following subtotal unilateral damage to the lateral cortical region. The cCPP may also contribute to the mild impairment of the upper limb contralateral to a unilateral cerebellar injury.

Disynaptic cerebrocerebellar pathways originating from multiple functionally distinct cortical areas

“…However, it was unclear if these sparse contralateral projections were fibers of passage or axon terminals; our results suggest the later for M1 projections and the former for all other cortical targets regions described here. Interestingly, the existence of functional synapses for contralateral corticopontine projections was also reported in primates, however, also exclusively after M1 injections ( Morecraft et al, 2018 ).…”

Terminal organization of the corticospinal projection from the lateral premotor cortex to the cervical enlargement (C5–T1) in rhesus monkey

“…Therefore, the fact that the CSP is randomly distributed throughout the laminae did not have affect the estimation process of total bouton number. The design of our stereological application (e.g., bouton definition, choice of disector probe for quantifying bouton numbers and injection site volumes, counting frame size, guard zone depth, and so on) and technical issues related to our use of multiple dextran tracers and experimental strategies have been discussed in great detail in our previous articles (Darling et al, ; McNeal et al, ; Morecraft, Ge, et al, ; Morecraft et al, , , ; Morecraft, McNeal, Stilwell‐Morecraft, Gedney, et al, ).…”

White matter tract crossing and bottleneck regions in the fetal brain

“…2. The Corticopontine-cerebellar tracts (PT) * involves projection form various cortical areas to the pontine nuclei, which then relay information to the cerebellum, via the middle cerebellar peduncles [50]. It facilitates communication between the cerebral cortex and the cerebellum, playing a crucial role in motor coordination and cognitive functions.…”