Localization of arm representation in the cerebral peduncle of the non‐human primate

Abstract

Motor deficit severity and the potential for recovery in patients with brain injury depend on the integrity of descending corticofugal projections. Clinical assessment of these conditions following subtotal brain trauma requires a comprehensive understanding of the anatomical structures involved in the lesion as well as those structures that are spared. To assist in this endeavor, we investigated motor fiber organization in the crus cerebri of the cerebral peduncle (ccCP) in the rhesus monkey. Fibers originating from the arm representations of the primary (M1), supplementary (M2), rostral cingulate (M3), caudal cingulate (M4), dorsolateral pre- (LPMCd) and ventrolateral pre- (LPMCv) motor cortices were studied. The projections from the frontal and cingulate motor cortices formed descending longitudinal bundles that occupied the medial three-fifths of the ccCP at superior and middle levels. Although considerable overlap characterized these corticofugal projections, a general topography was discernable. Fibers from M1 and M4 occupied the central subsector of the ccCP, and fibers from M3 resided medially. The main distribution of LPMCd, LPMCv, and M2 fibers occupied the centromedial region and overlapped extensively. Progressing inferiorly, all fiber bundles in the central and centromedial sectors gradually extended medially, and overlap increased. A common location of fiber passage occurred at the midbrain-pontine isthmus where all of the fiber bundles overlapped. Our findings indicate that the widespread distribution of corticofugal motor projections may account for the favorable levels of motor recovery that accompany subtotal midbrain injury. At superior and mid-levels of the ccCP anteromedial lesions may disrupt projections from M3, whereas anterolateral lesions may disrupt projections from M1 and M4. Fibers from M2, LPMCv, and LPMCd may be compromised to some degree in both situations. The compact and commixed nature of motor fiber organization at inferior levels and the midbrain-pontine isthmus suggests a vulnerable region of passage for comprehensive disruption of frontal and cingulate corticofugal projection fibers.

Long-Term Gliosis and Molecular Changes in the Cervical Spinal Cord of the Rhesus Monkey after Traumatic Brain Injury

“…The preparation and procedure of animal surgery were performed as previously described (Darling et al, 2006;Morecraft et al, 2001Morecraft et al, , 2002Morecraft et al, , 2004Morecraft et al, , 2007Nagamoto-Combs et al, 2007;Pizzimenti et al, 2007). Briefly, each animal was prepared for surgery by an initial administration of ketamine hydrochloride (10 mg=kg) and kept anesthetized during cortical exposure with a continuous administration of isofluorane (1-1.5% with surgical grade air=oxygen mixture) with the assistance of a mechanical respirator.…”

Absence of a proximal to distal gradient of motor deficits in the upper extremity early after stroke

“…It is possible that our finding of similar movement deficits across upper extremity segments reflects lesions that disrupt similar proportions of proximal and distal inputs. A similar proportion of inputs could be disrupted following stroke because motor cortical territory for proximal and distal muscles is strongly overlapping (Park et al, 2001) and as the axons descend through the subcortical structures, they are densely packed together (Morecraft et al, 2007). Additionally, the output from the motor cortical areas is divergent to multiple spinal motoneuron pools (Fetz and Cheney, 1980;Shinoda et al, 1981;Schieber, 2001), some of which may control more proximal muscles and some of which may control more distal muscles.…”

Role of primary motor cortex in the control of manual dexterity assessed via sequential bilateral lesion in the adult macaque monkey: A case study

“…Nevertheless, the location of the secondary lesion in the white matter suggests that the effects were prominent. There is evidence that the deeper a lesion in the white matter the more extensive are the effects: functional recovery following lesion targeting upper limb has been shown to progressively decrease in parallel to a move to the lesion location from the cortex, corona radiate to internal capsule (Shelton and Reding, 2001;Morecraft et al, 2002Morecraft et al, , 2007. This allowed assessing the role of the contralateral intact M1 for long-term recovery from a unilateral M1 lesion.…”