Localization of the corticofugal projection in the corona radiata (CR) and internal capsule (IC) can assist in evaluating a patient’s residual motor capacity following subtotal brain damage and predicting their potential for functional restitution. To advance our understanding of the organization of the corticofugal projection in this critical brain region, we studied the trajectories of the projection arising from six different cortical arm representations in rhesus monkeys. They included the arm representation of the primary (M1), ventral lateral pre‐ (LPMCv), dorsolateral pre‐ (LPMCd), supplementary (M2), rostral cingulate (M3) and caudal cingulate (M4) motor cortices. In the CR, each pathway was segregated as medial motor area fibres arched over the caudate and lateral motor area fibres arched over the putamen. In the IC, the individual corticofugal pathways were found to be widespread, topographically organized and partially overlapping. At superior levels of the IC, the corticofugal projection from the arm representation of M3 coursed through the middle and posterior portion of the anterior limb (ICa). The projection from M2 passed through the posterior portion of the ICa and the genu (ICg). The projection from LPMCv travelled through the genu and anterior portion of the posterior limb (ICp). The projection from LPMCd occupied the anterior portion of the ICp. The projection from M4 descended through the mid‐portion of the ICp. Fibres from M1 also travelled in the ICp, positioned immediately posterior to the M4 projection. As each fibre system progressed inferiorly within the IC, all fibres shifted posteriorly to occupy the ICp. Within the ICp, the projections from M3, M2, LPMCv, LPMCd, M4 and M1 maintained their anterior to posterior orientation, respectively. M2, LPMCd and LPMCv fibres overlapped extensively, as did fibres from M4 and M1. Our data suggest that CR and superior capsular lesions may correlate with more favourable levels of functional recovery due to the widespread nature of arm representation. In contrast, the extensive overlap and comparatively condensed organization of arm representation at inferior capsular levels suggest that lesions seated inferiorly are likely to correlate with poorer levels of recovery of upper limb movement. Based on the relative density of corticospinal neurones associated with the motor areas studied, our findings also suggest that motor deficit severity is likely to increase as a lesion occupies progressively more posterior regions of the IC.
Keywords: cingulate cortex; frontal lobe; limbic lobe; motor cortex; striatocapsular infarction; stroke, subcortical white matter
Abbreviations: ABC = avidin–biotin; BDA = biotinylated dextran amine; CR = corona radiata; DAB = 3,3′‐diaminobenzidine tetrahydrochloride; FD = fluorescein dextran; FR = fluoro ruby; IC = internal capsule; ICa = anterior limb of the internal capsule; ICg = genu of the internal capsule; ICp = posterior limb of the internal capsule; LYD = lucifer yellow dextran; LPMCd = dorsal lateral premotor cortex; LPMCv = ventral lateral premotor cortex; M1 = primary motor cortex; M2 = supplementary motor cortex; M3 = rostral cingulate motor cortex; M4 = caudal cingulate motor cortex; PHA‐L = Phaseolus vulgaris leucoagglutinin
Received April 5, 2001. Revised August 8, 2001. Second revision August 16, 2001. Accepted September 10, 2001.
Robert J.Morecraft, James L.Herrick, Kimberly S.Stilwell‐Morecraft, Jennifer L.Louie, Clinton M.Schroeder, Jonovan G.Ottenbacher, Matt W.SchoolfieldBrain(2002)125 (1):
176-198DOI: http://dx.doi.org/10.1093/brain/awf011First published online: 1 January 2002 (23 pages)